A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species

William G. R. Crampton Carlos D. de Santana Joseph C. Waddell Nathan R. Lovejoy About the authors

ABSTRACT

The bluntnose knifefish genus BrachyhypopomusMago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p., is diagnosed from other Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) by the presence of a disk-like ossification in the anterior portion of the palatoquadrate, and by the following external characters: short snout, 18.7-32.6% of head length (vs. 33.3-68.6% in Hypopomus, Gymnorhamphichthys, Iracema, and Rhamphichthys), absence of a paired accessory electric organ in the mental or humeral region (vs. presence in Hypopygus and Steatogenys), presence of 3-4 pectoral proximal radials (vs. 5 in Akawaio), presence of the antorbital + infraorbital, and the preopercular cephalic lateral line canal bones (vs. absence in Racenisia). Brachyhypopomus cannot be diagnosed unambiguously from Microsternarchus or from Procerusternarchus on the basis of external characters alone. Brachyhypopomus comprises 28 species. Here we describe 15 new species, and provide redescriptions of all 13 previously described species, based on meristic, morphometric, and other morphological characters. We include notes on ecology and natural history for each species, and provide regional dichotomous keys and distribution maps, based on the examination of 12,279 specimens from 2,787 museum lots. A lectotype is designated for Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.). Brachyhypopomus species are abundant in shallow lentic and slow-flowing freshwater habitats from southern Costa Rica and northern Venezuela to Uruguay and northern Argentina. Species diversity is highest in Greater Amazonia, where 20 species occur: B. alberti, new species, B. arrayae, new species, and B. cunia, new species, in the upper rio Madeira drainage; B. batesi, new species, in the central Amazon and rio Negro; B. beebei, B. brevirostris, B. regani, new species, B. sullivani, new species, and B. walteri, widespread through the Amazon and Orinoco basins and the Guianas; B. belindae, new species, in the central Amazon basin; B. benjamini, new species, and B. verdii, new species, in the upper Amazon basin; B. bennetti, in the upper, central, and lower Amazon, lower Tocantins, and upper Madeira basins; B. bullocki in the Orinoco, Negro and Essequibo drainages; B. diazi in the Orinoco Llanos; B. flavipomus, new species, and B. hamiltoni, new species, in the central and upper Amazon basin; B. hendersoni, new species, in the central Amazon, lower Negro and Essequibo basins; B. pinnicaudatus in the central and lower Amazon, lower, upper Madeira, lower Tocantins and Mearim basins, and coastal French Guiana; and B. provenzanoi, new species, in the upper Orinoco and upper Negro basins. Five species are known from the Paraná-Paraguay-Uruguay basin and adjacent southern Atlantic drainages: B. bombilla in the lower Paraná, upper, central, and lower Paraguay, Uruguay and Patos-Mirim drainages; B. brevirostris in the upper Paraguay basin; B. draco in the lower Paraná, lower Paraguay, Uruguay, Patos-Mirim, and Tramandaí basins; B. gauderio in the lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim and Tramandaí basins; and B. walteri in the lower Paraná and upper Paraguay basins. Two species occur in small Atlantic drainages of southern Brazil: B. janeiroensis in the São João, Paraíba and small intervening drainages; and B. jureiae in the Ribeira de Iguape and Una do Prelado. One species occurs in the middle and upper São Francisco basin: B. menezesi, new species. Three species occur in trans-Andean drainages: B. diazi in Caribbean drainages of northern Venezuela; B. occidentalis in Atlantic and Pacific drainages of southern Costa Rica and Panama to Darién, and the Maracaibo, Magdalena, Sinú and Atrato drainages; and B. palenque, new species, in Pacific drainages of Ecuador.

Keywords:
Biogeography; Bluntnose knifefish; Electroreception; Identification key; Rhamphichthyoidea

RESUMO

Peixes elétricos do gênero Brachyhypopomus Mago-Leccia, 1994, são diagnosticados dos outros Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) pela presença de uma ossificação discóide na porção anterior do palatoquadrado, e pelos seguintes caracteres externos: focinho curto, 18,7-32,6% do comprimento da cabeça (vs. 33,3-68,6% em Hypopomus, Gymnorhamphichthys, Iracema e Rhamphichthys), ausência de um órgão elétrico acessório pareado na região mental ou humeral (vs. presença em Hypopygus e Steatogenys), presença de 3-4 proximais peitorais radiais (vs. 5 em Akawaio), presença do antiorbital + infraorbital, e dos canais ossificados da linha lateral da região cefálica do pré-opérculo (vs. ausência em Racenisia). Brachyhypopomus não pode ser diagnosticado de maneira não-ambígua de Microsternarchus ou Procerusternarchus, com base em caracteres de morfologia externa. Brachyhypopomus compreende 28 espécies válidas. Aqui nós descrevemos 15 espécies novas, e fornecemos a redescrição de 13 espécies previamente descritas, baseado em caracteres merísticos, morfométricos e outros caracteres morfológicos. Nós incluímos notas sobre à ecologia e história natural para cada uma das espécies, e fornecemos chaves dicotômicas regionais e mapas de distribuição baseado no exame de 12.279 espécimes de 2.787 lotes de museus. Um lectótipo é designado para Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.). Espécies de Brachyhypopomus são abundantes em habitats de águas rasas lênticas e com correntes fracas, ocorrendo do sul da Costa Rica e norte da Venezuela ao Uruguai e norte da Argentina. A diversidade de espécies é maior na Grande Amazônia, onde 20 espécies ocorrem: B. alberti, espécie nova, B. arrayae, espécie nova e B. cunia, espécie nova, na drenagem do alto rio Madeira; B. batesi, espécie nova, na Amazônia central e rio Negro; B. beebei, B. brevirostris, B. regani, espécie nova, B. sullivani, espécie nova e B. walteri, amplamente distribuídas nas bacias Amazônicas e do Orinoco, e nas Guianas; B. belindae, espécie nova, bacia Amazônica central; B. benjamini, espécie nova e B. verdii, espécie nova, na bacia do alto Amazonas; B. bennetti, no alto, médio e porções baixas da bacia Amazônica, baixo Tocantins e alto rio Madeira; B. bullocki nas drenagens do Orinoco, Negro e Essequibo; B. diazi nos Llanos do Orinoco; B. flavipomus, espécie nova e B. hamiltoni, espécie nova, no médio e alto Amazonas; B. hendersoni, espécie nova, na Amazônia central, baixo Negro e Essequibo; B. pinnicaudatus no médio e baixo Amazonas, baixo e alto Madeira, baixo Tocantins, bacia do Mearim e rios costeiros da Guiana Francesa; e B. provenzanoi, espécie nova, nas bacias do alto Orinoco e alto Negro. Cinco espécies são conhecidas das bacias Paraná-Paraguai-Uruguai e bacias adjacentes das drenagens do sul do Brasil: B. bombilla no alto, médio e baixo Paraguai, baixo Paraná, Uruguai e drenagens Patos-Mirim; B. brevirostris da bacia do alto Paraguai; B. draco das bacias do baixo Paraguai, baixo Paraná, Uruguai, Patos-Mirim e Tramandaí; B. gauderio das bacias do alto, médio e baixo Paraguai, baixo Paraná, Uruguai, Patos-Mirim e Tramandaí; e B. walteri das bacias do alto Paraguai e baixo Paraná. Duas espécies ocorrem nas drenagens costeiras do sudeste do Brasil: B. janeiroensis no São João, Paraíba e em drenagens menores nas adjacências; e B. jureiae no Ribeira de Iguape e Una do Prelado. Uma espécie ocorre no médio e alto rio São Francisco: B. menezesi, espécie nova. Três espécies ocorrem nas drenagens trans-Andinas: B. diazi nas drenagens do Caribe no norte da Venezuela; B. occidentalis nas drenagens do Atlantico e Pacífico do sul da Costa Rica e Panamá até Darién, e nas drenagens do Maracaibo, Magdalena, Sinú e Atrato; e B. palenque, espécie nova, nas drenagens do Pacífico no Equador.

Introduction

The weakly electric "bluntnose knifefish" genus Brachyhypopomus Mago-Leccia, 1994 occurs in lowland tropical and subtropical freshwater habitats from southern Costa Rica to southern Uruguay (Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .; Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.). Brachyhypopomus species, listed in Table 1, are small to medium-sized, cryptically pigmented, and nocturnally active predators of aquatic invertebrates. They occur in a wide variety of lentic or slowly-flowing lotic environments, including streams, river margins, swamps, and floodplains - where they often constitute a species-rich and abundant component of the local ichthyofauna (Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.; Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.,bCrampton, W. G. R. 1996b. Gymnotiform fish: an important component of Amazonian floodplain fish communities. Journal of Fish Biology, 48: 298-301.; 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.). The genus is conspicuously absent from the bottoms of deep river channels (Crampton, 2007Crampton, W. G. R. 2007. Diversity and adaptation in deep channel Neotropical electric fishes Pp. 283-339. In: Sebert P., D. W. Onyango & B. G. Kapoor (Eds.). Fish life in special environments. Enfield, NH, Science Publishers.). Brachyhypopomus and other small hypopomids are not exploited as food fish, but they sometimes feature in the diet of Amerindians (Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.), and are occasionally exported as ornamental fish (Chao, 2001Chao, N. L. 2001. Fisheries, diversity and conservation of ornamental fishes of the Rio Negro basin, Brazil - a review of Project Piaba (1989-1999). Pp. 161-204. In: Chao N. L., P. Petry, G. Prang, L. Lonneschien & M. Tlusty (Eds.). Conservation and management of ornamental fish resources of the rio Negro basin, Amazonia, Brazil - Project Piaba. Manaus, Editora da Universidade do Amazonas.). Like all gymnotiform fish, Brachyhypopomus generate electric organ discharges (EODs), which, in combination with a cutaneous array of tuberous electroreceptors, facilitate active electrolocation and electrocommunication (Bullock et al., 2005Bullock, T. H., C. D. Hopkins, A. N. Popper & R. R. Fay(Eds.). 2005. Electroreception. New York, Springer, 467 pp.; Kramer, 1995Kramer, B. 1995. Electroreception and communication in fishes. Stuttgart, Georg Fischer Verlag, 119p.; Moller, 1995Moller, P. 1995. Electric fish: history and behavior. London, Chapman & Hall, 584 pp.). The head-to-tail recorded EODs of Brachyhypopomus are weak (< 1V), pulsed (at rates of <1-110 Hz) waveforms of ca. 0.5-5 msec duration, comprising from one to four phases of alternating polarity (Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Waddell et al., 2016Waddell, J. C., A. Rodríguez-Cattaneo, A. A. Caputi & W. G. R. Crampton. 2016. Electric organ discharges and near-field spatiotemporal patterns of the electromotive force in a sympatric assemblage of Neotropical electric fish. Journal of Physiology (Paris), in press DOI: 10.1016/j.jphysparis.2016.10.004.
https://doi.org/10.1016/j.jphysparis.201...
). Crampton et al. (2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
) provide a phylogenetic reconstruction of Brachyhypopomus (including all 28 species described or redescribed herein) based on a combination of morphological data and sequence data from the mitochondrial cytochrome b and nuclear rag2 genes.

Table 1
List of the 28 valid species of Brachyhypopomus, with authors and name-bearing types. The 15 species described herein are in bold. Name-bearing type refers to the holotype except for lectotype (LT), or syntypes (ST).

The first reported species of Brachyhypopomus was described as Rhamphichthys brevirostris by Steindachner (1868aSteindachner, F. 1868a. Die Gymnotidae des K.K.Hof-Naturaliencabinetes zu Wien. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe, 58: 249-264, pls. 241-242)., bSteindachner, F. 1868b. Abhandlung über die Gymnotiden des Wiener Museums. Anzeiger der Akademie der Wissenschaften in Wien, 5: 176-177.), based on specimens collected by Johann Natterer from the rio Guaporé. Thenceforth and until 1994, five additional species of Brachyhypopomus were described: B. beebei, B. diazi, B. janeiroensis, B. occidentalis, and B. pinnicaudatus (see Table 1 for authors and type localities). These were all assigned to the genus Hypopomus, which was erected earlier by Gill (1864Gill, T. N. 1864. Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16: 151-152.); see 'Taxonomic remarks' in the generic redescription herein.

Mago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.) divided HypopomussensuGill (1864Gill, T. N. 1864. Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16: 151-152.) into two genera: Hypopomus, and a new genus Brachyhypopomus. Hypopomus was restricted to Hypopomus artedi (Kaup, 1856Kaup, J. J. 1856. Family Gymnotidae. Pp. 124-142. In: Kaup J. J. (Ed.) Catalogue of apodal fishes. London, British Museum of Natural History.) and its now junior synonym H. mulleri (Kaup, 1856Kaup, J. J. 1856. Family Gymnotidae. Pp. 124-142. In: Kaup J. J. (Ed.) Catalogue of apodal fishes. London, British Museum of Natural History.) based on a longer, "projected" snout, and mouth in inferior position (among other characters). Brachyhypopomus was erected to accommodate B. beebei, B. brevirostris, B. diazi, B. janeiroensis, B. occidentalis, and B. pinnicaudatus based on a short snout and included mouth, the absence of a mesocoracoid bridge, a short and crescent-shaped maxillary bone, and posterior nares closer to eye.

Subsequent to Mago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.), seven additional species of Brachyhypopomus have been described, bringing the total to 13: B. bennetti, B. bombilla, B. bullocki, B. draco, B. gauderio, B. jureiae, and B. walteri (see Table 1 for authors and type localities). Two of these, B. bennetti and B. walteri, were assigned to a subgenus, Odontohypopomus Sullivan, Zuanon & Cox Fernandes, 2013, based on the shared presence of premaxillary teeth in adult specimens (Sullivan et al., 2013).

Brachyhypopomus belongs to the family Hypopomidae Mago-Leccia, which sensuMaldonado-Ocampo et al. (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.) contains six additional species in five genera: Akawaio penak Maldonado-Ocampo, López-Fernández, Taphorn, Bernard, Crampton & Lovejoy, Hypopomus artedi, and the tribe Microsternarchini Albert - comprising Microsternarchus bilineatus Fernández-Yépez, M. brevis Fernandes, Nogueira, Williston & Alves-Gomes, Procerusternarchus pixuna Fernandes, Nogueira & Alves-Gomes, and Racenisia fimbriipinna Mago-Leccia. Two genera, HypopygusHoedeman, 1962Hoedeman, J. J. 1962. Notes on the ichthyology of Surinam and other Guianas. 9. New records of gymnotid fishes. Bulletin of Aquatic Biology, Amsterdam, 3: 53-60., and SteatogenysBoulenger, 1898Boulenger, G. A. 1898. On a collection of fishes from the rio Rio Jurua. Transactions of the Zoological Society of London, 14 (part VII): 421-428, pls. 39-42., were until recently placed in the Hypopomidae, but were relocated to the family Rhamphichthyidae Regan by Maldonado-Ocampo et al. (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.) based on molecular phylogenetic evidence. The Hypopomidae and the Rhamphichthyidae together constitute the superfamily Rhamphichthyoidea.

The general biology of Brachyhypopomus is well known in comparison to other gymnotiforms, as reviewed below (see 'Functional biology and ecology', in the generic description), and one species, B. gauderio (formerly ascribed to B. pinnicaudatus), has served as a model species for understanding electroreception, electrogenesis, neuroethology, and the influence of steroid and peptide hormones on the electric organ and EOD communication signals; for recent reviews see Gavassa et al. (2013Gavassa, S., A. Goldina, A. C. Silva & P. K. Stoddard. 2013. Behavioral ecology, endocrinology and signal reliability of electric communication. Journal of Experimental Biology, 216: 2403-2411.), MarkhamMarkham, M. R. 2013. Electrocyte physiology: 50 years later. Journal of Experimental Biology, 216: 2451-2458. (2013), Salazar et al. (2013Salazar, V. L., R. Krahe & J. E. Lewis. 2013. The energetics of electric organ discharge in gymnotiform weakly electric fish. Journal of Experimental Biology, 216: 2459-2468.), Silva et al. (2013Silva, A. C., R. Perrone, L. Zubizarreta, G. Batista & P. K. Stoddard. 2013. Neuromodulation of the agonistic behavior in two species of weakly electric fish that display different types of agression. Journal of Experimental Biology, 216: 2412-2420.), and Giora et al. (2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.). Nonetheless, only 13 valid species of Brachyhypopomus have been described to date (Table 1), despite knowledge of considerable additional species diversity - especially in the Amazon basin (Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .; Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.; Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.; Heiligenberg & Bastian, 1980Heiligenberg, W. & J. Bastian. 1980. Species specificity of electric organ discharges in sympatric gymnotoid fish of the Rio Negro. Acta Biológica Venezuélica, 10: 187-203.; Schwassmann, 1978Schwassmann, H. O. 1978. Ecological aspects of electroreception. Pp. 521-533. In: Ali M. A. (Ed.) Sensory ecology. New York, Plenum.; Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.; Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.); see Fig. 1 for a local assemblage of 12 species from the central Amazon.

Here we provide a taxonomic revision of Brachyhypopomus. We confirm the validity of all 13 previously-described species, describe 15 new species (Table 1), and provide descriptions of morphology, ecology, and geographical distributions based on a thorough examination of available museum material. We also provide regional dichotomous identification keys to the species of Brachyhypopomus.

Fig. 1
Live individuals of 12 sympatric species of Brachyhypopomus and one species of Microsternarchus from the vicinity of Tefé, Amazonas, Brazil (Amazonas dr.). a. Brachyhypopomus batesi MCP 45312 (WC01.191293b), immature, 102 mm TL. b. Brachyhypopomus beebei head - uncat., immature, 75 mm TL; body - MCP 45450 (WC04.090600), female, 178 mm TL. c. Brachyhypopomus belindae MCP 45430, paratype, immature, 104 mm TL (photographed out of water, close up of head not available). d. Brachyhypopomus bennetti MCP 45451, male, 196 mm TL. e. Brachyhypopomus brevirostris uncat., immature, 224 mm TL. f. Brachyhypopomus flavipomus MCP 45453 (WC09.090600), female, 98 mm TL. g. Brachyhypopomus hamiltoni MCP 45482 (WC05.080301), holotype, female, 97 mm TL. h. Brachyhypopomus hendersoni MCP 45489, female, 164 mm TL. i. Brachyhypopomus pinnicaudatus MCP 45455, female, 135 mm TL. j. Brachyhypopomus regani, MCP 45285 (WC02.100301), male, 119 mm TL. k. Brachyhypopomus sullivani MCP 45464 (WC04.210201), immature, 79 mm TL. l. Brachyhypopomus walteri MCP 45458 (WC 03.090600), male, 161 mm TL. m. Microsternarchus bilineatus uncat., 85 mm TL.

Material and Methods

Specimens and collections. Examined specimens of Brachyhypopomus are listed in the species descriptions and redescriptions. Examined specimens of other gymnotiforms, with emphasis on other Rhamphichthyoidea are listed in Supplement 1. Many of the specimens examined in this study were collected by us (WGRC, NRL, JCW) using fine mesh dip nets or small seine nets, often with the aid of an electric fish detector (Crampton et al., 2007Crampton, W. G. R., J. K. Wells, C. Smyth & S. A. Walz. 2007. Design and construction of an electric fish finder. Neotropical Ichthyology, 5: 425-428.). Specimens were euthanized in a 600 mgl-1 solution of eugenol or in ice-ethanol slurry until apnea and EOD cessation, fixed in 10% formalin, and preserved in 70% EtOH. Sex was assessed via examination of the gonads through a short incision in the ventral part of the body cavity of fixed specimens; this permitted an evaluation of sexual dimorphism of caudal filament structure and body length.

Osteological characters were assessed from specimens cleared and counterstained (CS) for cartilage and bone using the method outlined by Taylor & Van Dyke (1985Taylor, W. R. & G. C. Van Dyke. 1985. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium, 9: 10719.). In some specimens with weak ossification, bones were stained with alizarin red in ethanol solution instead of KOH solution (Springer & Johnson, 2000Springer, V. G. & G. D. Johnson. 2000. Use and advantages of ethanol solution of alizarin red S dye for staining bone in fishes. Copeia, 2000: 300-301.). Examined cleared and stained specimens are listed in Supplements 1 and 2. Radiographs served as additional sources of osteological data for some species. We limit the presentation of osteological characters herein to those necessary to diagnose species where characters from non-invasive analyses were insufficient.

Species accounts. Species descriptions/redescriptions are presented in alphabetical order. Many taxonomic, ecological, behavioral and neurobiological papers make reference to Brachyhypopomus, and inevitably the high diversity of the genus coupled with the relatively small fraction of previously described species has resulted in incorrect identifications in the literature, assignment to cheironyms, or identification by alphabetic/numerical schemes. The synonymy sections herein provide an opportunity to correct many of these errors. Nonetheless, we adopt a conservative approach by confirming or correcting the identity of species mentioned in non-taxonomic papers only where photographs or other illustrations, or exclusive geographical distributions permit unequivocal identification. The differential diagnoses serve to unambiguously separate each species from all congeners and are confined where possible to external characters, or characters that can be analyzed without invasive procedures (e.g., vertebral counts from radiographs).

Material examined are ordered alphabetically by country, state or department (in bold), collection code following Sabaj-Pérez (2014Sabaj Pérez, M. H. 2014. Standard symbolic codes for institutional resource collections in herpetology and ichthyology: an Online Reference. Version 5.0 (22 September 2014). http://www.asih.org, Washington, DC., American Society of Ichthyologists, 60 pp.
http://www.asih.org...
), and then numerically by catalog number. Institutions not listed in Sabaj-Pérez are: SINCHI-CIACOL (Colección Ictiológica de la Amazonia Colombiana del Instituto Amazónico de Investigaciones Científicos, Leticia, Colombia), and ZOOA (Universidad de Azuay, Azuay, Ecuador).

Holotypes of new species are deposited in the following institutions: CBF, Colección Boliviana de Fauna, Museo Nacional de Historia Natural, Instituto de Ecología, Academia Nacional de Ciencias de Bolivia, La Paz; INPA, Instituto Nacional de Pesquisas da Amazônia, Manaus; MBUCV-V, Museo de Biología de la Universidad Central de Venezuela, Caracas; MCP, Museu de Ciências e Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre; MUSM, Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima; MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo; UF, University of Florida, Florida Museum of Natural History; UMSS, Universidad Mayor de San Simón, Facultad de Ciencias y Tecnología, Centro de Biodiversidad, Zoología, Laboratorio de Ictiología, Cochabamba.

Lots without reliable geographical coordinates are listed but excluded from the distribution maps. Geographical coordinates were taken from museum labels and corrected if necessary, or are given as approximate where a position within 30 km could be determined. Abbreviations are: affl. - affluent; confl. - confluence; dr/s. - drainage/s; hwy. - highway; mun. - county/municipality; nr. - near; prov. -province; rd. - road. Square parentheses denote corrections to and/or comments on localities.

Distribution maps. Localities were projected onto cartographic projections of South and Central America (Fig. 2) using the ArcGIS geographical information system software, version 9.3.1 (ESRI, Redlands, CA). River networks, and elevation data were obtained from HydroSHEDS (Hydrological Data and Maps based on Shuttle Elevation Derivatives at Multiple Scales) (Lehner et al., 2006Lehner, B., K. Verdin & A. Jarvis. 2006. HydroSHEDS technical documentation. Version 1.0 (http://hydrosheds.cr.usgs.gov). Washington, DC, World Wide Fund for Nature, US, 27p.
http://hydrosheds.cr.usgs.gov...
), from http://hydrosheds.cr.usgs.gov. HydroSHEDS derives from elevation data of the US NASA Space Shuttle Radar Topography Mission. We used the 30 arc-second resolution data set referenced to the WGS84 projection. Species distribution maps are presented in alphabetical order, and arranged to maximize cartographic magnification and ensure that species with overlapping geographical distributions are presented in separate figures.

Fig. 2
Collection records for Brachyhypopomus based on 11,750 specimens from 2,642 georeferenced museum lots. Map of South and southern Central America based on HydroSHEDS data. Elevation data refers to altitude above mean sea level.

Morphometric measurements. Body size measurements reported in this paper refer to total length (TL) - the distance from the tip of the snout to the end of the caudal filament, unless specified as length to end of anal fin (LEA) - the distance from the tip of the snout to the base of the last anal fin. Morphometric measurements are summarized in the schematic diagram in Fig. 3. Due to non-linear growth allometry we analyzed morphometric data only from specimens of reproductive size (above the minimum size at which gonadal development occurs for each species) (Crampton et al., 2011Crampton, W. G. R., N. R. Lovejoy & J. C. Waddell. 2011. Reproductive character displacement and signal ontogeny in a sympatric assemblage of electric fishes. Evolution, 65: 1650-1666.; Hulen et al., 2005Hulen, K. G., W. G. R. Crampton & J. S. Albert. 2005. Phylogenetic systematics and historical biogeography of the Neotropical electric fish Sternopygus (Teleostei : Gymnotiformes). Systematics and Biodiversity, 3: 407-432.). Measurements reported as a percentage of TL are given only for specimens with no damage or regeneration. Measurements reported as a percentage of LEA are given only for specimens with no damage or regeneration anterior to the anal-fin terminus. The following morphometrics represent the horizontal distance parallel to the long axis of the specimen, with the specimen extended on a flat surface - measured either with a ruler to the nearest 1 mm or, for smaller specimens, a digital caliper to the nearest 0.1 mm: Anal-fin length (AF) - the distance between the bases of the first and last rays of the anal fin. Caudal-filament length (CF) - the distance from the base of the last anal-fin ray to the tip of the caudal filament; we describe the caudal filament as "short" if < 15% TL, "moderate" if ≥15 < 25% TL, and "long" if ≥ 25% TL.

Fig. 3
Measurements used for morphometric analysis of Brachyhypopomus. See text for details. a. Body, lateral view: AF = Anal-fin length; ARL = Longest anal-fin ray; BD1 = Body depth at anal-fin origin; BD2 = Body depth at anal-fin middle; CD = Caudal-filament depth; CF = Caudal-filament length; LEA = Length to end of anal fin; TL = Total length. b. Body, dorsal view: BW1 = Body width at anal-fin origin; BW2 = Body width at anal-fin middle; CW = Caudal-filament width. c. Head, lateral view: AE = Internarial distance; BO = Branchial aperture; HD1 = Head depth at eye; HD2 = Head depth at occiput; HL = Head length; PRL = Longest pectoral-fin ray; OD = Orbital diameter; PB = Pectoral-fin base; PE = Posterior naris to eye; PO = Postorbital distance; PP = Snout to pectoral-fin base; PR = Preorbital distance (snout length); SA = Snout to anal-fin origin; SO = Snout to occiput. d. Head, dorsal view: HW1 = Head width at eye; HW2 = Head width at occiput; IO = Interorbital width. e. Head, ventral view: MW = Mouth width. Schematics based on B. diazi (UF 174333).

All other morphometrics, listed below, were measured using the ocular micrometer of a Meiji Techno RZ stereomicroscope, to the nearest 0.001 mm, as planar distances orthogonal to the body axis (i.e. point-to-point as distances between imaginary lines drawn vertically upwards from the specimen towards the horizontal plane of the micrometer). We chose ocular micrometer measurements instead of point-to-point caliper measurements because the latter lacked sufficient precision and replicability for characterizing morphometrics in specimens smaller than ca. 100 mm TL. We were unable to obtain ocular micrometer measurements from the holotype specimens of some previously-described species (all previous descriptions employ caliper-based measurements). In these cases we excluded the holotype from the tabulated morphometric ranges we present in the species redescription; this is clarified in the appropriate table legends.

The following measurements (Figs. 3a,c) were taken from the left side of the fish, with the lateral line held parallel to the measuring surface: Body depth at anal-fin origin (BD1) - body depth measured vertically from dorsal midline to ventral midline at the anal-fin origin; we describe the body depth as "shallow" if < 10% TL, "moderate" if ≥10 < 14% TL, and "long" if ≥ 14% TL. Body depth at anal-fin middle (i.e. middle of the length of the anal fin) (BD2) - body depth measured vertically from dorsal midline to ventral midline at a point half-way between the bases of the first and last rays of the anal fin. Branchial aperture (opening) (BO) - the distance from the posterodorsal to anteroventral extents of the branchial aperture. Caudal-filament depth (CD) - the vertical depth of the caudal filament measured at the base of the last anal-fin ray. Caudal-filament length (CF) - the distance from the base of the last anal-fin ray to the tip of the caudal filament. Head depth at eye (HD1) - the maximum head depth measured at the center of the eye; we describe the head as "shallow" if head depth < 72% HL, "moderate" if ≥72 < 87% HL, and "deep" if ≥ 87% HL. Head depth at occiput (HD2) - the maximum head depth measured at the occiput. Head length (HL) - the distance from the tip of the snout to the posterior-most margin of the bony operculum; we describe the head as "short" if head length is < 11% LEA, "moderate" if ≥11 < 14% LEA, and "long" if ≥ 14% LEA. Internarial distance (AE) - the distance from the posterior margin of the anterior naris to the anterior margin of the posterior naris. Longest anal-fin ray (ARL) - the distance from the base to the distal tip of the longest anal-fin ray (or estimated longest anal-fin ray). Orbital diameter (OD) - the horizontal diameter of the eye; we describe the eye as "small" if the orbital diameter < 9% HL, "moderate" if ≥9 < 14% HL, and "large" if ≥ 14% HL. Pectoral-fin base (PB) - the distance from the base of the dorsal most ray of the pectoral fin to the base of the ventral-most ray; we describe the pectoral fin as "narrow" if its base is < 10% HL, "moderate" if ≥10 < 15% HL, and "broad" if ≥ 15% HL. Posterior naris to eye (PE) - the distance from the posterior margin of the posterior naris to the anterior margin of the eye. Longest pectoral-fin ray (PRL) - the distance from the base to the end of the longest pectoral-fin ray. Postorbital distance (PO) - the distance from the posterior margin of the eye to the posterodorsal angle of the branchial opening. Preorbital distance (snout length) (PR) - the distance from the tip of the snout to the anterior margin of the eye. Snout to anal-fin origin (SA) - the distance from the tip of the snout to the base of the first anal-fin ray. Snout to occiput (SO) - the distance from the tip of the snout to the occiput. Snout to pectoral-fin base (PP) - the distance from the tip of the snout to the base of the dorsal most ray of the pectoral fin.

The following measurements (Figs. 3b,d-e) were taken with the dorsal surface of the specimen facing up or down, while holding the lateral line parallel to the measuring surface: Body width at anal-fin origin (BW1) - the maximum body width at anal-fin origin. Body width at anal-fin middle (i.e. middle of the length of the anal fin) (BW2) - the maximum body width at a point half-way between the bases of the first and last rays of the anal fin. Caudal-filament width (CW) - the horizontal width of the caudal filament measurement at the base of the last anal-fin ray. Head width at eye (HW1) - the maximum head width measured at the center of the eye; head width at occiput (HW2) - the maximum head width measured at the occiput; interorbital distance (IO) - the minimum width between the dorsal margins of the orbits; mouth width (MW) - the distance between the ricti.

Meristics. Counts were taken only from specimens of reproductive size. Anal-fin ray number - the total number of branched and unbranched rays counted from ethanol preserved specimens or from cleared and stained (CS) specimens using a stereomicroscope with backlit illumination. Electrocyte columns at anal-fin terminus - the number of horizontally aligned bilateral columns of electrocytes in the hypaxial electric organ at a vertical with the anal-fin terminus; counted from ethanol preserved specimens using a stereomicroscope and backlit illumination, with skin and scales overlying the electric organ peeled off if necessary. Electrocyte columns at mid-caudal filament - the number of horizontally aligned bilateral columns of electrocytes in the hypaxial electric organ at the midpoint between the anal-fin terminus and tip of the caudal filament (in intact, non-regenerated specimens only). Pectoral-fin rays - total number of branched and unbranched rays; counted from ethanol preserved specimens using a stereomicroscope with transmitted light, or from cleared-and-stained specimens. Precaudal vertebrae - all precaudal vertebrate including the first four vertebrae (which form part of the Weberian apparatus), the second and third of which often exhibit fused centra (Campos-da-Paz, 2000Campos-da-Paz, R. 2000. On Sternarchorhynchus Castelnau: a South American electric knifefish, with descriptions of two new species (Ostariophysi: Gymnotiformes: Apteronotidae). Copeia, 2: 521-535.: 524; Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.: 152), and all transitional vertebrae (which lack ribs and hemal spines); counted from digital X-ray images or from CS specimens. The number of precaudal vertebrae is a proxy for the length of the body cavity (Albert, 2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.). Radiographs were taken with a Kodak DXS Pro digital X-ray system. Scales above the lateral line - counted as number of rows from the lateral line to the dorsal midline (but excluding the lateral-line series) at midpoint from snout to anal-fin terminus using a stereomicroscope with transmitted light. Gill filaments on first gill arch - counted as the number of filaments on the first gill arch (including only the lateral, i.e. outer, hemibranch).

Results

Brachyhypopomus Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.

BrachyhypopomusMago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 47 (description and diagnosis for genus). -Alves-Gomes et al., 1995Alves-Gomes, J. A., G. Ortí, M. Haygood, W. Heiligenberg & A. Meyer. 1995. Phylogenetic analysis of the South American electric fishes (Order Gymnotiformes) and the evolution of their electrogenic system: A synthesis based on morphology, electrophysiology, and mitochondrial sequence data. Molecular Biology and Evolution, 12: 298-318.: 307-309, figs. 6-8, 312-314, figs. 9-10 (position in phylogeny of the Gymnotiformes). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p. (diagnosis for genus, position in phylogeny of the Rhamphichthyoidea). -Albert & Campos-da-Paz, 1998Albert, J. S. & R. Campos-da-Paz. 1998. Phylogenetic systematics of Gymnotiformes with diagnoses of 58 clades: A review of available data. Pp. 419-446. In: Malabarba L. R., R. E. Reis, R. P. Vari, Z. M. S. Lucena & C. A. S. Lucena (Eds.). Phylogeny and classification of neotropical fishes. Porto Alegre, Edipucrs.: 423, fig. 2, 426, 436, table 1, 439, table 2 (diagnosis for genus, position in phylogeny of the Gymnotiformes). -Albert, 2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.: 12, table 2, 56, table 3, 68-69 (diagnosis for genus, position in phylogeny of the Gymnotiformes). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 494 (catalog of hypopomids). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 78 (diagnosis for genus, position in phylogeny of the Rhamphichthyoidea). -Fernandes et al., 2014Fernandes, C. C., A. Nogueira & J. A. Alves-Gomes. 2014. Procerusternarchus pixuna, a new genus and species of electric knifefish (Gymnotiformes: Hypopomidae, Microsternarchini) from the Negro River, South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 163: 95-118.: 98, fig. 1 (position in phylogeny of the Rhamphichthyoidea). -Maldonado-Ocampo et al., 2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.: 6, 8, fig. 6 (position in phylogeny of the Rhamphichthyoidea). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 10 (position in phylogeny of the Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Odontohypopomus (subgenus of Brachyhypopomus) Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.: 6 (erected to contain B. bennetti and B. sullivani).

Type species. Rhamphichthys brevirostrisSteindachner (1868aSteindachner, F. 1868a. Die Gymnotidae des K.K.Hof-Naturaliencabinetes zu Wien. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe, 58: 249-264, pls. 241-242).). Type by original designation (Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 47).

Diagnosis. Brachyhypopomus is diagnosed unambiguously from all other Gymnotiformes, including all other rhamphichthyoid species, by a single unreversed shared and derived character: the presence of a disk-like ossification in the anterior portion of the palatoquadrate cartilage in adult specimens. See Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.: 7, fig. 1) for a photograph of the ossified palatoquadrate cartilage in a cleared and stained specimen of B. walteri. The disk-like ossification of the palatoquadrate cartilage is present in all species of Brachyhypopomus, but in some specimens is relatively hard to discern due to poor uptake of stain. Likewise, in many immature specimens the ossification is incomplete. This may explain why Sullivan (1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.) did not observe this character in some species of Brachyhypopomus (B. brevirostris, B. bullocki, B. bombilla, B. regani, B. sullivani), where we did. Moreover, because the ossification of the palatoquadrate cartilage is visible only in cleared and stained specimens, this character is inadequate for determining whether whole specimens belong to the genus Brachyhypopomus. The following combination of characters that do not require invasive techniques serves to delimit members of the genus from all other gymnotiforms.

Brachyhypopomus is diagnosed from the Apteronotidae by the absence of a caudal fin and dorsal electroreceptive filament and from the Gymnotidae and Sternopygidae by the absence of complete rows of teeth on the premaxilla in adults. Brachyhypopomus is diagnosed from the Rhamphichthyidae sensuMaldonado-Ocampo et al. (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.) (which includes Hypopygus and Steatogenys in the tribe Steatogeni) either by the short snout, 18.7-32.6% of HL, vs. 40.0-68.6% in Gymnorhamphichthys, 53.8-55.4% in Iracema, and 49.8-61.6% in Rhamphichthys (Carvalho & Albert, 2011Carvalho, T. P. & J. S. Albert. 2011. Redescription and phylogenetic position of the enigmatic Neotropical electric fish Iracema caiana Triques (Gymnotiformes: Rhamphichthyidae) using x-ray computed tomography. Neotropical Ichthyology, 9: 457-469.; Carvalho et al., 2011Carvalho, T. P., C. S. Ramos & J. S. Albert. 2011. A new species of Gymnorhamphichthys (Gymnotiformes: Rhamphichthyidae) from the Paraná-Paraguay basin. Copeia, 2011: 400-406.; Géry & Vu, 1964Géry, J. & T. T. Vu. 1964. Gymnorhamphichthys hypostomus petiti ssp. nov. Un curieux poisson Gymnotoïde arénicole. Vie et Milieu, 17 (Suppl.): 485-498.; Nijssen et al., 1976Nijssen, H., I. J. H. Isbrücker & J. Géry. 1976. On the species of Gymnorhamphichthys Ellis 1912, translucent sand-dwelling gymnotid fishes from South America (Pisces, Cypriniformes, Gymnotoidei). Studies On Neotropical Fauna and Environment, 11: 37-63.; Schwassmann, 1976Schwassmann, H. O. 1976. Ecology and taxonomic status of different geographic populations of Gymnorhamphichthys hypostomus Ellis (Pisces, Cypriniformes, Gymnotoidei). Biotropica, 8: 25-40.; Schwassmann, 1989Schwassmann, H. O. 1989. Gymnorhamphichthys rosamariae, a new species of knife fish (Rhamphichthyidae, Gymnotiformes) from the upper Rio Negro, Brazil. Studies On Neotropical Fauna and Environment, 24: 57-167.; Triques, 1999Triques, M. L. 1999. Three new species of Rhamphichthys Müller et Troschel, 1846. Revue Française d'Aquariologie-Herpétologie, 26: 1-6.), or by the absence of a paired accessory electric organ in the mental or humeral region, vs. presence in the Steatogeni (de Santana & Crampton, 2010de Santana, C. D. & R. P. Vari. 2010. Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies. Zoological Journal of the Linnean Society, 159: 223-371.).

Within the Hypopomidae sensuMaldonado-Ocampo et al. (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.), Brachyhypopomus is diagnosed from Akawaio by the presence of three or four pectoral proximal radials, vs. five in Akawaio (Maldonado-Ocampo et al., 2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.). Brachyhypopomus is diagnosed from Hypopomus by the shorter snout, 18.7-32.6% of HL, vs. 33.3-40.1% of HL in adult H. artedi (based on measurements taken from 30 specimens of H. artedi from diverse localities in the Guyana Shield). Brachyhypopomus is diagnosed from Racenisia by the presence of the antorbital + infraorbital, and the preopercular cephalic lateral line canal bones, vs. complete absence in Racenisia; these canal bones are clearly visible in alcohol preserved specimens.

Brachyhypopomus cannot be diagnosed unambiguously from Microsternarchus or from Procerusternarchus on the basis of external characters alone. However, with the exception of B. benjamini and B. provenzanoi, species of Brachyhypopomus are diagnosed from Microsternarchus by the presence of scales on the middorsal portion of the anterior third of the body, vs. absence in M. bilineatus and in M. brevis (Fernandes et al., 2015Fernandes, C. C., A. Nogueira, A. Williston & J. A. Alves-Gomes. 2015. A new species of electric knifefish from the rio Negro, Amazon basin (Gymnotiformes: Hypopomidae, Microsternarchini). Proceedings of the Academy of Natural Sciences of Philadelphia, 164: 213-227.).

Previous generic diagnoses. Brachyhypopomus was assigned to the new family Hypopomidae sensuMago-Leccia (1978Mago-Leccia, F. 1978. Los peces de la familia Sternopygidae de Venezuela. Acta Científica Venezolana, 29: 1-89.) based on the following combination of characters: absence of teeth in both oral jaws; relatively short snout; nares tubular in shape and well-separated, the anterior nares at the corner of the upper lip; 3-4 pectoral-fin radials; supraorbital canal embedded with frontal bone; posttemporal and supracleithrum not fused; fixed anus position; and anal-fin origin posterior to the pectoral fin base. Two of these characters are now known to apply variably to members of Brachyhypopomus: two species, B. bennetti and B. walteri, possess premaxillary teeth in adults (Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.); and the supraorbital canal is independent from the frontal bone in B. flavipomus and B. verdii. Albert (2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.) provided a revised diagnosis for the Hypopomidae, but many of the characters fail to accommodate recent increases in the species diversity of Brachyhypopomus (including many of the species described herein). A new formal generic diagnosis for the family - one which accommodates the recently-described genera Akawaio and Procerusternarchus, and one which excludes the Steatogeni, following Maldonado-Ocampo et al. (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.) - is necessary, but is beyond the scope of this paper.

Mago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 47) diagnosed six species of Brachyhypopomus from Hypopomus (but not from other genera) by "their short snout and included mouths, absence of mesocoracoid bridge, short and crescent-shaped maxillary bone" (Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 165, figs. 65d,f), and "posterior nares closer to eyes." Of these characters, only "short snout" is able to diagnose all 28 species of Brachyhypopomus recognized herein from Hypopomus. Albert and Campos-da-Paz (1998Albert, J. S. & R. Campos-da-Paz. 1998. Phylogenetic systematics of Gymnotiformes with diagnoses of 58 clades: A review of available data. Pp. 419-446. In: Malabarba L. R., R. E. Reis, R. P. Vari, Z. M. S. Lucena & C. A. S. Lucena (Eds.). Phylogeny and classification of neotropical fishes. Porto Alegre, Edipucrs.: 426) and Albert (2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.: 68) diagnosed the (as-then) six valid species of Brachyhypopomus (and seven undescribed species) from other Gymnotiformes based on four characters others than those listed previously by Mago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.): 1. "Premaxilla gracile with a curved anterior margin and forming a distinct angle with the maxilla in lateral view (... except B. beebei; also present in Steatogenys ...)"; 2. "Dentary gracile"; 3. "Body cavity with 16 - 17 PCV [precaudal vertebrae]"; 4. "Single transitional vertebrae (sic)." However, each of these four characters fails to unambiguously diagnose all 28 species of Brachyhypopomus recognized herein from other gymnotiforms.

Sullivan (1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.) proposed a single character diagnostic character for the genus, "medial portion of upper jaw (premaxillary portion) forms distinct angle with sides of upper jaw (maxillary portion) in lateral and frontal view" (not present in Microsternarchus and Hypopomus), but acknowledged that this character also occurs in Steatogenys and some sternopygid genera. Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.) revisited this character and considered it to be a "single possible synapomorphy" for Brachyhypopomus - contrasting with the condition in most other Rhamphichthyoidea, in which the "maxilla is straight to slightly curved, and the medial and upper portions of the upper jaw form a continuous curve with little to no inflection point, viewed externally". We found that the curvature of the area of the jaws in which the premaxilla and maxilla join is highly variable, and is an unreliable means to distinguish individuals of all 28 species of Brachyhypopomus from individuals of Microsternarchus bilineatus (and from specimens of additional undescribed species of Microsternarchus). For example, Brachyhypopomus batesi, B. benjamini¸ and B. provenzanoi are indistinguishable from Microsternarchus in jaw structure, viewed externally.

Description. Members of the genus exhibit relatively little variation in body and head shape, and are generally delimited by a combination of morphometric and meristic characters. For brevity, we describe here external characters common to all congeners rather than repeating these in each of the species descriptions and redescriptions presented below.

Maximum known body size 461 mm TL (see redescription of B. brevirostris). Body elongate and laterally compressed (body width as percentage of body depth 36.4-82.1% and 18.9-51.7% at anal-fin origin and anal-fin middle respectively), reaching maximum width and depth in posterior region of body cavity and tapering gently posteriorly; short to very long caudal filament located posterior to the anal-fin terminus (4.2-54.5% TL; 7.4-83.1% LEA in intact specimens) - comprising mostly electrocytes, vertebral centra or a cartilaginous rod-like structure, and associated blood vessels and nerves (Albert, 2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.). Greatest body depth and width located in area of body cavity or slightly posterior to body cavity, lateral sides of body more or less straight in dorsal view posterior to abdominal cavity. Dorsal profile of body straight or nearly straight in lateral view.

Single hypaxial electric organ (EO) extending just posterior to the urogenital orifice to the end (or near end) of the caudal filament; 1-6 bilateral horizontal (length way) columns of electrocytes along its length, 3-6 columns at anal-fin terminus, and 2-6 columns at a midpoint between anal-fin terminus and end of caudal filament. Paired subdermal accessory EO of unknown function in the opercular region are known from three species: B. bombilla, B. menezesi, and B. regani.

Anal fin elongate (71.6-94.0% LEA) with origin located in anterior portion of body cavity, posterior to cleithrum of pectoral girdle; 143 to 293 rays (branched and unbranched combined). Each anal-fin ray connected via a ball-and-socket joint to a proximal anal-fin pterygiophore, and articulated in circular movements by the pinnalis analis muscles (Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.). Anal-fin pterygiophores shorter than hemal spines at midbody.

Pectoral fin short to moderate (longest pectoral ray 3.2-8.5% LEA), broad and distally rounded or pointed, with 10-21 rays (branched and unbranched combined). Dorsal, adipose, and pelvic fins, and pelvic girdle absent, in common with all gymnotiforms. Caudal fin absent in common with all Rhamphichthyoidea, Sternopygidae, and Gymnotidae -although see de Santana et al. (2013de Santana, C. D., R. P. Vari & W. B. Wosiacki. 2013. The untold story of the caudal skeleton in the electric eel (Ostariophysi: Gymnotiformes: Electrophorus). PLoS One, 8: e68719.) for comments on the caudal skeleton of Electrophorus.

Body cavity restricted to no more than 2.5 head-lengths posterior to occiput, with viscera rotated so that the anus and urogenital orifice are positioned below the operculum, near the isthmus. Anus and urogenital orifice in close juxtaposition. Urogenital papilla developed into elevated tube in breeding males and females. Transparent and thin-walled non-vascularized and non-physostomous swim bladder, comprising a smaller anterior chamber, and a larger posterior chamber (Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.: 189, fig. 32). Body cavity short, with 15-26 precaudal vertebrae (including up to 3 transitional vertebrae). 1-3 slender displaced hemal spines embedded in hypaxial musculature posterior to body cavity, sometimes forked with bifurcated portions facing anteriorly.

Scales cycloid, with irregular ovoid shape; smaller dorsally and ventrally and larger laterally, especially in posterior region of body; partially or completely covered with skin and distributed over all of post-cranial portion of body except fins (exceptions are the absence of scales along the middorsal region of anterior third of body and over the anal-fin pterygiophores in B. benjamini and B. provenzanoi). 4-9 rows of lateral line scales above lateral line to dorsal midline at midbody. Anterior-most perforated lateral line scale located near vertical through pectoral-fin origin. Lateral line continuous in most species anterior to anal-fin terminus, but not continuing to end of caudal filament; usually terminating in the middle portion of the caudal filament. Dorsal branch of posterior lateral line nerve separate from recurrent ramus of anteroventral lateral line nerve (Albert, 2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.: character 117 therein). No fleshy dorsal electroreceptive organ (as in the Apteronotidae). Body variably pigmented with dark bands and mottled patterns of stellate chromatophores and subcutaneous pigment, but never translucent as in several sternopygid taxa, notably many Eigenmannia and Rhabdolichops species (Crampton, 2007Crampton, W. G. R. 2007. Diversity and adaptation in deep channel Neotropical electric fishes Pp. 283-339. In: Sebert P., D. W. Onyango & B. G. Kapoor (Eds.). Fish life in special environments. Enfield, NH, Science Publishers.). Chromatophores contract at night resulting in a striking pale appearance of most Brachyhypopomus under artificial illumination; even those that are very darkly pigmented during the day. Ampullary electroreceptors in rosettes, with highest density on snout and around mouth. Schreckstoff club cells and observable fright response absent (Fink & Fink, 1981Fink, S. V. & W. L. Fink. 1981. Interrelationships of the ostariophysan fishes (teleostei). Zoological Journal of the Linnean Society, 72: 297-353.: character 117 therein). Head widest in opercular region and deepest in occipital region. Eye small to relatively large in size (5.9-20.6% HL), laterally positioned on dorsal half of head, visible in dorsal view, and completely covered by thin translucent epidermis (orbital margin not free). Mouth small and terminal or slightly to moderately sub-terminal; closed lips meet ventral to a horizontal through ventral margin of eye. 3-7 small, needle-like premaxillary teeth present in all examined small juveniles (< 50 mm TL) but absent in adults except in B. bennetti and B. walteri (Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). Dentary edentate in adults, although small conical dentary teeth present in all examined small juveniles (< 50 mm TL). Maxilla edentate. Premaxillary and maxillary portions of upper jaw gently convex anteriorly, joining to form a slight concave angle or moderate to acute sigmoidal profile to upper jaw. Anterior and posterior nares present; both either ellipsoid or circular in shape. Anterior nares located at upper lip. Posterior nares located near eye (1.1-10.4% HL from anterior margin of orbit). Dorsal and ventral profile of head from almost straight to strongly convex. Snout short (18.7-32.6% HL) and rounded. Cephalic lateral line canals and pores complete in adults, with pores conspicuous (de Santana & Crampton, 2011de Santana, C. D. & W. G. R. Crampton. 2011. Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes). Zoological Journal of the Linnean Society, 163: 1096-1156.: 1104, fig. 2) - with the following two exceptions: i. The antorbital is absent in B. bennetti and B. walteri; ii. The branch of the infraorbital canal over the frontal is absent in B. alberti, B. arrayae, B. belindae, B. hamiltoni, and B. verdii. Branchial opening restricted to a short vertical aperture at posterior margin of opercle, branchial membranes joined at isthmus. 25-63 gill filaments on first arch. Sexual dimorphism of cranial morphology absent in all species in contrast to its presence in many apteronotid taxa (Albert & Crampton, 2009Albert, J. S . & W. G. R. Crampton. 2009. A new species of electric knifefish, genus Compsaraia (Gymnotiformes: Apteronotidae) from the Amazon River, with extreme sexual dimorphism in snout and jaw length. Systematics and Biodiversity, 7: 81-92.; de Santana & Vari, 2010de Santana, C. D. & R. P. Vari. 2010. Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies. Zoological Journal of the Linnean Society, 159: 223-371.; Fernandes et al., 2002Fernandes, C. C., J. G. Lundberg & C. Riginos. 2002. Largest of all electric-fish snouts: hypermorphic facial growth in Apteronotus hasemani and the identity of Apteronotus anas (Gymnotiformes: Apteronotidae). Copeia, 2002: 52-61.) and in the sternopygid genus Archolaemus (Vari et al., 2012Vari, R. P., C. D. De Santana & W. B. Wosiacki. 2012. South American electric knifefishes of the genus Archolaemus (Ostariophysi, Gymnotiformes): undetected diversity in a clade of rheophiles. Zoological Journal of the Linnean Society, 165: 670-699.).

Functional biology and ecology. Specializations associated with the Electrogenic and Electrosensory system: As with other Gymnotiformes, Brachyhypopomus species exhibit a suite of morphological specializations associated with active electroreception and nocturnal activity. The eyes are reduced in size and retinal projections to the brain are much reduced (Lázár et al., 1987Lázár, G. P., P. Tóth & T. Szabo. 1987. Retinal projections in gymnotiform fishes. Journal für Hirnforschung, 28: 13-26.). A culteriform (knife-shaped) body plan facilitates maximum dipole separation of the fish as a dipole source (and therefore maximizes field strength per unit body mass, Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.), and optimizes use of the body surface as a relatively rigid electroreceptive array. Locomotion by undulation of the elongated anal-fin permits backwards-forwards electroreceptive rostral probing ('scan swimming' sensuJulian et al., 2003Julian, D., W. G. R. Crampton, S. E. Wohlgemuth & J. S. Albert. 2003. Oxygen consumption in weakly electric Neotropical fishes. Oecologia, 137: 502-511.) (Albert & Crampton, 2005Albert, J. S . & W. G. R. Crampton. 2005. Electroreception and electrogenesis. Pp. 431-472. In: Evans D. (Ed.) The physiology of fishes. 3rd edition. New York, C.R.C. Press.; Lannoo & Lannoo, 1993Lannoo, M. J. & S. J. Lannoo. 1993. Why do electric fishes swim backwards? An hypothesis based on gymnotiform foraging behaviour interpreted through sensory constraints. Environmental Biology of Fishes, 36: 157-165.; Lissmann, 1961Lissmann, H. W. 1961. Ecological studies on gymnotids. Pp. 215-226. In: Chagas C. & A. Paes de Carvalho (Eds.). Bioelectrogenesis. Amsterdam, Elsevier.; Nanjappa et al., 2000Nanjappa, P., L. Brand & M. Lannoo. 2000. Swimming patterns associated with foraging in phylogenetically and ecologically diverse American weakly electric teleosts (Gymnotiformes). Environmental Biology of Fishes, 58: 97-104.; Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.) (in addition to anal-fin locomotion, Brachyhypopomus also swim in rapid bursts by anguilliform movement of the body when startled, Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.). Body rigidity is augmented by ossified intermuscular bones (Schlesinger, 1910Schlesinger, G. 1910. Die gymnonoten. Eine phylogenetisch-ethologische Studie. Zoologische Jahrbuecher, 29: 613-640.). Most of the post-cranial body and caudal filament is specialized for electrogenesis, with the body cavity confined to an area extending no more than 2.5 head-lengths posterior to the occiput (Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.: 189, fig. 32).

Electric Organs: The hypaxial electric organ (EO) comprises myogenic electrocytes (derived from muscle cells). Studies of B. gauderio demonstrate that the EO develops from the ventral hypaxial musculature in larvae, and is retained through development (Franchina, 1997Franchina, C. R. 1997. Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 181: 111-119.). Initially the EO comprises cylindrical, overlapping stalk-less electrocytes, but these later shorten along the rostrocaudal axis, separate into vertically aligned "rows", and form stalk-like caudal projections onto which the spinal electromotor neurons terminate (Bass, 1986Bass, A. H. 1986. Electric organs revisited: evolution of a vertebrate communication and orientation organ. Pp. 13-70. In: Bullock T. H. & W. Heiligenberg (Eds.). Electroreception. New York, Wiley.: 16, fig. 1; Franchina, 1997Franchina, C. R. 1997. Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 181: 111-119.: 115-117, figs. 7-10). EODs are first generated six days after hatching, at 7 mm TL in B. gauderio (Franchina, 1997Franchina, C. R. 1997. Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 181: 111-119.), and at 6-8 mm in B. beebei (Westby, 1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.). Beyond the late larval stage (TL > 37 mm), the EO of B. gauderio extends parallel to the body axis along the entire ventrolateral margin, from near the gill isthmus to the tip of the caudal filament (although in some species the distal portions of the caudal filament are sometimes free of electrocytes, especially in breeding males; see descriptions and redescriptions herein).

The adult EO of Brachyhypopomus comprises 3-6 bilateral longitudinal (horizontal) columns of cylindrical or box-shaped electrocytes bound by connective sheaths (Bass, 1986Bass, A. H. 1986. Electric organs revisited: evolution of a vertebrate communication and orientation organ. Pp. 13-70. In: Bullock T. H. & W. Heiligenberg (Eds.). Electroreception. New York, Wiley.; Bennett, 1961Bennett, M. V. L. 1961. Modes of operation of electric organs. Annals of the New York Academy of Sciences, 94: 458-509.; 1971aBennett, M. V. L. 1971a. Electric organs. Pp. 347-484. In: Hoar W. S. & D. J. Randall (Eds.). Fish physiology. New York, Academic Press.; Franchina, 1997Franchina, C. R. 1997. Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 181: 111-119.; Hopkins et al., 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.; Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.). An opercular accessory electric organ distinct from the main hypaxial EO was first reported by Sullivan (1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.) for B. regani (listed as B. electropomus), and has also been discussed by Crampton & Albert (2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.) and Carvalho (2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.). Caputi (1999Caputi, A. A. 1999. The electric organ discharge of pulse gymnotiforms: The transformation of a simple impulse into a complex spatiotemporal electromotor pattern. Journal of Experimental Biology, 202: 1229-1241.) and Caputi et al. (1998Caputi, A. A., A. C. Silva & O. Macadar. 1998. The electric organ discharge of Brachyhypopomus pinnicaudatus: The effects of environmental variables on waveform generation. Brain Behavior and Evolution, 52: 148-158.) review how the synchronized activity of electrocytes in the EO of B. gauderio - combined with the filtering properties of the skin and tissue of the fish, and the load of the surrounding water - determine in ensemble the spatiotemporally complex "near field" discharge that sums to the head-to-tail recorded EOD recorded in the far field.

Impedance matching: Impedance matching of electric organ anatomy to narrow ranges of conductivity has been noted in several species (Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; Hopkins, 1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.). Brachyhypopomus bullocki and B. brevirostris, which are restricted to low conductivity systems (< 30 µScm-1) exhibit a predominantly serial arrangement of electrocytes in the caudal portion of the organ (longer caudal filaments comprising relatively few horizontal bilateral columns of electrocytes). In contrast, B. bennetti, B. diazi, and B. occidentalis (and also B. palenque, see description herein), which are restricted to high conductivity systems (>60 µScm-1), exhibit a parallel arrangement of electrocytes (short caudal filaments with more electrocyte columns). The possibility that conductivity may serve as a barrier to the dispersal of some species, and consequently play a role in reproductive isolation, has been suggested by Crampton (1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.) and Hopkins (1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.).

Electric Organ Discharges:Crampton & Albert (2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.) reviewed the diversity of head-to-tail recorded EODs in Brachyhypopomus. Of 18 species for which EOD data have been presented, 12 generate biphasic or nearly biphasic EODs with durations varying from ca. 0.5-5 ms. One species, B. bennetti, generates a monophasic EOD. Five species generate relatively short (0.5 - 1.5 ms), more complex triphasic or tetraphasic EODs (Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.). Monophasic larval EODs have been documented in B. beebei, B. brevirostris, B. gauderio, and B. occidentalis, and this is presumed to be the case in other congeners, as in all other gymnotiforms (Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.). The EOD pulse rate of Brachyhypopomus varies from ca. 2 to 110 Hz, and typically increases from a lower resting day-time rate to a higher nocturnal active rate (Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.). Assad et al. (1999Assad, C., B. Rasnow & P. K. Stoddard. 1999. Electric organ discharges and electric images during electrolocation. Journal of Experimental Biology, 202: 1185-1193.), and Stoddard et al. (1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.) map heterogeneity of the near-field recorded EOD of B. beebei, B. gauderio, and B. walteri.

There is a rich and rapidly growing literature on the behavior, neuroethology, physiology, energetics, and hormonal basis of EOD generation and EOD plasticity in Brachyhypopomus - focused primarily on the model species B. gauderio, which is reviewed in part by Assad et al. (1999Assad, C., B. Rasnow & P. K. Stoddard. 1999. Electric organ discharges and electric images during electrolocation. Journal of Experimental Biology, 202: 1185-1193., 1998), Stoddard (2006Stoddard, P. K. 2006. Plasticity of the electric organ discharge waveform: contexts, mechanisms, and implications for electrocommunication. Pp. 623-646. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NJ., Science Publishers.), Gavassa et al. (2013Gavassa, S., A. Goldina, A. C. Silva & P. K. Stoddard. 2013. Behavioral ecology, endocrinology and signal reliability of electric communication. Journal of Experimental Biology, 216: 2403-2411.), Markham (2013Markham, M. R. 2013. Electrocyte physiology: 50 years later. Journal of Experimental Biology, 216: 2451-2458.), Silva et al. (2013), and Salazar et al. (2013Salazar, V. L., R. Krahe & J. E. Lewis. 2013. The energetics of electric organ discharge in gymnotiform weakly electric fish. Journal of Experimental Biology, 216: 2459-2468.).

Electroreceptors: In common with all other gymnotiforms, Brachyhypopomus possess a cutaneous array of ampullary and tuberous electroreceptors. Ampullary electroreceptors are tuned to low frequencies and facilitate passive electroreception of weak, low-frequency bioelectric fields. Tuberous electroreceptors are typically tuned to higher frequencies and facilitate both the active electrolocation of objects, and the passive detection of electric fields from other fish - an important component of electrocommunication (Hopkins, 2005Hopkins, C. D. 2005. Passive electrolocation. Pp. 264-289. In: Bullock T. H., C. D. Hopkins, A. N. Popper & R. R. Fay (Eds.). Electroreception. New York, Springer.; Hopkins et al., 1997Hopkins, C. D., K. Shieh, D. W. J. McBride & M. Winslow. 1997. A quantitative analysis of passive electrolocation behavior in electric fish. Brain Behavior and Evolution, 50 (suppl 1): 32-59.). The morphology of ampullary and tuberous electroreceptors in Brachyhypopomus, their distribution over the body surface, and their directional sensitivity are among the best known of all gymnotiforms, having been described by Bullock et al. (1961Bullock, T. H., S. Hagiwara, K. Kusano & K. Negishi. 1961. Evidence for a category of electroreceptors in the lateral line of gymnotid fishes. Science, 134: 1426-1427.), Hagiwara et al. (1962Hagiwara, S., K. Kusano & K. Negishi. 1962. Physiological properties of electroreceptors of some gymnotids. Journal of Neurophysiology, 25: 430-449.), Szamier & Wachtel (1970Szamier, R. B. & A. W. Wachtel. 1970. Special cutaneous receptor organs of fish. VI. Ampullary and tuberous organs of Hypopomus. Journal of Ultrastructure Research, 30: 450-471.), Bennett (1971bBennett, M. V. L. 1971b. Electroreception. Pp. 493-574. In: Hoar W. S. & D. J. Randall (Eds.). Fish physiology. New York, Academic Press .), Szabo (1974Szabo, T. 1974. Anatomy of the specialized lateral line organs of electroreception. Pp. 13-58. In: Fessard A. (Ed.) Handbook of sensory physiology, Vol. III. Electroreceptors and other specialized receptors in lower vertebrates. Berlin, Springer.), Yager & Hopkins (1993Yager, D. D. & C. D. Hopkins. 1993. Directional characteristics of tuberous electroreceptors in the weakly electric fish, Hypopomus (Gymnotiformes). Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 173: 401-414.), and McKibben et al. (1993McKibben, J. R., C. D. Hopkins & D. D. Yager. 1993. Directional sensitivity of tuberous electroreceptors- polarity preferences and frequency tuning. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 173: 415-424.). Tuberous electroreceptor frequency responses in the genus, showing a correspondence of electroreceptor tuning with peak frequency characteristics of the EOD, are described by Bastian (1976Bastian, J. 1976. Frequency response characteristics of electroreceptors in weakly electric fish (Gymnotoidei) with a pulse discharge. Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 112: 165-180.; 1977Bastian, J. 1977. Variations in the frequency response of electroreceptors dependent on receptor location in weakly electric fish (Gymnotoidei) with a pulse discharge. Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology , 121: 53-64.) and Hopkins & Heiligenberg (1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.).

Groove-like depigmented epidermal canals leading to tuberous electroreceptors, and which therefore may play a role in active electroreception are known from all members of the genus. Sullivan (1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.) noted for B. diazi and B. occidentalis that "Microscopic examination and histological sections of these canals show them to be narrow tubes overlying one or more scales with an external pore anteriorly and a tuberous electroreceptor at the posterior end (J. Sullivan and C. Hopkins unpubl.)." The epidermal canals of Brachyhypopomus vary in abundance between species (see species descriptions and redescriptions herein) but are mostly located in the posterior half of the body - where they are restricted to nearby and either side of the lateral line, either side of the dorsal midline, and approximately midway between the lateral line and dorsal midline. In B. diazi the epidermal canals cover a larger area of the body than in congeners, including much of the dorsal and ventral flank of the anterior half of the body. Groove-like epidermal canals are also observable in all other hypopomid genera sensuMaldonado-Ocampo (2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.), including Akawaio, Hypopomus, Procerusternarchus, and (in considerably lower densities), in Microsternarchus and Racenisia.

Auditory sensory apparatus: In addition to providing buoyancy, the swim bladder of Brachyhypopomus is involved in the ostariophysan hearing system, which involves a connection from the anterior chamber of the swim bladder to the stato-acoustic organ of the inner ear via the Weberian ossicles encased by the first four vertebrae. A pseudotympanum, a window-like thinning of the hypaxial muscles lateral to the anterior portion of the swim bladder is present, and comprises three distinct hiatuses in the obliquus inferioris and obliquus superioris muscles (Dutra et al., 2015Dutra, G. M., F. C. Jerep, R. P. Vari & C. D. De Santana. 2015. The pseudotympanum in the Gymnotiformes (Teleostei, Ostariophysi, Otophysi): homology and evolution of a previously unexplored system in Neotropical electric fishes. Zoological Journal of the Linnean Society, 174: 114-129.). The pseudotympanum may enhance sound detection by acting as a window through which sound waves reach the anterior chamber of the swim bladder (Dutra et al., 2015Dutra, G. M., F. C. Jerep, R. P. Vari & C. D. De Santana. 2015. The pseudotympanum in the Gymnotiformes (Teleostei, Ostariophysi, Otophysi): homology and evolution of a previously unexplored system in Neotropical electric fishes. Zoological Journal of the Linnean Society, 174: 114-129.).

Adaptations to hypoxia: The influence of dissolved oxygen on the distributions of Brachyhypopomus is discussed by Crampton (1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.; 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; 2008Crampton, W. G. R. 2008. Ecology and life history of an Amazon floodplain cichlid: the discus fish Symphysodon (Perciformes: Cichlidae). Neotropical Ichthyology, 6: 599-612.) and Crampton & Albert (2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.). Species that occur in seasonally or perennially dysoxic habitats such as whitewater floodplains and terra firme swamps are adapted to survive protracted periods of hypoxia (< 1mgl-1) or complete anoxia, while those that occur in permanently normoxic habitats, such as terra firme streams, are not (Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.,bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Some species are able to tolerate hypoxia by undertaking aerial gill respiration - either by periodically aspirating air bubbles into their gill chambers, or by opening their mouths at the surface meniscus to expose the gill lamellae to air (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.; Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.). Carter & Beadle (1931Carter, G. S. & L. C. Beadle. 1931. The fauna of the swamps of the Paraguayan Chaco in relation to its environment. II. Respiratory adaptations in the fishes. Journal of the Linnean Society of London, Zoology, 37: 327-366.) reported an expanded gill chamber, unusually long gill lamellae, and greatly expanded secondary folds of the gill lamellae in B. "brevirostris" (probably B. gauderio) from the Paraguayan Chaco, and also concluded that the air bladder and gill chamber epithelium play no significant role in air breathing. Crampton et al. (2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.) reported that species endemic to seasonally anoxic whitewater floodplain habitats exhibit significantly larger gills than species endemic to permanently normoxic terra firme stream systems. Many species of Brachyhypopomus also exhibit a reduction of activity and EOD pulse rate in response to declining oxygen levels (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.).

Regeneration: Brachyhypopomus species, as in other Rhamphichthyoidea and Sternopygidae, are able to regenerate the entire post-coelomic portion of the body following damage from predators, with the vertebrae replaced by a rigid cartilaginous rod (Albert, 2001Albert, J. S. 2001. Species diversity and phylogenetic systematics of American knifefishes (Gymnotiformes, Teleostei). Miscellaneous Publications Museum of Zoology University of Michigan, 190: 1-127.; Albert & Crampton, 2005Albert, J. S . & W. G. R. Crampton. 2005. Electroreception and electrogenesis. Pp. 431-472. In: Evans D. (Ed.) The physiology of fishes. 3rd edition. New York, C.R.C. Press.; Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.; Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). The proportion of individuals with caudal filament damage in natural populations has been estimated for three species: B. brevirostris - 8% (Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.); B. draco - 6.7%, with 22.1% exhibiting regeneration from earlier damage (Cognato et al., 2007Cognato, D. D. P., J. Giora & C. B. Fialho. 2007. Análise da ocorrência de lesões corporais em três espécies de peixe elétrico (Pisces: Gymnotiformes) do sul do Brasil. Pan-American Journal of Aquatic Sciences, 2: 242-246.); B. occidentalis - varying among populations from 12% to 46% (Dunlap et al., 2016Dunlap, K. D., A. Tran, M. A. Ragazzi & R. Krahe. 2016. Predators inhibit brain cell proliferation in natural populations of electric fish Brachyhypopomus occidentalis. Proceedings of the Royal Society B-Biological Sciences, 283: 283 20152113; DOI: 10.1098/rspb.2015.2113
https://doi.org/10.1098/rspb.2015.2113...
). Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.) and Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.) documented how damage to portions of the body posterior to the body cavity can influence the EOD waveform.

Reproductive anatomy: In B. gauderio, the males develop a paired, lobular testis of the unrestricted spermatogonial category, and females develop a paired saccular cystovary. In both sexes the gonads are positioned ventrally, and expand posteriorly until they reach the posterior wall of the abdominal wall (Quintana et al., 2004Quintana, L., A. Silva, N. Berois & O. Macadar. 2004. Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators in Brachyhypopomus pinnicaudatus from a temperate climate. Journal of Experimental Biology, 207: 1843-1853.). Gonadal morphology appears to be similar in other species. França et al. (2007França, G. F., C. Oliveira & I. Quagio-Grassiotto. 2007. Ultrastructure of spermiogenesis and spermatozoa of Gymnotus cf. anguillaris and Brachyhypopomus cf. pinnicaudatus (Teleostei: Gymnotiformes). Tissue and Cell, 39: 131-139.) and Giora & Burns (2011Giora, J. & J. R. Burns. 2011. Sperm ultrastructure in three different families of weakly electric fishes (Teleostei: Gymnotiformes). Neotropical Ichthyology, 9: 881-888.) describe the ultrastructure of spermatozoa in Brachyhypopomus.

Reproductive biology and life history: Detailed accounts of the reproductive ecology and life history of Brachyhypopomus are available for B. occidentalis from Panama (Hagedorn, 1986Hagedorn, M. 1986. The ecology, courtship and mating of gymnotiform electric fish. Pp. 495-525. In: Bullock T. H. & W. Heiligenberg (Eds.). Electroreception. New York, John Wiley and Sons.; 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.), and for three species from southern subtropical systems: B. bombilla (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.), B. draco (Schaan et al., 2009Schaan, A. B., J. Giora & C. B. Fialho. 2009. Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil. Neotropical Ichthyology, 7: 737-744.), and B. gauderio (Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.; Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.; Quintana et al., 2004Quintana, L., A. Silva, N. Berois & O. Macadar. 2004. Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators in Brachyhypopomus pinnicaudatus from a temperate climate. Journal of Experimental Biology, 207: 1843-1853.; Silva et al., 2007Silva, A., R. Perrone & O. Macadar. 2007. Environmental, seasonal, and social modulations of basal activity in a weakly electric fish. Physiology and Behavior, 90: 525-536.; Silva et al., 2002Silva, A., L. Quintana, J. L. Ardanaz & O. Macadar. 2002. Environmental and hormonal influences upon EOD waveform in gymnotiform pulse fish. Journal of Physiology -Paris, 96: 473-484.; Silva et al., 2008Silva, A., L. Quintana, R. Perrone & F. Sierra. 2008. Sexual and seasonal plasticity in the emission of social electric signals. Behavioral approach and neural bases. Journal of Physiology -Paris, 102: 272-278.) (and see species descriptions herein). The reproductive ecology of Amazon and Orinoco species is largely undocumented, although Alves-Gomes (1997) noted spawning preceding seasonal flooding in the rio Branco system of Roraima, Brazil, and Crampton (1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.) observed spawning coincident with the rising-water period and high water period in species from Amazonian floodplains.

At extreme southern latitudes Brachyhypopomus exhibit several adaptations to the austral winter - including gonadal quiescence, a general reduction in activity and feeding, and an accompanying reduction of the EOD pulse-rate (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.; 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.; Schaan et al., 2009Schaan, A. B., J. Giora & C. B. Fialho. 2009. Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil. Neotropical Ichthyology, 7: 737-744.; Silva et al., 2002Silva, A., L. Quintana, R. Perrone & F. Sierra. 2008. Sexual and seasonal plasticity in the emission of social electric signals. Behavioral approach and neural bases. Journal of Physiology -Paris, 102: 272-278.). Some species of Brachyhypopomus appear to live for only one year, with mortality following a terminal reproductive effort - including B. bennetti (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.) (listed therein as 'B. sp. 3'), B. gauderio (Silva et al., 2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.), B. occidentalis (Hagedorn, 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.), and B. pinnicaudatus (Kirschbaum & Schugardt, 2002Kirschbaum, F. & C. Schugardt. 2002. Reproductive strategies and developmental aspects in mormyrid and gymnotiform fishes. Journal of Physiology-Paris, 96: 557-566.). Fractional spawning has been observed in B. bombilla (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.), B. brevirostris (Kirschbaum et al., 2008Kirschbaum, F., U. Leyendecker, B. Nyonge, C. Schulz, H. Weitkamp, S. Didhiou, M. Thomas & C. Schugardt. 2008. Environmental control of cyclical reproduction of tropical freshwater fish: Evidence from comparative experimental data. Cybium, 32: 294-296.), B. draco (Schaan et al., 2009Schaan, A. B., J. Giora & C. B. Fialho. 2009. Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil. Neotropical Ichthyology, 7: 737-744.), B. gauderio (Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.; Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.), B. occidentalis (Hagedorn, 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.), and B. pinnicaudatus (Kirschbaum et al., 2008Kirschbaum, F., U. Leyendecker, B. Nyonge, C. Schulz, H. Weitkamp, S. Didhiou, M. Thomas & C. Schugardt. 2008. Environmental control of cyclical reproduction of tropical freshwater fish: Evidence from comparative experimental data. Cybium, 32: 294-296.). Kirschbaum & Schugardt (2002Kirschbaum, F. & C. Schugardt. 2002. Reproductive strategies and developmental aspects in mormyrid and gymnotiform fishes. Journal of Physiology-Paris, 96: 557-566.) reported egg diameters of approximately 1.7 mm in B. pinnicaudatus, with hatching on day three after spawning, and exogenous feeding beginning on day eight.

Neither nesting nor parental care are known for the genus, including species bred and observed carefully in captivity (pers. comm. P. K. Stoddard, Florida International University, USA, for B. gauderio; F. Kirschbaum, Humboldt University, Germany, for B. brevirostris and B. pinnicaudatus). Westby (1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.) reported small aggregations of larval Brachyhypopomus beebei in a coastal stream of French Guiana but these were apparently not attended by a parent. However, Giora et al. (2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.) reported aggregations of larval B. gauderio near single mature males.

Cytogenetics. Chromosomal rearrangements in gymnotiforms are suspected to play a significant role in reproductive isolation (Milhomem et al., 2008Milhomem, S. S. R., J. C. Pieczarka, W. G. R. Crampton, D. S. Silva, A. C. P. de Souza & J. R. Carvalho. 2008. Chromosomal evidence for a putative cryptic species in the Gymnotus carapo species-complex (Gymnotiformes, Gymnotidae). BMC Genetics, 9: 75.; Nagamachi et al., 2010Nagamachi, C. Y., J. C. Pieczarka, S. S. R. Milhomem, P. C. M. O'Brien, A. C. P. de Souza & M. A. Ferguson-Smith. 2010. Multiple rearrangements in cryptic species of electric knifefish, Gymnotus carapo (Gymnotidae, Gymnotiformes) revealed by chromosome painting. BMC Genetics, 11: 28.). Nonetheless, despite many descriptive cytogenetic studies of gymnotiform fishes (Oliveira et al., 2009Oliveira, C., F. Foresti & A. W. S. Hilsdorf. 2009. Genetics of neotropical fish: from chromosomes to populations. Fish Physiology and Biochemistry, 35: 81-100.), Brachyhypopomus remains poorly studied - with karyotypes available for only four species. Brachyhypopomus brevirostris exhibits a diploid number of 36, fundamental number (FN) of 42, and karyotypic formula 4m/2sm/8st/22a (Almeida-Toledo, 1987, cited in Cardoso et al., 2011Cardoso, A. L., J. C. Pieczarka, E. Feldberg, S. S. R. Milhomem, T. Moreira-Almeida, D. dos Santos Silva, P. Corrêa da Silva & C. Y. Nagamachi. 2011. Chromosomal characterization of two species of genus Steatogenys (Gymnotiformes: Rhamphichthyoidea: Steatogenini) from the Amazon basin: sex chromosomes and correlations with Gymnotiformes phylogeny. Review of Fish Biology and Fisheries, 21: 613-621.). Brachyhypopomus gauderio exhibits a diploid number of 42 in females (all acrocentric), and 41 for males (40 acrocentric, 1 metacentric), a FN of 42, and a karyotypic formula of 1m/42a in females and 1m/41a in males (Almeida-Toledo et al., 2000Almeida-Toledo, L. F., M. F. Z. Daniel-Silva, C. E. Lopes & S. Toledo-Filho. 2000. Sex chromosome evolution in fish. II. Second occurrence of an X1 X2 Y sex chromosome system in Gymnotiformes. Chromosome Research, 8: 335-340.; Mendes et al., 2012Mendes, V. P., A. L. D. Portela-Castro & H. F. Julio. 2012. First record of supernumary (B) chromosomes in electric fish (Gymnotiformes) and the karyotypic structure of three species of the same order from the upper Paraná River basin. Comparative Cytogenetics, 6: 1-16.). Brachyhypopomus pinnicaudatus exhibits a diploid number of 42 in females (all acrocentric) and 41 in males (40 acrocentric, 1 metacentric), and a FN of 42, as is the case in B. gauderio, and exhibits a karyotypic formula of 42st-a in females and 1m-sm/40st-a in males (Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.). Brachyhypopomus flavipomus (listed as B. n. sp. FLAV) exhibits a diploid number of 44 in females and 43 in male and a karyotypic formula of 44st-a in females and 1m-sm/42st-a in males (Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.). Cardoso et al. (2011Cardoso, A. L., J. C. Pieczarka, E. Feldberg, S. S. R. Milhomem, T. Moreira-Almeida, D. dos Santos Silva, P. Corrêa da Silva & C. Y. Nagamachi. 2011. Chromosomal characterization of two species of genus Steatogenys (Gymnotiformes: Rhamphichthyoidea: Steatogenini) from the Amazon basin: sex chromosomes and correlations with Gymnotiformes phylogeny. Review of Fish Biology and Fisheries, 21: 613-621.) highlighted the conservancy of the diploid number in the Steatogeni and Rhamphichthys (invariably 2n = 50), in contrast to its variability among Brachyhypopomus spp. (2n = 36, 41-42, or 43-44) and Hypopomus artedi (2n = 38), and noted that this pattern is consistent with the phylogenetic scheme of Alves-Gomes et al. (1995Alves-Gomes, J. A., G. Ortí, M. Haygood, W. Heiligenberg & A. Meyer. 1995. Phylogenetic analysis of the South American electric fishes (Order Gymnotiformes) and the evolution of their electrogenic system: A synthesis based on morphology, electrophysiology, and mitochondrial sequence data. Molecular Biology and Evolution, 12: 298-318.) (and also Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.; Maldonado-Ocampo et al., 2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.; Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.), in which the Steatogeni is placed within the Rhamphichthyidae.

Three of the four Brachyhypopomus with cytogenetic analyses exhibit morphologically differentiated sex chromosomes. Brachyhypopomus flavipomus (Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.), B. gauderio (Almeida-Toledo et al., 2000Almeida-Toledo, L. F., M. F. Z. Daniel-Silva, C. E. Lopes & S. Toledo-Filho. 2000. Sex chromosome evolution in fish. II. Second occurrence of an X1 X2 Y sex chromosome system in Gymnotiformes. Chromosome Research, 8: 335-340.; Mendes et al., 2012Mendes, V. P., A. L. D. Portela-Castro & H. F. Julio. 2012. First record of supernumary (B) chromosomes in electric fish (Gymnotiformes) and the karyotypic structure of three species of the same order from the upper Paraná River basin. Comparative Cytogenetics, 6: 1-16.), and B. pinnicaudatus (Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.) all exhibit an unusual multiple sex chromosome system of the X1X1X2X2: X1X2Y type. In contrast, B. brevirostris is chromosomally homomorphic, and sex determination mechanisms are unknown in this species (Cardoso et al., 2011Cardoso, A. L., J. C. Pieczarka, E. Feldberg, S. S. R. Milhomem, T. Moreira-Almeida, D. dos Santos Silva, P. Corrêa da Silva & C. Y. Nagamachi. 2011. Chromosomal characterization of two species of genus Steatogenys (Gymnotiformes: Rhamphichthyoidea: Steatogenini) from the Amazon basin: sex chromosomes and correlations with Gymnotiformes phylogeny. Review of Fish Biology and Fisheries, 21: 613-621.).

Taxonomic remarks. Here we provide comments on the early assignment of species now listed as Brachyhypopomus to the genus Hypopomus. Previous to the description of B. brevirostris (as Rhamphichthys brevirostris, see Introduction), the genus Rhamphichthys was erected by Kaup (1856Kaup, J. J. 1856. Family Gymnotidae. Pp. 124-142. In: Kaup J. J. (Ed.) Catalogue of apodal fishes. London, British Museum of Natural History.) to include two relatively short-snouted species - R. artedi (now Hypopomus artedi) and R. mulleri - now recognized as a junior synonym of Hypopomus artedi (Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .), and also five long-snouted species - now recognized as Rhamphichthys spp.

In a brief address to the Academy of Natural Sciences of Philadelphia, Gill (1864Gill, T. N. 1864. Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16: 151-152.) proposed a new genus Hypopomus to accommodate the relatively short-snouted Rhamphichthys mulleri, and separate this from the long-snouted species now assigned to the genus Rhamphichthys. Nonetheless, Gill's proposal was overlooked until 1903. For instance, Günther's (1870Günther, A. 1870. Catalogue of the fishes in the British Museum. London, British Museum of Natural History, 549 pp.) catalog of fishes in the British Museum instead divided the genus Rhamphichthys into two subgenera. The first subgenus, Rhamphichthys (Brachyrhamphichthys), diagnosed by "snout not tubiform; vent behind the eyes; anal fin commencing below the pectorals", corresponds to the modern genera Hypopomus and Brachyhypopomus (at the time this comprised H. artedi and its now junior synonym H. mulleri, and B. brevirostris). The second subgenus Rhamphichthys (Rhamphichthys), diagnosed by "snout produced into a tube; vent below or in advance of the eyes; anal fin commencing at the throat", corresponded to the modern genus Rhamphichthys. With respect to Brachyhypopomus brevirostris, Günther's (1870Günther, A. 1870. Catalogue of the fishes in the British Museum. London, British Museum of Natural History, 549 pp.) scheme was followed by Steindachner (1880Steindachner, F. 1880. Zur Fisch-fauna des Cauca und der Flüsse bei Guayaquil. Denkschriften der Kaiserlichen Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Classe, 42: 55-104, pls. 1-9. [Also published as a separate (1880), pp. 1-51, pls. 1-9.].) and Eigenmann & Eigenmann (1891Eigenmann, C. H. & R. S. Eigenmann. 1891. A catalogue of the freshwater fishes of South America. Proceedings of the United States National Museum, 14: 1-81.), and later modified by Eigenmann (1894Eigenmann, C. H. 1894. Notes on some South American fishes. A. Fishes collected by Frederick C. Hartt. Annals of the New York Academy of Sciences, 7 (art. 5): 625-637.), who listed Rhamphichthys (Brachyrhamphichthys) brevirostris as simply Brachyrhamphichthys brevirostris.

The first authors to abandon Günther's (1870Günther, A. 1870. Catalogue of the fishes in the British Museum. London, British Museum of Natural History, 549 pp.) scheme for short-snouted Rhamphichthyoidea, and instead adopt Gill's (1864Gill, T. N. 1864. Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16: 151-152.) proposed genus Hypopomus, which takes taxonomic priority, were Eigenmann & Kennedy (1903Eigenmann, C. H. & C. H. Kennedy. 1903. On a collection of fishes from Paraguay, with a synopsis of the American genera of cichlids. Proceedings of the Academy of Natural Sciences of Philadelphia, 55: 497-537) for "Hypopomus brevirostris" (referring in fact to B. gauderio, see synonymy section for B. gauderio), and later Eigenmann & Ward (1905Eigenmann, C. H. & D. P. Ward. 1905. The Gymnotidae. Proceedings of the Washington Academy of Sciences, 7: 158-188.) for B. brevirostris. Only in 1914, with Regan's description of Brachyhypopomus occidentalis was a second species added to Hypopomus sensuGill (1864Gill, T. N. 1864. Several points in ichthyology and conchology. Proceedings of the Academy of Natural Sciences of Philadelphia, 16: 151-152.). Thereafter, the name Hypopomus was used consistently until Mago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.) divided Gill's Hypopomus into Hypopomus and Brachyhypopomus (see Introduction).

Keys to species

Here we exclude the following regions represented by only one species: Caribbean drainages of northern Venezuela (B. diazi); rio São Francisco (B. menezesi); Atlantic and Pacific drainages of southern Costa Rica and Panama to Darién, and Maracaibo, Magdalena, Sinú and Atrato (B. occidentalis); Pacific drainages of Ecuador (B. palenque).

Key to the species of Brachyhypopomus occurring in the río Orinoco, Essequibo River, coastal drainages of the Guianas, and the rio Negro, including the rio Branco

1A. Absence of accessory electric organ (AEO) over opercular region .................... 2

1B. Presence of AEO over opercular region .................... B. regani (lower and middle Orinoco, upper Essequibo, some coastal drainages of Guianas)

2A. Presence of prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... 3

2B. Absence of pale prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... 4

3A. Anal-fin rays 214-230 .................... B. beebei (upper and lower Orinoco, Essequibo, coastal drainages of the Guianas, Negro including Branco).

3B. Anal-fin rays 176-196 .................... B. pinnicaudatus (small drainages of coastal French Guiana)

4A. Presence of scales in entire middorsal region .................... 5

4B. Absence of scales in middorsal region of anterior third of body .................... B. provenzanoi (upper Orinoco, upper Negro)

5A. Presence of dark suborbital stripe .................... 6

5B. Absence of dark suborbital stripe .................... 7

6A.Presence of horizontal dark-pigmented band along entire anal-fin base, over distal anal-fin pterygiophores .................... B. hendersoni (lower Negro, Essequibo)

6B. Absence of horizontal dark-pigmented band along anal-fin base .................... B. walteri (middle and lower Negro, Essequibo).

7A. Absence of series of diffuse horizontal dash-like dark markings along lateral line in posterior third of body, anterior to anal-fin terminus .................... 8

7B. Presence of series of diffuse horizontal dash-like dark markings along lateral line in posterior third of body, anterior to anal-fin terminus .................... B. hamiltoni (middle Negro)

8A. Anal-fin rays 143-184 .................... 9

8B. Anal-fin rays 190-293 .................... 10

9A. Presence of prominent dark flecks on flank .................... B. sullivani (upper, middle and lower rio Negro, Essequibo, central Orinoco)

9B. Absence of prominent dark flecks on flank .................... B. batesi (upper Negro)

10A. Absence of prominent wide brown saddles on flank, or saddles if present pale and restricted to dorsal region, not extending undisrupted across lateral line .................... 11

10B. Presence of prominent wide brown saddles on flanks, which extend undisrupted across lateral line .................... B. brevirostris (upper, central, and lower Orinoco, Essequibo, and coastal drainages of the Guianas).

11A. Orbital diameter 14.2-18.5% HL .................... B. bullocki (upper, middle and lower Orinoco, Negro including upper Branco, upper and middle Essequibo)

11B. Orbital diameter 9.6-13.0% HL .................... B. diazi (middle Orinoco in Llanos region, lower Orinoco)

Key to the species of Brachyhypopomus occurring in the upper Amazon, central Amazon, lower Amazon, and upper Madeira

1A. Absence of accessory electric organ (AEO) over opercular region .................... 2

1B. Presence of AEO over opercular region .................... 3

2A. Presence of prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... 4

2B. Absence of pale prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... 8

3A. Dorsal surface dorsal surface speckled with small brown chromatophores on light brown background; opercular accessory electric organ overlaid with dense scattering of chromatophores .................... B. bombilla (upper Madeira)

3B. Dorsal surface with large dark blotches on pale background; opercular accessory electric organ overlaid with depigmented skin .................... B. regani (upper, central, and lower Amazon, lower Madeira, upper Purus, Tapajós, Araguaia, lower Tocantins)

4A. Precaudal vertebrae 24-26 .................... 5

4B. Precaudal vertebrae 18-23 .................... 6

5A. Bilateral columns of electrocytes at anal-fin terminus 3 .................... B. verdii (upper Amazon)

5B. Bilateral columns of electrocytes at anal-fin terminus 4-5 .................... B. belindae (central Amazon)

6A. Anal-fin rays 175-212 .................... 7

6B. Anal-fin rays 214-230 .................... B. beebei (upper, central, lower Amazon, lower Madeira, lower Tocantins)

7A. Pectoral-fin rays 16-19 .................... B. arrayae (upper Madeira)

7B. Pectoral-fin rays 13-15 .................... B. pinnicaudatus (central and lower Amazon, lower, upper Madeira, lower Tocantins, Mearim)

8A. Presence of scales in entire middorsal region .................... 9

8B. Absence of scales in middorsal region of anterior third of body .................... B. benjamini (upper Amazon)

9A. Bilateral columns of electrocytes at anal-fin terminus 3-4 .................... 10

9B. Bilateral columns of electrocytes at anal-fin terminus 6 .................... B. bennetti (upper, central, lower Amazon, upper Madeira, lower Tocantins)

10A. Presence of scattered conspicuous black or charcoal flecks on flank .................... 11

10B. Absence of scattered conspicuous black or charcoal flecks on flank .................... 13

11A. Presence of horizontal dark band or heavy concentration of dark flecks along entire anal-fin base .................... 12

11B. Absence of horizontal dark band or heavy concentration of dark flecks along entire anal-fin base .................... B. sullivani (upper, central, and lower Amazon, upper Madeira, upper Tapajós, lower Tocantins)

12A. Mouth width 24.8-38.0% HL .................... B. cunia (upper Madeira)

12B. Mouth width 15.7-22.6% HL .................... B. hendersoni (central Amazon)

13A. Absence of dark suborbital stripe .................... 14

13B. Presence of dark suborbital stripe .................... B. walteri (upper, central, and lower Amazon, upper Madeira, Tapajós, upper Xingu, Araguaia, upper and lower Tocantins).

14A. Anal-fin rays 163-208 .................... 15

14B. Anal-fin rays 226-293 .................... B. brevirostris (upper, central, and lower Amazon, upper Madeira, upper Xingu)

15A. Head depth at occiput 69.9-87.9% HL .................... 16

15B. Head depth at occiput 61.0-67.9% HL .................... B. batesi (central Amazon)

16A.Mouth width 15.9-20.7% HL, absence of conspicuous patches of shiny yellow guanine on operculum and anterior to pectoral-fin base in live individuals .................... 17

16B. Mouth width 21.2-37.8% HL, presence of conspicuous patches of shiny yellow guanine on operculum and anterior to pectoral-fin base in live individuals .................... B. flavipomus (upper and central Amazon)

17A. Pectoral-fin rays 15-16 (mode 16) .................... B. alberti (upper Madeira)

17B. Pectoral-fin rays 12-15 (rarely 15), (mode 13) .................... B. hamiltoni (upper and central Amazon)

Key to the species of Brachyhypopomus occurring in the Paraná, Paraguay and Uruguay drainages, the Patos-Mirim lagoon system and nearby Atlantic drainages of Rio Grande do Sul, and coastal drainages of Brazil from states of São Paulo to Rio de Janeiro

1A. Absence of electric accessory organ over opercular region .................... 2

1B. Presence of electric accessory organ over opercular region .................... B. bombilla (lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim)

2B. Absence of pale prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... 3

2A. Presence of prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament .................... B. gauderio (lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim, Tramandaí)

3A. Absence of dark suborbital stripe .................... 4

3B. Presence of dark suborbital stripe .................... B. walteri (lower Paraná, upper Paraguay)

4A. Anal-fin rays 155-223 .................... 5

4B. Anal-fin rays 226-293 .................... B. brevirostris (upper Paraguay)

5A. Dorsal rami of the recurrent branch of the anterior lateral line nerve visible .................... 6

5B. Dorsal rami of the recurrent branch of the anterior lateral line nerve not visible .................... B. draco (lower Paraná, central, and lower Paraguay, Uruguay, Patos-Mirim, Tramandaí)

6A. Snout to pectoral-fin base 10.7-12.3% LEA .................... B. janeiroensis (São João, Paraíba and small intervening coastal drainages)

6B. Snout to pectoral-fin base 12.3-15.7% LEA .................... B. jureiae

(Ribeira de Iguape, Una do Prelado)

Brachyhypopomus alberti, new species

urn:lsid:zoobank.org:act:4791D07C-1995-453E-99EE-A87D60544613

(Fig. 4; Tables 2-6)

Brachyhypopomus sp. "alb". - Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3 (phylogeny, geographical and ecological distributions, gymnotiform biology).

Brachyhypopomus sp. "alberti". - Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 11, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. CBF 10284, male, 97 mm TL, 79 mm LEA, Bolivia, Beni, mun. Riberalta, stream nr. San José, nr. Riberalta, affl. río Beni, affl. rio Madeira, Amazonas dr., 10°55'32"S, 066°00'36"W, 28 Jun 2007, W. Crampton, J. Albert & M. Arraya.

Paratypes. 7 specimens, localities from mun. Riberalta, río Beni dr., affl. rio Madeira, Amazonas dr., collected by W. Crampton, J. Albert & M. Arraya. Bolivia. Beni. ANSP 197573, 1, female, 91 mm, 25 Jun 2007, CBF 10279, 1, female, 70 mm, 25 Jun 2007, CBF 10280, 1, immature, 64 mm, 25 Jun 2007, stream nr. lago San José, 10°54'47"S, 065°59'49"W. CBF 10281, 1, female, 72 mm, 28 Jun 2007, CBF 10282, 1, immature, 48 mm, 28 Jun 2007, CBF 10283, 1, immature, 58 mm, 28 Jun 2007, stream nr. San José, 10°55'32"S, 066°00'36"W. UMSS 07042, 1, male (CS), 84 mm, 6 Jul 2007, stream nr. Bocerón, on Riberalta-Guayaramerín rd., 11°02'51"S, 065°50'06"W.

Non-types. 9 specimens, localities from rio Madeira dr., Amazonas dr. Bolivia. Beni (localities from mun. Riberalta, río Beni dr.). UF 177345, 1, immature, 68 mm, Riberalta-Guayaramerín rd., nr. km 43, 11°00'30"S, 065°39'49"W. UMSS 7041, 1, male, 96 mm, stream nr. Bocerón, on Riberalta-Guayaramerín rd., 11°02'51"S, 065°50'06"W. UMSS 7043, 1, immature, 70 mm, stream nr. Hormiga, on Riberalta-Guayaramerín rd., 11°01'34"S, 065°52'58"W. UMSS 7044, 1, male, 111 mm, UMSS 7045, 1, female, 100 mm, Riberalta- Guayaramerín rd., nr. km 43, 11°01'58"S, 065°44'53"W. Brazil. Rondônia. UFRO-I 6482, 4, 53-57 mm, rio Guaporé upstream community Pedras Negras, affl. rio Mamoré, 12°52'03"S 62°52'38"W.

Diagnosis. Brachyhypopomus alberti is diagnosed from congeners by the following combination of characters: depigmented stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament in B. arrayae, B. beebei, B. belindae, B. gauderio, B. pinnicaudatus, and B. verdii; precaudal vertebrae 20-22 vs. 15-19 in B. batesi, B. benjamini, B. bennetti, B. bombilla, B. bullocki, B. cunia, B. diazi, B. hendersoni, B. menezesi, B. provenzanoi, B. regani, and B. sullivani; anal-fin rays 182-202 vs. 226-293 in B. brevirostris; continuous or discontinuous dark vertical or diagonally oriented bands or saddles present on body surface dorsal to lateral line, often extending across lateral line into ventral lateral surface, vs. absence of oblique bands or saddles on body surface dorsal to lateral line in B. draco, B. flavipomus B. jureiae, and B. palenque; bilateral columns of electrocytes at the anal-fin terminus 3 vs. 4-5 in B. janeiroensis and B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis); dark suborbital stripe absent, vs. present in B. walteri. Brachyhypopomus alberti can be distinguished from most but not all specimens of B. hamiltoni by a higher number of pectoral-fin rays - 15-16 (mode 16) vs. 12-15 (mode 13) (only 2 of 18 measured specimens of B. hamiltoni exhibited an overlapping number of pectoral-fin rays with B. alberti). Brachyhypopomus alberti can be further distinguished from B. hamiltoni by the absence of the first of five branchiostegal rays vs. presence in B. hamiltoniMago-Leccia (1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 175, fig. 77).

Description. Head and body shape, and pigmentation illustrated in Fig. 4. Meristic and morphometric data for examined specimens presented in Tables 2-6. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head slightly convex from occiput to snout, ventral profile of head straight to slightly convex between operculum and snout, snout rounded and bulbous. Eye moderate in size. Upper jaw with slight to moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 30-37 (median 36, n = 4). Precaudal vertebrae 20-22 (mode 22) including 1-2 (mode 2) transitional vertebrae. Pectoral fin narrow to moderate in width, pectoral-fin rays 16 in all specimens examined. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 172-191 (median 184). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 4-6 (mode 5). Lateral line discontinuous in all examined specimens; area in mid-body with no pored lateral-line scales for ca. 1-2 head lengths. Sparse groove-like depigmented epidermal canals found mainly in posterior half of body - as parallel lines either side of lateral line, on flank midway from lateral line to dorsal midline, and as a pair of long irregular lines either side of dorsal surface in dorsal portion of flank. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Table 2
Anal-fin ray counts for 28 species of Brachyhypopomus. Regions: type regions are preceded by an asterisk. Countries: BO = Bolivia, BR = Brazil, CO = Colombia, CR = Costa Rica, EC = Ecuador, FG = French Guiana, PN = Panama, PR = Paraguay, PE = Peru, VE = Venezuela. States/Departments: Brazil: Am = Amazonas, Ba = Bahia, Mg = Minas Gerais, Mt = Mato Grosso, Ms = Mato Grosso do Sul, Rj = Rio de Janeiro, Rs = Rio Grande do Sul, Sp = São Paulo; Paraguay: CE = Central, PH = Presidente Hayes; Peru: Lo = Loreto. For B. occidentalis: Pacific coast drainages (Colombia) = r. Baudó, r. San Juan; lago Maracaibo drainages = r. El Quebradón, r. Motatán, r. San Juan; eastern Atlantic drainages of Panama = r. Cartí, r. Chucubti, and r. Mandinga in the Cuna Yala region from ca. 077°25'W to 079°06'W; western Atlantic drainages of Panama = r. Cricamola from ca. 81°17'W to 081°49'W; eastern Pacific drainages of Panama = r. Bayano, r. Cristal, r. Mamoni, r. Pacora from ca. 079°03'W to 079°44'W. Numbers of examined specimens (N), with T = types, NT = non-types. Counts are recorded in bin intervals of ten, from 140 to 299. Median value shown in bold. Counts reported in original species description but not in the materials examined during this study are marked "^" to show full known range for each species. Missing count values intermediate between reported values are filled with "0" to better illustrate the species ranges. 1º Type = number of anal-fin rays for name-bearing type (parentheses denote count from original description; data for B. occidentalis refers to largest syntype specimen). ? = unavailable, D = damaged. Description = range from original description.

Table 3
Precaudal vertebrae counts for 28 species of Brachyhypopomus. Regions: type regions are preceded by an asterisk. See Table 2 for list of country and state abbreviations and additional notes on regions. Numbers of examined specimens (N), with T = type specimens, NT = non-type specimens. Precaudal vertebrae counts range from 15 to 26 and include the Weberian vertebrae, the remaining abdominal vertebrae, and all transitional vertebrae. Modal value is shown in bold (median value is underlined where there is no modal value). The number of transitional vertebrae is shown as a range followed by the mode in parentheses. 1º Type = total number of precaudal vertebrae for name-bearing type (data for B. occidentalis refer to largest syntype specimen). ? = unavailable. Description = number of precaudal vertebrae reported in original species description.

Table 4
Pectoral-fin ray counts for 28 species of Brachyhypopomus. Regions: type regions are preceded by an asterisk. See Table 2 for list of country and state abbreviations, and additional notes on regions. Numbers of examined specimens (N), with T = type specimens, NT = non-type specimens. Counts range from 10 to 21 and include both unbranched and branched rays. Modal value is shown in bold (or median value shown underlined where modal value not available). Missing count values intermediate between reported values are filled with "0" to better illustrate the species ranges. 1º Type = total number of pectoral-fin rays for name-bearing type, with count on right (R) side indicated in lieu of left side in case of damage, or in addition to left side if notably asymmetric (data for B. occidentalis refer to largest syntype specimen); asterisk indicates count obtained from original description. Description = number of pectoral-fin rays reported in original species description. Counts reported in an original species description but not from the materials examined during this study are marked "^" in order to show full known range for each species.

Table 5
Counts of the number of bilateral columns of electrocytes (EC1 = electrocyte columns at anal-fin terminus, EC2 = electrocyte columns at mid-caudal filament), and scale rows above lateral line (LL) for 28 species of Brachyhypopomus. Regions: type regions are preceded by an asterisk. See Table 2 for list of country and state abbreviations, and additional notes on regions. Electrocyte columns presented as range, with mode in parentheses. Data in the format "3/4" indicates alternation of 3 and 4 columns in individual specimens at the measurement point. N for electrocyte columns refer to immature specimens, mature females, and mature males, respectively (total in parentheses). For EC and SAL, mode is replaced by median (underlined) if no modal value.

Table 6
Morphometrics for Brachyhypopomus alberti, Brachyhypopomus arrayae, and Brachyhypopomus batesi. HT, holotype; SD, standard deviation. Ranges for each species refer to the holotype and to paratype specimens from the type region.

Coloration. (Fig. 4). Immature specimens and males with pale straw to tan background. Several diffuse and poorly defined vertical darker vertical bands comprising higher chromatophore densities located on lateral surface of body, traversing lateral line without disrupting ventrally. Dorsal region approximately uniformly pigmented with a speckling of brown chromatophores, without uninterrupted pale stripe along dorsal midline from occipital region to base of caudal filament. Irregular dark markings near upper portion of lateral surface but not on dorsal midline in some specimens. Very poorly defined light chocolate darker bands also located over anal-fin pterygiophores, sometimes forming inverted Y-shaped markings. Series of diffuse horizontal dash-like dark markings often present along lateral line in posterior third of body, anterior to anal-fin terminus. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Mature female specimens distinctly darker, with much higher density of brown chromatophores over entire body, head and dorsal regions, background color of lateral surface of body light brown with indistinct oblique darker bands of dark brown. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 4
Brachyhypopomus alberti. a. CBF 10284 (WC24.280607), holotype, male, 97 mm TL (head in lateral view, and body in lateral and dorsal views); b. ANSP 197573 (WC03.250607), paratype, female, 91 mm TL (body in lateral view); Bolivia, río Beni, Amazonas dr. Note the sexual dimorphism in body pigmentation, in which females are darker. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5mm.

Size. Small adult size, largest specimen examined 111 mm TL, 89 mm LEA (n = 17). Largest male specimen examined 111 mm TL, 89 mm LEA (n = 4). Largest female specimen examined 100 mm TL, 77 mm LEA (n = 4).

Sexual dimorphism. Brachyhypopomus alberti exhibits an unusual sexual difference in pigmentation, with sexually mature females exhibiting a much darker overall coloration (a character shared with B. arrayae) (Figs. 4a-b). No other secondary sexually dimorphic characters known.

Geographic distribution. Bolivia and Brazil (Fig. 5). Known from the upper rio Madeira (Amazonas dr.), above its series of falls beginning at the Cachoeira de Santo Antônio, near Porto Velho, Rondônia, Brazil; in the lower río Beni near the town of Riberalta, Bolivia; and from the rio Guaporé of Brazil.

Fig. 5
Collection records for Brachyhypopomus alberti (circles), B. batesi (squares), and B. benjamini (triangles). Holotype locations are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. The type series was collected from small low-conductivity clearwater and blackwater terra firme streams in tropical forest and savanna near Riberalta, Bolivia. It was encountered mostly commonly in marginal root mats, and in emergent or submerged aquatic vegetation. The following water parameters were recorded at the sample sites: conductivity 5-15 µScm-1, dissolved oxygen 3.0-5.0 mgl-1, temperature 22-24°C, and pH 5.2-5.5. Adults in breeding condition were found during the dry season in June-July 2007. However, the duration and timing of breeding are otherwise unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Brachyhypopomus alberti is known to co-occur in geographical sympatry and ecological syntopy with the following terra firme stream-occurring species: B. brevirostris, B. sullivani, and B. walteri. In the region of the type locality it exhibits an allotopic distribution with the following whitewater floodplain occurring species: B. arrayae, B. bombilla, and B. pinnicaudatus. Brachyhypopomus alberti co-occurs in geographical sympatry with its sister species B. arrayae, but the species exhibit a noteworthy difference in ecological distribution: B. alberti occurs in low-conductivity (ca. 5-15 μScm-1) terra firme forest and savanna streams, while B. arrayae mainly occurs in higher-conductivity whitewater floodplain systems (ca. 150 μScm-1 at the time of sampling). Nonetheless, B. alberti was sampled together with B. arrayae (and also B. pinnicaudatus) in the lower reaches of terra firme streams, at the ecotone with the río Beni floodplain.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of James S. Albert, American (USA) ichthyologist, collector of part of the type series, for his enormous contributions to the systematic biology of gymnotiform fishes.

Local names. Bolivia: cuchillo; Brazil: sarapó.

Brachyhypopomus arrayae, new species

urn:lsid:zoobank.org:act:836C199C-3EBA-4788-B8D5-AB4DEBEABF05

(Fig. 6; Tables 2-6)

Brachyhypopomus sp. "arr". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "arrayae". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. UMSS 7048, male, 77 mm TL, 66 mm LEA, Bolivia, Beni, mun. Riberalta, small stream nr. Puerto Hamburgo, affl. río Beni, affl. rio Madeira, Amazonas dr., 11°01'52"S 66°05'39"W, 6 Jul 2007, W. Crampton, M. Arraya & J. Albert.

Paratypes. 7 specimens, localities from río Beni dr., aff rio Madeira, Amazonas dr. Bolivia. Beni. ANSP 197574, 1, female, 128 mm; UF 177342, 2, male, 72-92 mm; UMSS 07047, 1, female (CS), 120 mm, mun. Riberalta, small stream nr. Puerto Hamburgo, 11°01'52"S, 066°05'39"W, 6 Jul 2007, W. Crampton, M. Arraya & J. Albert. AUM 35556 1, female, 95 mm, mun. Vaca Díez, affl. lago Tumi Chucua, 26 km S. S. W Riberalta, ca. 11°07'S, 066°11'W, 28 Nov 1981, K. Swing. CAS 81630, 1, 82 mm, lago Rogoagua, río Beni floodplain, ca. 13°58'S, 066°58'W, Nov 1921, N. Pearson. CBF 10277, 1, immature, 56 mm, mun. Riberalta, stream nr. lago San José, 10°54'47"S, 065°59'49"W, 25 Jun 2007, W. Crampton, M. Arraya & J. Albert.

Non-types. 68 specimens, localities from rio Madeira dr., Amazonas dr. Brazil. Rondônia. INPA POLO-464, 10, 89-133 mm (3 immature 70-89 mm, 6 female, 90-133, 1 male, 114 mm), mun. Porto Velho, rio Jamari, ca. 08°44'S, 063°27'W. MCP 41031 (part), 1, 63 mm, mun. Nova Mamoré, rio Ribeirão at hwy. BR-425, ca. 62 km S hwy. BR-364, affl. rio Guaporé, affl. rio Mamoré, 10°13'55"S, 065°16'55"W. MCP 41039, 4, 66-77 mm, mun. Porto Velho, affl. río São Sebastião, on hwy. BR-364, affl. rio Abunã, 09°39'05"S 65°33'53"W. Peru. Madre de Dios (localities from río Madre de Dios dr., affl. río Beni, aff río Madeira, Amazonas dr.). MUSM 2734, 1, prov. and mun. Tambopata, 3 km. Cocococha, no coordinates. MUSM 9597, 1, MUSM 9621, 1, prov. and mun. Tambopata, Reserva Nacional de Tambopata, Laguna Sandoval, 12°26'30"S, 069°02'18"W. MUSM 9827, 2, prov. and mun. Tambopata, 27 km Laberinto, no coordinates. MUSM 9873, 1, 160 mm, lago Tres Chimbadas, Reserva Nacional de Tambopata, río Tambobata, 12°47'26"S, 069°20'31"W. MUSM 21494, 1, MUSM 21675, 1, prov. Manu, mun. Madre de Dios, Trocha Huangana, río Los Amigos, 12°33'21"S 70°06'42"W. MUSM 21663, 1, prov. Manu, mun. Madre de Dios, Pozo minero, aguajal at "CICRA", no coordinates. MUSM 21683, 3, prov. Tambopata, cocha Huitoto, no coordinates. MUSM 21801, 4, MUSM 21909, 15, MUSM 21910, 1, mun. Tambopata, Aguajal Aguas Negras, Aguajal Oeste, km 35, ca. 12°00'S, 070°40'W. MUSM 21866, 3, mun. Inambari, Mazuco, aguajal, km 180, río Inambari, ca. 12°30'S, 069°05'W. MUSM 22004, 2, mun. Tambopata, Puerto Maldonado, ca. 12°36'S, 069°11'W. MUSM 22061, 1, prov. and mun. Tambopata, Aguajal Tripa, no coordinates. MUSM 22142, 1, MUSM 22157, 12, mun. prov. Tambopata, Puerto Maldonado, ca. 12°36'S, 069°11'W. MUSM 22642 (part), 1, 50 mm, prov. Tambopata, mun. Las Piedras, Planchón las Piedras, quebrada Planchón, affl. rio Tahuamanu [also known as río Las Piedras], ca. 12°30'S, 069°14'W. MUSM 35347, 1, prov. Tahuamanu, Mavila, cocha Bote 3, no coordinates. MUSM 37094, 1, 84 mm, quebrada Chorera, río Las Piedras, 12°02'12"S, 069°37'31"W.

Diagnosis. Brachyhypopomus arrayae is diagnosed from congeners by the following combination of characters: prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament present, vs. absent in all congeners except B. beebei, B. belindae, B. flavipomus, B. gauderio, B. pinnicaudatus, and B. verdii; anal-fin rays 174-212 vs. 214-230 in B. beebei; precaudal vertebrae 20-23, vs. 24-26 in B. belindae and B. verdii; pectoral-fin rays 16-19 (mode 16), vs. 12-15 (mode 13) for B. gauderio (except populations from Uruguay drainages) and vs. 13-15 (mode 14) for B. pinnicaudatus (except populations from coastal French Guiana). Brachyhypopomus arrayae exhibits similar pigmentation and overlapping meristic counts and morphometric proportions with some populations of B. gauderio and B. pinnicaudatus from which it can be distinguished by the contact of a small ascending process on the endopterygoid (mesopterygoid of Mago-Leccia, 1978Mago-Leccia, F. 1978. Los peces de la familia Sternopygidae de Venezuela. Acta Científica Venezolana, 29: 1-89.: 10, 57, fig. 8) with the orbitosphenoid (Arratia & Schultze, 1991Arratia, G. & H. Schultze. 1991. Palatoquadrate and its ossifications: Development and homology within Osteichthyans. Journal of Morphology, 208: 1-81.: 43, fig. 26; de Santana & Crampton, 2011de Santana, C. D. & W. G. R. Crampton. 2011. Phylogenetic interrelationships, taxonomy, and reductive evolution in the Neotropical electric fish genus Hypopygus (Teleostei, Ostariophysi, Gymnotiformes). Zoological Journal of the Linnean Society, 163: 1096-1156.: 1104, fig. 2), vs. the lack of a contact between the ascending process on the endopterygoid and the orbitosphenoid in B. gauderio and B. pinnicaudatus.

Description. Head and body shape, and pigmentation illustrated in Fig. 6. Meristic and morphometric data for examined specimens presented in Tables 2-6. Body shallow to moderate in depth. Head short to moderate in length and moderate in depth. Dorsal profile of head slightly convex from occiput to snout, ventral profile of head slightly convex between operculum and snout, snout rounded and bulbous. Eye moderate in size. Upper jaw with slight to moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 32-39 (median 36, n = 6). Pectoral fin moderate in width, pectoral-fin rays 16-19 (mode 17). Precaudal vertebrae 20-23 (mode 22) including 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 175-212 (median 201). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-6 (mode 5). Lateral line discontinuous in most examined specimens; area in mid-body with no pored lateral-line scales for ca. 0.5-1 head lengths. Sparse groove-like depigmented epidermal canals found mainly in posterior half of body - as parallel lines on either side of lateral line, on flank midway from lateral line to dorsal midline, and as a pair of long irregular lines either side of dorsal surface in dorsal portion of flank. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature specimens, mature females, and mature males. Caudal filament short to moderate in length.

Coloration. (Fig. 6). Immature specimens and males with pale straw to tan background. Several diffuse and poorly defined vertical darker vertical bands comprising higher chromatophore densities located on lateral surface of body, traversing lateral line without disrupting ventrally. Prominent pale stripe along dorsal midline from occipital region to base of caudal filament, flanked by dark borders from which vertical bands extend onto lateral surfaces. Very poorly defined light brown bands also located over anal-fin pterygiophores. Series of diffuse horizontal dash-like dark markings often present along lateral line in posterior third of body, anterior to anal-fin terminus. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Mature female specimens distinctly darker, with much higher density of brown chromatophores over entire body, and head and dorsal regions, background color of lateral surface of body light brown or tan with indistinct oblique darker bands of dark brown. Color in live individuals similar to preserved ones, with opercular region usually rosy due to underlying gills.

Fig. 6
Brachyhypopomus arrayae. a. UMSS 7048 (WC52.060707), holotype, immature male, 77 mm TL (head in lateral view, body in lateral and dorsal views); b. UF 177342 (WC54.060707), paratype, male, 97 mm TL (body in lateral view); c. ANSP 197574 (WC50.060707), paratype, female, 128 mm TL (body in lateral view); Bolivia, río Beni, Amazonas dr. Note the sexual dimorphism in body pigmentation, in which females are considerably darker. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5mm.

Size. Small adult size, largest specimen examined 133 mm TL, 102 mm LEA (n = 76). Largest male specimen examined 114 mm TL, 87 mm LEA (n = 4). Largest female specimen examined 133 mm, 102 mm LEA (n = 12).

Sexual dimorphism. Brachyhypopomus arrayae presents an unusual sexual difference in pigmentation, with sexually mature females exhibiting a much darker overall coloration (a character shared with B. alberti) (Figs. 6b-c). Sexually mature males somewhat smaller than mature females, but in the absence of a larger series of mature specimens, sexual size dimorphism is as yet unconfirmed. No other secondary sexually dimorphic characters known.

Geographic distribution. Bolivia, Brazil, and Peru (Fig. 7). Known from the upper rio Madeira (Amazonas dr.), with all but one record (from the rio Jamari, Rondônia, Brazil) occurring above its series of falls beginning at the Cachoeira de Santo Antônio; most records from the río Beni in Bolivia and the río Madre de Dios in Peru.

Fig. 7
Collection records for Brachyhypopomus arrayae (circles), B. belindae (squares), and B. bullocki (triangles). Holotype locations are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. The type series was collected from high-conductivity whitewater floodplain sites and from the lower, seasonally inundated reaches of terra firme streams. It was encountered most commonly in marginal root mats, and in emergent or submerged aquatic vegetation. The following water parameters were recorded at the sampling sites: conductivity 150-160 µScm-1, dissolved oxygen 5.0-6.0 mgl-1, temperature 27-28°C, and pH 7.5-7.6. Adults in breeding condition were found during the dry season in June-July 2007. However, the duration and timing of breeding are otherwise unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data). Co-occurring congeners: Brachyhypopomus arrayae is known to co-occur in geographical sympatry and ecological syntopy with the following whitewater floodplain-occurring species: B. bombilla, B. brevirostris, B. pinnicaudatus, and B. walteri. In the region of the type locality it exhibits a largely allotopic distribution with the following terra firme stream occurring species: B. alberti and B. sullivani (although B. arrayae was found with B. alberti at the ecotone between terra firme streams and floodplain systems).

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Bolivian biologist Mariana Arraya for her assistance in collecting the type series in Bolivia.

Local names. Bolivia: Cuchillo; Brazil: sarapó; Peru: macana.

Brachyhypopomus batesi, new species

urn:lsid:zoobank.org:act:728CA0A5-F5C5-465F-8793-D1176B3E7F57

(Figs. 1a, 8; Tables 2-6)

Brachyhypopomus sp. 1. - de Oliveira et al., 2009De Oliveira, R. R., M. S. Rocha, M. B. dos Anjos, J. Zuanon & L. H. Rapp Py-Daniel. 2009. Fish fauna of small streams of the Catua-Ipixuna Extractive Reserve, State of Amazonas, Brazil. Check List: Journal of Species Lists and Distribution, 5: 154-172.: fig. 41, color photograph (Brazil, Amazonas, Catuá-Ipixuna Reserve, ca. 03°48'S, 063°59'W).

Brachyhypopomus sp. "bat". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "batesi". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 47020, female, 104 mm TL, 82 mm LEA, Brazil, Amazonas, mun. Tefé, igarapé Xidarini, affl. lago Tefé (mouthbay of rio Tefé), Amazonas dr., 03°23'52"S, 064°41'17"W, 31 Dec 1996, W. Crampton.

Paratypes. 4 specimens, localities from Amazonas dr., collected by W. Crampton. Brazil. Amazonas. MCP 45308, 1, male, 78 mm, mun. Maraã, igarapé São Sebastião, affl. rio Baré, affl. lago Amanã, affl. rio Japurá, 02°17'05"S, 064°41'25"W, 17 Feb 1993, W. Crampton. MCP 45341, 2, (1 female, 99 mm, 1 male, 100 mm), collected with holotype. MCP 45357, immature, 75 mm, mun. Tefé, igarapé Xidarini, affl. lago Tefé, rio Tefé, 03°23'52"S, 064°41'17"W, 13 Aug 2001, W. Crampton.

Non-types. (24 specimens). Brazil. Amazonas (localities from Amazonas dr.). MCP 45312, 16 (11 immature, 76-115 mm, 4 female, 83-121 mm, 1 male, 120 mm), mun. Tefé, igarapé Xidarini, affl. lago Tefé, rio Tefé, 03°22'46"S, 064°41'17"W. MCP 45356, 2 (1 immature, 80 mm, 1 female [CS], 85 mm), mun. Tefé, igarapé Xidarini, affl. lago Tefé, rio Tefé, Amazonas dr., 03°23'52"S, 064°41'17"W. MZUSP 85041, 1, 104 mm, blackwater affl. rio Tiquié, Comunidade Fronteira, affl. rio Uaupés, affl. rio Negro, 00°15'35"N, 070°02'43"W. MZUSP 92234, 2, 53-73 mm, mun. São Gabriel da Cachoeira, ca. 500 m downstream São José II, igarapé Cunuri, affl. rio Tiquié, affl. rio Uaupés, affl. rio Negro, 00°13'N, 069°36'W. MZUSP 93067, 1, 60, mun. São Gabriel da Cachoeira, igarapé Castanha, nr. Sítio São Pedro, affl. rio Tiquié, affl. rio Uaupés, affl. rio Negro, 00°11'N, 069°35'W. Colombia. Vuapés: SINCHI-CIACOL. 1054, 2 (1 immature, 40 mm, 1 female, 101 mm), stream affl. río Cuduyarí, affl. río Vuapés, affl. rio Negro, 01°17'36"N, 070°16'53"W.

Diagnosis. Brachyhypopomus batesi is diagnosed from congeners by the following combination of characters: anal-fin rays 165-179, vs. 180-293 in B. alberti, B. beebei, B. belindae, B. bennetti, B. brevirostris, B. bullocki, B. diazi, B. gauderio, B. hendersoni, B. janeiroensis, B. jureiae, B. occidentalis, B. palenque, B. verdii, and B. walteri; scales present in entire middorsal region (although sparse and hard to see in some specimens), vs. absent in middorsal region of anterior third of body in B. benjamini and B. provenzanoi; accessory electric organ over the opercular region absent, vs. present in B. bombilla, B. menezesi, and B. regani; head depth at occiput 61.0-67.9% HL, vs. 71.4-94.6% in B. cunia, B. draco, B. flavipomus, B. hamiltoni, and B. pinnicaudatus; absence of scattered conspicuous black or charcoal flecks on flanks, vs. presence in B. sullivani.

Description. Head and body shape, and pigmentation illustrated in Figs. 1a and 8. Meristic and morphometric data for examined specimens presented in Tables 2-6. Body shallow in depth. Head short to moderate in length and shallow in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head approximately straight with convex and concave portions, snout truncated. Eye moderate in size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 61 (n = 1). Pectoral fin narrow to moderate in width, pectoral-fin rays 12-13 (mode 13). Precaudal vertebrae 16-18 (mode 18) including 1-2 (mode 2) transitional vertebrae. Anal-fin origin substantially posterior (between 0.25 and 0.75 HL distance) to tip of pectoral fin. Anal-fin rays 159-173 (median 168). Dorsal rami of recurrent branch of anterior lateral line nerve visible. Entire middorsal region of body scaled, although scales in anterior third of body sparse and mostly occluded by skin. Rows of scales above lateral line 5-6 (mode 5). Lateral line complete. Sparse groove-like depigmented epidermal canals found mainly in posterior half of body (mainly in posterior third of body), forming parallel or crisscrossing wavy lines either side of lateral line, as single wavy lines on flank midway from lateral line to dorsal midline, and as a pair of long irregular lines either side of dorsal surface in dorsal portion of flank. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Coloration. (Figs. 1a, 8). Pale straw to tan background. Several distinct, truncated, brown vertical bands extending from across upper portion of flank, fading towards lateral line and absent from below lateral line, most prominent for approximately one head length posterior to occiput. Dorsal region comprising irregular brown patches and a pale straw or tan background, with no pale stripe along dorsal midline from occipital region to base of caudal filament. Region over anal-fin pterygiophores straw colored with very faint irregular markings, mostly posteriorly. Head with evenly scattered dark chromatophores, darker dorsally. Eye usually with an indistinct or prominent suborbital patch or stripe of chromatophores and subcutaneous pigmentation extending from anteroventral portion of eye to chin. Pectoral and anal fins with hyaline membranes. Pectoral-fin rays hyaline. Anal-fin rays hyaline in anterior half of body, with light scattering of brown chromatophores in posterior half. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 8
Brachyhypopomus batesi. MCP 47020 (WC07.291297b), holotype, female, 104 mm TL (head in lateral view, body in lateral and dorsal views, specimen fixed in formalin and preserved in EtOH); Brazil, rio Tefé, Amazonas dr. Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 121 mm TL, 98 mm LEA (n = 28). Largest male specimen examined 120 mm TL, 100 mm LEA (n = 3). Largest female specimen examined 121 mm, 98 mm LEA (n = 8).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil and Colombia (Fig. 5). Known from the central Amazon, near the main stem of the rio Solimões (Amazon), and from the upper rio Negro.

Ecological notes. The type series was collected from the lower, seasonally flooded reaches of low-conductivity blackwater rainforest streams that flow into lago Tefé, and lago Amanã (large blackwater ria lakes of similar conductivity to the streams). Most specimens were encountered in marginal root mats or submerged leaf-litter along stream edges. The following water parameters were recorded at the time of sampling: conductivity 10-30 µScm-1, dissolved oxygen 2.0-5.2 mgl-1, temperature 24.3-27.0°C, and pH 4.5-6.0. During the high water period this species disappears from the flood-swollen lower stream reaches, probably due to declining dissolved oxygen levels, and apparently moves upstream to terra firme stream reaches above the seasonal river-floodplain flood influence. Breeding occurs during the early rising-water period, which in the Tefé region corresponds to the rainy season (WGRC unpublished data). Records of B. batesi outside the area of the type series are all from low-conductivity blackwater rainforest streams. Stomach contents of specimens from the type locality comprise aquatic insect larvae (primarily Chironomidae), and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the region of the type locality Brachyhypopomus batesi co-occurs in geographical sympatry and ecological syntopy with the terra firme stream-occurring species: B. beebei, B. brevirostris, B. sullivani, and B. walteri. It also exhibits an allotopic distribution with B. belindae, B. bennetti, B. flavipomus, B. hamiltoni, B. hendersoni, B. pinnicaudatus, and B. regani. In the rio Negro, B. batesi occurs in geographical sympatry with B. beebei, B. brevirostris, B. bullocki, B. hendersoni, B. regani, B. sullivani, and B. walteri.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Henry Walter Bates (1825-1892), British naturalist and explorer, for his contributions to the natural history of the Tefé region, where the type series was collected.

Local names. Brazil: sarapó (widespread).

Brachyhypopomus beebei (Schultz, 1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.)

(Figs. 1b, 9; Tables 2-5, 7)

Hypopomus beebeiSchultz, 1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.: 40, fig. 1, cephalic sensory pore arrangement; 46, pl. 1, fig. 4, black and white photograph of holotype (original description, type locality - Venezuela, Caripito, Monagas, río San Juan, Orinoco dr.). -Schultz, 1949Schultz, L. P. 1949. A further contribution to the ichthyology of Venezuela. Proceedings of the United States National Museum, 99: 1-211.: 66, key to the Hypopomidae, descriptive notes; fig. 9b, cephalic sensory pore arrangement; pl. 2, black and white photograph of holotype (Venezuela, listing of freshwater fish species). -Hoedeman, 1962Hoedeman, J. J. 1962. Notes on the ichthyology of Surinam and other Guianas. 9. New records of gymnotid fishes. Bulletin of Aquatic Biology, Amsterdam, 3: 53-60.: 60, fig. 6b, cephalic sensory pores and canals; fig. 7b, pigmentation (Suriname, listing of new gymnotiform records). -Hopkins & Heiligenberg, 1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.: 132, fig. 10, black and white photograph and EOD (Suriname, species and EOD diversity). -Westby & Shepherd, 1986Westby, G. W. M. & D. K. Shepherd. 1986. Waveform recognition in weakly electric fish. SERC Science and Engineering Research Council Bulletin, 3: 6-7.: 6, fig. 2; Westby, 1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.: 347, fig. 8, black and white photographs of adult male, female and larval specimen, with EODs (French Guiana, species and EOD diversity]. -Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.: 155, fig. 2, black and white photographs of preserved specimens (French Guyana, comparison to Brachyhypopomus pinnicaudatus). -Ferraris & Vari, 1992Ferraris, C. J. J. & R. P. Vari. 1992. Catalog of type specimens of Recent fishes in the National Museum of Natural History, Smithsonian Institution, 4: Gonorhynchiformes, Gymnotiformes, and Siluriformes (Teleostei: Ostariophysi). Smithsonian Contributions to Zoology, 535: 1-52.: 5 (type catalog).

Brachyhypopomus beebei. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48, 170, fig. 71, black and white photograph of head of holotype (listing of Brachyhypopomus). -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 17-18, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2, 9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1 reproductive biology (Brazil, central Amazon, ecology and signal diversity). -Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.: 396, color photograph of live individual (French Guiana, listing of Brachyhypopomus). -Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.: 523 (Brazil, Roraima, listing of gymnotiforms). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 110 (redescription). -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4, 834, fig. 9, drawing of adult specimen, with EOD (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance). -Provenzano et al., 1998Provenzano, F., A. Marcano & P. Mondaca. 1998. Catálogo de ejemplares tipos en la coleccíon de peces del Museo de Biología de la Universidad Central de Venezuela (MBUCV-V). Acta Biológica Venezuélica, 18: 1-24.: 11 (type catalog for MBUCV-V). -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Stoddard, 1999Stoddard, P. K. 1999. Predation enhances complexity in the evolution of electric fish signals. Nature, 400: 254-256.: 255, fig. 4, color photograph of mature female (EOD evolution). - Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.: 610, fig. 1, black and white photograph of mature female with EOD (EOD diversity in Brachyhypopomus). - Ponton & Mérigoux, 2001Ponton, D. & S. Mérigoux. 2001. Description and ecology of some early life stages of fishes in the River Sinnamary (French Guiana, South America). Folia Zoologica, 50, Monograph 1: 1-116.: 94, fig. 100, drawings of post-larval morphology (French Guiana, Sinnamary dr. larval ecology). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 494 (Bolivia, Brazil, Colombia, Ecuador, Guyana, Paraguay, Peru, Suriname, and Venezuela, catalog of hypopomids).-Triques & Khamis, 2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.: 63 (diagnosis against, and material examined; in description of B. jureiae). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Galvis et al., 2006Galvis, G., J. I. Mojica, S. R. Duque, C. Castellanos, P. Sánchez-Duarte, M. Arce, Á. Gutiérrez, L. F. Jiménez, M. Santos, S. Vejerano, F. Arbelaez, E. Prieto & M. Leiva. 2006. Peces del medio Amazonas - Región de Leticia. Bogotá, Conservation International, 548p.: 362, fig. 211, drawing of head; 528 (Colombia, Amazonas, catalog of fishes). -Vari et al., 2009Vari, R. P., C. J. Ferraris, A. Radosavljevic & V. A. Funk. 2009. Checklist of Freshwater Fishes of the Guiana Shield. Bulletin of the Biological Society of Washington, 17: 1-93.: 46 (Guiana Shield, catalog of fishes). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Mol, 2012Mol, J. H. 2012. The freshwater fishes of Suriname. Leiden, Brill Academic Publishers, 890 pp.: 596, color photograph of preserved specimen, reproduction of photograph from Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp. (Suriname, catalog of fishes). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 236, color photograph (Brazil, rio Madeira, listing of hypopomids). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (position in phylogeny of the Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 8, 14, 16-17, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Brachyhypopomus brevirostris. Kirschbaum, 1995Kirschbaum, F. 1995. Taxonomy, zoogeography and general ecology of South American knifefishes. Pp. 446-454. In: P. M. (Ed.) Electric fishes: history and behaviour. London, Chapman & Hall.: 452, black and white photograph (gymnotiform diversity).

Table 7
Morphometrics for Brachyhypopomus beebei, Brachyhypopomus belindae, and Brachyhypopomus benjamini. HT, holotype; SD, standard deviation. Data for holotype of B. beebei (Monagas, Venezuela) are from Schultz (1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.). Ranges for B. beebei refer to non-type specimens from the vicinity of Tefé, Amazonas, Brazil, and exclude the holotype. Ranges for both B. belindae and B. benjamini refer to the holotype and to paratype specimens from the type region.

Diagnosis. Brachyhypopomus beebei is diagnosed from congeners by the following combination of characters: prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament present, vs. absent in all congeners except B. arrayae, B. belindae, B. gauderio, B. pinnicaudatus, and B. verdii; anal-fin rays 214-230, vs. 174-212 in B. arrayae and B. pinnicaudatus; precaudal vertebrae 21-23, vs. 24-26 in B. belindae and B. verdii; longest anal-fin ray 1.6-3.9% LEA, vs. 3.9-5.4% in B. gauderio.

Description. Head and body shape, and pigmentation illustrated in Figs. 1b and 9. Meristic and morphometric data for examined specimens are presented in Tables 2-5, and 7. Data presented here refer to material from the central Amazon of Brazil unless otherwise stated. Body moderate to broad in depth. Head short to long, and shallow to moderate in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head straight to slightly convex between operculum and snout, snout rounded and bulbous. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 35-55 (median 50, n = 20). Pectoral fin moderate to broad in width, pectoral-fin rays 15-19 (mode 14). Precaudal vertebrae 21-23 (mode 22) including 1-3 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 214-230 (215-230, median 222 in population from central Amazon; 214 in type region). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Groove-like epidermal canals found mainly in posterior half of body - as abundant parallel crisscrossing depigmented grooves either side of lateral line, as isolated horizontal depigmented grooves on flank midway from lateral line to dorsal midline, and as long closely-spaced parallel dark-pigmented lines either side of dorsal surface in dorsal portion of flank. Three bilateral horizontal columns of electrocytes at anal-fin terminus in immature specimens, mature females, and mature males. Three bilateral horizontal columns of electrocytes at mid-point between anal-fin terminus and tip of caudal filament in immature specimens and mature females. Three to four columns of electrocytes at mid-point between anal-fin terminus and tip of caudal filament in mature males (three columns only in specimens from low-conductivity systems; four only in specimens from high-conductivity floodplain systems > 90 μScm-1). Caudal filament short to moderate in length.

Coloration. (Figs. 1b, 9). Background light tan or grey to dark brown. Head darker, especially dorsally. Dorsal region with prominent depigmented pale stripe extending along midline from occipital region to deep into caudal filament. Pale middorsal stripe flanked in anterior portion of body with very thin dark horizontally oriented lines from which thin wavy lines extend ventrally across dorsal and ventral portions of flank. Pale middorsal stripe flanked in posterior portion of body with approximately vertically oriented thin dark lines which extend down flank, some of which cross lateral line into ventral flank. Ventral region with thin wavy dark lines extending from anal-fin margin towards dorsal margin of pterygiophores, some of which extend dorsally to join lines descending from dorsal flank. In caudal filament dark markings form vertical patches or stripes. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Juvenile specimens typically exhibit high contrast dark lines on the flank, set against a pale background pigmentation. In large adults background is typically darker and boundaries of dark lines broken, and less distinctive. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 9
Brachyhypopomus beebei. a. MCP 45462 (WC04.150801b), immature female, 134 mm TL, non-type (head in lateral view, body in lateral and dorsal view, specimen fixed in formalin); Brazil, rio Tefé, Amazonas dr. b. USNM 120753, holotype, 103 mm TL (originally 136 mm TL, tail now lost) (body in lateral view, specimen preserved in EtOH); Venezuela, río San Juan, Orinoco dr. c. MCP 45424 (WC04.010599), male, 204 mm TL, non-type (body in lateral view, specimen fixed in formalin and preserved in EtOH); d. MCP 45427 (WC01.130300), female, 153 mm TL, non-type (body in lateral view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note the sexual dimorphism in caudal filament height. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 256 mm TL, 190 mm LEA (n = 865). Largest male specimen examined 256 mm TL, 190 mm LEA (n = 36). Largest female specimen examined 197 mm TL, 165 mm LEA (n = 62).

Sexual dimorphism. Males attain larger sizes than females. Males in breeding condition exhibit longer and deeper caudal filaments than immature individuals and breeding females (Figs. 9c-d), but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes (although we noted that mature males in high-conductivity systems have an extra horizontal column of electrocytes at mid caudal filament, Table 5). Breeding males nonetheless exhibit clearly enlarged electrocytes relative to immature specimens and females. Large males often with paddle-like lateral compression at caudal filament tip (Figs. 9c-d). No known sexual dimorphism in pigmentation.

Geographic distribution. Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela (Fig. 10). Widespread through cis-Andean northern South America, including large areas of the Amazonas and Orinoco drainages, and coastal drainages of the Guianas and Amapá State, Brazil. In the Amazon basin apparently absent from the rio Madeira above its series of falls beginning at the Cachoeira de Santo Antônio, near Porto Velho, Rondônia, Brazil. As yet unknown from some major tributaries of the Amazon, including the Juruá, Tocantins, and Xingu. Collection records from tributaries in the northern and western portions of the Orinoco drainage are sparse.

Fig. 10
Collection records for Brachyhypopomus beebei (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. Brachyhypopomus beebei is an ecologically cosmopolitan species, and is locally common in lentic and slow-flowing freshwater environments throughout its range (Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.; Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998aCrampton, W. G. R. 1996b. Gymnotiform fish: an important component of Amazonian floodplain fish communities. Journal of Fish Biology, 48: 298-301.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.; Hopkins & Heiligenberg, 1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.; Mol, 2012Mol, J. H. 2012. The freshwater fishes of Suriname. Leiden, Brill Academic Publishers, 890 pp.; Westby, 1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.). It occurs in seasonally inundated whitewater floodplains (in floating rafts of meadows and shallow newly-flooded forests), along the margins of rivers (in emergent and floating vegetation), in ephemeral or perennial swamps (in vegetation or submerged debris), and in terra firme forest and savanna streams (in emergent and submerged vegetation, leaf litter and debris, and in marginal root mats and holes). In the lowland Amazon, Brachyhypopomus beebei occurs in both low-conductivity blackwater forest streams and swamps (ca. 5-30 μScm-1) and in high-conductivity whitewater floodplain systems (ca. 90-250 μScm-1), as well as in waters of intermediate conductivity (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.). Brachyhypopomus beebei often occurs in extremely hypoxic swamp and floodplain systems and is able to tolerate protracted periods of hypoxia by undertaking aerial gill respiration and (during periods of anoxia) by reducing activity (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Breeding occurs during the rising and high water period in populations from central Amazonian floodplain floating macrophytes (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 165). Westby (1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.) reported the presence of larval B. beebei at the beginning of the rainy season in small streams of coastal French Guiana. Westby (1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.) also noted that larval B. beebei, estimated to be less than one week from hatching, occurred in "crèches" of 15-22 specimens. However, he found no evidence for parental care. Stomach contents in populations from the central Amazon comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136). Large specimens often consume larger aquatic invertebrates.

Co-occurring congeners: Because of its wide geographical range and occurrence in multiple habitats, B. beebei occurs in geographical sympatry and ecological syntopy with multiple congeners: in the Amazonas drainage and coastal drainages of the Guianas: B. batesi, B. belindae, B. benjamini, B. bennetti, B. brevirostris, B. cunia, B. hamiltoni, B. hendersoni, B. pinnicaudatus, B. regani, B. sullivani, B. verdii, B. walteri; in the Orinoco drainage: B. bullocki, B. diazi, B. brevirostris, B. provenzanoi, B. regani, and B. sullivani.

Local names. Brazil: sarapó; Colombia: cuchillo/cuchillo amarillo (Amazon and Orinoco), cuchilleja macana (Putumayo); Ecuador: cuchillo, yayo; French Guiana: poisson couteau (French), and multiple creole/Amerindian names (Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.); Peru: macana; Suriname: saprapi; Venezuela: cuchillo.

Material examined. 848 specimens. Brazil. Amapá. MNHN 1981-0494, 1 (of 3), 88 mm, rio Ipa, rio Oiapoque drainage, no coordinates. MPEG 3341, 2, 143-170 mm, mun. Ferreira Gomes, rio Cupixi, bridge on hwy. to Serra do Navio, rio Araguari drainage, ca. 00°55'N, 051°15'W. Amazonas (localities from Amazonas dr., localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1998.3.12.45-53, 9 (6 immature, 122-176 mm, 2 female, 150-190 mm, 1 male, 145 mm), IDSM 442, 8, 73-187 mm, MCP 45313, 1, immature, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12.54, 1, immature, 122 mm, mun. Tefé, floodplain lake, Ilha Panamim, rio Solimões, 03º17'38"S, 064º41'16"W. BMNH 1998.3.12.55, 1, immature, 150 mm, MCP 45381, 5 (2 immature [1CS], 105-140 mm, 2 female, 162-164 mm, 1 male, 220 mm), Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. IDSM 452, 3, 62-98 mm, Mamirauá Reserve, lago Jaraqui, 02º44'07"S, 065°04'38"W. IDSM 453, 6, 52-129 mm, MCP 45424, 5 (3 immature, 94-132 mm, 1 female, 171 mm, 1 male, 204 mm), MCP 45428, 5, 45-194 mm, MCP 45450, 5 (2 immature [2CS], 102-195 mm, 3 female [2CS], 138-178 mm), Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. INPA 9943, 15, 85-150 mm, Mamirauá Reserve, lago Mamirauá, ca. 03º07'S, 064º47'W. INPA 18335, 1, immature, 114 mm, Mamirauá Reserve, cano do lago Arauaé, 03º03'54"S 64º49'04"W. INPA 18336, 1, immature, 53 mm, MCP 45358, 1, immature, 109 mm, Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. INPA 18337, 1, immature, 90 mm, MCP 45361, 1, immature, 63 mm, MCP 45385, 2, immature, 120-146 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. INPA 18338, 1, immature, 114 mm, MCP 45343, 1, female, 198 mm, MCP 45380, 1, immature, 65 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º06'40"S, 64°47'52"W. INPA 18339, 1, immature, 50 mm, MCP 45427, 3 (2 female [1CS], 136-153 mm, 1 male, 170 mm), mun. Tefé, igarapé Curupira, Estrada Agrovila rd., affl. lago Tefé, rio Tefé, 03º25'48"S, 064º44'15"W. INPA 18340, 1, immature, 59 mm, MCP 45488, 1, female, 136 mm, mun. Tefé, terra firme swamp, igarapé Repartimento, Estrada Agrovila rd., affl. lago Tefé, rio Tefé, 03º24'25"S, 064º44'08"W. INPA 18341, 1, immature, 75 mm, Mamirauá Reserve, Paraná Maiana, 03º06'50"S, 064°47'48"W. MCP 45342, 1, immature, 133 mm, MCP 45344, 1, immature, 135 mm, Mamirauá Reserve, lago Arauaé, 03º02'52"S, 064º50'04"W. MCP 45382, 2, immature, 118-139 mm, Mamirauá Reserve, Ressaca do Itu, 02º49'51"S, 064º57'11"W. MCP 45383, 1, female, 185 mm, Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45387, 1, immature (CS), 97 mm, Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. MCP 45420, 1, male, 197 mm, Mamirauá Reserve, lago Curuçá Aberto, 03º06'07"S, 064°49'10"W. MCP 45421, 2 (1 immature, 132 mm, 1 male [CS], 201 mm), Mamirauá Reserve, cano do lago Mamirauá, 03º04'29"S, 064°48'29"W. MCP 45422, 1, male, 226 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º05'15"S, 064°48'03"W. MCP 45459, 3, 95-118 mm, Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S 64º55'50"W. MCP 45460, 1, immature, 72 mm, MCP 45462, 6 (5 not sexed, 83-151 mm, 1 female, 134 mm), mun. Tefé, igarapé Repartimento, 1.5 km downstream bridge Estrada Agrovila rd., affl. lago Tefé, rio Tefé, 03º24'25"S, 064º44'08"W. MPEG 22741, 1, 108 mm, Mamirauá Reserve, cano do lago Geraldo, 03º07'20"S, 064°48'06"W. MPEG 22742, 2, 90-145 mm, Mamirauá Reserve, lago Bolsinho, 03º03'47"S, 064°49'59"W. MZUSP 7293, 4, mun. Maués, igarapé do rio Maraú, affl. rio Maués-Açu, ca. 03º24'S, 057°42'W. MZUSP 23239, 9, lago Miuá, upstream Codajás, rio Solimões, ca. 03°40'S, 062°04'W. MZUSP 44164, 2, mun. Maués, igarapé Limãozinho, affl. rio Maués-Açu, ca. 03°23'S, 057°43'W [coordinates for Maués]. MZUSP 62069, 1, 53 mm, pool on beach, Tapera, rio Negro, ca. 00°11"N, 064°04"W. UF 177346, 13, 64-211 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. Maranhão. USNM 88283, 1, 140 mm, "Maranhão, Brazil", no coordinates. Pará (localities from Amazonas dr.). INPA 6887, 1, 131 mm, Pimental, rio Tapajós, ca. 04°34'S, 056°15'W. MCP 23359 (part), 1, 94 mm, Concórdia do Pará, rio Bujarú, affl. rio Guamá, affl. Baía do Guajará, ca. 02°06'S, 047°56'W. MPEG 7140, 1, 95 mm, mun. Barcarena, São Sebastião, rio Arienga, affl. Baía do Guajará, 01°38'S, 048°43'W. MPEG 10164, 1, 115 mm, mun. Portel, Floresta Nacional Caxiuanã, affl. rio Anapú, affl. rio Pará, affl. Baía do Guajará, ca. 01°44'S, 051°26'W. MPEG 15336, 1, 99 mm, mun. Faro, unnamed stream, affl. rio Nhamundá, 01°42'23"S, 057°12'10"W. MPEG 15646, 1, 130 mm, mun. Almeirim, rio Ipitinga, affl. rio Jari, 00°49'52"N, 053°57'20"W. MPEG 15679, 1, 122 mm, mun. Almeirim, rio Ipitinga, affl. rio Jari, 00°48'34"N, 053°55'52"W. SU 54499, 6, 74-106 mm, SU 66948, 1, 90 mm, Urumari brook into rio Tapajós, Santarém, ca. 02°26'S, 054°42'W [coordinates for Santarém]. Rondônia (localities from rio Madeira dr., Amazonas dr.). INPA 818, 2, 118-127 mm, INPA 1154, 2, 121-132 mm, igarapé "13.05", rio Mutum, Serra Pacaás Novos, affl. rio Mamoré [coordinates for Serra Pacaás Novos], ca. 10º47'S, 063º59'W. INPA 19947, 4, 61-153 mm, INPA 19948, 73, 34-131 mm, Lagoa do Feijoal, rio Jamari, upstream UHF Samuel, ca. 15 km, ca. 08°51'S, 063°19'W. UFRO-I 4470, 1, 118 mm, igarapé Lourdes, affl. igarapé Cristal, affl. rio Jí-Paraná, 10°25'13"S, 61°39'12"W. UFRO-I 6481, 1, 91 mm, flooded area immediately downstream Cachoeira Santo Antônio, rio Madeira, 08°46'30"S 63°56'28"W. Roraima (localities from rio Branco dr., affl. rio Negro, Amazonas dr.). INPA 6404, 4, 43-108 mm, Ilha de Maracá, stream at end of island, rio Uraricoera, ca. 03°22'N, 061°23'W. INPA 7387, 1, igarapé Viruaquim [Juruaquim], 48.8 km Normândia on hwy. RR-202, 03°50'N, 60°02'W (listed by Sullivan, 1997). MZUSP 23567, 1, stream ca. 1 km N Caracaraí, 01°52'N, 061°06'W. MZUSP 30037, 48, MZUSP 30039, 58, igarapé do Cujobim, Ilha de Maracá, rio Uraricoera, ca. 03°20'N, 061°40'W. MZUSP 30038, 10, igarapé do Bota Panela, nr. Cachoeira do Bem Querer, rio Branco, ca. 01°55'N, 061°00'W. Colombia. Amazonas. ROM 56332, 1, 207 mm, 5 mi. W Leticia, Amazonas dr., 04°09'02"S, 069°57'00"W. Caquetá. SINCHI-CIACOL 102, 2, 42-129 mm, Comunidad Aduche (San Miguel), Pueblo Andoke, Poblado Araracuara, affl. río Caquetá, Amazonas dr., 00°38'18"S, 072°10'54"W. Ecuador (localities from río Napo dr., Amazonas dr.) Francisco de Orellana. FMNH 102272, 1, 60 mm, Laguna Jatuncocha, río Yasuni, 01°00'S, 075°27'W. QCAZ-I 1369, 1, 123 mm, Chiruisla, río Huiririma, affl. río Tiputini, 00°38'54"S, 075°54'44"W. QCAZ-I 1802, 1, 147 mm, QCAZ-I 1803, 1, 162 mm, Chiruisla, Laguna Muyuna, affl. río Tiputini, 00°42'25"S, 075°56'08"W. Sucumbios. ANSP 130488, 5, 37-103 mm, swamp at Santa Cecília, río Aguarico, ca. 00°06'N, 076°51'W. FMNH 102271, 1, 76 mm, Laguna de Limoncocha, 00°23'42"S, 076°36'49"W. FMNH 102279, 1, 154 mm, small stream between Laguna Zancudo and Laguna Zancudococha, affl. quebrada Zancudococha, affl. río Aguarico, 00°33'42"S, 075°30'00"W. FMNH 102281, 6, 34-103 mm, ca. 2 km S Marian, río Aguas Negras, about 1-2 km upstream from rd. bridge, affl. río Cuyabeno, affl. río Aguarico, ca. 00°01'S, 076°19'W. FMNH 102284, 6, 20-93 mm, affl. Laguna Grande de Cuyabeno, affl. río Cuyabeno, affl. río Aguarico, ca. 00°00'S, 076°10'W. FMNH 102290, 1, 51 mm, affl. río Tarapuy, N bank just downstream rd. bridge, affl. río Cuyabeno, affl. río Aguarico, no coordinates. KU 12741, 1 (CS), 90 mm; KU 13799, 4, 38-120 mm; KU 13800, 24 (4 CS), 50-145 mm, swamp, S air strip at Santa Cecília, río Aguarico, ca. 03°52'S, 076°59'W. MUSM 5693 (part), 2, 107-117 mm, temporary lake, río Aguarico, ca. 00°38'S, 075°21'W [coordinates for mouth of río Aguarico]. French Guiana. Cayenne. BMNH 1926.3.2.658-660, 3, 78-85 mm, crique Iponcin, Approuage River dr., no coordinates. CU 71944, 2, on Rt. 1 Kourou to Sinnamary, km 86 in flooded border of crique Paracou, Kourou River dr., ca. 05°21'N, 052°56'W (listed by Sullivan, 1997). CU 71954, 1, Kourou River at Roche Leodate landing, ca. 32 km upstream from Kourou, Kourou River dr., 05°00'N, 052°39'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). CU 71955, 1, crique Papinabo, ca. 21 mi. from Kourou, Kourou River dr., 05°06'N, 052°40'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). CU 71956, 5, small coastal stream on "CTFT forestry estate" nr. crique Paracou, Kourou River dr., ca. 05°21'N, 052°56'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MNHN 1981-0495, 1, 78 mm, Trois Sauts (falls) on Oyapock River, rio Oiapoque dr., ca. 02°15'N, 052°51'W. MNHN 1981-0566, 1, 95 mm, saut Embouchure, Yaroupi River, affl. Oyapock River, rio Oiapoque dr., ca. 02°42'N, 053°01'W. MNHN 1999-1314, 10 (of 39), 28-49 mm, crique Papinabo, Kourou River dr., ca. 05°06'N, 052°41'W. MNHN 1999-1321, 1 (of 3), 120 mm, Oyapock River, rio Oiapoque dr., no coordinates. MNHN 1999-1364, 1 (part), 153 mm, Pont de Papinabo, crique de Papinabo, River Kourou dr., ca. 05°06'N, 052°41'W. NRM 29482, 1, 60 mm, locality marked "PK12", corresponds to following record from MNHN databases: Pont de Papinabo, crique de Papinabo, Kourou River dr., ca. 05°06'N, 052°41'W. NRM 32241, 2, 55-59 mm, flooded area along rd. Sinnamary-Saint-Laurent, Sinnamary River dr., ca. 05°25'20"N, 053°03'28"W. NRM 32242, 1, 51 mm, Oyapock River nr. St. Georges - Maripa Rd crossing, rio Oiapoque dr., ca. 03°52'13"N, 051°51'17"W. NRM 32243, 1, 50 mm, crique Soumouro, Kourou River dr., 05°07'27"N, 052°43'52"W. USNM 301964, 2, 165-176 mm. crique Karouabou, nr. Kourou city, Kourou River dr., ca. 05°09'N, 052°40"W. USNM 301965, 1, 138 mm. crique Papinabo, 200 m upstream from Kourou River, 20 km Kourou, Kourou river dr., ca. 05°00'N, 052°42"W. Guyana. Barima-Waini .BMNH 1911.10.31.556, 1, 143 mm, FMNH 53322, 1, 110 mm, Issorora rubber plantation, Mud Creek [probably on Aruka River], Aruka River dr., Barima-Kaituma River dr., 08°12'N, 059°44'W [coordinates for lower Aruka]. Cuyuni-Mazaruni. BMNH 1934.9.12.360, 1, 106 mm, Mazaruni River, pond in forest near small community, Essequibo River dr., no precise locality [coordinates for confl. with Essequibo River] 06°20'N, 058°41'W. Demerara [old division name]. FMNH 85374, 2, 101-110 mm, Dakara Creek, no coordinates. Potaro-Siparuni (localities from Essequibo River dr.).ANSP 175956, 4, 67-163 mm, Culvert creek crossing Kurupukari-Surama River rd., 04°19'57"N, 058°51'13"W. ANSP 175957, 1, 158 mm, blackwater creek, 5 min. upstream from Burro Burro campsite, Iwokroma, ca. 04°40'N, 058°50'W. ANSP 175958, 6, 52-75 mm, small lake, 04°45'15"N, 058°45'12"W. ANSP 192059, 2, 67-74 mm, creek, Tumble Down Falls, Tumble Down Creek, Siparuni River, 04°48'59"N, 058°50'56"W. BMNH 1973.3.29.14-15, 2, 96-101 mm, Kaieteur falls, 2 mi. above 'gauge', Potaro River, 05°09'N, 059°28'W. CAS 72220, 1, 59 mm, CAS 72226, 1, 54 mm, Chipoo Creek, affl. Ireng River, ca. 04°42'N, 059°06'W. FMNH 53325, 1, 121 mm, MCZ 30175, 1, 153 mm, Nickaparoo (or Nickaparu) Creek, affl. River Ireng, above the Karona falls, ca. 04°42'N, 059°06'W. INHS 49616, 1, 120 mm, 2.9 mi. E Chenapou, Arnick Creek, affl. Potaro River, 04°59'56"N, 059°32'20"W. SU 72222, 2, 113-119 mm, Nickaparoo Creek, into Ireng River, ca. 04°42'N, 059°06'W. Upper Takutu-Upper Essequibo (Localities listed for Takutu River are from the rio Branco dr., affl. rio Negro, Amazonas dr.). AUM 35866, 1, 43 mm, 31.2 km NW Sand Creek village, Sauriwau River, affl. Takutu River, 03°06'51"N, 059°46'31"W. BMNH 1972.7.27.458-518 (part), 2, 95-102 mm, Karanambo creek, Rupununi River, Essequibo River dr., 03°45'11"N, 059°18'36"W. FMNH 53327, 1, 112 mm, Twoca Pan, between Rupununi and Pununike, Essequibo River dr., no coordinates. MCZ 165853, 1, 102 mm, Dry creek bed 10 mi. E Nappi village, [probably Moco-Moco River], affl. Takutu River, ca. 03°25'N, 059°25'W. USNM 209199, 3, 101-127 mm, Rupununi, Moco-Moco Creek, affl. Takutu River, ca. 03°15'N, 059°39'W. Region not specified. AMNH 3247, 1, 65 mm, Guyana, no further locality data, drainage unknown, no coordinates, FMNH 53324, 1, 95 mm, Pacopoo Pan, drainage unknown, no coordinates. USNM 377591, 2, 115-128 mm, Hassar Creek, no coordinates. Peru (localities are from Amazonas dr.). Amazonas. LACM 41763-2, 1, 110 mm, 1 km upstream from Caterpiza, río Santiago, affl. río Marañón, Amazonas dr., ca. 03°54'S, 077°42'W. Loreto (localities listed from nr. Jenaro Herrera are from the río Ucayali dr., mun. Requena). ANSP 167725, 4, 55-78 mm, río Nanay, ca. 6 mi. upstream confl. with río Momón, ca. 03°44'50"S, 073°17'12"W. ANSP 167726, 2, 76-90 mm, nr. Mishana on path to Nauta rd., affl. río Nanay, 03°53'12"S, 073°28'57"W. ANSP 167727, 11, 60-85 mm, Laguna Rocafuerte, río Nanay, ca. 6.1 mi. upstream confl. with río Momón ca. 03°44'S, 073°17'W. ANSP 178219, 1, 53 mm, caño Santa Rita, R. bank affl. río Nanay, nr. Pueblo Pampa Chica, 03°45'23"S, 073°17'28"W. CAS 67701, 4, 87-128 mm, creek nr. Yurimaguas, affl. río Huallaga, affl. río Marañón, ca. 05°53'S, 076°04'W. CAS 67702, 4, 37-213 mm, stream, affl. río Itaya, affl. río Amazonas, ca. 03°48'S, 073°16'W. INHS 50010, 2, 102-108 mm, caño Ushpa, 4 km E Iquitos, affl. río Itaya, affl. río Amazonas, ca. 03°48'S, 073°16'W. MNRJ 3957, 1, 197 mm, rio Ampiyacu, nr. Pebas, affl. río Amazonas, ca. 03°19'S, 071°51'W. MUSM 6959 (part), 1, 72 mm, Isla Muyuy, cocha Amazonas, río Amazonas, ca. 03°54'S, 073°14'W. MUSM 10914, 1, mun. Urarinas, río Chambiras nr. San Juan, río Nanay, ca. 03°41'S, 073°45'W. MUSM 11009, 1, Pijuayal, río Hormiga, affl. rio Amazonas, 04°08'S, 070°03'W. MUSM 14498 (part), 1, 73 mm, mun. Maynas, Puesto de Vigilancia Arcadia, río Napo, 00°59'37"S, 075°18'30"W. MUSM 44675, 22 (14 immature, 48-163 mm, 5 female, 157-190 mm, 4 male, 148-222 mm), stream nr. Jenaro Herrera, 04°53'59"S, 073°38'51"W. MUSM 44681, 4, immature, 50-133 mm, stream nr. Jenaro Herrera, 04°53'35"S, 073°39'01"W. MUSM 44693, 8 (1 immature, 157 mm, 3 female, 148-185 mm, 4 male, 164-210 mm), stream nr. Jenaro Herrera, 04°51'51"S, 073°38'45"W. MUSM 44703, 14 (13 immature, 84-188 mm, 1 female, 169 mm), stream nr. cocha Capite, nr. Jenaro Herrera, 04°52'03"S, 073°40'39"W. MUSM 44712, 2, immature, 8133 mm, stream nr. Jenaro Herrera, 04°53'54"S, 073°38'23"W. MUSM 44718, 4 (3 immature 87-196 mm, 1 male, 155 mm), stream nr. Jenaro Herrera, 04°56'16"S, 073°39'20"W. MUSM 44721, 14 (8 immature, 5922 mm, 3 female, 14784 mm, 2 male, 154-192 mm), stream nr. Jenaro Herrera, 04°55'41"S, 073°38'46"W. MUSM 44762, 18, immature, 58-90 mm, stream nr. Jenaro Herrera, 04°54'36"S, 073°39'58"W. MUSM 44768, 7 (1 immature, 106 mm, 3 female, 91-155 mm, 3 male, 125-139 mm), cocha Capite, nr. Jenaro Herrera, 04°54'15"S, 073°36'53"W. NRM 27763, 1, 143 mm, stream nr. Jenaro Herrera, ca. 04°54'23"S, 073°37'27"W. SU 17230, 1, 204 mm, río Amazonas nr. Pebas, ca. 03°19'S, 071°37'W. UF 116551, 1, immature, 80 mm, río Nanay at Mishana, 03°52'48"S, 073°29'30"W. UF 116555, 1, immature, 86 mm, stream at km 23, Iquitos-Nauta rd., affl. río Nanay, 03°56'38"S, 073°23'54"W. UF 126211, 1, 112 mm, UF 131121, 1, 67 mm, Reserva Nacional (RN) Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°16'S, 074°27'W. UF 126237, 1, 127 mm, UF 126247, 3, immature, 11831 mm, UF 148564, 5 (2 immature, 68-76 mm, 3 female, 7416 mm), RN Pacaya Samiria, cocha Sapote, río Pacaya, affl. río Ucayali, 05°19'06"S, 074°29'18"W. UF 129052, 1, 76 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°25'18"S, 074°30'45"W. UF 129117, 1, 77 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°18'14"S, 074°30'45"W. UF 129157, 1, 110 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°23'57"S, 074°32'06"W. UF 129161, 3, 72-100 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°23'51"S, 074°30'23"W. UF 129406, 3, 52-102 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°19'20"S, 074°30'14"W. UF 148505, 4 (1 male, 130 mm, 3 female, 122-143 mm), stream nr. Jenaro Herrera, 04º55'38"S, 073º39'14"W. UF 148506, 2, immature, 34-42 mm, quebrada Salomé caño, stream nr. Jenaro Herrera, 04º54'32"S, 073º35'36"W. UF 148507, 1, immature, 66 mm, affl. quebrada Parnayari, nr. Jenaro Herrera, ca. 04º54'S, 073º37'W. UF 148508, 2 (1 immature 68 mm, 1 female, 164 mm), quebrada Parnayari, nr. Jenaro Herrera, 04º55'10"S, 073º38'40"W. UF 148509, 1, immature, 51 mm, stream, affl. quebrada Chica, nr. Jenaro Herrera, 04º55'23"S, 073º39'37"W. UF 148510, 3 (2 female, 170-197 mm, 1 male, 217 mm), quebrada Fierro caño, affl. quebrada Sapuenillo, nr. Jenaro Herrera, 04º51'39"S, 073º38'59"W. UF 148556, 1, immature, 88 mm, RN Pacaya Samiria, caño Yarina, río Pacaya, affl. río Ucayali, 05°20'08"S, 074°30'05"W. UF 148557, 1, immature, 7 mm, RN Pacaya Samiria, caño Yarina, río Pacaya, affl. río Ucayali, 05°19'20"S, 074°30'11"W. UF 148558, 3 (1 immature, 70 mm, 2 female, 102-129 mm), RN Pacaya Samiria, caño Yarina, río Pacaya, affl. río Ucayali, 05°18'16'S, 074°30'05"W. UF 148559, 17 (4 immature, 80-106 mm, 11 female, 90-136 mm, 2 male, 107-125 mm), RN Pacaya Samiria, cocha Yarina, río Pacaya, affl. río Ucayali, 05°23'51"S, 074°30'23"W. UF 148560, 3, (1 immature, 44 mm, 2 female, 126-135 mm), RN Pacaya Samiria, cocha Yarina, río Pacaya, affl. río Ucayali, 05°25'20"S, 074°30'45"W. UF 148561, 5 (4 immature, 104-149 mm, 2 female, 125-161 mm), RN Pacaya Samiria, cocha Yarina, río Pacaya, affl. río Ucayali, 05°23'58"S, 074°32'05"W. UF 148562, 4 (2 immature, 87-122 mm, 2 female, 160 mm), RN Pacaya Samiria, cocha Yarina, río Pacaya, affl. río Ucayali, 05°25'29"S, 074°31'41"W. UF 148563, 1, female, 133 mm, RN Pacaya Samiria, caño Tamara, río Pacaya, affl. río Ucayali, 05°16'40"S, 074°29'38"W. UF 148565, 3 (1 immature 73 mm, 2 female, 143-177 mm), RN Pacaya Samiria, río Pacaya, río Ucayali, affl. río Ucayali, 05°16'44"S, 074°31'06"W. UF 148566, 5 (4 immature, 64-72 mm, 1 female, 109 mm), RN Pacaya Samiria, cocha Shitari, affl. río Ucayali, ca. 05°17'S, 074°31'W. UF 183770, 1, 256 mm, río Nanay, 03°53'50"S, 073°40'01"W. UF 184013, 9 (6 immature, 56-199 mm, 2 female, 159-183 mm, 1 male, 96 mm), stream nr. Jenaro Herrera, 04°52'24"S, 073°38'49"W. UF 184022, 33 (16 immature, 56-158 mm, 8 female, 120-170 mm, 9 male, 148-198 mm), stream nr. Jenaro Herrera, 04°55'38"S, 073°39'14"W. UF 184023, 3 (2 immature, 64-139 mm, 1 female, 164 mm), stream nr. Jenaro Herrera, 04°54'15"S, 073°36'53"W. UMMZ 224598, 3, 62-156 mm, río Cayarí, nr. Benjamin Constant, affl. río Yavarí (rio Javari), ca. 04°22'S, 070°01'W [coordinates for Benjamin Constant]. UMMZ 224603, 2, 106-153 mm, río Tapira, río Tahwayo [Tahuayo], ca. 04°17'S, 073°12'W. UMMZ 224604, 1, 111 mm, río Momón, nr. Iquitos, affl. río Nanay, 03°37'55"S, 073°19'47"W. UMMZ 228983, 2, 131-135 mm, quebrada Carana, Buensuceso, rio Javari, 04°07'S, 070°25'W. UMMZ 228984, 13, 33-119 mm, río Momón, affl. río Nanay, ca. 03°37'S, 073°17'W. Ucayali. FMNH 84226, 1, 60 mm, first bridge over stream, ca. 34 km Pucallpa, on Pucallpa-Lima hwy., affl. río Ucayali, 08°34'17"S, 074°54'17"W. MUSM 39375, 5, 56-61 mm, pools in caño draining Supari cocha, nr. San Miguel village, río Purus, 09°58'12"S, 070°56'09"W. Suriname. Marowijne. UF 177358, 1, male, 161 mm, small unnamed stream on Paramaribo-Albina rd., affl. Cottica River, Commewijne River dr., 05°34'55"N, 054°15'49"W. ZMA 102.377, 1, 83 mm, Albina, Marowijne River dr., ca. 05°29'58"N, 054°03'44"W. Nickerie. USNM 22588, 21, 32-97 mm, Lana Creek, ca. 4 km upstream confl. with Corantijn River, Corantijn River dr., ca. 05°27'N, 057°15'W. USNM 225557, 1, 57 mm, creek at Camp MacClemmen, Dalibane Creek, Corantijn River drainage, 05°34'N, 057°11'W. USNM 225559, 5, 45-132 mm, Kapoeri Creek, ca. 4 km N confl. with Corantijn River, Corantijn River dr., 05°16'N, 057°10'W. USNM 225562, 4, 57-70 mm, creek ca. 2 km N Matapi, Corantijn River dr., 05°03'N, 057°17'W. USNM 225568, 2, 70-114 mm, small creek affl. Corantijn River, 350 m below Wilhelm II falls, Corantijn River dr., 03°34'N, 057°39'W. USNM 225572, 1, 100 mm, Makilikabroe Creek, Corantijn rivier dr., 05°26'N, 057°14'W. Paramaribo. ZMH 11630, 1, 127 mm, Paramaribo, Suriname River dr., ca. 05°53'N, 055°10'W. Sipaliwini. AMNH 54831, 1, 67 mm, stream nr. Avanavero Falls, ca. 3 mi. downstream Devis Falls, Corantijn River dr., ca. 04°49'N, 057°24'W. AMNH 244582, 2, 68-70 mm, small stream S Tiger Falls, km 405, Corantijn River dr., ca. 03°56'N, 057°56'W. FMNH 116894, 1, 112 mm, unnamed creek on Linker Coppename, Coppename River dr., 04°23'25"N, 056°31'52"W. USNM 225564 (part), 7, 75-125 mm, small stream 200 m upriver Dalbana Creek mouth, Corantijn River dr., ca. 04°47'N, 057°26'W. USNM 302003, 1, 143 mm, Matapi Creek ca. 1 km confl. with Corantijn rivier, Corantijn River dr., ca. 05°00'N, 057°16'W. ZMA 107.029, 5, 130-182 mm, stream into left bank Gran rio, 3 km NE Awaradam, affl. Gran rio, Suriname River dr., ca. 03°51'N, 055°25'W. ZMH 11629, 1, 143 mm, "upper Suriname", no coordinates. Venezuela. Amazonas. MBUCV-V 13895, 6 (3 measured: 136-167 mm), caño Niyayowa, W Parima, affl. rio Negro, Amazonas dr., ca. 03°30'N, 064°15'W. MBUCV-V 14766, 1, 141 mm, small stream, 1 km S La Neblina camp, affl. río Baria, aff .río Casiquiare, affl. rio Negro, Amazonas dr., ca. 00°50'N, 066°05'W. MCNG 23657, 3, Mauritia palm swamp, 1 km N Esmeralda, río Orinoco, Orinoco dr., 03°11'N, 065°33'W. MCNG 23894, 1, forest pools, río Ventuari, Orinoco dr., ca. 03°59'N, 067°02'W [coordinates for mouth of río Ventuari]. MCNG 23903, 1, morichal, río Guapuche, affl. río Ventuari, río Orinoco drainage, ca. 04°06'N, 066°46'W [coordinates for mouth of río Guapuche]. MHNLS 5873, 1, MHNLS 6437, 1, Malvaca, alto río Orinoco, Orinoco dr., 02°30'N, 065°09'W. UMMZ 228986, 2, pool of creek nr. Puerto Ayacucho, affl. río Orinoco, Orinoco dr., ca. 05°38'N, 067°36'W. Apure. MBUCV-V 10776, 1, 101 mm, caño Grande, 3 km S La Ceiba, affl. río Apure, Orinoco dr., ca. 07°19'N, 071°08'W. Barinas. MBUCV-V 5960, 2, 69-70 mm, caño San Antonio, ca. 10 km Santa Barbara de Barinas, río Anaro, affl. río Suripá, affl. río Apure, Orinoco dr., ca. 07°48'N, 071°10'W. Monagas. AMNH 15453, 2 (paratypes), 95-146 mm, MBUCV-V 15163, 1 (paratype), 130 mm, USNM 120753, 1 (holotype) (Fig. 9b, herein), 103 mm (originally 136 mm TL, 112 mm LEA (Schultz, 1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.), caudal filament now lost), Caripito, río San Juan, Orinoco dr., ca. 10°06'N, 063°06'W, C. Beebe, 1942. MBUCV-V 22343, 1, 94 mm, río Morichal Largo, río Orinoco delta, Orinoco dr., 09°26'N, 062°24'W. Country not specified. USNM 302011, 2, 101-130 mm, no locality, no coordinates.

Brachyhypopomus belindae, new species

urn:lsid:zoobank.org:act:B20030E3-840F-409D-841F-A99F658AA8B0

(Figs. 1c, 11; Tables 2-5, 7)

Brachyhypopomus sp. "belindae". - Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 45360, immature, 110 mm TL, 92 mm LEA, Brazil, Amazonas, mun. Alvarães, Mamirauá Reserve, lago Araçazinho, rio Solimões-Japurá floodplain, Amazonas dr., 02º59'35"S, 64º51'33"W, 5 Apr 1997, W. Crampton & J. Oliveira.

Paratypes. 5 specimens, localities from Amazonas dr., collected by W. Crampton & J. Oliveira. Brazil. Amazonas (localities listed from Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in the rio Solimões-Japurá floodplain, mun. Alvarães). INHS 70253, 1, 74 mm, lago Murumuru, Janauacá, ca. 42 km SW Manaus, ca. 03°26'S, 060°17'W, 29 Mar 1978, P. Bayley. MCP 45267, 1, immature, 90 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º05'15"S, 064°48'03"W, 18 Jun 1999. MCP 47867, 1, immature, 62 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W, Jun 1997. MCP 45430, 1, immature (CS), 102 mm, Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W, 15 Jun 1999. MCP 45431, 1, immature, 94 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º06'40"S, 064°47'52"W, 23 Jul 1999.

Diagnosis. Brachyhypopomus belindae is diagnosed from congeners by the following combination of characters: precaudal vertebrae 24-26, vs. 15-23 in all congeners except B. draco, and B. verdii; bilateral columns of electrocytes at the anal-fin terminus 4-5 (no mode, median 4.5), vs. 3 in B. draco and B. verdii.

Description. Known only from immature specimens. Head and body shape, and pigmentation illustrated in Figs. 1c and 11. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 7. Body shallow to moderate in depth. Head short to moderate in length and moderate in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head straight gently convex between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with slight to moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Pectoral fin narrow to moderate in width, pectoral-fin rays 15-17 (mode 16). Precaudal vertebrae 24-26 (mode 24) including 1-2 (no mode, median 1.5) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 200-220 (median 209). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-6 (mode 6). Lateral line continuous. Sparse groove-like depigmented epidermal canals found mainly in posterior half of the body - as parallel crisscrossing lines either side of lateral line, on flank midway from lateral line to dorsal midline, and as a pair of long irregular lines either side of dorsal surface in dorsal portion of flank. 4-5 bilateral horizontal columns of electrocytes at anal-fin terminus, and at mid-point between anal-fin terminus and tip of caudal filament in immature specimens (mature specimens not available). Caudal filament short to moderate in length.

Coloration. (Figs. 1c, 11). Background tan to light brown. Dorsal region with prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Pale middorsal stripe flanked in anterior portion of body by a thin dark horizontally oriented line from which broken or complete lines extend ventrally in a posterior to anterior direction across dorsal and ventral portions of flank to anal-fin margin. Upper flank in anterior portion of body with additional irregular markings. Markings and dark lines less pronounced in posterior portion of body. Caudal filament darker than body, especially dorsally and ventrally. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 11
Brachyhypopomus belindae. MCP 45360 (WC05.050497), holotype, immature, 110 mm TL (head in lateral view, body in lateral and dorsal views, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Scale bars = 5 mm.

Size. Largest specimen examined 110 mm TL, 92 mm LEA (n = 5).

Sexual dimorphism. Undetermined. Breeding males and females of this species have not yet been collected.

Geographic distribution. Brazil (Fig. 7). Known only from the central Amazon of Brazil; from the type series near Tefé, Amazonas, Brazil, and from a whitewater floodplain site near Manaus.

Ecological notes. A rare species known only from whitewater floodplain habitats. The type series was collected from floating rafts of macrophytes in high conductivity seasonally hypoxic whitewater floodplains at the confluence of the rio Solimões (Amazonas) and rio Japurá. Water parameters recorded at sites near the type locality, through an entire annual flood cycle were typically within the following ranges: conductivity 54-192 μScm-1 dissolved oxygen 0-6.3 mgl-1, temperature 26.5-34.0°C, and pH 6.3-7.3 (Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.). Reproductive biology is unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Brachyhypopomus belindae is known to co-occur in geographical sympatry and ecological syntopy with the following whitewater floodplain-occurring congeners: B. beebei, B. bennetti, B. brevirostris, B. flavipomus, B. hamiltoni, B. pinnicaudatus, B. regani, and B. walteri. It also exhibits an allotopic distribution with B. batesi, B. hendersoni, and B. sullivani.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Belinda Siew-Woon Chang, American (USA) evolutionary biologist, for her inspiration to NRL during the preparation of this work.

Local names. Brazil: sarapó.

Brachyhypopomus benjamini, new species

urn:lsid:zoobank.org:act:E93BCBF9-472A-42EF-B4B6-D60937293835

(Fig. 12; Tables 2-5, 7)

Brachyhypopomus sp. I. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EOD (gymnotiform species and EOD diversity).

Brachyhypopomus sp. "benj". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "benjamini". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MUSM 39915, male, 126 mm TL, 103 mm LEA, Peru, Loreto, mun. Requena, nr. Jenaro Herrera, quebrada Caño Fierro, affl. río Ucayali, Amazonas dr., 04°51'59"S, 073°38'48"W, 16 Jan 2004, B. Crampton, W. Crampton, H. Ortega, R. Reis, F. Lima & J. Oliveira.

Paratypes. 68 specimens, localities from Amazonas dr., collected by W. Crampton, E Correa Roldán, M. Guevara, J. Waddell, unless otherwise stated. Peru. Loreto (localities listed from nr. Jenaro Herrera are from the río Ucayali dr., mun. Requena). MUSM 44676, 1, female, 115 mm, stream nr. Jenaro Herrera, 04°53'59"S, 073°38'51"W, 28 Jul 2009. MUSM 44689, 2, immature, 109-131 mm, stream nr. Jenaro Herrera, 04°51'51"S, 073°38'45"W, 13 Jul 2009. MUSM 44694, 56 (48 immature, 79-135 mm, 8 female, 95-119 mm), stream nr. Jenaro Herrera, 04º52'09"S, 073º38'44"W, 15 Jul-5 Aug 2009. UF 148511, 1, male, 110 mm, stream nr. Jenaro Herrera, 04º53'S, 073º39'W. UF 148512, 2, 97-98 mm (1 immature 97 mm, 1 male, 98 mm), collected with holotype, 16 Jan 2004, W. Crampton, H. Ortega, R. Reis, F. Lima, B. Crampton, J. Oliveira. UF 184015, 4, immature, 89-117 mm, stream nr. Jenaro Herrera, 04°54'26"S, 073°36'44"W, 17 Jul 2009. USNM 405574, 2, immature (96-96 mm), stream nr. Jenaro Herrera, 04°54'26"S, 073°36'44"W, 25 Jul 2009.

Non-types. 8 specimens. Peru. Loreto. UF 183771, 8, 81-112 mm (5 immature, 1 CS, 81-100 mm, 2 female, 90-100 mm, 1 male, 112 mm), río Nanay, 50 km Iquitos, Amazonas dr., 03°53'50"S, 073°40'01"W.

Diagnosis. Brachyhypopomus benjamini is diagnosed from congeners by the following combination of characters: scales absent in middorsal region of anterior third of body, vs. present in all congeners except B. provenzanoi; dorsal surface of body speckled with small brown chromatophores on light brown background, vs. irregular pattern of distinct dark blotches on depigmented tan-colored background in B. provenzanoi.

Description. Head and body shape, and pigmentation illustrated in Fig. 12. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 7. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head straight from occiput to snout, ventral profile of head straight anteriorly, gently convex under operculum, snout truncated to rounded. Eye of moderate to large size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 30-36 (median 34, n = 5). Pectoral fin narrow to moderate in width, pectoral-fin rays 10-13 (mode 12). Precaudal vertebrae 16-17 (mode 17), including 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL) to moderately (reaching 0.33 HL) posterior to tip of pectoral fin, never anterior to tip of pectoral fin. Anal-fin rays 174-197 (median 186). Dorsal rami of recurrent branch of anterior lateral line nerve usually clearly visible. Middorsal region of body without scales in anterior third of body, scales in posterior two thirds of body small and completely occluded by skin. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Sparse groove-like depigmented or dark-pigmented epidermal canals found mainly in posterior half of body - parallel to and close to lateral line, mostly dorsal to lateral line. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female and mature male specimens. Caudal filament short to moderate in length.

Coloration. (Fig. 12). Background light tan to dark brown. Dorsal region speckled with small brown chromatophores on light brown background. No pale stripe in middorsal region. Dorsal areas of flank mottled with dark patches. Distinct stripes or saddles on flank absent. Ventral areas of flank with only sparse, irregular dark blotches. Caudal filament darker than body, with indistinct disrupted vertical bars. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral-fin and anal-fin membranes hyaline. Pectoral-fin rays hyaline and unpigmented. Anal-fin rays with light scattering of dark chromatophores. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 12
Brachyhypopomus benjamini. MUSM 39915 (WC10.160104), holotype, male, 126 mm TL (head, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Peru, río Ucayali, Amazonas dr. Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 135 mm TL, 107 mm LEA (n = 77). Largest male specimen examined 126 mm TL, 103 mm LEA (n = 4). Largest female specimen examined 119 mm TL, 109 mm LEA (n = 11).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Peru (Fig. 5). Known only from the type series near the town of Jenaro Herrera, Loreto - in forest stream tributaries of the lower río Ucayali, and in forest stream tributaries of the río Nanay, near Iquitos, Loreto.

Ecological notes. Occurs in small low-conductivity blackwater terra firme rainforest streams. In the region of the type locality B. benjamini is locally common in streams within undisturbed closed-canopy forest, and absent from streams in open cattle pastures or clearings. Brachyhypopomus benjamini occurs in and around submerged debris and leaf litter, and in root mats and holes along the stream banks. The following water parameters were recorded at the sample sites: conductivity 5-15 µScm-1, dissolved oxygen 1.8-6.0 mgl-1, temperature 25-27.5°C, and pH 4.5-6.5. Breeding occurs during the rainy season in the area of the type locality (approximately December to April) (JCW unpublished data). Stomach contents of specimens from the type locality comprise small aquatic invertebrates (JCW unpublished data).

Co-occurring congeners: Brachyhypopomus benjamini is known to co-occur in geographical sympatry and ecological syntopy with B. beebei, B. brevirostris, B. sullivani, B. verdii, and B. walteri. It also exhibits an allotopic distribution with B. bennetti, B. flavipomus, B. hamiltoni, and B. regani.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Benjamin T. D. Crampton, British diplomat and amateur ornithologist, collector of the holotype.

Local names. Peru: macana.

Brachyhypopomus bennetti Sullivan, Zuanon & Cox Fernandes, 2013

(Figs. 1d, 13; Tables 2-5, 8)

Brachyhypopomus sp. 3. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 19-21, color photographs; 37, fig. 3.5; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2, 9.3, table 9.1a,b, hypoxia tolerance; 164-169, figs.10.1, 10.2, table 10.1, reproductive biology (Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus bennetti. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 100 (description in unpublished thesis with disclaimer stating not available, a nomen nudum).

Brachyhypopomus sp. 2. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847., 821, table 4, 834, fig. 9, drawing of adult specimen, with EOD; 837, fig. 10, drawing of caudal filaments of male and female (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330., 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance).

Brachyhypopomus sp. B. -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq., 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers., 672, fig. 23.8 inset 11, color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity]. -Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235., 231, fig. 6, black and white photograph of head of live individual (Brazil, adaptations to hypoxia).

Brachyhypopomus sp. 1. -Stoddard, 1999Stoddard, P. K. 1999. Predation enhances complexity in the evolution of electric fish signals. Nature, 400: 254-256., 255, fig. 4, color photograph of live mature female specimen, with EOD (EOD evolution).

Brachyhypopomus sp. "benn". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press., 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus (Odontohypopomus) bennettiSullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34., 14, figs. 6-8, color photographs of holotype and paratypes, backlit electric organ, EODs (original description and assignment to subgenus Odontohypopomus, type locality - Brazil, Amazonas, nr. Manaus, Amazonas dr.). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp., 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 9, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus; Odontohypopomus not recognized).

Table 8
Morphometrics for Brachyhypopomus bennetti, Brachyhypopomus bullocki, and Brachyhypopomus cunia. HT, holotype; SD, standard deviation. Data for holotype of B. bennetti (near Manaus, Amazonas, Brazil) are from Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). Data for holotype of B. bullocki (Meta, Colombia) are from Sullivan & Hopkins (2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). Ranges for B. bennetti refer to non-type specimens from the vicinity of Tefé, Amazonas, Brazil. Ranges for B. bullocki refer to non-type specimens from the Orinoco drainage of Venezuela and exclude holotype. Ranges for B. cunia refer to holotype, paratype and non-type specimens from the type region.

Diagnosis. Brachyhypopomus bennetti is diagnosed by: bilateral columns of electrocytes at the anal-fin terminus 6, vs. 3-5 in all congeners.

Description. Head and body shape, and pigmentation illustrated in Figs. 1d and 13. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 8. Body moderate to broad in depth. Head moderate to long in length and shallow to moderate in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 40-51 (median 46, n = 6). Pectoral fin moderate to broad in width, pectoral-fin rays 14-17 (mode 16). Precaudal vertebrae 17-19 (mode 18), including 1-2 (mode 2) transitional vertebrae. Anal-fin origin substantially (0.25-0.33 HL distance) anterior to tip of pectoral fin, never posterior. Anal-fin rays 218-250 (218-240, median 231 in population from central Amazon). Dorsal rami of recurrent branch of anterior lateral line nerve usually visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Very sparse, almost unnoticeable depigmented epidermal canals found mainly in posterior third of body - as parallel wavy lines either side of lateral line. Epidermal canals absent from either side of mid-dorsal region, and absent on flank midway from lateral line to dorsal midline. Hypaxial electric organ very large. Six bilateral electrocyte columns at anal-fin terminus, and 5-6 columns midway between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Number of columns of electrocytes in mid-caudal filament sometimes continues to tip, or sometimes dwindles to 2-3 columns. Caudal filament short to moderate in length.

Coloration. (Figs. 1d, 13). Background pale straw to tan. Dorsal region with irregular brown blotches which extend to irregular-edged and sometimes divided brown bands which extend towards lateral line. No pale mid-dorsal stripe extending from occiput to base of caudal filament. A series of brown blotches is usually present along lateral line. Flank ventral to lateral line and pterygiophore region with very sparse and indistinct disrupted vertical bands. Caudal filament darker than body, with indistinct dark blotches and disrupted vertical bands. Head darker, especially dorsally. Eye with prominent suborbital patch of chromatophores and subcutaneous pigmentation (sometimes indistinct). Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Color in live individuals similar to preserved specimens, body sometimes with yellow-green tinge in waters with high sediment load, opercular region usually very rosy due to underlying gills.

Fig. 13
Brachyhypopomus bennetti. a. MCP 47021 (WC13.160893), female, 158 mm TL (head in lateral view, and body in lateral and dorsal views, specimen fixed in formalin and preserved in EtOH). b. MCP 45359 (WC18.050497), male, 192 mm TL (body in lateral view, specimen fixed in formalin and preserved in EtOH). c. MCP 45359 (WC12.050497), female, 169 mm TL (body in lateral view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note the sexual dimorphism in caudal filament height. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 235 mm TL, 215 mm LEA (n = 1,444). Largest male specimen examined 223 mm TL, 183 mm LEA (n = 51). Largest female specimen reported 215 mm TL, 176 mm LEA (holotype) (n = 89).

Sexual dimorphism. Mature males in breeding condition attain slightly larger sizes, and develop much deeper caudal filaments than immature individuals and breeding females (Figs. 13b-c). Breeding males without an elevated number of bilateral horizontal columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Breeding males with paddle-like lateral compression at caudal filament tip, which is partially or sometimes completely free of electrocytes. No known sexual dimorphism in pigmentation.

Geographic distribution. Bolivia, Brazil, Colombia, Ecuador, and Peru (Fig. 14). Restricted to whitewater floodplains of the main stem of the Amazon River and the lower reaches of its major whitewater tributaries, and known also from a single specimen (CAS 81631) from the upper río Beni floodplain, well above the major series of falls on the rio Madeira. This specimen was collected in 1921 by Nathan E. Pearson during the Mulford Expedition, and although faded, exhibits the diagnostic six horizontal electrocyte columns at the anal-fin terminus. One of us (WGRC) made extensive collections in the lower río Beni, near Riberalta, Bolivia, but failed to locate other specimens of B. bennetti in this area.

Fig. 14
Collection records for Brachyhypopomus bennetti (circles), B. cunia (squares), and B. diazi (triangles). Holotype locations for B. bennetti and B. cunia, and location of lost holotype for B. diazi are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. Brachyhypopomus bennetti is exceptionally common (usually the most common gymnotiform) in floating rafts of macrophytes in whitewater floodplains along the main stem of the Amazon, and the lower reaches of its major whitewater tributaries (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.,bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.; 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.; 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.; Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). Water parameters for a typical central Amazon whitewater floodplain fluctuate within the following ranges through the annual flood cycle: conductivity 54-192 μScm-1 dissolved oxygen 0-6.3 mgl-1, temperature 26.5-34.0°C, and pH 6.3-7.3 (Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.). During the low water period B. bennetti is found in floating macrophytes along the edges of floodplain channels or lakes, or in smaller pockets of water in low-lying areas of the floodplain. During the rising water period it is common both in floating macrophytes, and in submerged forest leaf-litter at the margin of the advancing flood waters. During the high water period, when the bottom waters are completely deoxygenated, B. bennetti is almost completely restricted to floating macrophytes. Reproduction occurs during the rising and high water period in floating macrophytes (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 165). Size class data from floodplain floating macrophytes indicate that B. bennetti has an annual life history; it reaches maturity and breeds within one year, and exhibits post-reproductive mortality (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 166, fig. 10.1). The species is also relatively common in rooted and floating macrophytes along the edge of major whitewater river channels. Brachyhypopomus bennetti is absent in blackwater and clearwater systems except very close to their confluences with major whitewater rivers (for example in lago Tefé, near its confluence with the rio Solimões), where there are frequent ingresses of high-conductivity water.

Brachyhypopomus bennetti is a high-conductivity specialist, and its electric organ exhibits impedance matching to systems with low resistance (high conductivity) - with many bilateral columns of electrocytes (Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). Brachyhypopomus bennetti is also adapted to protracted periods of anoxia, by undertaking aerial gill respiration (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998bCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.), and its gill lamellae are greatly expanded in comparison to species form normoxic systems, such as terra firme forest streams (Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.). Brachyhypopomus bennetti reproduces during the late-rising and high water period (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.). Stomach contents in populations from the central Amazon comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 165).

Co-occurring congeners: Brachyhypopomus bennetti is known to co-occur in geographical sympatry and ecological syntopy with the whitewater floodplain-occurring species: B. beebei, B. belindae, B. brevirostris, B. flavipomus, B. hamiltoni, B. pinnicaudatus, B. regani, and B. walteri (and B. arrayae, and B. bombilla in the upper Madeira). It also exhibits an allotopic distribution with: B. batesi, B. benjamini¸ B. hendersoni, B. sullivani, and B. verdii (and with B. alberti in the upper Madeira).

Local names. Brazil: sarapó; Colombia: cuchillo; Ecuador: cuchillo, yayo; Peru: macana.

Material examined. 1,466 specimens, localities from Amazonas dr. Bolivia. Beni. CAS 81631, 1, 142 mm (126 mm LEA), Reyes, pampa town, 24 mi. NE Rurrenabaque, río Beni, affl. rio Madeira, 14°17'42"S, 067°20'27"W. Note: Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.) mistakenly duplicated the record for CAS 81631 with CAS 72216 in the non-type list of the original description, CAS 81631 was in fact dismembered from CAS 72216. Brazil. Amazonas (localities listed from Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). ANSP 194026, 4, INPA 39562, 5, rio Camatiã, Monte Sinai, São Paulo de Olivença, 03°27'34"S, 068°56'00"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). BMNH 1998.3.12 56-62, 7, immature, INPA 18353, 2, immature, 51-85 mm, MCP 45252, 1, immature (CS), 83 mm, Mamirauá Reserve, lago Juruazinho, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12 63-64, 2, female, mun. Tefé, lago do Içé, Ilha do Içé, rio Solimões, 03°16'04"S, 064°41'29"W. BMNH 1998.3.12.67-74, 8, BMNH 1998.3.12.65, 1, male, 210 mm, BMNH 1998.3.12.66, 1, male, 192 mm, BMNH 1998.3.12.80, 1, male, 181 mm, BMNH 1998.3.12.81, 1, female, 154 mm, INPA 18352, 1, female, 139 mm, INPA 18356, 1, immature, 50 mm, MCP 33278, 2, 170-178 mm, MCP 45330, 1, male, 200 mm, MCP 45389, 1, female, 165 mm, MCP 46934, 1 (CS) 73 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12.75, 1, immature, 156 mm, BMNH 1998.3.12.76, 1, female, 151 mm, BMNH 1998.3.12.77, 1, male, 210 mm, BMNH 1998.3.12.78, 1, female, 152 mm, Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. BMNH 1998.3.12.79, 1, female, 175 mm, Mamirauá Reserve, Ressaca do Pau, 03º02'03"S, 064º52'13"W. BMNH 1998.3.12.82, 1, immature, 90 mm, Mamirauá Reserve, lago Sumaumeirinha I, 02º48'26"S, 065º04'33"W. Rio Juruá nr. confl. with rio Solimões, CU 97640, 3 (paratypes), ca. 02°40'S, 065°45'W. IDSM 454, 3, 97-110 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. IDSM 455, 2, 81-83 mm, Mamirauá Reserve, lago Jaraqui, 02º44'07"S, 065°04'38"W. INHS 44485, 5, 110-199 mm, INHS 70542 (part), 5, MZUSP 75571 (part), 6, 106-155 mm, USNM 306929, 6, 71-162 mm, USNM 306947, 1, lago Camaleão, Ilha da Marchantaria, rio Solimões, 03°14'22"S, 059°56'37"W. INPA 6403, 5 (1 measured, 118 mm), lago Janauacá, Ilha Janauacá, rio Amazonas, 03°24'S, 060°15'W. INPA 39560, 1 (holotype), 215 mm, examined from photograph in Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.), Paraná do Paracuúba, nr. mouth of lago Janauari, rio Amazonas, 03°12'36"S, 059°59'24"W. INPA 8940, 3 (paratypes), 1, 190 mm, examined from photograph in Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.), INPA 39581, 1 (paratype), 175 mm, examined from photograph in Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.), nr. lago Janauari, rio Amazonas, 03°12'36"S, 060°01'54"W. INPA 9944, 40, 52-175 mm, Mamirauá Reserve, lago Mamirauá, 03º07'S, 064º47'W. INPA 13569, 2, 45-67 mm, Ilha da Marchantaria, rio Solimões, 03°14'22"S, 059°56'37"W. INPA 15816, 4 (2 female, 170 mm, 2 male, 160-88 mm), INPA 18243, 1, immature, 192 mm, INPA 18362, 1, female, 139 mm, MCP 33279, 1, 176 mm, MCP 45253, 2 (1 female, 179 mm, 1 male, 219 mm), MCP 45255, 8 (4 immature, 119-135 mm, 3 female, 116-145 mm, 1 male, 196 mm), Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. INPA 18241, 1, male, 221 mm, MCP 45251, 2 (1 immature, 129 mm, 1 male, 216 mm), Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. INPA 18242, 1, male, 210 mm, Mamirauá Reserve, lago Periquito Redondo, 03º04'50"S, 064°46'35"W. INPA 18244, 11 (6 female, 121-168 mm, 5 male, 173-223 mm), MCP 45254, 3 (1 female [CS], 141 mm, 2 male, 179-189 mm), Mamirauá Reserve, lago Geraldo, 03º06'53"S, 064°49'06"W. INPA 18245, 4 (1 female, 152 mm, 3 male, 190-208 mm), MCP 45392, 2 (1 immature, 103 mm, 1 female, 170 mm), Mamirauá Reserve, lago Curuçá Aberto, 03º06'07"S, 064°49'10"W. INPA 18246, 3 (2 female, 150-166 mm, 1 male, 203 mm), MCP 33281, 3, 169-179 mm, MCP 45393, 1, male, 190 mm, Mamirauá Reserve, lago Curuçá Comprido, 03º05'31"S, 064°48'58"W. INPA 18348, 1, female, 145 mm, INPA 18349, 1, female, 162 mm, MCP 45345, 10 (5 female, 160-170 mm, 5 male, 190-208 mm), Mamirauá Reserve, cano do lago Arauaé, 03º03'54"S, 064º49'04"W. INPA 18350, 1, female, 161 mm, MCP 45348, 3, female, 156-177 mm, MCP 45394, 1, immature, 132 mm, Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. INPA 18351, 2 (1 female, 139 mm, 1 male, 160mm), MCP 45347, 1, female, 138 mm, MCP 45399, 1, male, 170 mm, Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. INPA 18354, 3, immature, 46-102 mm, INPA uncat.$$ (ex. 18356), 1, immature, 41 mm, MCP 45346, 3, female (1CS), 142-156 mm, MCP 45390, 1, immature, 107 mm, MCP 45391, 1, female, 110 mm, Mamirauá Reserve, lago Juruá Grande, 03º01'51"S, 064º51'07"W. INPA 18355, 3, female, 142-162 mm, MCP 45401, 1, immature, 77 mm, Mamirauá Reserve, lago Promessa, 03º04'29"S, 064°47'02"W. INPA 18357, 3 (1 immature, 45 mm, 1 female, 148 mm, 1 male, 206 mm), MCP 33280, 1, 76 mm, Mamirauá Reserve, lago Curuçá Redondo, 03º06'13"S, 064°49'06"W. INPA 18358, 2 (1 immature, 52 mm, 1 female, 156 mm), Mamirauá Reserve, lago Miratinin, 03º04'44"S, 064°50'17"W. INPA 18359, 2, immature, 50-59 mm, MCP 45256, 1, female, 165 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º05'15"S, 064°48'03"W. INPA 18360, 4, immature, 42-55 mm, MCP 45257, 2, immature, 87-91 mm, MCP 45465, 2, female, 142-178 mm, Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. INPA 18361, 2, immature, 54-63 mm, MCP 45429, 1, immature, 78 mm, Mamirauá Reserve, lago Apolônio, 03º07'03"S, 064°48'30"W. INPA 32091, 3, Lago do Rei, rio Amazonas floodplain, ca. 03º09'S, 059°41'W. INPA 33187, 3, Ressaca do Luizinho, rio Jutaí, 02º42'58"S, 066º48'13"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33196, 1, Palmares, Tabatinga, rio Solimões, 03º57'53"S, 069°20'11"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33255, 3, Ilha da Paciência, rio Solimões floodplain, 03º16'41"S, 060°16'35"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33270, 3, Lago Ressaca Grande, Fonte Boa, 02º28'26"S, 063°09'17"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 39563, 4, Coari, 03º51'10"S, 063°28'07"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). MCP 45315, 2, female, 146-164 mm, MCP 45316, 1, male, 156 mm, MCP 45359, 17 (13 female [2 CS], 140-175 mm, 4 male [1 CS], 164-206 mm), Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. MCP 45384, 4 (3 female, 157-162 mm, 1 male, 195 mm), MCP 45388, 1, immature, 152 mm, Mamirauá Reserve, lago Arauaé, 03º02'52"S, 064º50'04"W. MCP 45400, 1, immature, 98 mm, Mamirauá Reserve, lago Tracajá, 03º05'43"S, 064°46'31"W. MCP 45451, 1, male, 196 mm, Mamirauá Reserve, Paraná Maiana, 03º06'50"S, 064°47'48"W. MCP 45466, 1, female, 136 mm, MCP 45467, 4, immature, 82-125 mm, mun. Tefé, floodplain lake, Ilha Panamim, rio Solimões, 03°19'06"S, 064°38'36"W. MCP 45471, 2, immature, 102-122 mm, mun. Tefé, lago Jacaré, 03°11'11"S, 064°43'05"W. MCP 47021, 1, female, 158 mm, Mamirauá Reserve, lago Pagão, 03º02'32"S, 064º50'25"W. MCZ 9354, 6, 80-95 mm, mun. Parintins, Villa Bella [Vila Bela], rio Amazonas at Parintins and environs, ca. 02°38'S, 056°45'W. MCZ 78163 (part), 7, 83-122, lago Jacaretinga, nr. Careiro de Várzea, rio Amazonas, 03°13'00"S, 059°49'41"W. MPEG 1111, 2, 103-151 mm, mun. Iranduba, rio Solimões, nr. Manaus, ca. 03°17'S, 060°11'W [coordinates for Iranduba]. MPEG 1123 (part), 7, 57-82, mun. Tefé, Costa Capivara, rio Solimões, ca. 03°16'38"S, 064°38'09"W. MPEG 22745, 8, 88-215 mm, Mamirauá Reserve, lago Mamirauá, 02º59'38"S, 064°54'26"W. MPEG 22746, 2, 96-131 mm, Mamirauá Reserve, lago Bolsinho, 03º03'47"S, 064°49'59"W. MZUSP 6326 (part), 1, 95 mm, lago Castro, Boca do rio Purus, rio Purus, 03°42'S, 061°28'W. MZUSP 78954 (part), 1, 120 mm, Costa do Anori, nr. mouth of rio Purus, rio Solimões, 03°46'S, 061°37'W. USNM 306841, 1, Paraná do lago Janauacá, rio Amazonas, ca. 03°22'S, 060°10'W. USNM 306859, 1, lago Terra Preta, lago do Janauari, rio Amazonas, ca. 03°13'S, 060°00'W. USNM 306875, 1, lago Janauari, nr. mouth, rio Amazonas, ca. 03°13'S, 060°00'W. Pará. INPA 39564, 1, mun. Almeirim, Paranaguara, rio Amazonas, 01°44'29"S, 053°10'15"W (listed by Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). MPEG 2403, 7, 101-143, MPEG 3722, 1, 109 mm, mun. igarapé-Açu, Pantanal do rio Livramento, nr. iron bridge [on hwy. PA-230], rio Jambu-Açu, affl. rio Marapanin (Amazon estuary), 01°07'21"S, 047°41'28"W. MCP 49401, 6, mun. Curuá, Lago Preto, Ilha São Luiz, rio Amazonas, Amazonas dr., 02°06'22"S, 055°10'17"W. MPEG 7588, 1, 85 mm, MPEG 7597, 1, 59 mm, mun. Ponta de Pedras, Ilha de Marajó, Sitio Castanhal, rio Quiã-Paraná, affl. rio São José, affl. rio Marajó-Açu, affl. Baía do Guajará (Amazon estuary), 01°29'09"S, 048°55'24"W. MPEG 12562, 3, 118-147 mm, mun. Peixe Boi, branch of rio Peixe Boi, affl. rio Maracanã, (Amazon estuary), ca. 01°00'S, 047°23'W [coordinates for mouth of rio Peixe Boi]. UF 238557, 2, 131-140 mm, mun. Santarém, Lago de Santana, Ilha Marimarituba, rio Amazonas, 02°11'13"S, 055°02'21"W. UF 238570, 10, 66-107 mm, UF 238575, 1, 113 mm; UF 238577, 8, 66-104 mm; UF 238580, 3, 100-102 mm; mun. Santarém, lago Pajau, rio Amazonas, 02˚11'29"S, 054˚51'28"W. Colombia. Amazonas. FMNH 85363, 38, 50-162 mm, río Amazonas 2-3 mi. upstream Leticia, ca. 04°12'S, 069°57'W. UF 25560, 1, 121 mm, UF 25561, 1, 66 mm, N shore río Amazonas, just upstream Leticia, 04°08'S, 070°01'W. UF 33843, 1, 151 mm, pools on banks of río Amazonas at Leticia, ca. 04°12'S, 069°56'W. USNM 216870, 1, Leticia, río Amazonas, ca. 04°12'S, 069°56'W. Ecuador. Francisco de Orellana. FMNH 102276, 8, 60-128, Laguna Anangucocha, río Napo, 00°32'00"S, 076°26'42"W. Sucumbios. FMNH 102270, 2, 63-130, Laguna de Limoncocha, río Napo, 00°23'42"S, 076°36'49"W. QCAZ-I 1960, 1, 149 mm, QCAZ-I 1965 1, 176 mm, QCAZ-I 1968, 1, 138 mm, floodplain lake nr. Sacha Lodge, río Napo, 00°28'24"S, 076°27'24"W. Peru. Loreto. AMNH 78060, 14 (7 examined), 88-119 mm, río Yarapá, affl. río Ucayali, 04°31'S, 073°22'W. ANSP 178397, 1, mouth of caño Chincana, río Yanayacu, 04°19'51"S, 073°18'01"W. INHS 36829, 3, 72-193 mm, caño Ushpa, affl. río Itaya, affl. río Amazonas, ca. 03°48'S, 073°16'W. INHS 39732, 1, 85 mm, INHS 43679, 9, 60-120 mm, INHS 52031, 3, 130-144 mm, INHS 53874, 3, 98-132 mm, caño Moena nr. confl. with caño Ullpa, affl. río Itaya, affl. río Amazonas, 03°46'20"S, 073°14'17"W. INHS 54795, 6, 49-125 mm, floodplain S Nauta, río Marañón, 04°30'36"S, 073°34'06"W. MCP 26186, 29, 35-166 mm, MCP 26196, 8, 58-98 mm, Reserva Nacional Pacaya Samiria (RN Pacaya Samiria), río Pacaya, affl. río Ucayali, no coordinates. MCP 49413, 3, RN Samiria, Nauta Caño, affl. río Marañón, 04°39'33"S, 073°39'03"W. MUSM 4319, 5, 78-139 mm, quebrada Mondongo, río Huallaga, nr. Yurimaguas, affl. río Marañón, ca. 05°53'S, 076°04'W. MUSM 4499, 4, nr. Contamana, río Ucayali, 07°20'S, 075°01'W. MUSM 14498 (part), 1, 133 mm, Puesto de Vigiliancia Arcadia, río Napo, 00°59'37"S, 075°18'30"W. MUSM 17333, 8, MUSM 17341, 22, RN Pacaya Samiria, caño Yarina, Puesto de Vigilancia II, río Pacaya, affl. río Ucayali, 05°20'S, 074°30'W. MUSM 44757, 1, immature, 117 mm, cocha Supay, nr. Jenaro Herrera, río Ucayali floodplain, 04°55'16"S, 073°42'32"W. MUSM 44769, 52 (42 immature, 34-131 mm, 7 female, 71-109 mm, 3 male, 115-192 mm), cocha Capite, nr. Jenaro Herrera, río Ucayali floodplain, 04°51'21"S, 073°40'24"W. NRM 13522 (part), 1, 101 mm, NRM 27700, 1, 86 mm, caño Sacarita, opposite Pebas, río Ampiyacu, affl. río Amazonas, ca. 03°19'S, 071°50'W. NRM 27523 (part), 1, 106 mm, lago Matamata, affl. caño, río Yavarí (rio Javari) upstream from Atalaia do Norte (Brazil), 04°12'S, 070°17'W. UF 114640, 7, 64-90 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°20'53"S, 074°30'18"W. UF 126151, 10, 60-150 mm, UF 126193, 1, 90 mm, UF 131416, UF 129752, 6, 64-181 mm, 1, immature, 112 mm, RN Pacaya Samiria, caño Yarina, affl. río Ucayali, 05°20'09"S, 074°30'05"W. UF 126161, 1, 116 mm, UF 129790, 2, 75-85 mm, UF 131417, 1, immature, 108 mm, RN Pacaya Samiria, cocha Sapote, río Pacaya, affl. río Ucayali, 05°19'06"S, 074°29'18"W. UF 126172, 1, 110 mm, UF 128802, 24, 98-183 mm, UF 128870, 13, 95-175 mm, UF 128875, 50, 48-230 mm, UF 128876, 39, 62-155 mm, UF 128913, 54, 31-130 mm, UF 128915, 35, 55-165 mm, UF 128929, 17, 52-200 mm, UF 128953, 4, 65-193 mm, UF 128955, 26, 65-185 mm, UF 128966, 14, 33-200 mm, UF 129099, 37, 61-175 mm, UF 129100, 14, 53-190 mm, UF 129122, 4, 65-120 mm, UF 129177, 1, 160 mm, UF 129178, 11, 63-235 mm, UF 129230, 33, 68-170 mm, UF 129240, 11, 57-180 mm, UF 129245, 22, 60-190 mm, UF 129251, 57, 40-190 mm, UF 129273, 62, 37-175 mm, UF 129299, 18, 80-114 mm, UF 129325, 15, 97-176 mm, UF 129331, 20, 75-140 mm, UF 129333, 35, 90-110 mm, UF 129335, 59, 45-160 mm, UF 129410, 40, 87-207 mm, UF 129814, 4, 35-110 mm, UF 131418, 12, 71-200 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°16'S, 074°27'W. UF 126301, 2, 74-87 mm, UF 129800, 26, 58-110 mm, RN Samiria, río Pacaya upstream caño Narina, affl. río Ucayali, 05°25'48"S, 074°30'19"W. UF 129456, 42, 45-145 mm, RN Pacaya Samiria, caño Tamara, affl. río Ucayali, 05°16'40"S, 074°29'38"W. UF 129458, 1, 160 mm, RN Pacaya Samiria, cocha Yanayacu, río Pacaya, affl. río Ucayali, 05°18'14"S, 074°26'12"W. UF 129751, 2, 138-175 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°17'37"S, 074°29'53"W. UF 131421, 1, male, 190 mm, RN Pacaya Samiria, caño Yarina, río Pacaya, affl. río Ucayali, 05°18'16"S,074°30'02"W. UMMZ 185108, 1, 115 mm, caño Moena, mouth of caño Ullpa, affl. río Itaya, affl. rio Amazonas, 03°46'19"S, 074°30'02"W. Ucayali. MCP 44238, 2, 87-92 mm, caño Cashibo, Yarinacocha, affl. río Ucayali, 08°17'08"S, 074°37'50"W. MUSM 1550, 1, 143 mm, MUSM 1791, 1, 117 mm, cocha Tacshitea, N Pucallpa, río Ucayali, 08°02'S, 074°39'W. MUSM 3586, 3 (2 immature, 79-102 mm, 1 male, 118 mm), MUSM 3606, 7 (3 immature, 69-113 mm, 1 female, 139 mm, 3 male, 114-164 mm), MUSM 3629, 1, 128 mm, lago Imiria, Bella Flor, Coronel Portillo, affl. río Ucayali, 08°51'S, 074°16'W. MUSM 6245, 15 (6 immature, 49-111 mm, 6 female, 111-166 mm, 3 male, 127-137 mm), Cashibococha, nr. Pucallpa, río Ucayali, 08°20'S, 074°39'W. MUSM 9285, 1, immature, 61 mm, MUSM 10874, 3 (2 immature, 93-100 mm, 1 male, 159 mm), floodplain nr. Contamana, río Ucayali, 07°21'S, 075°00'W.

Brachyhypopomus bombilla Loureiro & Silva, 2006Loureiro, M. & A. Silva. 2006. A new species of Brachyhypopomus (Gymnotiformes, Hypopomidae) from northeastern Uruguay. Copeia, 2006: 665-673.

(Fig. 15; Tables 2-5, 9)

Rhamphichthys brevirostris. -Boulenger, 1896Boulenger, G. A. 1896. On a collection of fishes from the Rio Paraguay. Transactions of the Zoological Society of London, 14 (part II): 1-39, pls. 31-38.: 38 (Brazil, Mato Grosso, Descalvados, list of fishes collected in the Paraguay river by C. Ternetz, record corresponds to BMNH 1895.5.17.265-268; identified as B. bombilla [part, n = 3], B. gauderio [part, n = 1]).

Hypopomidae indet. -Hagedorn & Keller, 1996Hagedorn, M. & C. H. Keller. 1996. Species diversity of gymnotiform fishes in Manu Bioreserve, Pakitza, Perú. Pp. 483-502. In: Wilson D. E. & A. Sandoval (Eds.). Manu: the biodiversity of southeastern Peru. Washington DC, Smithsonian Institution Press.: 491, fig. 2b, drawing of adult specimen (Peru, Pakitza, Manu Reserve; diversity of gymnotiform species and EODs).

Brachyhypopomus electropomus. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 122, 322, fig. 54, line drawing of MZUSP 45032, Paraguay drainage (description in unpublished thesis with disclaimer stating nomenclatural acts therein not available, a nomen nudum; name therein refers also to B. menezesi and B. regani).

Brachyhypopomus sp. N. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (species and EOD diversity).

Brachyhypopomus bombillaLoureiro & Silva, 2006Loureiro, M. & A. Silva. 2006. A new species of Brachyhypopomus (Gymnotiformes, Hypopomidae) from northeastern Uruguay. Copeia, 2006: 665-673.: 666, fig. 1, black and white photograph of holotype (original description, type locality - Uruguay, Rocha Department, Cuatro Palmas stream, Patos-Mirim dr.). -Almirón et al., 2010Almirón, A., J. Casciotta, L. Ciotek, P. Giorgis, P. Soneira & F. Ruíz Díaz. 2010. Pisces, Gymnotiformes, Hypopomidae, Brachyhypopomus Mago-Leccia, 1994: First country record of three species of the genus, Argentina. Check List: Journal of Species Lists and Distribution, 6: 572-575.: 573, fig. 2, photograph of live individual (Argentina, Entre Ríos, Pre-Delta National Park, Paraná dr., listing of Brachyhypopomus). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662. (reproductive and trophic ecology). -Koerber, 2011Koerber, S. 2011. List of Freshwater Fishes from Argentina - Update 14. Ichthyological Contributions of Peces Criollos, 26: 1-11.: 7 (Argentina, species list). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 177, fig. 37B color photograph of head showing position of accessory electric organ; 472, fig. 1, color photographs of head; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Mirande & Koerber, 2015Mirande, J. M. & S. Koerber. 2015. Checklist of the freshwater fishes of Argentina (CLOFFAR). Ichthyological Contributions of Peces Criollos, 36: 1-68.: 48 (Argentina, catalog of fishes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 9
Morphometrics for Brachyhypopomus bombilla. HT., holotype; SD, standard deviation. Data for holotype (Rocha, Uruguay) are from Loureiro & Silva (2006Loureiro, M. & A. Silva. 2006. A new species of Brachyhypopomus (Gymnotiformes, Hypopomidae) from northeastern Uruguay. Copeia, 2006: 665-673.). Ranges for the type region (laguna dos Patos drainage of Brazil) refer to non-type specimens (data for holotype excluded). Ranges for the other populations refer to non-type specimens from the Paraguay drainage of Brazil and Paraguay (Paraná drainage) and the rio Beni drainage of Bolivia (Upper Madeira drainage).

Diagnosis. Brachyhypopomus bombilla is diagnosed from congeners by the following combination of characters: presence of accessory electric organ over the opercular region, vs. absence in all congeners except B. menezesi and B. regani; dorsal surface uniformly speckled with small brown chromatophores on a pale background, vs. presence of large dark blotches against a lighter background in B. menezesi and B. regani.

Description. Head and body shape, and pigmentation illustrated in Fig. 15 and in the original description. Meristic and morphometric data for examined specimens are presented in Tables 2-5 and 9. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight from occiput to snout, concave above eye, ventral profile of head straight, snout truncated to rounded. Eye small to moderate in size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum present; skin over AEO with similar pattern of chromatophores to surrounding area, obscuring margin of AEO and rendering AEO difficult to see in most specimens. Gill filaments on first gill arch 29-34 (median 32, n = 6). Pectoral fin narrow to moderate in breadth, pectoral-fin rays 14-17 (mode of 15 in populations from Patos-Mirim lagoon system and upper Madeira, mode of 14 in populations from Uruguay drainages). Precaudal vertebrae 15-18 (mode of 18 from Patos-Mirim, 16 from río Paraguay drainages of Brazil and Paraguay, and 17 from upper Madeira), including 1-2 transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 155-193 (median of 183 in populations from Patos-Mirim, 171 from río Paraguay, and 176 from upper Madeira). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Multiple groove-like depigmented epidermal canals, some with dark borders, form parallel striations mostly dorsal to lateral line in posterior portion of body, beginning ca. two thirds of LEA; striations reaching 1-4 scales (including lateral line series) dorsally, and occasionally (with much lower density) 1-2 scales ventrally. Epidermal canals absent in anterior portion of body, never form a pair of long irregular lines either side of dorsal surface in dorsal portion of flank, and do not form isolated horizontal wavy line midway from lateral line to dorsal midline in midbody or anterior portion of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Electrocytes of hypaxial electric organ extend anterior to anal and urogenital pores and appear to extend into opercular area to form paired accessory electric organ. Caudal filament short to moderate in length.

Coloration. (Fig. 15). Background pale straw. Dorsal region with more or less homogenous speckling of small brown chromatophores, declining in density ventrally. Dorsal region without pale stripe extending along midline from occiput to base of caudal filament. Flank ventral to lateral line only sparsely pigmented with irregular small clusters of brown stellate chromatophores. Caudal filament darker. Hypaxial electric organ conspicuous in posterior half to third of body. Head with evenly scattered dark chromatophores, darker dorsally. Eye usually with suborbital patch of subcutaneous pigmentation, of varying darkness and prominence. Region around lips usually depigmented. Presence of chromatophores over entire operculum disrupts borders of AEO, rendering it difficult to see in many specimens. This may account for why the authors of the original description failed to report the presence of this important character (although we inspected the holotype and found the AEO conspicuous). Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline. Anal-fin rays with uniform light brown pigmentation near bases, hyaline distally. Color in life faintly yellow in individuals from sediment-rich waters, with opercular region usually rosy due to underlying gills.

Fig. 15
Brachyhypopomus bombilla. MCP 19847 (part), male, 156 mm TL, non-type (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Ibicuí, Uruguay dr. Inset of head emphasizes outline of the opercular accessory electric organ with a black line. Scale bars = 5 mm.

Size. Small to moderate adult size, largest specimen examined 161 mm TL, 140 mm LEA (n = 537). Largest male specimen examined 161 mm TL, 140 mm LEA (n = 13). Largest female specimen examined 147 mm TL, 124 mm LEA (n = 43).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Argentina, Bolivia, Brazil, Paraguay, Peru, and Uruguay (Fig. 16). Known from the Patos-Mirim lagoon system, Uruguay drainage, Paraná below the former Guaíra Falls, lower and upper Paraguay, and upper Madeira (Amazon drainage) above its major series of rapids beginning at the Salto Santo Antônio (near Porto Velho, Rondônia, Brazil).

Fig. 16
Collection records for Brachyhypopomus bombilla (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found complete overlap in the range of meristics (Tables 2-5) and morphometric proportions (Table 9), and observed similar pigmentation among populations of B. bombilla in the Patos-Mirim system, Paraguay dr., and upper rio Madeira. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. bombilla are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners (although we were unable to obtain specimens for genetic analyses from the type locality in the Laguna Merín drainage).

Ecological notes. Brachyhypopomus bombilla occurs in floodplains, swamps and along the edges of slow-moving creeks and rivers - always in association with dense root mats of floating aquatic vegetation (Almirón et al., 2010Almirón, A., J. Casciotta, L. Ciotek, P. Giorgis, P. Soneira & F. Ruíz Díaz. 2010. Pisces, Gymnotiformes, Hypopomidae, Brachyhypopomus Mago-Leccia, 1994: First country record of three species of the genus, Argentina. Check List: Journal of Species Lists and Distribution, 6: 572-575.; Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.; Koerber, 2011Koerber, S. 2011. List of Freshwater Fishes from Argentina - Update 14. Ichthyological Contributions of Peces Criollos, 26: 1-11.; Loureiro & Silva, 2006Loureiro, M. & A. Silva. 2006. A new species of Brachyhypopomus (Gymnotiformes, Hypopomidae) from northeastern Uruguay. Copeia, 2006: 665-673.). Giora et al. (2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.) document the reproductive ecology of B. bombilla from southern Brazil. Breeding occurs during the austral spring and summer. In the upper Madeira, WGRC collected B. bombilla during the low water period from floating aquatic vegetation in floodplain pools and channel-margins of the río Beni floodplain (conductivity ca. 150 μScm-1, pH 7.3-7.6, dissolved oxygen 5-6 mgl-1, temperature ca. 28-32°C). Hagedorn & Keller (1996Hagedorn, M. & C. H. Keller. 1996. Species diversity of gymnotiform fishes in Manu Bioreserve, Pakitza, Perú. Pp. 483-502. In: Wilson D. E. & A. Sandoval (Eds.). Manu: the biodiversity of southeastern Peru. Washington DC, Smithsonian Institution Press.) report B. bombilla (identifications confirmed from voucher specimens at the USNM) from creeks of upper Madeira drainages in Peru. In the Paraná-Paraguay drainage, collection records indicate that B. bombilla is found in a variety of habitats, including swamps, riverine floodplains and slow-flowing creeks. Throughout its range B. bombilla appears to be adapted to a wide range of temperature, conductivity, and other parameters. In high latitudes it exhibits a period of dormancy in the austral winter, which is apparently unique among congeners (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.). At this time it burrows in muddy substrates, slows its EOD, ceases to forage, and exhibits arrested gonadal development (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.). Stomach contents in populations from southern Brazil (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.) and from the upper Madeira (WGRC pers. obs.) comprise mostly aquatic insect larvae, microcrustacea, and other small aquatic invertebrates.

Co-occurring congeners: In the upper Madeira B. bombilla occurs in geographical sympatry and ecological syntopy with B. arrayae, B. brevirostris, B. pinnicaudatus, and B. walteri. It also exhibits an allotopic distribution with B. alberti and B. sullivani. In the upper portions of the Paraguay, B. bombilla co-occurs in sympatry and syntopy with B. brevirostris, B. draco, B. gauderio, and B. walteri. In the lower Paraná, B. bombilla co-occurs in sympatry and syntopy with B. draco, B. gauderio and B. walteri. In the lower portions of the Paraguay, and in the Patos-Mirim system, B. bombilla co-occurs in sympatry and syntopy with B. draco and B. gauderio.

Local names. Argentina, Paraguay: morenita; Bolivia: Cuchillo; Brazil: tuvira, moreninha (southern Brazil); Peru: macana; Uruguay: morenita, limpiavidrio (Nion et al., 2002Nion, H., C. Ríos & P. Meneses. 2002. Peces del Uruguay: lista sistemática y nombres comunes. Montevideo, Dirección Nacional de Recursos Acuáticos/InfoPesca, 105 pp.).

Material examined. 527 specimens. Argentina. Corrientes. AI 267, 10, 91-132 mm, Esteros del Iberá, Laguna Galarza, Paraná dr., 28°04'56"S, 056°42'04"W. MACN-ict 9457, 2, 91-96 mm, Iberá wetlands, río Corrientes, Paraná dr., 28°42'45"S, 058°06'40"W. Entre Ríos. MACN-ict 9458, 1, 65 mm, Arroyo Las Mangas, Pre-Delta National Park, Paraná dr., 32°07'59"S, 060°39'37"W. Bolivia. Beni (localities are from the rio Madeira dr., Amazonas dr.). CAS 81632, 1, 100 mm, Reyes, 24 mi. NE Rurrenabaque, río Beni, 14°17'42"S, 067°20'27"W. CBF 10271, 1, immature, 93 mm, UMSS 7035, 1, female, 106 mm, mun. Riberalta, stream nr. Hormiga, on Riberalta-Guayaramerín rd., affl. río Beni, 11°01'34"S, 065°52'58"W. CBF 10272, 1, immature, 87 mm, CBF 10273, 1, immature (CS), 91 mm, CBF 10274, 1, male (CS), 96 mm, CBF 10275, 1, immature, 105 mm, CBF 10276, 1, female, 101 mm, UF 177344, 2, immature, 82-90 mm, UMSS 7036, 1, female, 99 mm, UMSS 7037, 1, immature, 90 mm, UMSS 7038, 1, female, 90 mm, UMSS 7039, 1, immature, 87 mm, UMSS 7040, 1, female, 83 mm, mun. Riberalta, arroyo Tres Cuchillos, río Beni floodplain, 10°51'44"S, 066°04'50"W. INHS 37243, 3, 74-87 mm, 41km E Estación Biológica del Beni, on rd. to San Ignacio [de Moxos], río Chevejecure, affl. río Apere, affl. río Mamoré, 14°52'S, 065°57'W. INHS 50011, 2, 65-85 mm, 46 km E Estación Ecológica del Beni on rd. to San Ignacio [de Moxos], río Moseruna, affl. río Apere, affl. río Mamoré, ca. 14°55'S, 065°54'W. UF 81921, 2, 102-104 mm, Bella Vista, rio Blanco, affl. rio Guaporé, 13°16'S, 063°41'W. UMMZ 66420, 1, 89 mm, lago Rogoagua, lake and nearby lagoons, río Beni floodplain, ca. 13°58'S, 066°58'W. La Paz. CAS 72232, 1, 124 mm, Ixiamas, 60 mi. NW Rurrenbaque, río Beni, ca. 13°45'S, 068°03'W. Pando. FMNH 106643, 1, 78 mm, FMNH 106644, 28, 57-75 mm, FMNH 106645, 4, 57-72 mm, río Manuripi, ca. 20 km upstream Puerto Rico, río Manuripi, affl. río Orthon, affl. río Madre de Dios, affl. río Beni, ca. 11°09'06"S, 067°33'41"W. FMNH 106646, 11, 53-129 mm, FMNH 106647, 17, 41-68 mm, río Manuripi, ca. 13 km upstream Puerto Rico, río Manuripi, affl. río Orthon, affl. río Madre de Dios, affl. río Beni, ca. 11°13'S, 067°34'W. Santa Cruz. UF 82190, 3, 65-79 mm, 71 km N San José de Chiquitos, río San Diablo, affl. río Itonama, affl. río San Martín, affl. río Guaporé, affl. río Mamoré, 17°18'S, 060°35'W. UF 82309, 1, 65 mm, creek 22 km W San Javierito and 49 km W San Ignacio, río Paragua, affl. río Guaporé, affl. río Mamoré, ca. 16°21'S, 061°05'W. Brazil. Acre. MCP 41034, 2, 66-107 mm, Fazenda Uberaba, ca. 6 km hwy. BR-317, rio Iná, affl. rio Xipamanu, affl. rio Abunã, 10°44'13"S, 068°11'16"W. Mato Grosso (localities in rio Paraguai dr., Paraná dr., unless otherwise stated). ANSP 53894, 2, 57-78 mm, BMNH 1895.5.17.265-268 (part), 3, 71-107 mm, mun. Cácares, Descalvados, 16°43'59"S, 057°44'54"W. BMNH 1900.4.14.91-94 (part), 1, 72 mm, mun. Carandàzinho, rio Cuiabá, ca. 16°27'S, 056°08'W. FMNH 54551, 10, 54-127 mm, MCP 15629, 9 (9 immature, 76-110 mm), mun. Cáceres, nr. Cáceres, ca. 16°04'S, 057°39'W. FMNH 54553, 1, nr. Conceição [Porto Conceição], ca. 15°57'S, 060°10'W. FMNH 70397, 1, 88 mm, nr. Conceição, ca. 17°09'S, 057°23'W. MCP 15646, 1, female, 69 mm, Porto Esperidião, arroio Zé do Cacete, km 70 on Cáceres-Porto Esperidião hwy. BR-174, 15°49'S, 058°17'W. MCP 41030, 1, 80 mm, mun. Vila Bela da Santíssima Trindade, stream 10 km rd. between Pontes e Lacerda and Vila Bela da Santíssima Trindade, affl. rio Guaporé, affl. rio Mamoré, affl. rio Madeira, Amazonas dr., 15°13'58"S, 059°24'30"W. MNRJ 12242, 6, 93-115 mm, mun. Cáceres, Fazenda Pantanalzinho, district of Porto Espiridião, Córrego Carrapato, rio Jauru, ca. 15°51'S, 058°27'W. MZUSP 19243, 1, male, 98 mm, Poconé, ca. 16°14'S, 056°37'W. MZUSP 25137, 3 (1 immature, 94 mm, 2 female, 87-97 mm), mun. Cáceres, Ilha da Taiamã [Estação Ecológica Taiamã], rio Paraguai, 16°53'S, 057°27'W [coordinates from center of island]. MZUSP 25257, 1, 93 mm, Fazenda Santo Antônio do Paraíso, rio Piquiri-Itiquira, 17°12'S, 054°09'W. MZUSP 43681, 26, MZUSP 45032, 1, 101 mm, mun. Cáceres, Descalvados, ca. 16°44'S, 057°44'W. MZUSP 44261, 9, mun. Cácares, Cácares and vicinity, ca. 16°04'S, 057°40'W. USNM 326426, 10, 61-106 mm, nr. Cáceres, ca. 16°04'S, 057°39'W. ZUEC 4291, 1, 76 mm, ZUEC 4329, 1, 72 mm, mun. Poconé, rio Piraputanga, affl. rio Vermelho, affl. rio Cuiabá, ca. 16°20'S, 053°56'W. ZUEC 4351, 1, 94 mm, ZUEC 5449, 3, 73-90 mm, mun. Poconé, km 19, Transpantaneira hwy., rio Bentes Gomes, ca. 16°33'S, 56°42'W. Mato Grosso do Sul (localities in rio Paraguai dr., Paraná dr.). FMNH 54553, 1, 105 mm, FMNH 108540, 16, 38-88 mm, Corumbá, rio Vermelho, 19°37'13"S, 56°57'16"W. FMNH 108539, 3, 70-80 mm, rio Vermelho at Fazenda Xarães, 19°36'44"S, 56°55'25"W. MUSM 16955, 1, immature, 99 mm, Taquari, rio Bonito, 18°16'23"S, 053°27'27"W. MUSM 17021, 4, 71-81 mm, Brazo de Santana Sofia, 19°35'59"S, 056°20'47"W. MZUSP 36341, 2, Ladário, nr. Corumbá, 19°00'S, 057°36'W. MZUSP 48334, 3, female, 69-80 mm, Pantanal do Paiaguás, Baía da Sede, 18°30'S, 054°45'W. MZUSP 59406, 1, female, 87 mm, Córrego da Furna, riacho Água Clara, 18°15'45"S, 053°27'59"W. MZUSP 59411, 1, male, 97 mm, Corumbá, rio Negro on rd. between Nhecolândia and hwy. BR-262, 19°17'16"S, 057°03'39"W. MZUSP 59412, 1, immature, 49 mm, Corumbá, rio Abobral, 19°27'37"S, 057°01'14"W. MZUSP 59441, 33, (15 measured: 2, immature, 61-78 mm, 13 female, 61-100 mm), Corumbá, rio Miranda, bay on left bank, rio Vermelho,19°37'22"S, 056°57'27"W. MZUSP 59444, 4 (1 immature, 99 mm, 2 female, 72-93 mm, 1 male, 100 mm), Aquidauana, Fazenda Taboco, dead end of rio Taboco, 20°04'38"S, 055°38'51"W. MZUSP 59445, 2, female, 68-79 mm, rio Verde de Mato Grosso, Anhuma, on rd., rio Negro, 19°09'57"S, 055°17'56"W. MZUSP 60051 (part), 2, immature, 76-99 mm, rio Verde de Mato Grosso, rio Negro, 19°18'17"S, 055°10'20"W. MZUSP 95081, 12 (10 immature, 52-83 mm, 2 female, 89-102 mm), mun. Barão de Melgaço, rio Mutum, between Vila de Mimoso and Joselândia, Pantanal de Paiaguás, 16°19'30"S, 055°49'59"W. Rio Grande do Sul. BMNH 1889.8.24.8, 1, 124 mm, mun. Camaquã, Camaquã, arroio Duro, affl. rio Camaquã, Patos-Mirim dr., ca. 30°51'S, 051°48'W. BMNH 1891.3.16.103-105, 3, 89-140 mm, "Rio Grande do Sul", drainage unknown, no coordinates. MCP 15326, 1, female, 73 mm, canals along hwy. BR-290 between 1 and 6 km junction with hwy. BR-116, rio Guaíba, Patos-Mirim dr., between 30°02'39"S, 051°21'20"W and 30°02'48"S, 051°23'27"W. MCP 19545, 1, male, 149 mm, 13.7 km, from São Gabriel, rio Vacacaí, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°27'18"S, 054°22'26"W. MCP 19807, 4 (1 immature, 88 mm, 2 female, 81-98 mm, 1 male, 117 mm), river at Barra do Ribeiro, affl. rio Guaíba, Patos-Mirim dr., 30°17'03"S, 051°18'04"W. MCP 19847 (part), 6 (3 immature, 127-140 mm [2 CS], 2 female, 100-147 mm, 1 male, 156 mm), bridge over Banhado do Inhatium, hwy. BR-290, 21 km São Gabriel, affl. rio Ibicuí, Uruguay dr., 30°15'43"S, 054°31'33"W. MCP 19869, 1, male, 161 mm, MCP 45355, 3, 51-65 mm, bridge on São Gabriel-Tiaraju hwy., affl. rio Vacacaí, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°17'29"S, 054°20'18"W. UFRGS 6495, 1, male, 131 mm, UFGRS 6496, 1, male, 133 mm, UFRGS 6498, 1, male, 136 mm, mun. Rosário do Sul, stream at km 82 on hwy. BR-290, affl. rio Santa Maria, affl. rio Ibicuí, Uruguay dr., 30°12'42"S, 055°03'17"W. UFRGS 6741, 1, 138 mm, UFRGS 6742, 1, 63 mm, UFRGS 6743, 1, 65 mm, UFRGS 6744, 1, 59 mm, UFRGS 6745, 1, 88 mm, UFRGS 6746, 1, UFRGS 6747, 1, 49 mm, UFRGS 9273, 18, 57-126 mm, UFRGS 9282, 15, 58-99 mm, UFRGS 9284, 17, 61-132 mm, Rosário do Sul, Sanga do Jacaré, stream at BR-290, affl. rio Ibicuí, Uruguay dr., 30°12'42"S, 055°03'19"W. UFRGS 10561, 2, 94-108 mm, mun. Rosário do Sul, arroio do Jacaré, affl. rio Ibicuí, Uruguay dr., 30°12'43"S, 055°03'18"W. Rondônia (localities from rio Madeira, dr., Amazonas dr.). INPA 19944, 5, 71-97 mm, rio Mamoré, upstream Surprêsa, ca. 11°53'S, 064°59'W. MCP 41031 (part), 2, 87-88 mm, mun. Nova Mamoré, rio Ribeirão at hwy. BR-425, ca. 62 km S hwy. BR-364, affl. rio Guaporé, affl. rio Mamoré, 10°13'55"S, 065°16'55"W. UFRO-I 6478, 6, 61-76 mm, rio Madeira, no specific locality, no coordinates. UFRO-I 6507, 2, 112-112 mm, UFRO-I uncat. CAU2010010701, 1, 85 mm, mouth of the rio Cautário, affl. rio Guaporé, affl. rio Mamoré, 12°10'51"S, 064°34'00"W. Paraguay (localities from río Paraguay dr., Paraná dr.). Alto Paraguay. FMNH 108057, 1, 49 mm, MZUSP 54330, 1, 86 mm, Estancia Voluntad, at Puerto Voluntad, 20°42'S, 057°57'W. FMNH 108058, 1, 103 mm, rio Negro, 20°09'S, 058°10'W. Caaguazú. ANSP 175179, 1, 97 mm, stream crossing rd. N Coronel Oviedo, 24°52'59"S, 056°20'10"W. Canindeyú. NRM 32529, 1, 116 mm, río Jejui-Guazú, 76 km, rd. to Curuguaty, 24°19'42"S, 055°05'13"W. NRM 32530, 1, female, 111 mm, stream nr. rd. 3km before Curuguaty, 24°29'29"S, 055°39'12"W. NRM 32531, 1, male, 115 mm, small stream, ca. 12 km on Curuguaty-Mbutuy rd., 24°29'47"S, 055°47'08"W. UMMZ 206285, 2, male, 115-142 mm, Arroyo Carimbatay, ca. 15.6 km WSW Curuguaty, Arroyo Curuguaty, río Jejui-Guazú, 24°31'06"S, 056°43'30"W. UMMZ 206470, 1, 84 mm, small stream, affl. río Jegui-Guazú, ca. 79 km by dirt rd. ENE turnoff to Curuguaty, nr. Santo Domingo, ca. 24°21'S, 055°06'W [coordinates for Santo Domingo]. UMMZ 206536, 1, 96 mm, small stream, affl. Arroyo Curuguaty, ca. 5.3 km NNW Curuguaty, río Jejui-Guazu, 24°25'06"S, 055°40'48"W. Central. BMNH 1935.6.4.370-372, 2, 75-85 mm, riacho Caracara, W Asunción, ca. 25°18'S, 057°38'W. Concepción. MZUSP 54331, 1, female, 86 mm, riacho Blandengue, nr. confl. with río Apa, 22°14'S, 057°21'W. Guairá. NRM 41902, 1, male, 118 mm, stream crossing rd. from Mauricio J. Troche to Independencia, 5 km S río Tebicuary bridge, 25°40'59"S, 056°18'40"W. Itapúa. NRM 42291, 1, female, 136 mm, NRM 42294, 1, 75 mm, Bella Vista, Arroyo Posore at 12 km before Pirapó on rd. from Obligado, 26°54'34"S, 055°36'37"W. Paraguarí. NRM 32533, 1, 98 mm, lago Ypoá, Estancia Ypoá, 25°56'43"S, 057°27'03"W. San Pedro. NRM 23195, 1, female, 122 mm, Estancia Laguna Blanca, Arroyo Mborebi from outlet from Laguna Blanca, 23°48'48"S, 056°17'44"W. Peru. Madre de Dios (localities from río Madre de Dios dr., affl. río Beni, affl. río Madeira, Amazonas dr.). MUSM 1388, 1, 132 mm, MUSM 1428, 1, 126 mm, MUSM 3947, 2, 118-122 mm, MUSM 4524, 4, 120-136 mm, MUSM 4526, 2, 113-118 mm, MUSM 5068, 1, 109 mm, Parque Nacional (PN) Manú, Pakitza Biological Station, nr. Aguajal, ca. 12°52'S, 069°16'W. MUSM 2553, 1, 105 mm, PN Manú, Pakitza Biological Station, nr. Aguajal, quebrada Fortaleza, ca. 11°45'S, 070°17'W. MUSM 4520, 8, 84-122 mm, MUSM 14015, 73, 56-133 mm, PN Manú, Pakitza Biological Station, nr. Aguajal, quebrada Carpintero, ca. 12°52'S, 069°16'W. MUSM 4564, 1, 129 mm, MUSM 14016, 11, 79-140 mm, PN Manú, Pakitza Biological Station, nr. Aguajal, quebrada Trompetero, ca. 12°52'S, 069°16'W. MUSM 21691, 1, Huitoto, no coordinates. MUSM 25041, 1, Planchón las Piedras, stream at km. 50, río Manuripe, no coordinates. MUSM 37016, 2, 120-155 mm, stream nr. Soledad Lodge, río Las Piedras, 12°02'03"S, 069°47'47"W. ROM 62201, 5, 74-120 mm, PN Manú, Pakitza Biological Station, stream in aguajal, ca. 12°52'S, 069°16'W. Puno. MUSM 3692, 2, Zona Reservada (ZR) Tambopata-Candamo, río Tambopata, ca. 13°30'S, 069°34'W. MUSM 11786, 1, 111 mm, ZR Tambopata-Candamo, río Pacal, affl. río Candamo, ca. 13°31'S, 069°41'W. MUSM 11186, 2, 106-128 mm, ZR Tambopata-Candamo, río Candamo, ca. 13°31'S, 069°41'W. Uruguay. Artigas. ZVC-P 5687, 1, 90 mm, 30º26'20"S, 056º48'14"W, ZVC-P 5916, 2, 133-133 mm, Tres Cruces stream, Uruguay dr., 30º18'09"S, 057º23'21"W. Durazno. UF183773, 2, immature (1CS), 105-130 mm, Laguna Lavalle, río Negro, Uruguay dr., 33°01'16"S, 055°22'30"W. Rocha. CU 77188, 1, Velasquez stream, Patos-Mirim dr., 34°03'S, 054°28'W. CU 77189, 1, Sauces stream, Patos-Mirim dr., ca. 34°00'S, 053°51'W. ZVC-P 6287, 1 (holotype), 154 mm, Arroyo Cuatro Palmas, Route 15, km 268, nr. Cebollatí, affl. Arroyo Pelotas, affl. Laguna Merín, Patos-Mirim dr., 33º23'43"S, 053º51'53"W. Tacuarembó. ZVC-P 5685, 1, 137 mm, Batoví stream, Uruguay dr., 31º54'28"S, 056º01'03"W.

Brachyhypopomus brevirostris (Steindachner, 1868)

(Figs. 1e, 17; Tables 2-5, 10)

Rhamphichthys brevirostris Steindachner, 1868b: 177 (original description, no locality given). -Steindachner, 1868aSteindachner, F. 1868a. Die Gymnotidae des K.K.Hof-Naturaliencabinetes zu Wien. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe, 58: 249-264, pls. 241-242).: 254, pl. 2, fig. 2 (redescription, Guaporè [rio Guaporé, Amazonas dr.]).

Rhamphichthys (Brachyrhamphichthys) brevirostris. -Günther, 1870Günther, A. 1870. Catalogue of the fishes in the British Museum. London, British Museum of Natural History, 549 pp.: 6 (Brazil, rio Guaporé, catalog of fishes in British Museum). -Steindachner, 1880Steindachner, F. 1880. Zur Fisch-fauna des Cauca und der Flüsse bei Guayaquil. Denkschriften der Kaiserlichen Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Classe, 42: 55-104, pls. 1-9. [Also published as a separate (1880), pp. 1-51, pls. 1-9.].: 89 (Brazil, rio Guaporé and rio Amazonas nr. Santarém, catalog of fishes).

Brachyrhamphichthys brevirostris. -Eigenmann & Eigenmann, 1891Eigenmann, C. H. & R. S. Eigenmann. 1891. A catalogue of the freshwater fishes of South America. Proceedings of the United States National Museum, 14: 1-81.: 62 (Brazil, rio Guaporé, Santarém, catalog of South American fishes).-Eigenmann, 1894Eigenmann, C. H. 1894. Notes on some South American fishes. A. Fishes collected by Frederick C. Hartt. Annals of the New York Academy of Sciences, 7 (art. 5): 625-637.: 625 (Brazil, Itaituba [lower Tapajós], listing of collections by Frederick C. Hartt).

Hypopomus brevirostris. -Eigenmann & Ward, 1905Eigenmann, C. H. & D. P. Ward. 1905. The Gymnotidae. Proceedings of the Washington Academy of Sciences, 7: 158-188.: 170 (Amazon and tributaries, Paraguay, catalog of gymnotiforms). -von Ihering, 1907von Ihering, R. 1907. Os peixes de água doce do Brasil. Part 1A. Revista do Museu Paulista, 7: 258-336.: 281 (Venezuela, lower Amazon, Guaporé, and Paraguay, catalog of Brazilian fishes). -Eigenmann, 1910Eigenmann, C. H. 1910. Catalogue of the freshwater fishes of tropical and south temperate America. Pp. 375-511. In: Scott W. B. (Ed.) Reports of the Princeton University expeditions to Patagonia 1896-1899, Volume III, Part IV. Princeton, University of Princeton.: 449 (Guyana to Paraguay, catalog of freshwater fishes). -Eigenmann, 1912Eigenmann, C. H. 1912. The freshwater fishes of British Guiana, including a study of the ecological groupings of species and the relation of the fauna of the plateau to that of the lowlands. Memoirs of the Carnegie Museum, 5: i-xxii,1-578, pls. 571-103.: 433 (Guyana, multiple locations, catalog of freshwater fishes). -Ellis, 1913Ellis, M. M. 1913. The gymnotid eels of tropical America. Memoirs of the Carnegie Museum, 6: 109-195.: 134: fig. 7, head shape; 189, fig. 32, anatomy of swim bladders (lists distribution as Paraguay, lower Tapajós, lower Amazon, Uruguay basin, Rio Grande do Sul, Brazil, and Guyana [records in Rio Grande do Sul and middle or lower Paraguay basin likely refer to B. gauderio, B. bombilla, or B. draco], gymnotiform diversity and anatomy). -Meek & Hilderbrand, 1916Meek, S. E. & S. F. Hildebrand. 1916. The fishes of the fresh-waters of Panama. Field Museum Natural History Publications, Zoölogical Series, 10: 1-374, pls. 376-332.: 310 ("south to the rio Plata" from NW South America [records in Panama refer to B. occidentalis]). -Eigenmann, 1922Eigenmann, C. H. 1922. The fishes of western South America. Part I: The fresh-water fishes of northwestern South America, including Colombia, Panama, and the Pacific slopes of Ecuador and Peru, together with an appendix upon the fishes of the Rio Meta in Colombia. Memoirs of the Carnegie Museum, 9: 1-346, pls. 341-338.: 174 ("south to Paraguay" from NW South America [records in Panama refer to B. occidentalis], catalog of fishes in NW South America). -Schindler, 1937Schindler, O. 1937. Bemerkungen zu Hypopomus brevirostris (Steind.). Zoologischer Anzeiger, 119: 19-25.: 19, fig. 3, outline of head based on original description; fig, 4, figs. 5-11, outline of heads of syntypes, table with morphometric analysis of syntypes [including designation of lectotype, "Typus", and paralectotype, "Co-typus", specimens], discussion of additional specimens of Brachyhypopomus from Paraguay). -Eigenmann & Allen, 1942Eigenmann, C. H. & W. R. Allen. 1942. Fishes of western South America. Lexington, University of Kentucky, 494 pp.: 314 (Guianas, Paraguay, Peru at Iquitos and Yurimaguas, listing of gymnotiforms). -Schultz, 1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.: 40 (diagnosis against by key and morphological data, in description of B. beebei). -Fowler, 1945Fowler, H. W. 1945. Colombian Zoological Survey. Part I. The freshwater fishes obtained in 1945. Proceedings of the Academy of Natural Sciences of Philadelpia, 97: 93-135.: 179 (Peru at Iquitos and Yurimaguas, Guianas, Brazil, and Paraguay, listing of congeners). -Schultz: 1949Schultz, L. P. 1949. A further contribution to the ichthyology of Venezuela. Proceedings of the United States National Museum, 99: 1-211., 65 (key to the Hypopomidae]. -Heiligenberg & Bastian: 1980Heiligenberg, W. & J. Bastian. 1980. Species specificity of electric organ discharges in sympatric gymnotoid fish of the Rio Negro. Acta Biológica Venezuélica, 10: 187-203.: 197, fig. 1, black and white photograph (Brazil, Amazonas, rio Negro, EOD diversity in sympatric gymnotiforms). -Ortega & Vari, 1986Ortega, H. & R. P. Vari. 1986. Annotated checklist of the freshwater fishes of Peru. Smithsonian Contributions to Zoology, 437: 1-25.: 13 (Peru, listing of members of genus). -Kawasaki & Heiligenberg, 1989Kawasaki, M. & W. Heiligenberg. 1989. Distinct mechanisms of modulation in a neuronal oscillator generate different social signals in the electric fish Hypopomus. Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 165: 731-741.: 732, fig.1A, black and white photograph of male and female (EODs and communication).

Hypopomus artedi. -Hopkins & Heiligenberg, 1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.: 132, fig. 10, black and white photograph (Suriname, EOD evolution in sympatric gymnotiforms).

Brachyhypopomus brevirostris. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48, 168, fig. 68, reproduction of plate 2, fig. 2 from Steindachner, 1868aSteindachner, F. 1868a. Die Gymnotidae des K.K.Hof-Naturaliencabinetes zu Wien. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe, 58: 249-264, pls. 241-242). (listing of Brachyhypopomus). -Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.: 396, color photograph of live individual (French Guiana, listing of Brachyhypopomus). -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 27-29, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 97, fig. 6.7; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1, reproductive biology (Brazil, central Amazon, ecology and signal diversity). -Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.: 523 (Brazil, Roraima, listing of gymnotiforms). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 86 (redescription). -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4, 834, fig. 9, drawing of adult specimen, with EOD; 837, fig. 10, drawing of caudal filament of male and female (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance). -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 494 (Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, Venezuela, catalog of hypopomids). -Goulding et al., 2003Goulding, M., C. Cañas, B. R. B. Forsberg & H. Ortega. 2003. Amazon headwaters: rivers, life and conservation of the Madre de Dios river basin. Lima, Asociación para la Conservación de la Cuenca Amazónica, Amazon Conservation Association, Gráfica Biblos S.A., 198p.: 177, center photograph, live individual (Peru, upper río Madre de Dios, photographic album of fishes). -Maldonado-Ocampo, 2004Maldonado-Ocampo, J. A. 2004. Peces de la Orinoquia Colombiana: una aproximacíon al estudo actual de su conocimento. Pp. 303-368. In: Diazgranados M. C. & F. Trujillo (Eds.). Fauna acuática en la Orinoquia Colombiana. Pontificia Universidad Javeriana, Bogotá.: table 1 (Colombia, Orinoco dr. and Meta dr., listing of Brachyhypopomus). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Galvis et al., 2006Galvis, G., J. I. Mojica, S. R. Duque, C. Castellanos, P. Sánchez-Duarte, M. Arce, Á. Gutiérrez, L. F. Jiménez, M. Santos, S. Vejerano, F. Arbelaez, E. Prieto & M. Leiva. 2006. Peces del medio Amazonas - Región de Leticia. Bogotá, Conservation International, 548p.: 212, illustration of head and body; 529, plate 104a, photograph of live specimen (Colombia, Amazonas, catalog of fishes). -Ferreira et al., 2007Ferreira, E. J. G., J. Zuanon, B. Forsberg, M. Goulding & Briglia-Ferreira, S. R.. 2007. Rio Branco: peixes, ecologia e conservação de Roraima. Manaus, Amazon Conservation Association, Instituto Nacional de Pesquisas da Amazônia, Sociedade Civil Mamirauá, 201pp.: 164, center left photograph, live specimen (Brazil, Roraima, rio Branco, photographic album of fishes]. -Vari et al., 2009Vari, R. P., C. J. Ferraris, A. Radosavljevic & V. A. Funk. 2009. Checklist of Freshwater Fishes of the Guiana Shield. Bulletin of the Biological Society of Washington, 17: 1-93.: 46 (Guiana Shield, catalog of fishes). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Mol: 2012Mol, J. H. 2012. The freshwater fishes of Suriname. Leiden, Brill Academic Publishers, 890 pp., 596 (Suriname, catalog of fishes). -de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.: 545 (Brazil, rio Madeira, lago Cuniã, listing of fish).-Carvalho: 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp., 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 236, color photograph (Brazil, rio Madeira, listing of hypopomids). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 9, 14, 16, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 10
Morphometrics for Brachyhypopomus brevirostris. LT, lectotype; SD, standard deviation. Ranges for the type region refer to the lectotype (rio Guaporé) and to non-type specimens from the rio Guaporé in Brazil and río Beni and Mamoré in Bolivia. Ranges for the other populations refer to non-type specimens from the vicinity of Tefé, Amazonas, Brazil (Central Amazonas basin), the río Orinoco drainage in Venezuela (Orinoco drainage), and the upper rio Paraguay drainage in Brazil (upper Paraguay drainage).

Diagnosis. Brachyhypopomus brevirostris is diagnosed from congeners by the following combination of characters: anal-fin rays 226-293, vs. 143-225 in all congeners except B. beebei, B. bennetti, B. bullocki, B. diazi, B. occidentalis, B. palenque, and B. walteri; bilateral columns of electrocytes at the anal-fin terminus 3, vs. 4-6 in B. bennetti, B. diazi, B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis), and B. palenque; pale stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament present in B. beebei; precaudal vertebrae 18-21, vs. 15-17 in B. bullocki; distinct dark suborbital stripe absent, vs. present in B. walteri.

Description. Head and body shape, and pigmentation illustrated in Figs. 1e and 17. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 10. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head approximately straight between operculum and snout. Snout rounded. Eye moderate to large in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 40-63 (median 55, n = 38). Pectoral fin narrow to broad in width, pectoral-fin rays 15-20 (mode of 17 in populations from upper Madeira (Guaporé), Orinoco, and upper Paraguay; mode of 18 in a population from central Amazon). Precaudal vertebrae 18-21 (mode of 19 in populations from upper Madeira, central Amazon, and upper Paraguay; mode of 20 in a population from Orinoco), including 1-2 transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 226-293; range and median values of all examined populations are similar. Dorsal rami of recurrent branch of anterior lateral line nerve visible in most juvenile and some lightly-pigmented adults; mostly in anterior third of body. Middorsal region of body scaled. Rows of scales above lateral line 7-9 (mode 8). Lateral line continuous. Epidermal canals sparse and in some specimens more or less absent; when present located only in posterior two thirds of body. Isolated short sections of depigmented canals midway between the lateral line and dorsal midline in middle third of the body. Sparse crisscrossing epidermal canals close to and either side, of but mostly dorsal to lateral line in posterior third of body, merging near anal-fin terminus with canals midway between the lateral line and dorsal midline. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Extreme tip of caudal filament free of electrocytes. Caudal filament moderate in length to long.

Coloration. (Figs. 1e, 17). Background tan to light brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Prominent wide brown saddles, which extend to dark bands that traverse flank, often exhibiting a misalignment in their continuation at lateral line. Dark bands become fainter ventrally, breaking up into indistinct marks over anal-fin pterygiophores. Indistinct dark markings often present in pale interband area. Contrast between dark bands and saddles and background is typically greater in juveniles but varies among populations. Some large adults become very dark and bands and saddles become indistinct. Caudal filament darker than body, especially dorsally, ventrally, and near tip; with irregular bands along entire length; darkened tip of caudal filament resembles root tips of water hyacinths when viewed underwater. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline with light scattering of brown chromatophores. Anal-fin rays with scattered or uniform dark pigmentation; darker in posterior half of fin. Color in live specimens similar to preserved ones, with opercular region usually rosy due to underlying gills.

Fig. 17
Brachyhypopomus brevirostris. a. MCP 45470 (WC11.110801b), immature female, 193 mm TL, (head only, specimen fixed in formalin); Brazil, rio Tefé, Amazonas dr. b. NMW 65040, lectotype, sex not determined, 163 mm TL (body in lateral view, specimen preserved in EtOH), Brazil, rio Guaporé, Amazonas dr. c. MCP 45262 (WCNR06.090600), male, 366 mm TL, non-type (body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); d. MCP 45260 (WC02.180598), female, 305 mm TL, non-type (body in lateral view; specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note the extreme sexual dimorphism in caudal-filament length. Scale bars = 5mm.

Size. Moderate to large adult size, largest specimen examined 461 mm TL, 210 mm LEA (n = 1701). No congener reaches greater total length. Largest male specimen examined 461 mm TL, 210 mm LEA (n = 39). Largest female specimen examined 315 mm TL, 230 mm LEA (n = 84).

Sexual dimorphism. Breeding male specimens develop extremely elongated caudal filaments in comparison to immature individuals and breeding females, and consequently reach considerably greater total lengths (Figs. 17c-d), but not lengths as measured to anal-fin terminus. Despite possessing longer caudal filaments, breeding males do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes. Instead they exhibit clearly enlarged electrocytes relative to immature specimens and females. In breeding males caudal filament tip forms a paddle-like laterally compressed structure, some 15-40 mm in length, often completely free of electrocytes. In some males the posterior portion of the caudal filament is entirely free of electrocytes for as much as 48% of caudal-filament length. Some females exhibit a shorter and only slightly laterally compressed caudal filament tip, without electrocytes in terminal portion for up to 10% of caudal-filament length. No sexual differences in pigmentation.

Geographic distribution. Bolivia, Brazil, Colombia, French Guiana, Guyana, Peru, Suriname, and Venezuela (Fig. 18). Widespread through cis-Andean northern South America, including large areas of the Amazonas and Orinoco drainages, northern portions of the Paraguay drainage, coastal drainages of the Guianas and Amapá state, Brazil, and coastal drainages of Pará state, Brazil. As yet unknown from some major tributaries of the Amazon, including the Juruá, upper Japurá-Caquetá, Napo, and upper Xingu, and many southwestern tributaries of the río Orinoco.

Fig. 18
Collection records for Brachyhypopomus brevirostris (circles). Precise locality of the lectotype is not known. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found complete overlap in the range of meristic counts (Tables 2-5) and morphometric proportions (Table 10), and observed similar pigmentation among populations of B. brevirostris in the upper Madeira, central Amazon, Orinoco, and upper Paraguay drainages. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. brevirostris are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners (although we were unable to obtain specimens for genetic analyses from the Paraguay basin).

Ecological notes. Brachyhypopomus brevirostris is an ecologically cosmopolitan species, and varies from being locally rare to exceptionally abundant in lentic and slow-flowing environments throughout its range (Alves-Gomes, 1997Alves-Gomes, J. A. 1997. Informações preliminares sobre a bio-ecologia de peixes elétricos (Ordem Gymnotiformes) em Roraima. Pp. 47-55. In: Barbosa R. I., E. J. G. Ferreira & E. G. Castellón (Eds.). Homen, ambiente e ecologia no estado do Roraima. Manaus, INPA.; Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.; de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.; Hopkins & Heiligenberg, 1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.; Mol, 2012Mol, J. H. 2012. The freshwater fishes of Suriname. Leiden, Brill Academic Publishers, 890 pp.). It occurs in seasonally inundated floodplains (in floating rafts of meadows and shallow newly-flooded forests), along the margins of rivers (in emergent and floating vegetation), in ephemeral or perennial swamps (in vegetation or submerged debris), and in terra firme forest and savanna streams (in emergent and submerged vegetation, leaf litter and debris, and in marginal root mats and holes). In the lowland Amazon, B. brevirostris occurs in low-conductivity blackwater and clearwater streams, river margins, and floodplain systems (ca. 5-30 μScm-1), and also high-conductivity whitewater river margins and floodplain systems (ca. 90-250μScm-1), as well as in waters of intermediate conductivity. Nonetheless, it is most abundant in low-conductivity systems. Brachyhypopomus brevirostris is less tolerant of prolonged hypoxia than congeners from the central Amazon, and is unusual among congeners in not exhibiting air-breathing of any kind (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Breeding occurs during the rising and high water period in populations from Amazonian floodplain floating macrophytes (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 165). Stomach contents in populations from the central Amazon comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136). Large specimens often consume larger aquatic invertebrates.

Co-occurring congeners: Because of its wide geographical range and occurrence in multiple habitats, B. brevirostris occurs in geographical sympatry and ecological syntopy with multiple congeners: in the Amazonas drainage and coastal drainages of the Guianas - B. batesi, B. beebei, B. belindae, B. benjamini, B. bennetti, B. cunia, B. hamiltoni, B. hendersoni, B. pinnicaudatus, B. regani, B. sullivani, B. verdii, B. walteri; in the Orinoco drainage - B. beebei, B. bullocki, B. diazi, B. provenzanoi, B. regani, and B. sullivani; in the Paraguay drainage - B. bombilla, B. draco, B. gauderio, and B. walteri.

Local names. Brazil: sarapó (north), tuvira (Paraguay drainage); Colombia: cuchillo/cuchillo amarillo (Amazon and Orinoco), cuchilleja macana (Putumayo); French Guiana: poisson couteau (French) and multiple creole/Amerindian names, see Planquette et al. (1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.); Peru: macana; Suriname: saprapi; Venezuela: cuchillo.

Remarks. Comments on the type series: In the original brief description, Steindachner (1868bSteindachner, F. 1868b. Abhandlung über die Gymnotiden des Wiener Museums. Anzeiger der Akademie der Wissenschaften in Wien, 5: 176-177.) did not mention specimens, and in the redescription (1868aSteindachner, F. 1868a. Die Gymnotidae des K.K.Hof-Naturaliencabinetes zu Wien. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe, 58: 249-264, pls. 241-242).) he only referred to "several small specimens 2"11"' - 71/2" long". The type series consequently consists of several syntypes. Schindler (1937Schindler, O. 1937. Bemerkungen zu Hypopomus brevirostris (Steind.). Zoologischer Anzeiger, 119: 19-25.) recognized eight specimens in the NMW as syntypes and designated one of them as (NMW 65040) as "Typus", consequently a lectotype under the International Code of Zoological Nomenclature, Article 74.5. Schindler considered it to be identical with the specimen on plate 2, fig. 2 in Steindachner (1868aSteindachner, F. 1868b. Abhandlung über die Gymnotiden des Wiener Museums. Anzeiger der Akademie der Wissenschaften in Wien, 5: 176-177.).

Comments on erroneous geographical references: Prior to, and even for several decades after Regan's (1914Regan, C. T. 1914. Fishes from the Condoto river, Colombia collected by Dr. H.G.F. Spurrell. Annals and Magazine of Natural History, (8) 14: 13-32.) description of B. occidentalis (the only species of Brachyhypopomus to occur in trans-Andean Colombia, Panama, and Costa Rica), the name B. brevirostris was repeated in reference to material collected from Trans-Andean Panama, and Colombia (Eigenmann, 1922Eigenmann, C. H. 1922. The fishes of western South America. Part I: The fresh-water fishes of northwestern South America, including Colombia, Panama, and the Pacific slopes of Ecuador and Peru, together with an appendix upon the fishes of the Rio Meta in Colombia. Memoirs of the Carnegie Museum, 9: 1-346, pls. 341-338.; Eigenmann & Allen, 1942Eigenmann, C. H. & W. R. Allen. 1942. Fishes of western South America. Lexington, University of Kentucky, 494 pp.; Eigenmann & Eigenmann, 1891Eigenmann, C. H. & R. S. Eigenmann. 1891. A catalogue of the freshwater fishes of South America. Proceedings of the United States National Museum, 14: 1-81.; Eigenmann & Fisher, 1914Eigenmann, C. H. & H. G. Fisher. 1914. The Gymnotidae of Trans-Andean Colombia and Ecuador (Contributions from the Zoological Laboratory of Indiana University, No. 141). Indiana University Studies, 25: 235-237.; Eigenmann & Ward, 1905Eigenmann, C. H. & D. P. Ward. 1905. The Gymnotidae. Proceedings of the Washington Academy of Sciences, 7: 158-188.; Fowler, 1945Fowler, H. W. 1945. Colombian Zoological Survey. Part I. The freshwater fishes obtained in 1945. Proceedings of the Academy of Natural Sciences of Philadelpia, 97: 93-135.; Meek & Hildebrand, 1916Meek, S. E. & S. F. Hildebrand. 1916. The fishes of the fresh-waters of Panama. Field Museum Natural History Publications, Zoölogical Series, 10: 1-374, pls. 376-332.; Steindachner, 1880Steindachner, F. 1880. Zur Fisch-fauna des Cauca und der Flüsse bei Guayaquil. Denkschriften der Kaiserlichen Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Classe, 42: 55-104, pls. 1-9. [Also published as a separate (1880), pp. 1-51, pls. 1-9.].). Several reports prior to ca. 1945 list B. brevirostris as occurring in "Paraguay" although it is unclear whether the country or river is referenced; although present in the upper Paraguay basin of Brazil, B. brevirostris has not yet been collected in Paraguay.

Material examined. 1,787 specimens. Bolivia/Brazil frontier. NMW 65038, 1, 183 mm, 152 mm LEA (paralectotype) corresponds in size to "Co-typus" specimen from first column of table 2 in Schindler (1937Schindler, O. 1937. Bemerkungen zu Hypopomus brevirostris (Steind.). Zoologischer Anzeiger, 119: 19-25.), rio Guaporé, affl. rio Mamoré, affl. rio Madeira, Amazonas dr., no coordinates, J. Natterer. NMW 65040, 1, 164 mm TL, 123 mm LEA (lectotype), collected with NMW 65038. Bolivia. Beni (localities from rio Madeira dr., Amazonas dr.). AMNH 40086 (part), 1, 202 mm, rio Baures, 2 km above mouth, affl. río Guaporé, affl. río Mamoré, 12°30'32"S, 064°16'46"W. CBF 10259, 1, male, 234 mm, UMSS 07033, 1, immature, 160 mm, stream at km 43 on Riberalta-Guayaramerín rd., affl. río Beni, 11°00'30.2"S, 065°39'49.4"W. UMMZ 204512, 1, 131 mm, 9 km SE Costa Marquez (Brazil), río Iténez (rio Guaporé), affl. río Mamoré, ca. 12°30'42"S, 64°10'18"W. UMMZ 204743, 2, 92-167 mm, 6 km SW Costa Marques, río Iténez at mouth of río Baures, affl. río Mamoré, 12°31'S, 064°19'W. UMMZ 205163, 3, 155-167 mm, Backwater of río Iténez, 10km SE Costa Marques, affl. río Mamoré, 12°33'00"S, 064°12'24"W. UMMZ 246440, 1, 170 mm, río Baures (río Blanco), ca. 500 m above mouth on left bank río Iténez, affl. río Mamoré, 12°31'06"S, 064°19'00"W. UMSS 07024, 1, immature, 229 mm, stream at Bocerón, Riberalta - Guayaramerín rd., affl. río Beni, 11°02'50"S, 065°50'07"W. Brazil. Amazonas (localities are from the Amazonas dr.; localities listed from Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1985.6.22.51, 1, 270 mm, rio Tarumazinho [rio Tarumã Mirim], affl. rio Negro, 02°54'S, 060°13'W. BMNH 1998.3.12.133-141, 9, immature, BMNH 1998.3.12.145-156, 12, immature, 2 measured, 200-220 mm, IDSM 444, 7, 90-214 mm, MCP 44605, 1, male (CS), 374 mm, MCP 44759, 17 (2CS), 48-243 mm, MCP 45258, 3, female, 210-264 mm, mun. Tefé, Ressaca do Cachorro, lago Tefé, rio Tefé, 03°19'50"S, 64°42'15"W. BMNH 1998.3.12.142-144, 3, immature, BMNH 1998.3.12.157, 1, male, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, ca. 03°34'S, 64°58'W. BMNH 1998.3.12.158, 1, 225 mm, MCP 45332, 1, female, 260 mm, Igarapé Baré, lago Amanã, affl. río Japurá, 02°25'05"S, 64°42'58"W. IDSM 443, 1, 80 mm, MCP 45331, 3 (1 immature, 272 mm, 1 male, 340 mm, 1 unsexed, 223 mm), Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. INHS 70542, 1 (part), lago Camaleão, Ilha da Marchantaria, rio Solimões floodplain, 03°14'S, 059°56'W. INHS 71264, 1, 223 mm, lago do Janauari, rio Amazonas floodplain, 03°13'S, 060°00'W. INPA 4388, 2, 128-150 mm, INPA 12265, 1, 200 mm, INPA 19936, 1, 160 mm, INPA 19937, 2, 125-136 mm, Arquipelago das Anavilhanas, rio Negro, 02°41'S, 060°44'W. INPA 8857, 33, km 55 on Manaus-Manacapuru hwy. AM-070, stream, affl. rio Solimões, ca. 03°13'S, 060°26'W. INPA 9947, 19, 127-310 mm, Mamirauá Reserve, lago Caetano, 02º50'58"S, 064º55'42"W. INPA 9948, 3, 290-420 mm, INPA 9949, 3, 218-240 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°34'S, 064°58'W. INPA 15814, 6 (3 immature, 54-145 mm, 1, female, 253 mm, 2 male, 370-461 mm), MCP 44606, 7 (3 immature [2CS], 124-175 mm, 2 female, 233-270 mm, 2 male [1CS], 295-308 mm), mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°36'55"S, 064°57'33"W. INPA 15815, 7, immature, 36-108 mm, INPA 18344, 3, immature, 77-78 mm, MCP 45379, 6 (4 immature, 85-132 mm, 1, female, 203 mm, 1 male, 285 mm), MCP 45470, 20, immature, 97-218 mm, mun. Tefé, Ressaca do Socorro, lago Tefé, rio Tefé, 03°18'45"S, 064°41'50"W. INPA 17185, 6, 80-180 mm, lago Campina, rio Purus, 04°55'59"S, 062°56'25"W. INPA 17186, 5, 90-202 mm, Paraná do Seixo, lago Jari, rio Purus, 04°54'41"S, 062°27' 26"W. INPA 17189, 21, 56-213 mm, lake nr. Sacado da Santa Luzia, rio Purus, 04°42'17"S, 062°22' 26"W. INPA 18247, 1, female, 238 mm, INPA 18345, 2 (1 female, 276, 1 male, 205), MCP 45386, 1, male, 225 mm, Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. INPA 18248, 3 (1 immature, 227 mm, 1, female, 230 mm, 1 male, 216 mm), Mamirauá Reserve, lago Arauaé, 03º02'52"S, 064º50'04"W. INPA 18249, 1 male, 279 mm, MCP 45395, 2 (1 immature, 238 mm, 1 female, 240 mm), Mamirauá Reserve, cano do lago Arauaé, 03º03'54"S, 064º49'04"W. INPA 18250, 1, male, 293 mm, INPA 18251, 1, immature, 222 mm, MCP 45260, 2, female, 237-305 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. INPA 18252, 1, female, 305 mm, mun. Tefé, Ilha do Martelo, rio Tefé, 03°46'56"S, 064°59'39"W. INPA 18342, 1, female, 150 mm, INPA 18346, 1, female, 192 mm, Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. INPA 18343, 1, female, 227 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°38'01"S, 064°57'59"W. INPA 18347, 12 ( 9 female, 180-293 mm, 3 male, 175-220 mm), mun. Tefé, lago Caiambé, rio Caiambé, 03º35'34"S, 064º26'36"W. INPA 19934, 1, 155 mm, igarapé de Duas Bocas, Paraná do Jari, rio Purus, 04°55'33"S, 062°21'58"W. MCP 33367, 1, 208 mm, MCP 45362, 1, female, 188 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. MCP 44758, 9 (1 immature [CS], 257 mm, 4 female [1CS], 242-265 mm, 4 male, 250-395 mm), MCP 45262, 1, male, 366 mm, MCP 45323, 25 (1 immature, 259 mm, 19 female, 138-258 mm, 5 male, 208-311 mm), Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45259, 1, female, 235 mm, Mamirauá Reserve, lago Matá Matá, 03º06'17"S, 064°47'17"W. MCP 45261, 1, female, 228 mm, Mamirauá Reserve, lago Promessa, 03º04'29"S, 064°47'02"W. MCP 45263, 2 (1 female, 269 mm, 1 male, 397 mm), MCP 45472, 1, immature, 150 mm, mun. Tefé, rio Tefé, 03°41'23"S, 064°59'08"W. MCP 45317, 7 (6 immature, 86-127 mm, 1 female, 315 mm), MCP 46930, 2, immature (2 CS), 110-178 mm, MCP 46935, 1 post-larval (CS), 30 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º03'51"S, 064º51'05"W. MCP 45318, 3 (2 immature, 149-225 mm, 1 male, 265 mm), MCP 46927, 1, immature (CS), 136 mm, Mamirauá Reserve, lago Bolsinha, 03º03'47"S, 064º50'03"W. MCP 45319, 1, immature, 161 mm, MCP 45404, 1, female, 279 mm, Mamirauá Reserve, lago Pagão, 03º02'32"S, 064º50'25"W. MCP 45322, 2 (1 immature, 111 mm, 1 male, 156 mm), MCP 45378, 2, female, 170-215 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°35'41"S, 064°58'05"W. MCP 45326, 2, immature, 103-175 mm, Mamirauá Reserve, lago Sumaumeirinha I, 02º48'26"S, 065º04'33"W. MCP 45363, 1, female, 275 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º06'40"S, 064°47'52"W. MCP 45396, 2, female, 250-273 mm, Mamirauá Reserve, lago Periquito Redondo, 03º04'50"S, 064°46'35"W. MCP 45402, 1, immature, 100 mm, Mamirauá Reserve, lago Tracajá, 03º05'43"S, 064°46'31"W. MCP 45403, 1, female, 230 mm, Mamirauá Reserve, lago Juruazinho, 03º02'34"S, 064º51'00"W. MCP 45452, 1, immature, 231 mm, mun. Tefé, igarapé Xidarinini, affl. lago Tefé, rio Tefé, 03°22'46"S, 064°41'17"W. MCP 45468, 7, immature, 72-269 mm, mun. Tefé, floodplain lake, Ilha Panamim, rio Solimões, 03°19'29"S, 064°38'37"W. MCZ 9427 (part), 1, 171 mm, mun. Manaus, lago Hyanuary [lago do Janauari], rio Amazonas floodplain, 03°13'S, 060°00'W. MCZ 60046, 1, 84 mm, mun. Parintins, lago Maximo [lago do Maximo], nr. Parintins, rio Amazonas floodplain, ca. 02°40'S, 056°45'W. MCZ 78163 (part), 1, 162 mm, MCZ 78164, 1, 109 mm, mun. Manaus, lago Jacaretinga, nr. Careiro de Várzea, rio Amazonas floodplain, 03°13'00"S, 059°49'41"W. MCZ 165856, 4, 164-196 mm, mun. Manaus, rio Negro nr. lago Alexo [lago do Aleixo], rio Amazonas floodplain, 03°05'28"S, 059°53'09"W. MPEG 967, 1 (part), 86 mm, MPEG 970 (part), 1, 120 mm, MPEG 978, 1, 202 mm, MZUSP 30044 (part), 98, 82-233 mm, mun. Tefé, lago Jurupari, rio Tefé, 03°48'S, 065°00'W. MPEG 968, 3, 140-157 mm, MPEG 975, 3, 157-203 mm, MZUSP 30047, 5, 195-250 mm, mun. Tefé, lago Supiã-Puçu, rio Tefé, 03°45'S, 064°57'W. MPEG 977, 2, 87-225 mm, MZUSP 30046, 6, 110-225 mm, MZUSP 30048, 31, 74-235 mm, mun. Tefé, Arana-tuba, rio Tefé, ca. 04°02'S, 065°01'W. MPEG 979, 7 (part), 110-200 mm, mun. Tefé, Ipanema da Baixa, rio Tefé, no coordinates. MPEG 980, 23, 84-242 mm, mun. Tefé, Janari-Atuba, rio Tefé, ca. 03°52'S, 065°01'W. MPEG 1123 (part), 1, 142 mm, mun. Tefé, Costa Capivara, rio Solimões, ca. 03°16'38"S, 064°38'09"W. MPEG 1128, 2, 226-260 mm, mun. Iranduba, rio Solimões nr. Manaus, ca. 03°17'S, 060°11'W [coordinates for Iranduba]. MPEG 22738, 1, 305 mm, Mamirauá Reserve, lago Mamirauá, 02º59'38"S, 064°54'26"W. MPEG 22739, 1, 165 mm, mun. Tefé, igarapé Repartimento, affl. lago Tefé, rio Tefé, 03°24'19"S, 064°43'54"W. MZUSP 30045, 79 (1CS), 59-233 mm, Jauari-atuba, rio Tefé, ca. 03°56'S, 065°01'W. MZUSP 30049 (part), 2, 55-90 mm, MZUSP 30057, 2, 56-62 mm, Vista Escura, rio Tefé, no coordinates. MZUSP 30061 (part), 17, 85-157 mm, MZUSP 30062, 5, 48-98 mm, lago Mucura, rio Tefé, no coordinates. MZUSP 62060, 2, 87-99 mm, Poça de Praia, Tapera, rio Negro, 00°11'S, 064°04'W. MZUSP 78032 (part), 1, 181 mm, mun. Maraã, Paraná do Castanho, lago Amanã, affl. rio Japurá, 02°44'S, 064°39'W. MZUSP 91651, 1, 164 mm, rio Uapés, affl. rio Negro, no coordinates [listed coordinates invalid]. MZUSP 92250, 65, 123-225 mm, mun. São Gabriel da Cachoeira, igarapé Cunurim, affl. rio Tiquié, ca. 500 m below São José II, affl. rio Uaupés, affl. rio Negro, 00°13"N, 069°36"W. MZUSP 92496, 17, 95-205 mm, mun. São Gabriel da Cachoeira, igarapé Castanha, nr. mouth, affl. rio Tiquié, affl. rio Uaupés, affl. rio Negro, 00°12"N, 069°35"W. MZUSP 93091, 1, 220 mm, mun. São Gabriel da Cachoeira, igarapé Castanha nr. São Pedro, affl. rio Tiquié, affl. rio Uaupés, affl. rio Negro, 00°11"N, 069°35"W. MZUSP 94034, 7, 105-160 mm, MZUSP 99169, 7, 73-197 mm, canal do lago Amanã, affl. rio Japurá, ca. 03°00'S, 064°23'W. MZUSP 95226 (part), 1, 158 mm, mun. Santa Isabel do rio Negro, nr. Paricatuba, lagoon on margin of rio Negro, 00°31'S, 065°01'W. USNM 198081, 2, 138-181 mm, igarapé da Mãe Joana, lago Grande do Manacapuru, affl. rio Solimões, ca. 03°13'S, 060°44'W. USNM 229425, 1, 192 mm, USNM 306868, 2, 159-190 mm, mun. Manaus, lago Janauari, nr. mouth, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 300973, 2, 67-120 mm, rio Unini, affl. rio Negro, ca. 01°41'S, 061°31'W [coordinate for mouth of rio Unini]. USNM 306835, 7, 190-259, mun. Manaus, lago do Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 306878, 1, 215 mm, lago Camaleão, Ilha da Marchantaria, rio Solimões floodplain, 03°14'22"S, 059°56'37"W. USNM 306902, 1, 80 mm, USNM 306925, 1, 167 mm, lago Terra Preta, lago do Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 306904, 3, 190-257 mm, USNM 306934, 1, 259 mm, lago Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 306921, 1, 234 mm, lago Canta Galos, lago Janauari, rio Amazonas floodplain, 03°13'S, 060°00'W. USNM 327307, 1, 96 mm, mun. Barcelos, lago de Caatinga, rio Ererê, affl. rio Negro, ca. 00°14'S, 063°53'W. Mato Grosso. INPA 4385, 3, 139-169 mm, stream nr. Castanhal, rio Aripuanã, affl. rio Madeira, Amazonas dr., ca. 10°10'S, 059°29'W [coordinates for town of Aripuanã]. MNRJ 25152, 4, 62-93 mm, mun. Ribeirão Cascalheira, Ribeirão Manda Brasa, affl. rio Suiá-miçu, affl. rio Xingu, Amazonas dr., ca. 12°54'S, 051°49'W. MZUSP 48311 (part), 1, 122 mm, Fazenda Santo Antônio, Baía da Sede, Pantanal do Paiaguás, nr. Coxim, rio Paraguai, Paraná dr., 18°30'S, 054°45'W. MZUSP 90178, 3, 129-182 mm, mun. Cáceres, rio Sepotuba (lower course), affl. rio Paraguai, Paraná dr., 15°47'33"S, 057°39'20"W. MZUSP 95068 (part), 5, 177-207 mm, mun. Barão de Melgaço. rio Mutum, between Vila de Mimoso and Joselandia (Pantanal de Paiaguás), rio Paraguai, Paraná dr., 16°19'30"S, 055°49'59"W. Mato Grosso do Sul. MZUSP 36436, 1, mun. Corumbá, Ladário, rio Paraguai, Paraná dr., 19°00'S, 057°36'W. Pará (localities from Amazonas dr.). AMNH 12966, 2, 213-327 mm, rio Tocantins, high above waterfall, no coordinates. BMNH 1926.10.27.241-242, 2, 204-207 mm, Monte Alegre, rio Amazonas, 02°00'S, 054°00'W. INPA 6399, 1, 142 mm, margin of lago Tapagem, rio Trombetas, 01°24'S, 056°51'W. MCP 16307, 1, 184 mm, mun. Belém, nr. Belém, Baía de Marajó, ca. 01°26'S, 048°23'W. MCP 23360, 2, 125-188 mm, Ourém, rio Guamá, affl. Baía de Marajó, ca. 01°33'S, 047°06'W. MCP 23361, 1, 146 mm, Tomé-Açu, rio Acará-Mirim, affl. rio Acará, affl. Baía de Marajó, 02°25'S, 048°09'W. MCP 28565, 1, 32 mm, Ihnangapi, São Domingos do Capim, affl. rio Guamá, affl. Baía de Marajó, 01°27'02"S, 47°48'26"W. MCP 49397, 1, mun. Santarém, rio Mentai at Cachoeirinha do Mentai, affl. rio Arapiuns, affl. rio Tapajós, 02°43'12"S, 055°36'15"W. MCP 49399, 2, mun. Santarém, Igarapé do Henrique, affl. Rio Maró, affl. rio Arapiuns, affl. rio Tapajós, 02°51'31"S, 055°41'04"W. MCP 49402, 1, mun. Curuá, Lago Preto, Ilha São Luiz, rio Amazonas, 02°06'22"S, 055°10'17"W. MCP 49404, 6; ZUEC 12326, 4, mun. Belterra, stream at Aramanai, affl. rio Tapajós, 02°43'03"S, 055°00'07"W. MCP 49405, 1, mun. Belterra, rio Tapajós at São Domingos, 02°45'02"S, 055°01'05"W. MCP 49406, 3, mun. Santarém, stream affl. Lago Anumã, affl. Rio Tapajós, 02°37'27"S, 055°11'09"W. MCP 49408, 1, mun. Santarém, Igarapé Sucurijú, affl. rio Mentai, affl. rio Arapiuns, affl. rio Tapajós, 02°43'38"S, 055°35'41"W. MCP 49409, 3, mun. Santarém, rio Maró, nr. Fé em Deus, affl. rio Arapiuns, affl. rio Tapajós, 02°50'58"S, 055°41'06"W. MCZ 45194, 1, 192 mm, mun. Belém, nr. Icoaraci, igarapé Paracuri, affl. Baía de Marajó, ca. 01°18'S, 048°28'W. MCZ 165862 (part), 1, 178, mun. Santarém, Santarém and environs, rio Tapajós, ca. 02°26'S, 54°41'W. MPEG 1113, 2, 130-197 mm, MPEG 1114, 6, 75-135 mm, MPEG 1115, 5, 112-230 mm, rio Guamá at Belém, affl. Baía de Marajó, ca. 01°24'S, 048°25'W. MPEG 1131, 1, 201 mm, MPEG 2397, 8, 150-320 mm, mun. Castanhal, Boa Vista do Apeú, rio Apeú, affl. rio Guamá, affl. Baía de Marajó, ca. 01°18'S, 047°59'W. MPEG 1132, 1, 182 mm, MPEG 1133, 1, 173 mm, MPEG 2731, 1, 158 mm, MPEG 6774, 4, 125-192 mm, mun. Cachoeira do Arari, Taperebá, rio Goapi, llha de Marajó, affl. Baía de Marajó, ca. 01°00'S, 048°57'W [coordinates for Cachoeira do Arari]. MPEG 3720, 1, 154 mm, MPEG 3736, 1, 135 mm, MPEG 3739, 1, 164 mm, MPEG 4066, 1, 146 mm, mun. Melgaço, Estação Científica Ferreira Pena, rio Puraquequara, affl. rio Anapú, affl. rio Pará, affl. Baía de Marajó, ca. 01°44'S, 051°27'W. MPEG 4706, 2, 162-177 mm, mun. Ourém, rio Guamá, Furo do Guamá, Lagoa Velha, affl. Baía de Marajó, ca. 01°33'S, 047°06'W [coordinates for Ourém]. MPEG 6385, 1, 127 mm, mun. Peixe-Boi, rio Peixe-Boi, affl. rio Maracanã (rio Amazonas estuary), 01°11'31"S, 047°18'14"W [coordinates for rio Peixe-Boi at Peixe-Boi]. MPEG 6775, 3, 110-147 mm, mun. Cachoeira [do Arari], mouth of rio Goapi, llha de Marajó, affl. Baía de Marajó, 01°00'27"S, 048°57'44'W. MPEG 6884, 4, 150-270 mm, mun. Paragominas, igarapé Poraquequara, behind camp of Companhia Vale do rio Doce, affl. rio Capim, affl. rio Guamá, affl. Baía de Marajó, 03°14'50"S, 047°45'40'W. MPEG 6917, 1, 110 mm, MPEG 7295, 6, 110-417 mm, MPEG 7397, 1 (part), 43 mm, mun. Paragominas, igarapé Paraquequara at Fazenda do Sr. Paulo/ Fazenda Monte Santo, affl. rio Capim, affl. rio Guamá, affl. Baía de Marajó, 03°16'05"S, 047°46'05'W. MPEG 7310, 1, 180 mm, mun. Paragominas, Vale do rio Doce facility, confl. igarapé Cachoerinha and Paraquequara, affl. rio Capim, affl. rio Guamá, affl. Baía de Marajó, 03°09'25"S, 047°41'51'W. MPEG 7319, 1 (part), 175 mm, mun. Paragominas, Fazenda Potiritá, igarapé Potiritá, affl. rio Potiritá, affl. rio Capim, affl. rio Guamá, affl. Baía de Marajó, 03°12'13"S, 047°39'52'W. MPEG 9884, 2, 63-68 mm, mun. Portel, Floresta Nacional Caxiuanã, affl. rio Anapú, affl. rio Pará, affl. Baía de Marajó, ca. 01°44'S, 051°26'W. MPEG 12573, 2, 139-188 mm, mun. Benevides, Itá, affl. rio Guamá, affl. Baía de Marajó, ca. 01°21'S, 048°14'W. MPEG 17818, 1, 92 mm, mun. Benevides, igarapé Taiassuí, affl. rio Guamá, Baía de Marajó, 01°23'46"S, 048°14'59'W. MZUSP 8412, 7, mun. Santarém, igarapé Jacundá, Alter do Chão, affl. rio Tapajós, 02°29'S, 054°47'W. MZUSP 15567, 1, 165 mm, Cabeceira da Serrinha, lago Jacaré (Reserva Biológica de Trombetas), rio Trombetas, 01°20'S, 056°50'W. MZUSP 22291, 1, 167 mm, mun. Castanhal, Boa Vista, rio Apeu, ca. 01°17'S, 047°55'W. MZUSP 23865, 1, 90 mm, rio Caranandeua, rio Capim, affl. rio Guamá, affl. Baía de Marajó [coordinate for mouth of rio Capim], 01°40'S, 47°46'W. MZUSP 23894, 1, rio Capim, lago Jurunundéua, no coordinates. MZUSP 25006, 5, 197-368 mm, rio Curuã-Una, just upstream of dam, 02°49'S, 054°16'W. SU 54502, 1, 113 mm, SU 54503, 3, SU 64189, 1, Cabeceira lago Grande, nr. Santarém, Ajamury, ca. 02°26'S, 054°41'W [coordinates for Santarém]. UF 36600, 1, 54 mm, igarapé Pirelli, affl. rio Maguari, affl. Baía de Marajó, 01°21'24"S, 048°19'36"W. UF 238564, 11, 119-237 mm, UF 238565, 11, 106-293 mm, UF 238566, 4, 159-205 mm; UF 238567, 12, 77-234, UF 238568, 12, 91-255, stream at SEPAq station, 39 km SE Santarém on rd. to Santa Rosa, 02˚40'01"S, 054˚33'09"W. ZUEC 12327, 6, mun. Santarém, igarapé do Mato Grosso, nr. Jaguarari, affl. rio Tapajós, 02°55'01"S, 055°03'54"W. ZUEC 12331, 3, mun. Santarém, lago Bravo, nr. Santo Amaro, affl. rio Tapajós, 02°58'22"S, 055°13'42"W. ZUEC 12333, 5, mun. Santarém, igarapé Santo Amaro, nr. Santo Amaro, affl. rio Tapajós, 02°59'15"S, 055°13'59"W. ZUEC 12334, 6, mun. Santarém, Igarapé do Macaco, affl. rio Mentai, affl. rio Arapiuns, affl. rio Tapajós, 02°40'28"S, 055°35'55"W. ZUEC 12335, 1, mun. Santarém, Igarapé Branquinho, affl. rio Mentai, affl. rio Arapiuns, affl. rio Tapajós, 02°41'48.4"S, 055°35'43"W. Rondônia (localities from rio Madeira dr., Amazonas dr.). FMNH 117761, 1, 158 mm, Maciel, rio Guaporé, affl. rio Mamoré, ca. 12°30'S, 062°20'W. INPA 9722, 3, 92-212 mm, INPA 9726, 18, 130-287 mm, rio Pacaás Novos, nr. confl. with rio Guaporé, ca. 15 km Guajará Mirim, affl. rio Mamoré, 10°51'S, 065°16'W. INPA uncat. (POLO-663), 2, 140-148 mm, rio Guaporé opposite Costa Marquez, affl. rio Mamoré, 12°27'S, 064°20'W. INPA uncat. (POLO-683), 13, INPA uncat. (POLO-731), 18, rio Pacaás Novos, ca. 15 km upstream of Guajará-Mirim, affl. rio Mamoré, 10°54'S, 065°09'W. MCP 46938, 2, 100-200 mm, mun. Calamã, Calamã, rio Madeira floodplains lake, 08º01'37"S, 062°52'28"W. UFRO-I 6476, 38, 59-290 mm, lago Cuniã, rio Madeira floodplain, 08°19'40"S, 063°30'11"W. UFRO-I 6483, 1, 40 mm, nr. Sítio Santa Helena, in front of Ilha das Pedras, rio Karipunas, 09°11'32"S, 064°34'17"W. UFRO-I 6485, 42, 53-385 mm, UFRO-I uncat. (field no. CAU2010010701), 3, 180-245 mm, mouth of rio Cautário, 12°10'51"S, 064°34'04"W. UFRO-I 6487, 9, 105-215 mm, rio Guaporé upstream of Pedras Negras, affl. rio Mamoré, 12°52'03"S, 62°52'38"W. UFRO-I 6490, 3, 88-117 mm, UFRO-I 6516, 1, 255 mm, lago Cuniã, 1 km ICMBio base, rio Madeira floodplain, 08°19'20"S, 063°30'14"W. UFRO-I 6496, 1, 83 mm, mouth of rio Pacaás Novos, affl. rio Mamoré, 10°52'07"S, 065°15'42"W. UFRO-I 6503, 4, 118-160 mm, Furo Variante, lago Cuniã, rio Madeira floodplain, 08°21'18"S, 063°30'11"W. UFRO-I 6505, 9, 37-122 mm, Arrozal do lago, rio Madeira floodplain, 08°19'36"S, 063°29'59"W. UFRO-I 6512, 2, 195-204 mm, Arrozal do lago, rio Madeira floodplain, 08°21'10"S, 063°30'26"W. UFRO-I 7924, 1, female, 166 mm, mun. Porto Velho, igarapé Mato Grosso, nr. campus Universidade Federal de Rondônia, nr. Cachoeira Santo Antônio, affl. rio Madeira, 08°49'41"S, 063°56'30"W. UFRO-I 7925, 11 (5 immature, 136-253 mm, 1 female, 203 mm, 5 male, 181-297 mm), mun. Porto Velho, lago Cuniã, rio Madeira floodplain, ca. 08°19'S, 063°28'W. UFRO-I uncat. 1, 181 mm, rio Madeira at Abunã, ca. 09°42'S, 065°21'W. Roraima (localities from rio Branco dr., affl. rio Negro, Amazonas dr.). INPA 7358, 1, INPA 7359, 1, INPA 7360, 1, INPA 7361, 1, INPA 73661, 1, INPA 7372, 1, INPA 7381, 1, INPA 7382, 1, INPA 7388, 1, INPA 7392, 1, lago Caracanã, 23 km Normândia on hwy. RR-202, 03°54'12"N, 059°49'17"W. INPA 7373, 1, INPA 73791, 119 mm, INPA 7380, 1, igarapé do Gentil, 34 km Boa Vista on Boa Vista to Bonfim hwy., ca. 02°58'N, 060°26'W. INPA 7413, 3, INPA 7414, 2, Fazenda Santa Cecília, 7 km Boa Vista on Boa Vista-Bonfim hwy., 02°48'N, 060°36'W. INPA 7424, 2, 112-159 mm, Fazenda Chico Paraíba, ca. 4 km Bonfim, rio Tacutu, ca. 03°21'N, 059°50'W. INPA 9833, 3, 80-108 mm, Ilha de Maracá, stream at end of island, rio Uraricoera, 03°22'N, 061°23'W. MZUSP 31775, 1, 221 mm, igarapé do Cujobim, 'rio Branco' opposite Ilha de Maracá, rio Uraricoera, ca. 03°21'N, 061°26'W. MZUSP 31777, 1, 176 mm, igarapé do Bota Panela, nr. Cachoeira do Bem Querer on rio Branco, ca. 01°55'N, 061°00'W. Colombia. Guainía. MBUCV-V 7536, 1, caño Caramacoa, apróx. 45 min de Puerto Inírida, affl. río Inírida, affl. río Guainía, Orinoco dr., ca. 03°51'N, 067°55'W. French Guiana. Cayenne. CU 71942, 4, Kaw River, ca. 3.5 km NW Kaw, Kaw River dr., 04°31'N, 052°04'W. MNHN 1999-1325, 3 (of 7), 210-224 mm, Kaw River dr., no coordinates. MNHN 1999-1374, 1, 211 mm, crique Gabrielle, Comté River dr., ca. 04°44'N, 052°19'W. Guyana. Demerara Mahaica. AUM 27917, 7, 12356, Maduni stop-off, 22.3 mi. from Georgetown, Conservancy Canal, affl. Maduni River, Mahaica River dr., 06°30'01"N, 058°02'14"W. CAS 67700, 1, 164 mm, FMNH 53329, 1, 52 mm, FMNH 53337, 1, 143 mm, INHS 49037, 1, 270 mm, Lama stop-off, Conservancy Canal, affl. Lama River, Mahaica River dr., 06°37'33"N, 057°55'55"W. FMNH 96203, 1, 44 mm, Kuru Kuru creek on Soesdyke-Linden hwy., Demerara River dr. 06°24'12"N, 058°14'26"W. INHS 49063, 9, 104-158 mm, Maduni stop-off, Conservancy Canal, affl. Maduni River, affl. Mahaica River, 06°30'01"N, 058°02'14"W. Potaro Siparuni. ANSP 175955, 1, 70 mm, creek, affl. Essequibo River, ca. 18 min. upstream from Maipuri campsite, Essequibo River dr., ca. 04°34'N, 058°35'W. ANSP 177494, 1, 147 mm, Siparuni River, Red Hill Creek between Levi Falls and Blackwater camp, Essequibo River dr., 04°44'14"N, 058°59'17"W. Upper Demerara-Berbice. AMNH 13421, 1, 169 mm, AMNH 30418, 1, Malali, Mari-Mari River, Demerara River dr., 05°37'N, 058°21'W. AUM 35812, 1, 127 mm, unnamed river at Kurukupari, Essequibo River dr. 04°39'41"N, 058°40'31"W. CAS 67703, 2, Demerara River at Wisden (formerly Wismar), Demerara River dr. 06°00'N, 058°18'W. CAS 67705, 2, 156-167 mm, FMNH 53338, 2, Gluck Island, Essequibo River, nr. Rockstone, Essequibo River dr., 05°58'N, 058°31'W. FMNH 53339, 1, Kumaka, Berbice River dr., 05°35'N, 057°56'W. INHS 49107, 1, 81 mm, 5.05 mi. SSW Linden, Demerara River dr., 05°56'00"N, 058°18'22"W. INHS 49143, 1, 129 mm, 5.05 mi. SSW Linden, Demerara River dr., 05°56'00"N, 058°18'22"W. ROM 86803, 3, 157-237 mm, ROM 88618, 5, 143-270 mm, side channel by island, Berbice River, Berbice River dr., 05°09'03"N, 058°11'46"W. Upper Takutu-Upper Essequibo (localities from Takutu River are in the rio Branco dr., affl. rio Negro, Amazonas dr.). ANSP 179504, 2, 106-133 mm, AUM 35863, 2, 83-104 mm, stream 10.3 km NW Karanambo, affl. Rupununi River, Essequibo River dr., 03°48'27"N, 059°23'06"W. AUM 38187, 1, 142 mm, Kuyuwini River, 48.4 km E Kuyuwini Landing, Essequibo River dr., 02°03'54"N, 058°48'33"W. BMNH 1972.7.27.447-450, 4, 133-156 mm, Dadanawa pools, Rupununi River, Essequibo River dr., ca. 02°50'N, 059°31'W. BMNH 1972.7.27.451-455, 6, 64-158 mm, "Guyana", no coordinates. CU 71959, 9, Jawar pond, Manari Ranch, N Lethem, Rupununi savanna, affl. Takutu River, ca. 03°26'N, 059°46'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCZ 48553, 1, 204 mm, Agua Branca River, affl. Manari River, affl. Takutu River, ca. 03°29'N, 059°48'W. MCZ 48554, 2, 157-191 mm, dry creek bed, 10 mi. E Nappi, affl. Takutu River, ca. 03°25'N, 059°25'W. MCZ 165855, 1, 241 mm, small pond 5 mi. N Manari Ranch, Takutu River, ca. 03°26'N, 059°46'W. UMMZ 215583, 1, 244 mm, Shebe pond, Rupununi, no coordinates. UMMZ 215603, 1, 218 mm, pond at Juari Ranch, E Takutu River, no coordinates. Region not specified. UMMZ 187500, 3, 118-184 mm, aquarium specimen, no coordinates. USNM 376799, 1, 183 mm, Waterguage Pond, unknown locality in Guyana, no coordinates. Peru. Loreto (all localities are from Amazonas dr.). ANSP 166267, 1, 76 mm, stream of río Yanayacu, W Miraflores, rio Marañón, ca. 04°42'S, 074°17'W. ANSP 167729, 8, 98-172 mm, stream 0.5 mi. below Santa Clara (R bank), río Nanay, ca. 03°46'S, 073°20'W. ANSP 178218, 4, 81-156 mm, ANSP 178220, 2, 55-63 mm, caño Santa Rita, R. bank affl. río Nanay, nr. Pueblo Pampa Chica, 03°45'23"S, 073°17'28"W. ANSP 178655, 1, 172 mm, río Nanay at Pueblo Pampa Chica, 03°45'09"S, 073°17'00"W. ANSP 180311, 1, 121 mm, río Nanay, upstream from Santa Clara, 03°46'45"S, 073°22'06"W. ANSP 182935, 3, 119-159 mm, caño Shirui (also known as Santa Rita), R. bank affl. río Nanay, nr. Pueblo Pampa Chica, 03°45'23"S, 073°17'28"W. ANSP 191848, 1, 176 mm, río Nanay, R. bank, downstream mouth caño Shirui, 03°45'06"S, 073°17'14"W. INHS 36785, 2, 117-137 mm, quebrada Santa Clara, río Nanay, ca. 03°47'S, 073°20'W. INHS 52490, 3, 99-136 mm, caño Santa Rita, nr. Pampa Chica, affl. río Nanay, 03°45'23"S, 073°17'28"W. MCP 43159, 1, 183 mm, UF 114499, 4, 128-250 mm, UF 116556, 1, female, 242 mm, stream at km 23 on Iquitos-Nauta hwy., affl. río Nanay, 03°56'38"S, 073°23'54"W. MUSM 1992, 9, 108-331 mm, río Nanay at Iquitos, ca. 03°42'S, 073°15'W. MUSM 7123 (part), 5, 73-85, Laguna Rimachi, río Pastaza, affl. río Marañón, 04°25'S, 076°43'W. MUSM 44702, 3 (1 immature, 175 mm, 2 female, 279-296 mm), forest stream nr. Jenaro Herrera, affl. río Ucayali, 04°54'26"S, 073°36'44"W. SU 66949, 1, 41 mm, río Ampiyacu nr. Pebas, ca. 03°19'S, 071°50'W. UF 116549, 1, immature, 65 mm, río Nanay, N bank, 1 km upstream Mishana, 03°52'12"S, 073°29'38"W. UF 131127, 1, 130 mm, Iquitos, procured by ornamental fish catchers, no coordinates. UF 148471, 1, 52 mm, quebrada Sapuenillo, nr. Jenaro Herrera, affl. río Ucayali, 04°54'26"S, 073°36'44"W. UF 184006, 17 (3 immature, 50-135 mm, 9 female, 157-285 mm), Laguna Quistococha, río Itaya, 03°49'56"S, 073°19'12"W. USNM 284624, 9, 108-331 mm, río Amazonas, nr. Iquitos, 03°45'S, 073°15'W. ZMH 11628 (part), 1, 80 mm, between Iquitos and Leticia, río Amazonas, no coordinates. Madre de Dios (localities from río Madre de Dios dr., affl. Río Beni, affl. Río Madeira, Amazonas dr.). MUSM 9159, 1, 288 mm, MUSM 9605, 4, 158-207 mm, Reserva Nacional (RN) de Tambopata, Laguna Sandoval, 12°26'30"S, 069°02'18"W. MUSM 25368, 1, Las Piedras, quebrada Malecón, affl. río Manuripe, ca. 12°30'S, 069°14'W. USNM 264073, 1, 235 mm, RN de Tambopata, Laguna Cocococha, 5.1 km E Explorer's Inn, 12°49'00"S, 069°16'30"W. Suriname. Marowijne. UF 177359, 2 (1 female, 261 mm, 1 male, 210 mm), small stream on rd. from Paramaribo to Albina, affl. Cottica River, Commewijne River dr., 05º34'50"N, 054º15'31"W. Nickerie. USNM 225560, 1, 65 mm, Corantijn River at km 180, side channel, Corantijn River dr., ca. 05°54'N, 57°04'W. USNM 302005, 1, 91 mm, affl. Sisa Creek, N side, ca. 700 m downstream of crossing of Amotopo-Camp Geologie rd., Corantijn River dr., 03°42'N, 057°42'W. Para. UF 177361, 1, female, 207 mm, mun. Zanderij, Kola kreek, affl. Para River, Suriname River dr., 05°27'09"N, 055°14'58"S. Sipaliwini. BMNH 1981.6.9.932-986 (part), 1, 190 mm, stream entering Lucie River, Corantijn River dr. ca. 03°35'N, 057°40'W. USNM 225561, 1, 191 mm, Matapi creek ca. 1 km intersection with Corantijn River, Corantijn River dr., 05°00'N, 057°16'W. USNM 225563, 2, 95-170 mm, stream ca. 0.5 km inland of Camp Mataway, Corantijn River dr., ca. 04°48'N, 057°43'W. Venezuela. Amazonas. FMNH 94429, 4, 161-183 mm, "upper Orinoco", Orinoco dr., no coordinates. MBUCV-V 8063, 1, 104 mm, caño Moriche, ca. 10 km N San Fernando de Atabapo, affl. río Orinoco, Orinoco dr., ca. 03°57'N, 067°38'W. MBUCV-V 14710, 1, 95 mm, nr. Santa Lucia, rio Negro, Amazonas dr., ca. 01°18'N, 066°52'W. MBUCV-V 14734, 1, 204 mm, small affl. río Orinoco, Puerto Ayacucho-El Burro rd., Orinoco dr., ca. 05°47'N, 067°29'W. MCNG 21516, 3, Maroa, río Guainía, affl. rio Negro, Amazonas dr., ca. 02°43"N, 067°33'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 22090, 1, Piaroa San José, río Yureba, Orinoco dr., ca. 04°02'N, 067°33'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). UF 177350, 7 (2 immature, 170-199 mm, 5 female, 167-201 mm), caño Viejita, rd. from San Fernando de Atabapo to Santa Barbara, affl. río Atabapo, Orinoco dr., 03°55'59"N, 067°36'34"W. Anzoátegui. MBUCV-V 25751, 1, 325 mm, Hato Morichalito, río Zuata, Orinoco dr., ca. 08°33'N, 064°57'W. Apure (localities from Orinoco dr.). ANSP 141616, 4, Jabillal, nr. San Fernando de Apure, affl. río Arauca, ca. 07°44'N, 067°58'W. AUM 22561, 1, 130 mm, caño Guarico, affl. río Apure, 07°42'47"N, 069°19'50"W. AUM 22756, 19, 100-190 mm, INHS 89761, 11, 127-164 mm, caño La Pastora, affl. río Apure, 07°26'40"N, 069°26'05"W. MBUCV-V 13229, 1, 246 mm, Mantecal, río Arauca, 07°34'N, 069°08'W. MCNG 2138, 1, MCNG 2489, 22, MCNG 3635, 5, MCNG 3715, 44, MCNG 3799, 6, MCNG 3898, 27, MCNG 4906, 2, MCNG 5134, 4, MCNG 7467, 2, MCNG 28738, 22, Módulo UNELLEZ, río Caicara, affl. río Apure, 07°24'N, 069°32'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 3906, 26, Muñoz, Módulo F.C., río Caicara, aff, río Apure, ca. 07°35'N, 069°25'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 9777, 3, caño Guaritico, aff río Apure, ca. 07°45'N, 069°03'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 10144, 5, MCNG 10344, 1, MCNG 11032 (part), 1, MCNG 12566 (part), 4, MCNG 15744, 2, caño Maporal, nr. módulo UNELLEZ, affl. río Caicara, affl. río Apure, 07°24'N, 069°32'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 28579, 5, affl. of río Caicara, no precise locality, no coordinates (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). TNHC 14928, 10, 146-201 mm, caño Maporal, nr. módulo UNELLEZ, affl. río Caicara, affl. río Apure, 07°27'N, 069°32'W. TNHC 17490, 5, 150-244 mm, TNHC 47217, 1, 212 mm, nr. módulo UNELLEZ, río Caicara, affl. río Apure, ca. 07°24'N, 069°32'W. UF 77335, 4, 162-208 mm, ca. 30 km SW La Ye, caño Caicara, affl. río Guaratico, affl. río Apure, 07°45'N, 069°03'W. UF 176887, 10 (1 immature, 197 mm, 1 female, 187 mm, 3 male, 153-170 mm, 5 unsexed [2 CS], 74-231 mm), MCNG 9698, 1, Hato El Frio, nr. Mantecal, floodplain lake of río Guaratico, affl. río Apure, 07°49'32"N, 068'55'23"W. Bolívar. ANSP 166372, 1, 140 mm, lago Maldonado, El Almacén, río Orinoco floodplain, Orinoco dr., ca. 08°06'N, 063°48'W. AUM 36512, 3, 204-288 mm, northernmost arm of Uraima Falls, río Paragua, affl. río Caroní, Orinoco dr., 06°18'05"N, 063°37'39"W. MBUCV-V 3971, 38, 10-45 mm, floodplain lake of río Las Claritas, on El Dorado-Santa Elena de Uairén hwy., affl. río Cuyuní, Essequibo River dr., ca. 06°10'N, 061°25'W. MBUCV-V 4013, 2, stream at km 67 on El Dorado-Santa Elena de Uairén hwy., affl. río Cuyuní, Essequibo River dr., ca. 06°13'N, 061°21'W. MBUCV-V 7457, 8, 43-66 mm, stream, km 88 on El Dorado-Santa Elena de Uairén hwy., affl. río Cuyuní, River Essequibo dr., 06°05'N, 061°23'W. MBUCV-V 9490, 1, 337 mm, MBUCV-V 9513, 1, 377 mm, MBUCV-V 9517, 1, 220 mm, MBUCV-V 9791, 1, 168 mm, MBUCV-V 14029, 1, 220 mm, 40 km S El Dorado, Isla de Jacobo, nr. raudal de Kinotovaca, affl. río Cuyuní, River Essequibo dr., ca. 06°23'N, 061°37'W. MBUCV-V 9537, 1, 262 mm, Boca del río Chicanán (at El Dorado), affl. río Cuyuní, River Essequibo dr., ca. 06°42'24"N, 061°38'05"W. MBUCV-V 10693, 3 (2 examined), 30-42 mm, La Paragua, río Paragua, aff río Caroní, Orinoco dr., 06°50'N, 63°22'W. MHNLS 5720, 2, MHNLS 6992, 1, Bandera, lago Guri, rio Caroní, Orinoco dr., 07°46'N, 062°59'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MZUSP 96453, 1, 59 mm, mun. Caicara del Orinoco, rio caño, Pelo Ojo, Orinoco dr., 07°32'22"N, 066°08'29"W. MZUSP 96484, 21, 23-162 mm, mun. Caicara del Orinoco, Laguna de Castilleros, margin of río Orinoco, Aquaculture Station, Universidad de Oriente, Orinoco dr., 07°30'51"N, 066°09'20W. SU 54418, 1, 173 mm, SU 54495, 1, 188 mm, SU 64174, 10, mun. Caicara del Orinoco, caño de Quiribana, Orinoco dr., ca. 07°32'N, 066°08'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). TCWC 8308.18, 2, 106-114 mm, TCWC 8310.24, 2, 182-185 mm, TCWC 8311.24, 2, 158-181 mm, TCWC 8320.05, 1, 297 mm, Campamento del Guri, Guri Reservoir, río Caroní, Orinoco dr., ca. 07°46'14"N, 063°00'34"W. Delta Amacuro. MBUCV-V 10352, 4 (3 examined), 192-209 mm, caño El Chano, Coporito arriba, nr. Tucupita, affl. caño Mamano, río Orinoco delta, Orinoco dr., ca. 09°03'N, 062°03'W. Guárico (localities from Orinoco dr.). MBUCV-V 25739, 1, 118 mm, S Requena, mouth of río Zuata, 07°58'N, 065°31'W. MCNG 1760, 1, Hato Santiago, no coordinates. Monagas (localities from Orinoco dr.). LACM 43349-12, 16, 92-199 mm, MBUCV-V 10696, (part) 20 (4CS), 97-222 mm, Laguna Guatero nr. Barrancas, affl. río Orinoco, ca. 08°42'N, 062°12'W. MBUCV-V 18905, 1, 43 mm, MBUCV-V 22404, 12, 71-214 mm, río Morichal Largo, río Orinoco delta, 09°26'N, 062°24'W. MCNG 11201, 1, río Uracoa, río Orinoco delta, 09°00"N, 062°21'W. MCNG 15932, 4, río Yabo, at bridge nr. El Pelón, río Orinoco delta, ca. 08°57"N, 062°47'W. MHNLS 6417, 3, Laguna San José, nr. Coloradito, río Orinoco delta, ca. 08°45'N, 063°29'W. MHNLS 6621, 1, lake at Los Cocos, 08°32'N, 062°25'W. Region not specified. ANSP 85366, 1, 138 mm, La Fria, Pueblo Nueva, no coordinates.

Brachyhypopomus bullocki Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.

(Fig. 19; Tables 2-5, 8)

Hypopomus sp. 4. -Heiligenberg & Bastian, 1980Heiligenberg, W. & J. Bastian. 1980. Species specificity of electric organ discharges in sympatric gymnotoid fish of the Rio Negro. Acta Biológica Venezuélica, 10: 187-203.: 197, fig. 1, black and white photograph (Brazil, Amazonas, rio Negro, species and EOD diversity).

Brachyhypopomus bullocki. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 91 (description in unpublished thesis with disclaimer stating that nomenclatural acts not available, a nomen nudum).

Brachyhypopomus sp. -Hopkins, 1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.: 1218, fig. 1, black and white photographs of breeding male and female (electric organ morphology and impedance matching).

Brachyhypopomus sp. J. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681 notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus bullockiSullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.: 185-186, fig. 1, black and white photograph of holotype (breeding male) and breeding male and female paratypes; 191, fig. 3, EODs (original description, type locality - Venezuela, Meta State, río Metica-Meta dr.). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Diagnosis. Brachyhypopomus bullocki is diagnosed from congeners by the following cobination of characters: orbital diameter 14.2-18.5% HL, vs. 5.9-14.1% in all congeners except B. batesi, B. benjamini, B. brevirostris, B. cunia, B. flavipomus, B. hamiltoni, B. hendersoni, B. janeiroensis, B. provenzanoi, and B. walteri; caudal filament length 31.4-62.9% LEA, vs. 14.1-30.0% in B. batesi, B. benjamini, B. hamiltoni, and B. provenzanoi; precaudal vertebrae 15-17, vs. 18-21 in B. brevirostris, B. flavipomus, and B. janeiroensis; distinct dark suborbital stripe absent, vs. present in B. cunia and B. walteri; interorbital distance 24.0-30.0% HL, vs. 16.4-20.4% in B. hendersoni.

Description. Head and body shape, and pigmentation illustrated in Fig. 19, and in original description. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 8. Body shallow to moderate in depth. Head short and moderate to broad in depth. Dorsal profile of head convex from occiput to snout, ventral profile of head slightly concave between operculum and snout, snout rounded. Eye large. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 33-36 (median 34, n = 6). Pectoral fin moderate to broad in width, pectoral-fin rays 11-15 (mode 13). Precaudal vertebrae 15-17 (mode 16), including 1-2 transitional vertebrae (mode 2). Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 196-233. Dorsal rami of recurrent branch of anterior lateral line nerve visible in most juvenile and some lightly-pigmented adults - mostly in anterior third of body. Middorsal region of body scaled. Rows of scales above lateral line 4-7 (mode 6). Lateral line continuous. Epidermal canals very sparse and in some specimens more or less absent; when present located only in posterior half of body. Discontinuous meandering horizontal scratch-like epidermal canals in dorsal flank, midway between lateral line and dorsal midline, variably present. Some short epidermal canals as short grooves close to and parallel to lateral line, mainly in posterior third of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Tip of caudal filament free of electrocytes in some specimens. Caudal filament moderate in length to long.

Coloration. (Fig. 19). Background pale straw to dark tan. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Irregular dark saddles crossing dorsal surface in anterior third of body, extending ventrally as indistinct bands which break up before reaching lateral line. Indistinct bands and irregular patches over dorsal surface in posterior two thirds of body, not forming saddles that cross entire dorsal surface. Banding absent or faint in posterior third of body. Sparse indistinct dark markings over rest of flank. Indistinct series of dark dots form a line along upper margin of anal-fin pterygiophores in posterior third of body. Caudal filament darker with sparse irregular darker bands and dark tip; underwater, tip of caudal filament resembles root tips of water hyacinths. Head with sparse dark chromatophores on cheeks and operculum, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline with light scattering of brown chromatophores. Anal-fin rays with scattered chromatophores, sometimes fusing to form darker patches. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 19
Brachyhypopomus bullocki. a. MZUSP 96498, male, 188 mm TL (head in lateral view and body in lateral and dorsal view); b. TNHC 17486, female, 140 mm TL (body in lateral view); Venezuela, río Parguaza, Orinoco dr. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 221 mm TL, 121 mm LEA (n = 363). Largest male specimen examined 221 mm TL, 121 mm LEA (n = 12). Largest female specimen examined 152 mm TL, 96 mm LEA (n = 11).

Sexual dimorphism. Males attain larger sizes than females. Breeding males develop very elongated caudal filaments in comparison to immature individuals and breeding females, and reach greater lengths (Figs. 19a-b), but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Tip of caudal filament in large males often exhibits paddle-like laterally compressed structure. Caudal filament of males often entirely free of electrocytes near tip, with electrocytes sometimes absent in as much as the terminal 25% of caudal filament. No sexual differences in pigmentation.

Geographic distribution. Brazil, Colombia, Guyana, and Venezuela (Fig. 7). Widespread throughout Orinoco drainage, rio Negro drainage (Amazonas drainage), upper rio Branco (affl. rio Negro), and upper and middle portions of the Essequibo River drainage.

Ecological notes. Sullivan & Hopkins (2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.) report B. bullocki from low-conductivity (< 25 μScm-1) shallow clear water in Mauritia palm swamps and open savanna, and from small pools fed by streams (Orinoco), and from a low-conductivity blackwater stream (rio Negro), but report its absence from high-conductivity sites (> 100 μScm-1) in the Venezuelan llanos. WGRC and NRL collected B. bullocki from low-conductivity streams, Mauritia palm swamps, and savanna gallery forest in the vicinity of San Fernando de Atabapo, Amazonas, Venezuela. Here the following water parameters were recorded at the time of sampling: conductivity 7-13 µScm-1, dissolved oxygen 1.6-3.8 mgl-1, temperature 25.8-28.2°C, and pH 3.1-4.5. Reproductive biology is unknown. Stomach contents comprise aquatic insect larvae, primarily Chironomidae larvae, and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the Orinoco drainage, we captured B. bullocki in ecological syntopy with B. brevirostris, B. provenzanoi, and B. sullivani, and it may also occur in syntopy with B. beebei and B. regani - both known from low-conductivity systems in the Orinoco. Brachyhypopomus bullocki also occurs in sympatry but ecological allotopy with B. diazi, which is restricted to systems with higher conductivity (Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). In the rio Negro and Essequibo River drainages, both low-conductivity systems, B. bullocki occurs in sympatry and syntopy with B. batesi, B. beebei, B. brevirostris, B. hendersoni, B. pinnicaudatus (only near mouth of rio Negro), B. regani, B. sullivani, and B. walteri.

Local names. Brazil: sarapó; Colombia and Venezuela: cuchillo.

Material examined. 332 specimens. Brazil. Amazonas (localities from rio Negro dr., Amazonas dr.). CU 94737, 1, stream above mouth rio Branco, rio Branco dr., ca. 01°20'S, 061°54'W. INPA 19949, 1, 135 mm, INPA 19951, 1, 173 mm, Arquipelago das Anavilhanas, 02°41'S, 060°44'W. MZUSP 54578, 2 (1 immature, 68 mm, 1 female, 117 mm), MZUSP 95226 (part), 26 (10 immature, 74-125 mm, 12 female, 98-136 mm, 4 male, 136-148 mm), mun. Santa Isabel do rio Negro, Paricatuba, lake on margin of rio Negro, 00°31'S, 065°01'W. Roraima (localities from rio Branco dr., affl. rio Negro, Amazonas dr.). INPA 7370, 1, igarapé do Gentil, 34 km Boa Vista on Boa Vista to Bonfim hwy., 02°58'N, 060°26'W. INPA 7425, 1, 132 mm, Boa Vista, on rd. to Bonfim, 02°49'N, 060°35'W. INPA 9829, 1, 73 mm, Ilha de Maracá, rio Uraricoera, 03°22'N, 061°23'W. Colombia (localities from río Meta dr., Orinoco dr.). Meta. ANSP 128100, 2, Hacienda Mozambique, Laguna N lago Mozambique at outlet to río Metica, affl. río Metica, 03°58'N, 073°04'W. ANSP 138024, 17 (paratypes), 150-216 mm, 2 examined from photograph in original description (1 male 215 mm; 1 female, 176 mm), ANSP 187477, 1 (holotype), 221 mm, examined from photograph in original description, rancho Llano Grande, N Hacienda Mozambique, affl. río Metica, 04°02'N, 073°03'W. AUM 35487, 2, 108-112 mm, 19 km S Puerto Gaitán, Estero ca. 1 km up caño Pajaro Grande, affl. río Manacacías, ca. 04°09N, 072°07'W. UF 19475, 1, 114 mm, UF 111998, 1, 120 mm, ca. 10 km SE Puerto Gaitán, 04°15'N, 072°00'W. UF 33734, 1, 115 mm, ca. 15 km E Puerto Gaitán, 04°18'N, 071°55'W. UF 148456, 1, 70 mm, UF 148457, 1, 125 mm, UF 148531, 1, 85 mm, ca. 4.7 km W Puerto Gaitán, affl. río Yucao, 04°18'N, 072°07'W. Vichada. IAVH-P uncat. 1, 110 mm (photograph from S. Gavassa, specimen ca. 110 mm), mun. Santa Rosalia, El Dera ranch, 46 km Santa Rosalia, small creek, affl. caño Grande, affl. río Tomo, Orinoco dr., 04°50'59"N, 070°33'52"W. Vuapés. USNM 320021, 2, 142-146 mm, río Mitu, affl. río Vuapes, affl. rio Negro, Amazonas dr., ca. 01°16'N, 070°13'W. Guyana. Upper Demerara Berbice. ROM 62548, 1 (of 3), 111 mm, unnamed creek ca. 7 km. SE Tambikabo inlet, Essequibo River, Essequibo River dr., 04°45'N, 058°43'W. Upper Takutu-Upper Essequibo. AUM 35813, 1, 79 mm, Rupununi River at Massara's Landing, 1.1 km NE Massara, Essequibo River dr., 03°53'41"N, 059°17'37"W. AUM 50025, 2, 123-133 mm, lake nr. Yukupari, Essequibo River dr., 03°41'38"N, 059°23'40"W. BMNH 1972.7.27.456-457, 2, 65-95, small ponds in Rupununi River, Essequibo River dr., ca. 02°52'N, 059°32'W. BMNH 1972.7.27.458-518 (part), 27, 42-100 mm, Karanambo creek, Rupununi River, Essequibo River dr., 03°45'11"N, 059°18'36"W. BMNH 1972.7.27.519-525, 1, 110 mm, Rupununi River, Essequibo River dr., no coordinates. CU 71946, 4, to 141 mm, 15 mi. E Lethem, pond nr. Moco-Moco Creek, Takutu River, affl. rio Branco, affl. rio Negro, Amazonas dr., 03°19'N, 059°40'W. CU 71947, 1, ca. 2 km Lethem, confl. Buru and Arara Creeks, Takutu River, affl. rio Branco, affl. rio Negro, Amazonas dr., 02°23'N, 059°48'W. MCZ 48555, 1, male, 149 mm, 5 mi. N Manari Ranch, Takutu River, affl. rio Branco, affl. rio Negro, Amazonas dr., 03°26'N, 059°46'W. USNM 190552, 2, 93-107 mm, Rupununi, Essequibo River dr., no coordinates. Region not specified. AMNH 35363, 1, 85 mm, Kora-Kora creek, Demerara [Essequibo River dr.?], no coordinates. Venezuela. Amazonas (localities from Orinoco dr.). ANSP 188069, 3, Pozo de Lucas nr. San Fernando de Atabapo, affl. río Orinoco, ca. 03°56'N, 067°36'W. CU 83825, 13, nr. Puerto Ayacucho, affl. río Orinoco, ca. 05°39'N, 067°31'W. CU 83832, 2, nr. San Fernando de Atabapo, affl. río Orinoco, ca. 04°03'N, 067°42'W. INHS 61558, 1, 90 mm, caño Pozo Azul, nr. Puerto Ayacucho, affl. río Orinoco, 05°45'49"N, 067°29'21"W. MAC-PAY 01237, 2, Laguna Provincial, ca. 20 km N Puerto Ayacucho, affl. río Orinoco, ca. 05°50'N, 067°37'W (listed in Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). MCNG 21515, 4, Maroa, río Guainía, 02°43"N, 067°33'W. MBUCV-V 15751, 1, female, 152 mm, río Autana, ca. 8 km confl. with río Sipapo, 04°43'N, 067°45'W. UMMZ 228985, 1, 181 mm, creek nr. Puerto Ayacucho, affl. río Orinoco, ca. 05°39'N, 067°37'W. UF 77949, 1, male, 125 mm, Yavi, río Ventuari, ca. 05°25'N, 066°00'W. UF 177348, 3, immature (2 CS), 105-183 mm, on rd. from San Fernando de Atabapo to Santa Barbara, affl. río Orinoco, 03°58'59"N, 067°38'27"W. UF 177349, 1, female, 132 mm, caño Viejita, on rd. from San Fernando de Atabapo to Santa Barbara, affl. río Orinoco, 03°55'59"N, 067°36'34"W. Anzoátegui. MHNLS 5859, 1, MHNLS 5974, 1, MHNLS 6088, 1, MHNLS 6195, 25, Laguna de Mamo, río Orinoco floodplain, Orinoco dr., ca. 08°25'56"N, 063°07'10"W (listed in Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). Apure (localities from Orinoco dr.). ANSP 128106, 1, ca. 13 km N San Fernando de Apure, Camaguán swamp, hwy. to San Fernando de Apure, affl. río Apure, 08°00'N, 067°28'W. ANSP 165517, 1, female, 112 mm, Morichal along San Fernando de Apure-Puerto Páez hwy., affl. río Capanaparo, 06°57'N, 067°28'W. AUM 22501, 1, 121 mm, Puerto Páez-San Fernando rd., río Claro, affl. río Cunaviche, 07°09'08"N, 067°38'06"W. CU 94795, 6, CU 94796, 28 (1 CS), CU 94797, 19 (1CS), CU 94798, 4, 10 km. S Santa Juana in Parque Nacional (PN) los Santos Luzardo, affl. río Capanaparo, 06°55'N, 067°27'W. CU 94799, 1, Caño La Pica, 12 km S Santa Juana, in PN los Santos Luzardo, affl. río Capanaparo, 06°54'N, 067°30'W. CU 94800, 8, blackwater lake E of rd. S from Santa Juana, affl. río Capanaparo, 06°56'N, 067°25'W. INHS 27703, 2 (paratypes), 102-141 mm, on San Fernando de Apure-Puerto Páez hwy., río Cinaruco, 06°33'06"N, 067°30'43"W. MBUCV-V 19847, 5 (3 measured: 1 female, 133 mm, 2 male, 141-152 mm), río Capanaparo, no coordinates. MBUCV-V 21369, 1, female, 130 mm, La Montañita, on San Fernando de Apure-Puerto Páez hwy., río Claro, affl. río Cunaviche, 07°09'N, 67°38'W. MCNG 2273, 1, MCNG 4842, 3, MCNG 4451, 3, MCNG 10261, 1, MCNG 10754, 1, MCNG 11525, 6, MCNG 28643, 2, TNHC 11833, 1, 115 mm, TNHC 11850, 6, 104-127 mm, TNHC 17535, 1, 108 mm, caño Maporal, nr. módulo de UNELLEZ, río Caicara, affl. río Apure, ca. 07°24'N, 069°32'W. TNHC 17486, 3 (1 immature, 135 mm, 1 female, 140 mm, 1 male, 179 mm), río Caicara, affl. río Apure, 07°24'N, 069°32'W. UMMZ 217073, 1, 109 mm, ca. 20 km N Paso de Caballo, río Guariquito, affl. río Apure, 08°36'N, 067°08'W. USNM 260261, 2, caño Caicara, at bridge rd. from Montecal, affl. río Apure, 07°22'N, 069°21'W. Bolívar (localities from Orinoco dr.). ANSP 187476, 3, 93-120 mm, Morichal Zamori on Maripa-Ciudad Bolivar hwy, affl. río Orinoco, 07°28'N, 064°54'W. ANSP 189185, 1, 06°57'N, 064°50'W, MBUCV-V 24065, 4, 2 measured, female, 115-122 mm, Morichal de los Pavones, affl. río Sipapo, affl. río Caura, 07°35'N, 065°25'W. MHNLS 4897, 1, Laguna Chirere, ca. 30 km W Puerto Ordaz, río Orinoco floodplain, ca. 08°17'N, 062°59'W (listed in Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). MZUSP 96498, 1, male, 189 mm, mun. Cedeño, río Parguaza, Puente Parhuena, affl. río Orinoco, 05°53'30"N, 067°24'14"W. SU 54496, 2, 97-130 mm, SU 69738, 2, 114-126 mm, Caicara, caño de Quiribana, affl. río Orinoco, ca. 07°32'N, 066°08'W. Delta Amacuro (localities from río Orinoco delta, Orinoco dr.). CU 94867, 2, 74-88 mm, Caño Anabeta, Isla Portuguesa, 08°37'N, 061°45'W. MBUCV-V 10660, 1, female, 94 mm, Los Castillos, ca. 08°40'N, 062°24'W. Guárico (localities from Orinoco dr.). INHS 34036, 2, 116-118 mm, 20 km ENE La Esperanza, Parque Nacional Aguaro-Guariquito, Morichal Charcote, affl. río Manapire, 08°24'16"N, 066°34'23"W. INHS 34586, 1, 155 mm, N Medano de Gomez, río Guariquito, 07°50'41"N, 066°32'10"W. MBUCV-V 8992, 1, 115 mm, caño Caracol, on San Fernando de Apure-Guayabal rd., affl. río Guárico, affl. río Portuguesa, affl. río Apure, 07°58'N, 067°23'W. MBUCV-V 12047, 1, immature, 114 mm, caño Realito, affl. río Guariquito, ca. 07°49'N, 066°31'W. MBUCV-V 12068, 8 (7 immature, 78-100 mm, 1 male, 118 mm), Cabecera del río Guariquito, no coordinates. MHNLS 2021, 1, lagoon 30 km N Cabruta, 07°54'N, 066°15'W (listed in Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). Monagas. MBUCV-V 1727, 1, 90 mm, MBUCV-V 14042, 1, 110 mm, USNM 233321, 1, 108 mm, Laguna Guatero, nr. Barrancas, affl. río Orinoco, Orinoco dr., 08°43'N, 062°11'W. MHNLS 6586, 20, Laguna San José, Coloradito, río Orinoco delta, Orinoco dr., ca. 08°45'N, 063°29'W (listed in Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.). Portuguesa. TNHC 14893, 4, 98-134 mm, 35 km SE Guanare, caño (río) Maraca at Urriola Ranch, affl. río Portuguesa, affl. río Apure, Orinoco dr., 08°52'30"N, 069°27'40"W.

Brachyhypopomus cunia, new species

urn:lsid:zoobank.org:act:E9E6020F-21D4-42B5-8F2D-0F1A1D4E8645

(Fig. 20; Tables 2-5, 8)

Brachyhypopomus sp. 3. -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 240, color photograph (Brazil, rio Madeira, listing of hypopomids). -de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.: 545, table 1 (Brazil, rio Madeira, lago Cuniã, listing of fish species).

Brachyhypopomus sp. "cunia". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. INPA 37690, male, 142 mm TL, 104 mm LEA, Brazil, Rondônia, Reserva Extrativista do lago do Cuniã, igarapé do Campo, affl. lago Cuniã, rio Madeira floodplain, Amazonas dr., 08°19'14"S, 063°28'05"W, 1 Dec 2008, T. Araújo & F. Vieira.

Paratypes. 40 specimens, localities from rio Madeira dr., Amazonas dr. Brazil. Rondônia. INPA 37691, 4 (1 immature, 124 mm, 3 female [1 CS], 113-121 mm), MPEG 24297, 10, 99-137 mm, UFRO-I 1323, 3, 80-125 mm, collected with holotype. MCP 46939, 10 (7 immature, 87-149 mm, 3 female, 126-136 mm), MZUSP 110994, 5 (1 immature, 90 mm, 2 female, 114-141 mm, 1 male, 117 mm), UFRO-I 6398, 1, female, 116 mm, UFRO-I 6399, 1, female, 119 mm, UFRO-I 6400, 1, immature, 112 mm, UFRO-I 6401, 1, immature, 128 mm, UFRO-I 6402, 1, immature, 144 mm, UFRO-I 7928, 4 (2 immature, 107-139 mm, 1 female, 118 mm, 1 male, 154 mm), mun. Porto Velho, lago Cuniã, rio Madeira floodplain, 08°19'S, 063°28'W, 6 Jun 2010, T. Araújo & F. Vieira.

Non-types. 216 specimens, localities from rio Madeira dr., Amazonas dr. Brazil. Mato Grosso. FMNH 54552, 7, 48-112 mm, Bastos [Porto Bastos], rio Alegre, affl. rio Guaporé, affl. rio Mamoré, ca. 15°06'S, 059°57'W. USNM 301979, 3, 83-135 mm, Brazil-Bolivia border, region between Guajará-Mirim and Mato Grosso, rio Guaporé, affl. rio Mamoré, ca. 13°42'S,060°31'W. Rondônia. MCP 46937, 3 (2 CS), 92-118 mm, mun. Calamã, nr. Calamã, rio Madeira floodplain lake, 08º01'37"S, 062°52'28"W. UFRO-I 6467, 4,75-95 mm, Colocação Três Praias, rio Jaciparaná, 09°27'29"S, 064°25'22"W. UFRO-I 6470, 14, 95-146 mm, lago Cuniã, 08°21'10"S, 063°30'26"W. UFRO-I 6471, 2, 130-147 mm, lago Cuniã, 08°19'45"S, 063°28'06"W. UFRO-I 6474, 14, 128-176 mm, UFRO-I 6475, 2, 143-148 mm, lago Cuniã, 08°19'36"S, 063°29'59"W. UFRO-I 6477, 25, 147-165 mm, mouth of rio Cautário, affl. rio Guaporé, affl. rio Mamoré, 12°10'51"S, 064°34'00"W. UFRO-I 6479, 74, 80-152 mm, nr. igarapé do Campo, lago Cuniã, 08°19'09"S, 063°28'44"W. UFRO-I 6514, 68, 67-150 mm, nr. ICMBio base, lago Cuniã, 08°19'40"S, 063°30'11"W.

Diagnosis. Brachyhypopomus cunia is diagnosed from congeners by the following combination of characters: precaudal vertebrae 16-17, vs. 18-26 in B. alberti, B. arrayae, B. beebei, B. belindae, B. brevirostris, B. draco, B. flavipomus, B. gauderio, B. hamiltoni, B. janeiroensis, B. jureiae, B. palenque, B. pinnicaudatus, and B. verdii; head depth at eye 47.8-60.0% HL, vs. 36.3-47.7% in B. batesi, B. bombilla, B. provenzanoi, B. regani, and B. sullivani; scales present in middorsal region of anterior third of body, vs. absent in B. benjamini; pectoral-fin rays 10-13, vs. 14-20 in B. bennetti, B. diazi, B. menezesi, and B. occidentalis; mouth width 24.8-38.0% HL, vs. 15.7-22.6% in B. hendersoni. Brachyhypopomus cunia exhibits overlapping meristic counts and morphological measurements with B. bullocki and B. walteri, but differs in possessing a very distinctive pigmentation pattern in which the ventral portions of the flank, over the anal-fin pterygiophores, are darkly pigmented, forming a dark stripe along the base of the anal fin (also shared with B. hendersoni), and in possessing numerous discrete dark spots (each comprising a cluster of dark chromatophores) which are scattered over the anal-fin pterygiophores, and in some specimens form an irregular dotted line along the lateral line, vs. absence of dark stripe along the anal-fin base and absence of discrete dark spots over the ventral flank in B. bullocki and B. walteri.

Description. Head and body shape, and pigmentation illustrated in Fig. 20. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 8. Body shallow to moderate in depth. Head short and moderate to broad in depth. Dorsal profile of head slightly to moderately convex from occiput to snout, ventral profile of head approximately straight to slightly convex between operculum and snout, snout rounded. Eye moderate to large in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Pectoral fin narrow to moderate in width, pectoral-fin rays 10-13 (mode 12). Precaudal vertebrae 16-17 (mode 16), including 1-2 transitional vertebrae (mode 2). Anal-fin origin slightly (< 0.25 HL distance) anterior or posterior to, or near, tip of pectoral fin. Anal-fin rays 177-224 (median 209). Dorsal rami of recurrent branch of anterior lateral line nerve visible in anterior third of body in most specimens. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Sparse depigmented epidermal canals in posterior two thirds of body; present as a meandering and bifurcating single groove in dorsal flank, approximately midway from lateral line to dorsal midline; and as sparse scratch-like marks dorsal to and near lateral line, sometimes connecting to a longer canal in dorsal flank. Three columns at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament moderate in length to long.

Coloration. (Fig. 20). Background tan to light brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal surface with irregular patches and vague thin bands; few or none crossing entire dorsal surface, some forming faint oblique bands from dorsal surface to near lateral line which slant in an anteroventral to dorsoposterior direction. No bands on ventral surfaces of flank. Prominent dark flecks scattered over flank and anal-fin pterygiophores, and forming an irregular dotted line along lateral line. Ventral flank over anal-fin pterygiophores, especially in ventral half along anal-fin base with darker background pigmentation forming a dark horizontal band along anal-fin margin (more conspicuous in some specimens than others). Caudal filament darker than body, especially distally; darkened tip of caudal filament resembles root tips of water hyacinths when viewed underwater. Eye always with distinct suborbital patch or stripe of chromatophores and subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays and anal-fin rays with light scattering of brown chromatophores. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 20
Brachyhypopomus cunia. INPA 37690, holotype, male, 142 mm TL (head in lateral view and body in lateral and dorsal view); Brazil, rio Madeira, Amazonas dr. Specimen fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Moderate size, largest specimen examined 176 mm TL, 121 mm LEA (n = 257). Largest male specimen examined 154 mm TL, 103 mm LEA (n = 3). Largest female specimen examined 141 mm TL, 102 mm LEA (n = 11).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil (Fig. 14). Known only from the rio Madeira; from its lower reaches below its major series of falls and rapids as far downstream as a site near the town of Calamã, Rondônia, Brazil (near the mouth of the rio Machado), and from sites above the major series of falls, along most of the length of the rio Guaporé. Not known from lower reaches of the Madeira downstream of its confluence with the rio Machado.

Ecological notes. Known from low-conductivity floodplain habitats. The type series was collected from floating macrophytes on the margins of lago Cuniã, a low-conductivity seasonally flooded blackwater lake near the main stem of the lower Madeira. Here the flood season occurs between October and March, and the low-water season from April to September (de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.). Water parameters collected from November 2008 to March 2010 are typical of a lowland blackwater lake: conductivity 2.3-11.2 µScm-1, transparency measured with a Secchi disk 0.35-2.69 m, dissolved oxygen 2.2-5.8 mgl-1, temperature 27.1-31.3°C, and pH 4.52-6.88 (de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.). Brachyhypopomus cunia is also common from low-conductivity clearwater (and some blackwater) floodplain sites along most of the length of the rio Guaporé. Mean water parameters, averaged from multiple sites along the rio Guaporé, and over several seasons, include: conductivity 19.5 µScm-1 (SD 16.79), transparency with Secchi disk 1.04 m (SD 0.44), dissolved oxygen 4.22 mgl-1 (SD 1.98), temperature 27.5°C (SD 2.44), and pH 7.12 (SD 1.06) (L. de Queiroz, unpublished data). Reproductive biology is unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Above the major series of rapids and falls in the lower Madeira, Brachyhypopomus cunia co-occurs in geographical sympatry with the following congeners: B. alberti, B. arrayae, B. bombilla, B. brevirostris, B. pinnicaudatus, B. sullivani, and B. walteri. Below the lower Madeira rapids, Brachyhypopomus cunia is known to occur in sympatry and ecological syntopy with B. brevirostris, B. pinnicaudatus, and B. walteri (de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.).

Etymology. The specific name refers to the type locality, lago Cuniã, a floodplain lake of the lower rio Madeira inside the Reserva Extrativista do lago do Cuniã. A noun in apposition.

Local names. Brazil: sarapó.

Brachyhypopomus diazi (Fernández-Yépez, 1972Fernández-Yépez, A. 1972. Analisis ictiológico del complejo hidrográfico (04) río Yaracuy Caracas, Dirección de Obras Hidraulicas: Ministerio de Obras Públicas. República de Venezuela, 25p.)

(Fig. 21; Tables 2-5, 11)

Hypopomus diaziFernández-Yépez, 1972Fernández-Yépez, A. 1972. Analisis ictiológico del complejo hidrográfico (04) río Yaracuy Caracas, Dirección de Obras Hidraulicas: Ministerio de Obras Públicas. República de Venezuela, 25p.: 20, pl. 20, black and white photograph of holotype (original description, type locality - Venezuela, Carabobo, río Alpargatón).

Brachyhypopomus occidentalis. -Mago-Leccia, 1976Mago-Leccia, F. 1976 Los peces Gymnotiformes de Venezuela: un estudio preliminar para la revisión del grupo en la América del Sur. Unpublished Ph.D. dissertation, Universidad Central de Venezuela, Caracas. 376p. (systematics of Gymnotiformes, B. diazi listed as junior synonym of B. occidentalis).

Brachyhypopomus diazi. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48, fig. 72, black and white photograph of MBUCV-V 13443 (listing of Brachyhypopomus). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 137 (redescription). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 495 (Venezuela, listing of Brachyhypopomus). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 11, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 11
Morphometrics for Brachyhypopomus diazi. SD, standard deviation. Ranges for the type region (río Alpargatón drainage, Venezuela) and for the Orinoco drainage, Venezuela, refer to non-type specimens. No data are available for the (lost) holotype from the original description.

Diagnosis. Brachyhypopomus diazi is diagnosed from congeners by the following combination of characters: bilateral columns at anal-fin terminus 4-5, vs. 3 in all congeners except B. belindae, B. janeiroensis, B. jureiae, B. occidentalis, and B. palenque, and vs. 6 columns in B. bennetti; pale stripe along middorsal region of body absent, precaudal vertebrae 16-19, vs. 20-26 in B. belindae and B. jureiae; dorsal rami of the recurrent branch of the anterior lateral line nerve not visible, vs. visible in B. janeiroensis; continuous or discontinuous dark vertical or diagonally oriented stripes or saddles present on body surface dorsal to lateral line, vs. mottled pattern with no stripes in B. palenque (and preopercular sensory canals incised in preopercle, vs. preopercular sensory canals independent of preopercle in B. palenque). Brachyhypopomus diazi exhibits similar pigmentation and overlapping counts and morphometric proportions with B. occidentalis. The two species can be distinguished by a more extensive network of depigmented and dark-margin epidermal canals in B. diazi (including in the anterior half of the body) than in B. occidentalis, and by the first branchiostegal ray distinctly narrower than the third branchiostegal ray, vs. the first branchiostegal ray is approximately as wide as the third in B. occidentalis.

Description. Head and body shape, and pigmentation illustrated in Fig. 21, and in the original description. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 11. Body moderate in depth. Head moderate in length and shallow to broad in depth. Dorsal profile of head slightly convex from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 37-57 (median 47, n = 8). Pectoral fin moderate to broad in width, pectoral-fin rays 15-20 (mode of 17 in a population in the río Alpargatón on the Caribbean coast of N Venezuela, and 16 in populations from the río Apure of the Venezuelan Llanos). Precaudal vertebrae 16-19 (mode of 18 from the río Alpargatón, and 17 from the río Apure), including 2-3 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 190-226 (median of 209 from the río Alpargatón and 206 from the río Apure). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Extensive network of prominent depigmented epidermal canals along much of body length; from approximately one head length posterior to nape, to near anal-fin terminus. In anterior half of body canals occur in low density in upper portions of flank, and curve gently in a shallow anterodorsal to posteroventral slope. In second half of body canals occur as multiple parallel wavy lines in two series: one dorsal to lateral line, and another in upper dorsal flank. A lower density of parallel epidermal canals branch from lateral line over body cavity and extend about half a head length ventrally, in an oblique anterodorsal to posteroventral direction. Region below lateral line completely or almost completely free of epidermal canals in posterior half of body (contrasting with many other congeners in which epidermal canals are found parallel to lateral line on both dorsal and ventral side). 4-5 (mode 4) bilateral horizontal columns of electrocytes at anal-fin terminus in immature specimens, mature females, and mature males. 4-6 (mode 5) columns at mid-point between anal-fin terminus and tip of caudal filament in immature specimens and mature females and 5-6 (mode 5) in mature males. Caudal filament short to moderate in length.

Coloration. (Fig. 21). Background tan to dark brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Prominent narrow brown saddles cross much of dorsal surface in anterior third of body. Dorsal region of posterior portion of body is marked with irregular dark patches, which sometimes form an alternating series of blotches either side of dorsal midline. Thin vertical or anteroventral to posterodorsally oriented brown bands extending from dorsal surface. In anterior third of body bands extend across lateral line and across ventral portion of body, often with a misalignment in their continuation across lateral line. In posterior two thirds of body bands usually reach only to lateral line, where they either peter out or fuse to horizontally-oriented dark lines near lateral line. Thin dark lines or vertically elongated dark patches extend from anal-fin margin to dorsal margin of anal-fin pterygiophores in posterior two thirds of body. Wide pale patch with no prominent dark bands or spots extending from about third body length behind head to about one head length anterior to anal-fin terminus in many specimens. Caudal filament darker than body, especially dorsally, ventrally, and near tip; with irregular bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline. Anal-fin rays with uniform light scattering of chromatophores, which fade at distal fin margin, fin rays darker in posterior half. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 21
Brachyhypopomus diazi. a. MBUCV-V 35655 (WC04.210304), male from type locality, 160 mm TL (head in lateral view, body in lateral and dorsal view); b. UF 174333 (WC03.210304), female from type locality, 141 mm TL (body in lateral view); Venezuela, río Alpargatón, río Salado dr. Note sexual dimorphism in caudal filament height. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 193 mm TL, 184 mm LEA (n = 241). Largest male specimen examined 193 mm TL, 184 mm LEA (n = 15). Largest female specimen examined 143 mm TL, 115 mm LEA (n = 15).

Sexual dimorphism. Sexually mature males attain larger sizes than females, and exhibit longer and substantially deeper caudal filaments than immature individuals and breeding females (Figs. 21a-b), but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes; although the range of electrocyte columns midway from anal-fin terminus to caudal fin filament is sometimes higher in breeding males (5-6, mode 5) than immature specimens and breeding females (4-6, mode 5). Breeding males nonetheless exhibit clearly enlarged electrocytes relative to immature specimens and females. Breeding males with paddle-like lateral compression at caudal filament tip. No known sexual dimorphism in pigmentation.

Geographic distribution. Venezuela (Fig. 14). Brachyhypopomus diazi is known from the northern Orinoco drainage of Venezuela (with most records from the Llanos wetlands), and from coastal drainages of the Caribbean coast of northern Venezuela, from the río Tocuyo drainage to the río Patanemo drainage.

Population variation: We found complete overlap in the range of meristic counts (Tables 2-5) and morphometric proportions (Table 11), and observed similar pigmentation, between trans-Andean populations of B. diazi from the río Alpargatón on the Caribbean coast of N Venezuela, and cis-Andean populations from the río Apure of the Venezuelan Llanos. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. diazi are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners, and unique among congeners in exhibiting a trans- and cis-Andean distribution.

Ecological notes. Locally common in high-conductivity rivers (100-400 μScm-1) draining the Andes of the Venezuelan llanos (and their associated floodplains), and from streams and small rivers draining the coastal Andean range of the north Venezuelan Caribbean coast. Brachyhypopomus diazi is typically found in dense marginal emergent aquatic vegetation, or among floating macrophytes (Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.) (WGRC unpublished data). WGRC and NRL recorded the following water parameters at the type locality in the rio Alpargatón drainage, on March 21 2004: conductivity 340 μScm-1, dissolved oxygen 5.2 mgl-1, temperature 27.3°C, and pH 7.1. Here, reproductively mature male and female specimens were captured along with small juveniles (20-40 mm) in marginal grasses and roots. The duration of the breeding season in the río Alpargatón, and the duration and seasonality of breeding in the Llanos populations, and elsewhere, are unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the Orinoco drainage B. diazi co-occurs in geographical sympatry with B. brevirostris, B. bullocki B. beebei, B. regani, and partially with B. sullivani. Of these species, B. diazi only occurs in ecological syntopy with B. brevirostris, B. beebei, and B. regani.Sullivan & Hopkins (2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.) note that B. diazi and B. bullocki exhibit habitat partitioning; the former occurring in systems with high conductivity (conductivity > 100 μScm-1), and the latter in system with low conductivity (< 15μScm-1). Brachyhypopomus sullivani is likewise a low-conductivity specialist throughout its geographical range. In Caribbean coastal drainages of Northern Venezuela, B. diazi occurs in the absence of congeners.

Local names. Venezuela: cuchillo.

Remarks. Comments on the type series: The holotype of B. diazi is only known only from the photograph in Fernández-Yépez's original description. Museum catalog numbers were not provided for the holotype and sole paratype listed in the description, and these specimens have subsequently been lost (pers. comm., F. Provenzano, MBUCV). The collection locality of the lost holotype is given as ["Station 138"] from the "rio Yaracuy" hydrogeographic complex (a complex which includes the río Salado). Plate 21 of the description includes photographs of "various views of the collecting sites of the species, all west of Puerto Cabello", one of which features a plaque labeled "139 río Salado". During a 2004 visit to Carabobo, two of us (WGRC and NRL) located a site where the río Alpargatón (a tributary of the río Salado) crosses the main road leading west from Puerto Cabello and Morón (10°27'N, 68°8'W). The site corresponded clearly to photographs from Plate 21, including a distinctive bridge, and a view towards forested hills. At this site we collected a sizable topotype series (MBUCV-V 35655 and UF 174333).

Material examined. 240 specimens. Venezuela. Apure (localities from río Apure dr., Orinoco dr.). CU 71961, 56, nr. Arichuna, edge of río Apure, 07°42'N, 067°08'W. INHS 32076, 8, 96-150 mm, caño Guaritico, 07°33'21"N, 069°38'59"W. MBUCV-V 10809, 3, 48-77 mm, 4 km San Juan de Payara on Biruaca-San Juan de Payara rd., caño Payara, affl. río La Piedra, affl. río Arichuna, 07°40'N, 067°34'W. MBUCV-V 11033, 1, 112 mm, El Negro, San Fernando de Apure, Caramacate, affl. río Negro, ca. 07°50'N, 067°28'W. MBUCV-V 14123, 1, female, 110 mm, San Fernando to Apure-Arichuna hwy., ca. 1.5 km past bridge over río Manglar, ca. 07°50'N, 067°28'W. MBUCV-V 19923, 7 (4 measured: 2 immature 62-63 mm, 1 female, 107 mm, 1 male, 120 mm), Laguna nr. caño Boquerones, nr. Arichuna, affl. río Apure, ca. 07°43'N, 67°17'W. MBUCV-V 20666, 2 (1 measured, female, 102 mm), río Apure, nr. San Fernando de Apure, 07°53'N, 067°28'W. MCNG 13934, 2, caño Las Mercedes, affl. río Apure, 07°53'N, 067°31'W. MCNG 13955, 1, hwy. via San Fernando de Apure, no precise locality/coordinates. MCNG 24161, 1, on Boquerones-San Fernando de Apure hwy., no coordinates. UF 176888, 12 (2 immature, 74-93 mm, 5 female [3CS], 80-106 mm, 5 male, 91-130 mm), Hato El Frio, nr. Mantecal, floodplain lake of río Guaratico, 07°49'32"N, 068'55'23"W. USNM 260254, 2, río El Canito, at rd. from San Fernando to Cunaviche, affl. río Cunaviche, 07°28'N, 067'39'W. USNM 260263, 1, 118 mm, ca. 5 km W San Fernando de Apure, side channel of río Apure, 07°53'N, 067°29'W. Barinas. MBUCV-V 7549, 1, 80 mm, quebrada La Yuca, Puente Blanco, ca. 20 km E Barinas, affl. río Masparro, affl. río Apure, Orinoco dr., ca. 08°35'N, 069°59'W. Carabobo. MBUCV-V 13443, 5, 47-193 mm (2 sexed, males, 171-193 mm), río Patanemo, E Puerto Cabello, río Patanemo dr., ca. 10°26'N, 067°55'W. MBUCV-V 16986, 3 (2 measured: 1 female, 136 mm, 1 male, 178 mm), río Urama, río Urama dr., 10°32'N, 068°12'W. MBUCV-V 35655, 1 (topotype), male, 160 mm, UF 174333, 16 (topotypes) (7 immature [2CS], 20-132 mm, 4 female [1CS], 100-143 mm, 5 male [1CS], 115-176 mm), mun. Morón, río Alpargatón, at rd. and railway bridge on hwy. 1, 8.4 km Morón, río Salado dr., 10°27'58"N, 068°15'38"W. Cojedes. MBUCV-V 10787, 1, 135 mm, quebrada El Pozuelo, bridge on San Carlos-Acarigua rd., affl. río Portuguesa, Orinoco dr., ca. 09°35'N, 068°45'W. MCNG 13623, 1, caño El Pozuelo, affl. río Portuguesa, affl. río Apure, Orinoco dr., ca. 09°35'N, 068°45'W. MCNG 15605, 2, caño Cañafistolo, no coordinates. Guárico (localities from Orinoco dr.). MBUCV-V 14124, 1, female, 123 mm, km 273.6, Calabozo-Camaguan hwy., río Apure, no coordinates. MCNG 14404, 7, stream E Guayabal, affl. río Orituco, affl. río Guárico, affl. río Apure, 09°09'N, 066°43'W [coordinates for Guayabal]. MCNG 14483, 3, stream between hwy. 2 and Uverito, affl. río Manapire, ca. 09°22'N, 065°54'W [coordinates for Uverito] (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Lara. MBUCV-V 10827, 1, female, 69 mm, 60 km W Carora, río Camoruco, río Todistinctive0°08'N, 070°37'W. MBUCV-V 16985, 1, 63 mm, río Los Quediches, headwaters downstream of dam, río Tocuyo dr., ca. 09°57'N, 070°25'W. MCNG 10854, 1, stream at km 408, no precise locality/coordinates (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Monagas . MBUCV-V 10696, (part) 4, 117-142 mm, Barrancas, Laguna el Guatero, affl. río Orinoco, Orinoco dr., ca. 08°42'N, 062°12'W. Portuguesa (localities from río Apure dr., Orinoco dr.). INHS 61362, 2, 104-112 mm, MCNG 15416, 2, MCNG 23675, 2, MCNG 26821, 3, caño Maracá, affl. caño Igues, affl. río Portuguesa, 08°53'11"N, 069°29'18"W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 27290, 1, caño Maracá, at bridge on Guanare-Guanarito hwy., affl. caño Igues, affl. río Portuguesa, 08°49'09"N, 069°19'43"W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MUSM 13406, 1, 58 mm, TNHC 12508, 1, 112 mm, TNHC 12579, 1, 131 mm, TNHC 12663, 3, 95-138 mm, TNHC 12706, 17, 39-141 mm, TNHC, 12774, 2, 149-169 mm, TNHC 12608, 16, 93-135 mm, TNHC 12891, 1, 146 mm, TNHC 12896, 1, 118 mm, TNHC 12938, 4, 68-112 mm, TNHC 13018, 5, 44-124 mm, TNHC 13237, 1, 182 mm, TNHC 13277, 1, 99 mm, TNHC 13313, 3, 129-133 mm, TNHC 13347, 1, 90 mm, TNHC 13367, 4, 110-153 mm, TNHC 15036, 23, 61-174 mm, TNHC 17127, 3, 113-119 mm, 35km SE Guanare, caño (río) Maraca at Urriola Ranch, affl. río Portuguesa, 08°52'30"N, 069°27'40"W. UF 174334, 2, 125-163 mm, río de las Marias, nr. Guanare, affl. río Portuguesa, ca. 09°04'N, 069°39'W.

Brachyhypopomus draco Giora, Malabarba & Crampton, 2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.

(Fig. 22; Tables 2-5, 12)

Brachyhypopomus beebei. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 306, fig. 41; 235-241, table 39 (Paraná-Paraguay basin and coastal drainages of southern Brazil, redescription of B. beebei).

Brachyhypopomus sp. -Cognato et al., 2007Cognato, D. D. P., J. Giora & C. B. Fialho. 2007. Análise da ocorrência de lesões corporais em três espécies de peixe elétrico (Pisces: Gymnotiformes) do sul do Brasil. Pan-American Journal of Aquatic Sciences, 2: 242-246.: 244, fig. 1b, color photograph; fig. 2b, caudal filament damage, fig. 2d caudal filament regeneration (S Brazil, damage and regeneration in gymnotiform fishes).

Brachyhypopomus dracoGiora et al., 2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.: 161, fig. 1, color photograph of male holotype and female paratype; fig. 2, color photograph of head and tip of caudal filament of holotype (original description, type locality - Brazil, Rio Grande do Sul, Patos-Mirim lagoon system). -Almirón et al., 2010Almirón, A., J. Casciotta, L. Ciotek, P. Giorgis, P. Soneira & F. Ruíz Díaz. 2010. Pisces, Gymnotiformes, Hypopomidae, Brachyhypopomus Mago-Leccia, 1994: First country record of three species of the genus, Argentina. Check List: Journal of Species Lists and Distribution, 6: 572-575.: 573, fig. 5, color photograph of live male (Argentina, Entre Rios, Paraná dr., listing of Brachyhypopomus). -Claudino et al., 2010Claudino, M. C., F. Corrêa, R. F. Bastos & A. Miranda Garcia. 2010. Pisces, Gymnotiformes, Hypopomidae, Brachyhypopomus draco (Giora, Malabarba and Crampton, 2008): New species record at Lagoa do Peixe National Park, state of Rio Grande do Sul, Brazil. Check List: Journal of Species Lists and Distribution, 6: 358-359.: 358, fig. 1, color photograph of live female (Brazil, Rio Grande do Sul, Lagoa do Peixe National Park, range extension). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Koerber, 2011Koerber, S. 2011. List of Freshwater Fishes from Argentina - Update 14. Ichthyological Contributions of Peces Criollos, 26: 1-11.: 7 (Argentina, species list]. -Malabarba et al., 2013Malabarba, L. R., P. C. Neto, V. A. Bertaco, T. P. Carvalho, J. F. dos Santos & L. G. S. Artioli. 2013. Guia de identificação dos peixes da bacia do rio Tramandaí. Porto Alegre, Editora Via Sapiens, 140 pp.: 96, color photograph of live individual (Brazil, Rio Grande do Sul, rio Tramandaí, catalog of fishes]. -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 143, fig. 3C outline of head; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Mirande & Koerber, 2015Mirande, J. M. & S. Koerber. 2015. Checklist of the freshwater fishes of Argentina (CLOFFAR). Ichthyological Contributions of Peces Criollos, 36: 1-68.: 48 (Argentina, catalog of fishes). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 12
Morphometrics for Brachyhypopomus draco. HT, holotype; SD, standard deviation. Data for holotype (Rio Grande do Sul, Brazil) are from Giora et al. (2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.). Ranges for the type region refer to non-type specimens from laguna dos Patos, rio Tramandaí, and rio Uruguay drainages, Brazil (holotype data excluded). Specimens from the Paraguay drainage refer to non-type specimens from the río Paraguay of Paraguay.

Diagnosis. Brachyhypopomus draco is diagnosed from congeners by the following combination of characters: precaudal vertebrae 21-25, vs. 15-20 in B. batesi, B. benjamini, B. bennetti, B. bombilla, B. bullocki, B. cunia, B. diazi, B. flavipomus, B. hendersoni, B. janeiroensis, B. jureiae, B. menezesi, B. occidentalis, B. provenzanoi, B. regani, B. sullivani, and B. walteri; pale stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament present in B. arrayae, B. beebei, B. belindae, B. gauderio, B. pinnicaudatus, and B. verdii; anal-fin rays 155-204, vs. 226-293 in B. brevirostris; caudal filament length 15.7-35.0% LEA, vs. 7.4-14.0% in B. palenque; absence of oblique stripes or saddles on body surface, vs. presence of continuous or discontinuous dark vertical or diagonally oriented stripes or saddles absent on body surface dorsal to lateral line, and often extending across lateral line into ventral lateral surface, in B. alberti and B. hamiltoni.

Description. Head and body shape, and pigmentation illustrated in Fig. 22, and in original description. Meristic and morphometric data for examined specimens are presented in Tables 2-5 and 12. Body moderate in depth. Head short to moderate in length and moderate to broad in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head approximately straight with areas of concavity and convexity between operculum and snout, snout truncate to rounded. Eye small to moderate in size. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 36 (n = 1). Pectoral fin moderate to broad in width, pectoral-fin rays 14-17 (mode of 16 in populations from Uruguay dr. and coastal drainages of southern Brazil, and 15 in populations from río Paraguay). Precaudal vertebrae 21-25 (mode of 23 in populations from Uruguay dr. and coastal drainages of southern Brazil, and 22 in populations from río Paraguay), including 1-3 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) posterior to, or near, tip of pectoral fin. Anal-fin rays 155-200, with somewhat higher median value in populations from the río Paraguay (189-197, median 195) than in populations from Uruguay dr. and coastal drainages of southern Brazil (168-200, median 179) (Table 2). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 4-6 (mode 5). Lateral line continuous. Sparse depigmented epidermal canals; as an irregular interrupted single groove either side of dorsal midline along most of posterior half body, and as sparse scratch like marks dorsal to and near lateral line in posterior third of body. Three bilateral electrocyte columns at anal-fin terminus in immature, mature female, and mature male specimens. Three columns of electrocytes at or near a mid-point between anal-fin terminus and tip of caudal filament in mature females, and three or four (or three alternating with four) in immature specimens and mature males. Number of columns tapering from 3 or 4 to 2-3 in distal portion of caudal filament. Caudal filament short to moderate in length.

Coloration. (Fig. 22). Background tan to dark brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament (although in some specimens dorsal midline is somewhat paler than areas adjacent to midline). Dorsal surface without dark markings, or with irregular dark marks or flecks that are sometimes vertically elongated but never form distinct bands. Series of diffuse horizontal dash-like dark markings often present along lateral line in posterior third of body, anterior to anal-fin terminus. Flank below lateral line over body cavity with irregular dark flecks, but rarely vertically elongated bands. Multiple vertically elongated incomplete bands usually, but not always, present over pterygiophores. Caudal filament darker than body, especially dorsally, ventrally, and near tip; with or without irregular, incomplete dark bands. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline with light scattering of brown chromatophores. Anal-fin rays with scattered or uniform dark pigmentation; darker in posterior half of fin. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 22
Brachyhypopomus draco. a. MCP 19847 (part), male, 138 mm TL (head in lateral view, body in lateral and dorsal view); Brazil, rio Ibicuí, Uruguay dr. b. MCP 13643, female, 132 mm TL (body in lateral view); Brazil, rio Sanga, rio Tramandaí dr. Note sexual dimorphism in caudal filament height. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 182 mm TL (LEA of this specimen not available) (n = 264). Largest male specimen examined 177 mm TL, 137 mm LEA (n = 27). Largest female examined 134 mm, 109 mm LEA (n = 14). Maximum male size in type series 151.8 mm LEA vs. 128.4 mm LEA for females (Giora et al., 2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.).

Sexual dimorphism. Sexually mature males attain larger sizes than females. Breeding mature males exhibit longer and deeper caudal filaments than immature individuals and breeding females, and reach slightly larger sizes (Figs. 22a-b) but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Tip of caudal filament in breeding males often with paddle-like lateral compression (sometimes very widened), with electrocytes reaching near tip or terminating as far as around half-way along paddle-like structure. No known sexual dimorphism in pigmentation.

Geographic distribution. Argentina, Brazil, Paraguay, and Uruguay (Fig. 23). Widely distributed through lower portions of the Paraguay, Paraná, and Uruguay drainages as far north as 25°S, the Patos-Mirim lagoon system of southeast Brazil/northeast Uruguay, and some other coastal drainages of Brazil north of Lagoa dos Patos.

Fig. 23
Collection records for Brachyhypopomus draco (circles), B. janeiroensis (squares), and B. jureiae (triangles). Holotype locations are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found complete overlap in the range of meristics (Tables 2-5) and morphometric proportions (Table 12), and observed similar pigmentation among populations of B. draco from Uruguay dr./coastal drainages of southern Brazil, and from the río Paraguay. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. draco are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners.

Ecological notes. The original description of B. draco notes that it occurs most commonly in "river edges, slow moving creeks, lagoons and flooded areas with muddy or sandy bottom and abundant emergent or floating vegetation". Schaan et al. (2009Schaan, A. B., J. Giora & C. B. Fialho. 2009. Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil. Neotropical Ichthyology, 7: 737-744.) provides a detailed account of the natural history and reproductive biology of B. draco. Breeding occurs primarily during the late austral winter and austral summer, which corresponds to a period of higher temperature and rainfall, and substantially longer photoperiod. At this time the sex ratio approximates 1:1. During the austral winter B. draco exhibits gonadal quiescence, a general reduction in activity and feeding, and an accompanying reduction of the EOD pulse-rate (Giora et al., 2011Giora, J., H. M. Tarasconi & C. B. Fialho. 2011. Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil, with evidence for a domancy period. Environmental Biology of Fishes, 94: 649-662.; Schaan et al., 2009Schaan, A. B., J. Giora & C. B. Fialho. 2009. Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil. Neotropical Ichthyology, 7: 737-744.). Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Through most of its range, B. draco occurs in geographical sympatry and in ecological syntopy with B. bombilla and B. gauderio. Brachyhypopomus draco probably also co-occurs with B. walteri in the northern part of the former's distribution in the Paraguay-Paraná system (see distribution for B. walteri, Fig. 47), but not with B. brevirostris, which occurs as far south as 19°S (Fig. 18) (compared to 25°S for the highest known latitude for B. draco, Fig. 23).

Local names. Argentina, Paraguay: morenita; Brazil: tuvira, moreninha, tuvira dragão (Malabarba et al., 2013Malabarba, L. R., P. C. Neto, V. A. Bertaco, T. P. Carvalho, J. F. dos Santos & L. G. S. Artioli. 2013. Guia de identificação dos peixes da bacia do rio Tramandaí. Porto Alegre, Editora Via Sapiens, 140 pp.); Uruguay: morenita, limpiavidrio (Nion et al., 2002Nion, H., C. Ríos & P. Meneses. 2002. Peces del Uruguay: lista sistemática y nombres comunes. Montevideo, Dirección Nacional de Recursos Acuáticos/InfoPesca, 105 pp.).

Material examined. 264 specimens. Argentina. Entre ríos. AI 268, 2, 118-129 mm, Pre-Delta National Park, Pozo Hondo, Arroyo las Tortugas, Paraná dr., 32°08'40"S, 060°39'02"W. Brazil. Rio Grande do Sul. FURG 2186, 3, 42-80 mm, wetlands draining into Parque Nacional Lagoa do Peixe, 6 km W Mostardas, Patos-Mirim dr., 31°06'05"S, 050°51'17"W. MCP 9487, 3, 64-96 mm, Vila Itapevi, Cecequi-São Francisco de Assis rd., rio Uruguai, Uruguay dr., ca. 29°47'S, 55°07'W. MCP 13643, 3 (1 immature, 71 mm, 1 female, 134 mm, 1 male, 96 mm), stream, affl. of Lagoa dos Quadros, nr. Praia do Barco, rio Tramandaí dr., ca. 29°42'S, 050°05'W. MCP 19546, 1, male, 149 mm, Fazenda Pirai rd., 4.5 km São Gabriel, rio Vacacaí, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°18'51"S, 054°21'35"W. MCP 19846, 1, female (CS), 130 mm, MCP 19847 (part), 1, male, 139 mm, Banhado do Inhatium, hwy. BR-290, 21 km São Gabriel, affl. rio Ibicuí, Uruguay dr., 30°15'43"S, 054°31'33"W. MCP 20215, 5, 64-80 mm, Eldorado do Sul, BR-290, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'36"S, 051°20'56"W. MCP 20217, 3, 58-68 mm, arroio Passos dos Carros, rd. linking BR16 to Guaíba, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°05'55"S, 051°23'15"W. MCP 20711, 1, 73 mm, Osório, channel linking Lagoa Emboaba and Emboabinha, rio Tramandaí dr., 29°57'57"S, 050°13'45"W. MCP 23795, 2 (1 immature, 44 mm, 1 female, 90 mm), mun. Tapes, arroio Teixeira on BR-16 E, Patos-Mirim dr., 30°38'34"S, 051°32'45"W. MCP 41537 (paratype), 1, female, 108 mm LEA, MCP 41538, 2 (paratypes) (1 female, 92 mm LEA, 1 male, 88 mm LEA), MCP 41539, 1 (paratype), male, 147 mm LEA, MCP 41540, 1 (holotype), male, 177 mm TL, 137 mm LEA, MNRJ 30916, 2 (paratypes) (1 female, 128 mm LEA, 1 male, 152 mm LEA), MNRJ 30917, 1 (paratypes) male, 150 mm LEA, MNRJ 30918, 1 (paratype) male, 138 mm LEA, MZUSP 94429, 1 (paratype) male, 139 mm LEA, UFRGS 6515, 1, male, 135 mm, UFRGS 6521, 1, female, 114 mm, UFRGS 6522, 1, female, 127 mm, UFRGS 6523, 1, male, 117 mm, UFRGS 8888, 1 (paratype), male, 126 mm LEA, mun. Viamão, Lagoa Verde, Parque Estadual de Itapuã, Patos-Mirim dr., 30°22'52"S, 051°01'25"W. MCP 41938, 2 (1 female, 110 mm, 1 male, 80 mm), mun. Cacequi, stream, affl. rio Ibicuízinho, on hwy. Cacequi-Estação São Lucas, Uruguay dr., 29°50'12"S, 054°27'423"W. MCP 41961, 2 (1 female, 112 mm,1 male, 95 mm), mun. Cacequi, Fazenda da Convenção, affl. rio Ibicuí, Uruguay dr., 29°50'58"S, 054°53'02"W. MCP 45352, 1, 134 mm, mun. Pelotas, nr. bridge to Pelotas, rio São Gonçalo, Patos-Mirim dr., 31°46'19"S, 52°20'33"W. MCP 45353, 1, 57 mm, mun. Eldorado do Sul, arroio Passos dos Carros on hwy. connecting hwy. BR-16 to Guaíba, rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°05'55"S, 051°23'15"W. UFRGS 732, 1 (paratype), female, 86 mm LEA, mun. Viamão, arroio Alexandrina, Patos-Mirim dr., ca. 30°06'S, 050°57'W. UFRGS 820, 1 (paratype), male, 117 mm LEA, mun. Guaíba, BR-290 hwy., Patos-Mirim dr., ca. 30°07'S, 051°20'W. UFRGS 821, 1, 110 mm, UFRGS 822, 1 (paratype), male, 119 mm, mun. Viamão, stream flowing into Praia de Fora, Lagoa dos Patos, Parque Itapuã, Patos-Mirim dr., 30°23'09"S, 051°01'00"W. UFRGS 3938, 1, 27 mm, mun. Osório, Lagoa Emboaba, rio Tramandaí dr., 29°57'00"S, 050°13'00"W. UFRGS 4096, 7, 56-130 mm, mun. Tramandaí, Lagoa do Passo, rio Tramandaí dr., 29°52'01"S, 050°06'W. UFRGS 4236, 2, 86-99 mm, mun. Viamão, Lomba do Pinheiro, affl. rio Guaíba, Patos-Mirim dr., 30°05'00"S, 051°07'59"W. UFRGS 4317, 1 (paratype), 59 mm, mun. Viamão, arroio Itapuã, Patos-Mirim dr., ca. 30°15'S, 051°02'W. UFRGS 4503, 1, 50 mm, mun. lago Emboaba, rio Tramandaí dr., 29°57'S, 050°13'W. UFRGS 4802, 23, 2169 mm, UFRGS 4812, 7, 75-170 mm, UFRGS 4814, 3, 57-82 mm, mun. Viamão, Parque Estadual de Itapuã, Patos-Mirim dr., ca. 30°20'S, 051°00'W. UFRGS 5887, 1, 62 mm, mun. Arambaré, unnamed stream, Arambaré - Santa Rita do Sul hwy. Lagoa dos Patos, Patos-Mirim dr., 30°57'09"S, 051°30'04"W. UFRGS 6486, 1 (paratype), male, 113 mm, UFRGS 6487, 1, female, 104 mm, UFRGS 6488, 1 (paratype), male, 113 mm, UFGRS 6489, 1 (paratype), male, 112 mm, UFRGS 6490, 1 (paratype), female, 111 mm, UFRGS 6491, 1 (paratype), male, 93 mm, UFRGS 6492, 1, female, 96 mm, mun. Capão da Canoa, stream, Estrada do Mar (hwy. RS-389) km 38, rio Tramandaí dr., 29°43'09"S, 050°00'56"W. UFRGS 6493, 1, male, 100 mm, UFRGS 6494, 1 (paratype), male, 100 mm, UFRGS 6497, 1 (paratype), male, 106 mm, UFRGS 6785, 4 (paratypes) (2 females, 84-85 mm LEA, 2 male, 79-105 mm LEA), mun. Rosário do Sul, stream, hwy. BR-290, affl. rio Santa Maria, affl. rio Ibicuí, Uruguay dr., 30°12'42"S, 055°03'17"W. UFRGS 6507, 1 (paratype), male, 109 mm, UFRGS 6508, 1, male, 126 mm, UFRGS 6509, 1 (paratype), female, 102 mm, UFRGS 6510, 1, female, 86 mm, UFRGS 6511, 1 (paratype), male, 126 mm, UFRGS 6513, 1, female, 113 mm, UFRGS 6514, 1, male, 107 mm, mun. São Gabriel, stream on margin hwy. BR-290, affl. rio Cacequí, affl. rio Santa Maria, affl. rio Ibicuí, Uruguay dr., 30°18'57"S, 054°24'23"W. UFRGS 6525, 1, male, 130 mm, UFRGS 6526, 1 (paratype), male, 129 mm, UFRGS 6527, 1, immature, 100 mm, mun. El Dorado do Sul, rd. hwy. BR-290, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'56"S, 051°23'33"W. UFRGS 6671, 3 (paratypes) (1 female, 96 mm LEA, 2 male, 86-107 mm LEA), mun. Terra de Areia, creek affl. rio Três Forquilhas, hwy. RS 486, rio Tramandaí dr., 29°33'22"S, 050°04'19"W. UFGRS 6748, 1 (paratype) male, 91 mm LEA, UFRGS 6750, 14, 46-128 mm LEA, mun. Alegrete, Sanga do Jacaré, stream crossing BR-290, affl. rio Ibicuí, Uruguay dr., 30°12'42"S, 055°03'19"W. MZUSP 94428, 8 (paratypes) (2 male, 96-127 mm LEA, 6 female, 52-104 mm LEA), UFRGS 6752, 1, 100 mm, UFRGS 6753 (paratype), 1 male, 88 mm LEA, UFGRS 6754, 1, 61 mm, UFRGS 6789, 4 (paratypes) (2 females, 72-80 mm LEA, 2 male, 106-126 mm LEA), mun. Rosário do Sul, stream at margin hwy. BR-290, affl. arroio Gueromana, affl. rio Ibirapuitã, affl. rio Ibicuí, Uruguay dr., 30°01'00"S, 055°23'18"W. UFRGS 6780, 11, São Gabriel, rio Vacacaí system, Patos-Mirim dr., ca. 30°20'S, 054°19'W. UFRGS 7686, 30, UFRGS 7707, 3, Viamão, Patos-Mirim dr., ca. 30°05'S, 051°01'W. UFRGS 8263, 28, Charqueadas, rio Jacuí, Patos-Mirim dr., ca. 29°57'S, 051°37'W. UFRGS 8475, 4, Pantano Grande, rio Pardo, Patos-Mirim dr., ca. 30°15'S, 052°20'W. UFRGS 8938, 1, rio Tramandaí dr., no coordinates. UFRGS 14562, 2, 136-137 mm, mun. Águas Claras, Refúgio da Vida Silvestre, Banhado dos Pachecos, rio Tramandaí dr., 30°04'40"S, 050°50'59"W. UFRGS 15292, 2, 103-114 mm, mun. Arambaré, Patos-Mirim dr., no coordinates. UMMZ 143283, 2, 48-100 mm, Conceição do arroio, ca. 20 mi. N Tramandaí, rio Maquiné, rio Tramandaí dr., ca. 29°43'S, 050°08'W. Paraguay (localities from Paraná dr.). Alto Paraná. UMMZ 206908, 1, female, 103 mm, stream, ca. 30 km NW Hernandarias, rd. to Itakyry, affl. río Paraguay, 25°14'12"S, 054°52'48"W. Caaguazú. UMMZ 206252, 5, 33-14 mm, Estancia San Ignacio, 24 km Carayao, río Hondo, affl. río Paraguay, 25°01'36"S, 056°25'48"W. Central. UMMZ 205706, 2, 110-115 mm, río Paraguay, NW Asunción, ca. 25°17'S, 057°39'W. UMMZ 206001 (part), 1, male, 132 mm, río Salado (nr. mouth) nr. N Limpio, affl. río Paraguay, 25°08'42"S, 057°25'12"W. UMMZ 208106, 2, 84-100 mm, ca. 1.0 km S Puente Remanso bridge, río Paraguay, 25°17'36"S, 057°33'00"W. Cordillera. ANSP 185112, 1, female, 105 mm, ANSP 185119, 2, 76-79 mm, stream crossing Caacupe-Tobati rd., 7.0 km Route 2 in direction of Tobati, affl. río Paraguay, ca. 25°22'S, 057°13'W. UMMZ 205767, 1, 107 mm, Arroyo Tobati, 1.6 km S Tobati, affl. río Piribebuy, affl. río Paraguay, 25°18'30"S, 057°04'12"W. Misiones. ANSP 170412, 1, 118 mm, bridge on Ayolas-Asunción-Encarnacíon hwy. (Ruta 1) at km 4/A262, affl. río Paraná, ca. 27°24'S, 056°48'W. ANSP 175180, 1, 85 mm, stream crossing rd. to Ayolas, affl. río Paraná, 27°03'29"S, 056°47'22"W. ANSP 185113, 1, 45 mm, marshes, rd. from Ayolas to Asunción-Encarnacíon hwy, affl. río Paraná, ca. 27°23'S, 056°47'W. Paraguarí. USNM 181483, 5, 88-138 mm, nr. Pueblo Ybytymí, Arroyo Pachongo, affl. río Paraguay, ca. 25°46'S, 056°47'W. Presidente Hayes. ANSP 185111, 2 (1 female, 103 mm, 1 male, 114 mm), Puente Remanso, affl. río Paraguay, 25°10'S, 057°33'W. Uruguay. Artigas. ZVC-P 2727, 1, Laguna Redonda on margin of río Uruguay, Franquia, nr. Bella Unión, Uruguay dr., 30º14'46"S, 057º36'22"W.

Brachyhypopomus flavipomus, new species

urn:lsid:zoobank.org:act:8368D549-9BE7-45FC-BE01-05742AFA0851

(Figs. 1f, 24; Tables 2-5, 13)

Brachyhypopomus sp. 1. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 15-16, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1, reproductive biology (Brazil, central Amazon, ecology and signal diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance).

Hypopomidae sp. 1. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4, 834, fig. 9, drawing of adult specimen, with EOD (Brazil, Amazonas, species and EOD diversity).

Brachyhypopomus sp. A. -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.: 231, fig. 6, black and white photograph of head of live individual (Brazil, Amazonas, adaptations to hypoxia).

Brachyhypopomus sp. "fla". -Crampton 2011: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus n. sp. FLAV. -Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.: 214 (Brazil, Amazonas, cytogenetics).

Brachyhypopomus sp. "flavipomus". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 45366, immature, 92 mm TL, 73 mm LEA, Brazil, Amazonas, mun. Alvarães, Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá], Ressaca do Caetono, rio Solimões-rio Japurá floodplain, Amazonas dr., 02º50'15"S, 064º55'50"W, 11 May 1997, W. Crampton & J. Oliveira.

Paratypes. 57 specimens, localities from Amazonas dr., collected by W. Crampton & J. Oliveira. Brazil. Amazonas (localities listed from the Mamirauá Reserve are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1998.3.12.25, 1, female, 113 mm, 20 Jan 1995, BMNH 1998.3.12.26 and 28-41, 15 unsexed, 75-107 mm, 20 Jan 1995, BMNH 1998.3.12.27, 1, immature, 93 mm, 20 Jan 1995, BMNH 1998.3.12.43-44, 2, immature, 90-108 mm, 11 Apr 1994, MCP 45265, 1, female, 98 mm, 14 Mar 2001, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12.42, 1, female, 117 mm, 10 Apr 1994, INPA 9942, 21, 58-87 mm, Oct 1993, INPA 18365, 1, immature, 83 mm, 11 May 1997, Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. INPA 18363, 2, immature, 62-73 mm, 2 Jul 1996, MCP 45349, 1, immature, 85 mm, 4 Jul 1996, Mamirauá Reserve, cano do lago Arauaé, 03º02'52"S, 064º50'04"W. INPA 18364, 1, immature, 79 mm, 11 Jul 1996, MCP 45350, 2, immature, 80-82 mm, 11 Jul 1996, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. INPA 18366, 1, immature, 76 mm, 18 Jun 1999, MCP 45425, 1, immature, 62 mm, 1 May 1999, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. INPA 18367, 1, immature, 70 mm, 24 Jul 1999, MCP 45266, 1, female, 91 mm, 19 Mar 2001, Mamirauá Reserve, cano do lago Mamirauá, 03º06'40"S, 064°47'52"W. INPA 18368, 1, immature, 53 mm, 25 May 1999, MCP 45367, 1, male, 104 mm, 17 May 1997, Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45405, 1, immature, 73 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º04'29"S, 064°48'29"W, 16 Jun 1998. MCP 45406, 1, immature, 48 mm, Mamirauá Reserve, Paraná do Apara, 03º06'50"S, 064°47'48"W, 23 Jun 1998.

Non-types. 150 specimens, localities from Amazonas dr. Brazil. Amazonas (localities listed from the Mamirauá Reserve are in rio Solimões-Japurá floodplain, mun. Alvarães). IDSM 450, 1, 107 mm, IDSM 455, 5, 64-99 mm, MCP 45368, 14, 58-83 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. MCP 45264, 1, female, 86 mm, Mamirauá Reserve, lago Geraldo, 03º06'53"S, 064°49'06"W. MCP 45329, 2, immature, 69-74 mm, MCP 45365, 11 (3 immature, 86-97 mm, 5 female [3CS], 85-107 mm, 3 male [1CS], 91-97 mm), Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. MCP 45364, 1, immature, 91 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. MCP 45453, 1, female, 98 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. MPEG 22743, 5, 60-104 mm, Mamirauá Reserve, cano do lago Rato, 03º02'50"S, 064º51'27"W. MZUSP 23402, 1, 88 mm, igarapé Tucuxi, affl. rio Ati-Paraná, NW Fonte Boa, affl. rio Solimões, ca. 02°06'S, 066°28'W. MZUSP 23425, 1, 62 mm, lago Buiuçu, affl. rio Ati-Paraná, affl. rio Solimões, ca. 02°06'S, 066°28'W. Colombia. Amazonas. USNM 216857, 1, 66 mm, Leticia, río Amazonas, 04°13'S, 069°56'W. Peru. Loreto. ANSP 179835, 1, 71 mm, caño Moena and mouth of its affl. caño Ullpa, affl. río Itaya, affl. río Amazonas, 03°46'19"S, 073°14'16"W. INHS 39732, 1, 74 mm, INHS 52030, 1, 79 mm, INHS 53873, 2, 76-95 mm, caño Moena, affl. río Itaya, 03°46'20"S, 073°14'17"W. INHS 94214, 3, 56-62 mm, caño Ushpa, affl. río Itaya, ca. 03°48'S, 073°16'W. INHS 56227, 1, 60 mm, caño Ullpa, 2-3 mi. upstream from mouth and village Ullpa, affl. río Itaya, 03°47'37"S, 073°14'44"W. MUSM 6959 (part), 3, (1 female, 77 mm, 2 male, 90-92 mm), Isla Muyuy, cocha Amazonas, affl. río Amazonas, ca. 03°54'S, 073°14'W. MUSM 44760, 1, immature, 64 mm, nr. Jenaro Herrera, floodplain lake, río Ucayali, 04°54'18"S, 073°43'12"W. MUSM 44770, 37 (32 immature, 37-82 mm, 5 female, 54-100 mm), nr. Jenaro Herrera, cocha Capite, floodplain lake, río Ucayali, 04°51'21"S, 073°40'24"W. NRM 13522 (part), 1, 69 mm, Sacarita del Tuyé, opposite Pebas, río Ampiyacu, ca. 03°20'S, 071°49'W. UF 114641, 1, 55 mm, UF 148052, 1, immature, 75 mm, Reserva Nacional (RN) Pacaya Samiria, cocha Yanayacu, affl. río Pacaya, affl. río Ucayali, 05°23'29"S, 074°31'21"W. UF 126156, 1, 52 mm, UF 126327, 1, 69 mm, UF 128883, 2, 40-53 mm, UF 128981, 8, 47-79 mm, UF 129035, 1, 76 mm, UF 129047, 1, 70 mm, UF 129086, 6, 37-74 mm, UF 129144, 8, 47-102 mm, UF 129187, 6, 45-80 mm, UF 129414, 1, 52 mm, UF 129798, 2, 67-82 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°16'S, 074°27'W. UF 126238, 5, 63-81 mm, UF 129006, 1, immature, 70 mm, UF 129797, 1, 65 mm, RN Pacaya Samiria, cocha Sapote, affl. río Pacaya, affl. río Ucayali, 05°20'14"S, 074°29'40"W. UF 129010, 1, immature, 58 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, 05°16'12"S, 074°30'09"W. UF 129012, 1, immature, 53 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, 05°16'44"S, 074°31'06"W. UF 148053, 2 (1 immature, 74 mm, 1 female, 78 mm), RN Pacaya Samiria, caño Tamara, affl. río Pacaya, affl. río Ucayali, 05°16'39"S, 074°29'39"W. UF 148547, 3 (2 immature, 75-76 mm, 1 female, 75 mm), NN Pacaya Samiria, caño Yarina, affl. río Pacaya, affl. río Ucayali, 05°19'20"S, 074°30'14"W. UF 148549, 1, male, 95 mm, RN Pacaya Samiria, cocha Sapote, affl. río Pacaya, affl. río Ucayali, 05°20'15"S, 074°29'40"W. UF 148554, 1, immature, 84 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, 05°18'15"S, 074°30'10"W. UF 148555, 2, female, 84-92 mm, RN Pacaya Samiria, cocha Yanayacu, affl. río Pacaya, affl. río Ucayali, 05°18'14"S, 074°26'12"W.

Table 13
Morphometrics for Brachyhypopomus flavipomus, Brachyhypopomus hamiltoni, and Brachyhypopomus hendersoni. HT, holotype; SD, standard deviation. Ranges for each species refer to the holotype and to paratype and non-type specimens from the type regions.

Diagnosis. Brachyhypopomus flavipomus is diagnosed by the presence of conspicuous patches of shiny yellow guanine on the operculum and anterior to pectoral-fin base in live individuals, vs. absence in all congeners.

Description. Head and body shape, and pigmentation illustrated in Figs. 1f and 24. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 13. Body moderate to broad in depth. Head moderate in length and depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout triangular. Eye moderate to large in size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 33-39 (median 34, n = 5). Pectoral fin narrow to moderate in width, pectoral-fin rays 11-13 (mode 12). Precaudal vertebrae 18-20 (mode 19), with 1-2 (mode 1) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 175-186 (median 179). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-6 (mode 5). Lateral line continuous. Sparse depigmented epidermal canals; as an irregular interrupted single groove either side of dorsal midline along most of posterior half body, scratch like marks dorsal to and near lateral line almost absent, present sporadically and sparsely in some specimens. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at or near a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Number of electrocyte columns sometimes increases to four posterior to mid-point between anal-fin terminus and tip of caudal filament, before tapering to 2-3 distally. Caudal filament short to moderate in length.

Coloration. (Figs. 1f, 24). Background dark brown dorsally fading to pale yellow to tan ventrally. Background of region of body over body cavity below lateral line whitish to yellow in live individuals, pale tan in preserved specimens. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Prominent pair of irregular horizontal lines formed by aggregations of dark chromatophores either side of dorsal region, visible both dorsally and laterally (in upper part of flank) in anterior third of body, from which short irregular dark patches extend dorsally. Some irregular dark markings along lateral line and over pterygiophores in posterior half of body, but flank otherwise marked only with irregular scatterings of chromatophores; banding absent. Caudal filament darker than body, with irregular dark markings or bands along entire length. Head with very pale background color ventrally, darker dorsally. Irregular dark chromatophores scattered over head, reaching highest density on dorsal surface of head and anterior to eye. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Color in live specimens (Fig. 1f) similar to preserved ones, but with very conspicuous shiny yellow patches of guanine over operculum (forming one or two vertical yellow lines) and anterior to pectoral-fin base (forming a vertically elongated patch) and with conspicuous white or pale yellow color below lateral line over body cavity. Yellow guanine patches and white-yellow background color over body cavity fade soon after fixation. Live individuals with posterior portion of opercular region (posterior to guanine patch) rosy due to underlying gills.

Fig. 24
Brachyhypopomus flavipomus. MCP 45366 (WC19.110597), holotype, immature, 92 mm TL (head, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões/rio Japurá confluence, Amazonas dr. Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 117 mm, 89 mm LEA (n = 208). Largest male specimen examined 104 mm TL, 77 mm LEA (n = 7). Largest female specimen examined 117 mm TL, 89 mm LEA (n = 21).

Sexual dimorphism. Females reach larger body size than males. Males in breeding condition have somewhat deeper and longer caudal filaments than immature specimens or breeding females but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit slightly enlarged electrocytes relative to immature specimens and females. Breeding males without paddle-like lateral compression at caudal filament tip. No known sexual dimorphism in pigmentation.

Geographic distribution. Brazil and Peru (Fig. 25). Known only from whitewater floodplain habitats along the main stem of the Amazon River of the upper and central Amazon, from the río Ucayali-río Marañón confluence in the west to the rio Solimões (Amazonas) - rio Japurá confluence in the east.

Fig. 25
Collection records for Brachyhypopomus flavipomus (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. Brachyhypopomus flavipomus is restricted to whitewater floodplain habitats where it is encountered throughout the year in floating macrophytes. It is most abundant in sheltered floodplain lakes surrounded by high levee forest, but has a patchy distribution, and varies in abundance at a given site from year to year (WGRC unpublished data). See description of B. belindae for water quality parameters of the area of the type locality. During the early rising water period B. flavipomus also occurs in leaf litter along the margins of newly flooded forest. Brachyhypopomus flavipomus is able to tolerate protracted periods of hypoxia at high water by aerial gill respiration (Crampton, 1998b), and its gill lamellae are greatly expanded in comparison to species from normoxic system (Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.). Brachyhypopomus flavipomus breeds during the rising and high water period (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p., 165). Stomach contents of specimens from the type locality comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136).

Co-occurring congeners: Brachyhypopomus flavipomus is known to co-occur in geographical sympatry and ecological syntopy with the whitewater floodplain-occurring species B. beebei, B. belindae, B. bennetti, B. brevirostris, B. hamiltoni, B. pinnicaudatus, B. regani, and B. walteri. It also exhibits allotopic distributions across parts of its range with: B. batesi, B. benjamini¸ B. hendersoni, B. sullivani, and B. verdii.

Etymology. The specific name is an adjective with alternative endings -us, -a, -um, derived from flavus, Latin adjective = yellow; and pomus, latinized from Greek πῶμα = lid, cover. In reference to the conspicuous patches of yellow guanine on the operculum of live individuals.

Local names. Brazil: sarapó; Peru: macana.

Brachyhypopomus gauderio Giora & Malabarba, 2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.

(Fig. 26; Tables 2-5, 14)

Rhamphichthys brevirostris. -Perugia, 1891Perugia, A. 1891. Appunti sopra alcuni pesci sud-americani conservati nel Museo Civico di Storia Naturale di Genova. Annali del Museo Civico di Storia Naturale di Genova (Serie 2), 10: 605-657.: 56 (Argentina, Chaco, Resistencia, based on three specimens collected by Spegazzini (MSNG 27458); one of the three was identified as Eigenmannia trilineata, and two, incorrectly, as Brachyhypopomus bombilla by Azpelicueta & Koerber, 2015Azpelicueta, M. & S. Koerber. 2015. On some freshwater fish species reported by Perugia (1891) from Argentina. Aqua - Journal of Ichthyology and Aquatic Biology, 21: 39-46.: 40-42, fig. 3, color photograph of specimens [in discussion of Perugia listings]). -Ringuelet et al., 1967Ringuelet, R. A., R. H. Arámburu & A. Alonso de Arámburu. 1967. Los peces argentinos de agua dulce. La Plata, Argentina, Gobernación de la provincia de Buenos Aires, Comisión de Investigacíon Científica.: 253; Lopez et al., 2003: 65 (repeat listings from Perugia, 1891Perugia, A. 1891. Appunti sopra alcuni pesci sud-americani conservati nel Museo Civico di Storia Naturale di Genova. Annali del Museo Civico di Storia Naturale di Genova (Serie 2), 10: 605-657.). -Boulenger, 1896Boulenger, G. A. 1896. On a collection of fishes from the Rio Paraguay. Transactions of the Zoological Society of London, 14 (part II): 1-39, pls. 31-38.: 38 (Brazil, Mato Grosso, Descalvados, list of fishes collected in río Paraguay by C. Ternetz, record corresponds to BMNH 1895.5.17.265-268; identified herein as B. gauderio (part, n = 1), B. bombilla (part, n = 3).

Hypopomus brevirostris. -Eigenmann & Kennedy, 1903Eigenmann, C. H. & C. H. Kennedy. 1903. On a collection of fishes from Paraguay, with a synopsis of the American genera of cichlids. Proceedings of the Academy of Natural Sciences of Philadelphia, 55: 497-537: 530 (Paraguay, listing of fishes collected by J. Daniel Anisits, "Four specimens (108, 158, 220), Mato Grosso or Asunción. Campo Grande and Arroyo Chagalalina."; we identified these four specimens as AMNH 1009, CAS 72215, FMNH 5251, all B. gauderio). -Carter & Beadle, 1931Carter, G. S. & L. C. Beadle. 1931. The fauna of the swamps of the Paraguayan Chaco in relation to its environment. II. Respiratory adaptations in the fishes. Journal of the Linnean Society of London, Zoology, 37: 327-366.: l337, pl. 21, fig. 7, transverse section of the mouth and gill chamber; pl. 31, fig. 8, illustrations of gill-lamellae morphology (Paraguay, ecology with discussion of respiratory adaptations; identified from context as B. gauderio). -Casciotta et al., 2005Casciotta, J., A. Almirón & J. Bechara. 2005. Peces del Iberá: Hábitat y diversidad. La Plata, Argentina, Grafikar, 244 pp.: 71, line-drawing; 237, fig. 108, color photograph (Argentina, Iberá wetlands, catalog of fishes).

Brachyhypopomus pinnicaudatus. -Franchina, 1997Franchina, C. R. 1997. Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 181: 111-119.: 115, figs. 7-10, black and white photographs of electrocyte arrangements in caudal filament (electric organ ontogeny). -Stoddard, 1999Stoddard, P. K. 1999. Predation enhances complexity in the evolution of electric fish signals. Nature, 400: 254-256.: 255, fig. 4, color photograph of mature female (EOD evolution). -Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.: 610, fig. 1, black and white photograph of mature male and female (EOD evolution). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 494 (rio de la Plata basin, Paraguay, Brazil, Uruguay, catalog of hypopomids). -Curtis & Stoddard, 2003Curtis, C. C. & P. K. Stoddard. 2003. Mate preference in female electric fish, Brachyhypopomus pinnicaudatus. Animal Behaviour, 66: 329-336.: 330, fig. 1, black and white photographs of mature male and female (communication). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Graça & Pavanelli, 2007Graça, W. J. & C. S. Pavanelli. 2007. Peixes da planície de inundação do alto rio Paraná e áreas adjacentes. Maringá, Universidade de Maringá, 241p.: 168, color photograph of live individual (Brazil, upper rio Paraná, species lists - presumed to be an introduced species, see 'Remarks', below).

Brachyhypopomus sp. -Giora et al., 2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.: 167 (Brazil, Rio Grande do Sul, listed in comparative material for description of B. draco).

Brachyhypopomus gauderioGiora & Malabarba, 2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.: 62, fig. 1, color photograph of male holotype (original description, type locality - Brazil, Rio Grande do Sul, Palmares do Sul, Patos-Mirim dr.). -Almirón et al., 2010Almirón, A., J. Casciotta, L. Ciotek, P. Giorgis, P. Soneira & F. Ruíz Díaz. 2010. Pisces, Gymnotiformes, Hypopomidae, Brachyhypopomus Mago-Leccia, 1994: First country record of three species of the genus, Argentina. Check List: Journal of Species Lists and Distribution, 6: 572-575.: 573, fig. 7, color photograph (Argentina, Entre Rios, Pre-Delta Matinal Park, Paraná dr., listing of Brachyhypopomus). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Koerber, 2011Koerber, S. 2011. List of Freshwater Fishes from Argentina - Update 14. Ichthyological Contributions of Peces Criollos, 26: 1-11.: 7 (Argentina, species list, phylogeny, geographical and ecological distributions, gymnotiform biology). -Malabarba et al., 2013Malabarba, L. R., P. C. Neto, V. A. Bertaco, T. P. Carvalho, J. F. dos Santos & L. G. S. Artioli. 2013. Guia de identificação dos peixes da bacia do rio Tramandaí. Porto Alegre, Editora Via Sapiens, 140 pp.: 97, color photograph of live individual (Brazil, Rio Grande do Sul, rio Tramandaí, catalog of fishes). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 168, fig. 25a, color photograph of head; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Mirande & Koerber, 2015Mirande, J. M. & S. Koerber. 2015. Checklist of the freshwater fishes of Argentina (CLOFFAR). Ichthyological Contributions of Peces Criollos, 36: 1-68.: 48 (Argentina, catalog of fishes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Brachyhypopomus bombilla. -Azpelicueta & Koerber: 2015Azpelicueta, M. & S. Koerber. 2015. On some freshwater fish species reported by Perugia (1891) from Argentina. Aqua - Journal of Ichthyology and Aquatic Biology, 21: 39-46., 40-42, fig. 3, color photograph of two specimens, MSNG 27458 (discussion of fish specimens listed in Perugia, 1891Perugia, A. 1891. Appunti sopra alcuni pesci sud-americani conservati nel Museo Civico di Storia Naturale di Genova. Annali del Museo Civico di Storia Naturale di Genova (Serie 2), 10: 605-657.).

Table 14
Morphometrics for Brachyhypopomus gauderio. HT, holotype; SD, standard deviation. Data for holotype (Rio Grande do Sul, Brazil) are from Giora & Malabarba (2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.). Range for the type region refers to non-type specimens from the lagoa dos Patos and Uruguay drainages in Brazil and Uruguay (holotype data excluded). Specimens from the Paraguay drainage refer to non-type specimens from the río Paraguay of Paraguay.

Diagnosis. Brachyhypopomus gauderio is diagnosed from congeners by the following combination of characters: prominent pale stripe along middorsal region of present, vs. absent in all congeners except B. arrayae, B. beebei, B. belindae, B. pinnicaudatus, and B. verdii; longest anal-fin ray 3.9-5.4% LEA, vs. 1.6-3.9% in B. beebei; precaudal vertebrae 18-21, vs. 24-26 in B. belindae and B. verdii. Brachyhypopomus gauderio exhibits similar pigmentation and overlapping meristic counts and morphometric proportions with some populations of B. arrayae and B. pinnicaudatus. Brachyhypopomus gauderio can be distinguished from B. arrayae by the absence of a contact between a small ascending process on the endopterygoid and the orbitosphenoid vs. a contact between these two bones in B. arrayae (see diagnosis for B. arrayae for details). Brachyhypopomus gauderio can be distinguished from B. pinnicaudatus by the absence of a medial bridge on the posterior portion of the basihyal (de Santana & Vari, 2010de Santana, C. D. & R. P. Vari. 2010. Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies. Zoological Journal of the Linnean Society, 159: 223-371.: 250. fig. 15; Fernandes et al., 2014Fernandes, C. C., A. Nogueira & J. A. Alves-Gomes. 2014. Procerusternarchus pixuna, a new genus and species of electric knifefish (Gymnotiformes: Hypopomidae, Microsternarchini) from the Negro River, South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 163: 95-118.: 104, fig. 7), vs. presence in B. pinnicaudatus.

Description. Head and body shape, and pigmentation illustrated in Fig. 26 and in original description. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 14. Body moderate to broad in depth. Head short to moderate in length and moderate to broad in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye small to moderate in size. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 35-45 (median 40, n = 6). Pectoral fin moderate in width, pectoral-fin rays 12-17; range and mode higher in populations from Patos-Mirim lagoon system and Uruguay drainage (14-17, mode 15) than from Paraguay drainage (12-15, mode 13). Precaudal vertebrae 18-21; range and mode slightly higher in populations from Lagoa dos Patos and Uruguay drainages (20-21, mode 21) than from Paraguay drainage (18-21, mode 20); transitional vertebrae 1-2 (mode 2) in populations from Lagoa dos Patos and Uruguay drainages and 2-3 (mode 2) in populations from the Paraguay drainage. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 180-216; ranges and median values very similar in populations from Lagoa dos Patos and Uruguay drainages (187-206, median 200 in examined specimens) and from Paraguay drainage (183-211, median 201). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 4-7 (mode 5). Lateral line continuous. Epidermal canals not conspicuous, but present in form of single bifurcating and sometimes branched horizontal depigmented groove, with darkened margins, on either side of dorsal surface in dorsal portions of flank, beginning approximately two head lengths posterior to occiput and extending to approximately two head lengths anterior to anal-fin terminus. Epidermal canals also variably present in posterior half of body as very sparse single or sometimes parallel double depigmented grooves either side of, but mostly dorsal to, lateral line. Three bilateral horizontal columns at anal-fin terminus, and three or sometimes three alternating with four at or near a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Some regenerated specimens exhibit four columns of electrocytes in regenerated portions of caudal filament. Caudal filament short to moderate in length.

Coloration. (Fig. 26). Background pale tan to dark brown. Pigmentation highly variable. Dorsal region with prominent depigmented or lightly pigmented stripe extending along midline from occipital region to base of caudal filament, or deep into caudal filament, bordered by prominent dark horizontal wavy reticulated lines from which short irregular patches extend ventrally. Dorsal pigmentation pattern strongly resembles that of B. pinnicaudatus, but pale depigmented stripe is not as conspicuous (and in some specimens the depigmented stripe is obscured). Irregular small dark patches or horizontally elongated spots often extend along lateral line. Ventral flank with irregular broken vertical bands and vertically elongated spots, especially over anal-fin pterygiophores. Caudal filament darker than body, with irregular dark markings or bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays with light scattering of brown chromatophores. Anal-fin rays with light or dark patches of chromatophores, with overall anal-fin pigmentation varying greatly, from almost unpigmented to dark mottled pattern. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 26
Brachyhypopomus gauderio. a. MZUSP 59646, female, 138 mm TL (head in lateral view, body in lateral and dorsal view); Brazil, rio Miranda, Paraguay dr. b. NRM 35349, male, 171 mm TL (body in lateral view); Paraguay, río Negro, Paraguay dr. Note sexual dimorphism in caudal filament height. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 200 mm (n = 754). Largest male specimen examined 181 mm TL, 139 mm LEA (n = 25). Largest female specimen examined 172 mm TL, 137 mm LEA (n = 37). Maximum male size in type series 149.0 mm LEA vs. 133.3 mm LEA for females (Giora & Malabarba, 2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.).

Sexual dimorphism. Sexually mature males attain slightly larger sizes, and develop longer and deeper caudal filaments than immature individuals and breeding females (Figs. 26a-b), but do not exhibit an elevated number of bilateral horizontal columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Tip of caudal filament in large breeding males usually with paddle-like compression, sometimes free of electrocytes in tip. No known sexual dimorphism in pigmentation.

Geographic distribution. Argentina, Bolivia, Brazil, Paraguay, and Uruguay (Fig. 27). Widely distributed through Patos-Mirim lagoon system, some coastal drainages of Rio Grande do Sul north of Lagoa dos Patos, Uruguay drainage, Paraná downstream of the former Guaíra Falls, and lower to upper Paraguay to as far north as 14°45'S.

Fig. 27
Collection records for Brachyhypopomus gauderio (circles) and B. menezesi (squares). Holotype locations are marked with open symbols. Grey circles refer to suspected anthropogenic introductions of B. gauderio to upper Paraná dr. (see species redescription in text). Elevation data refers to altitude above mean sea level (see Fig. 2 for legend). Note that the most southerly record for B. menezesi is in a headwater of the rio São Francisco, near the drainage divide with rio Paraná headwaters.

Population variation: The osteological diagnostic characters listed in the differential diagnoses that distinguish B. gauderio from B. pinnicaudatus were observed in cleared and stained specimens of B. gauderio from both the Uruguay and Paraná drainages. We also found complete overlap in the range of meristics (Tables 2-5) and morphometric proportions (Table 14), and observed similar pigmentation among populations of B. gauderio from the Patos-Mirim lagoon system, Uruguay drainage, and Paraguay drainage. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. gauderio are members of a single geographically widespread species, which is morphologically and genetically distinct from its allopatric sister species B. pinnicaudatus, known from the Amazon basin and coastal drainages of French Guiana, and from all other congeners.

Ecological notes. Brachyhypopomus gauderio inhabits vegetated river banks, slow-moving creeks, swamps, lagoons, and flooded areas, often with low dissolved oxygen concentrations (< 0.5 mgl-1) (Giora & Malabarba, 2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.). It is typically the most locally abundant congener throughout its range, and is often one of the most common fishes in aquatic vegetation. Brachyhypopomus gauderio is typically found in systems with relatively high electrical conductivity (50-250 μScm-1) and pH values ranging from 6.5 to 8.5, but is also found in higher conductivity systems (250-750 μScm-1), and less commonly in lower conductivity systems (<50 μScm-1) (Silva et al., 2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.: 333, fig.2). Silva et al. (2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.) report large seasonal variations in temperature, conductivity, and pH from collecting sites in Uruguay. Populations from high latitudes are exposed to a colder, drier austral winter and most foraging and breeding occurs during the warmer summer months (Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.). Respiratory adaptations associated with hypoxia tolerance are discussed by Carter & Beadle (1931Carter, G. S. & L. C. Beadle. 1931. The fauna of the swamps of the Paraguayan Chaco in relation to its environment. II. Respiratory adaptations in the fishes. Journal of the Linnean Society of London, Zoology, 37: 327-366.).

Reproductive seasonality, life history, and ecology in B. gauderio are documented by several authors (Gavassa et al., 2012Gavassa, S., A. C. Silva, E. Gonzalez, J. Molina & P. K. Stoddard. 2012. Social competition masculinizes the communication signals of female electric fish. Behavioral Ecology and Sociobiology, 66: 1057-1066.; Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.; Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.; Quintana et al., 2004Quintana, L., A. Silva, N. Berois & O. Macadar. 2004. Temperature induces gonadal maturation and affects electrophysiological sexual maturity indicators in Brachyhypopomus pinnicaudatus from a temperate climate. Journal of Experimental Biology, 207: 1843-1853.; Silva et al., 2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.). It breeds during the austral summer, with maturation probably triggered by rising temperature and a change in photoperiod. During the breeding season it lives in dense social groups, and exhibits a sex ratio of mature individuals highly skewed towards females (around 3:1, despite observations of a primary sex ratio close to unity in a long-term laboratory population), possibly due to elevated male mortality related to stress from intrasexual competition (Gavassa et al., 2012Gavassa, S., A. C. Silva, E. Gonzalez, J. Molina & P. K. Stoddard. 2012. Social competition masculinizes the communication signals of female electric fish. Behavioral Ecology and Sociobiology, 66: 1057-1066.; Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.). Males exhibit a wider spacing, and move less than females - consistent with a polygynous or polygynandrous mating strategy resembling exploded lek polygyny (Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.). During the austral winter B. gauderio exhibits gonadal quiescence, reduced activity and feeding, and a slower EOD rate (Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.; Silva et al., 2002Silva, A., L. Quintana, J. L. Ardanaz & O. Macadar. 2002. Environmental and hormonal influences upon EOD waveform in gymnotiform pulse fish. Journal of Physiology -Paris, 96: 473-484.; Silva et al., 2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.). Sullivan (1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.) cites a personal communication from D. Stewart (State University of New York, Syracuse) reporting that five specimens from FMNH lot 86684 from the Pantanal of Mato Grosso, Brazil (listed below) were "found aestivating in dry soil".

The spawning behavior of B. gauderio has been observed from infra-red video recordings in aquaria (pers. comm., P. Stoddard). Females usually spawn in the presence of one or more males, which fertilize the eggs as they leave the ovipositor. This species also deposits individual fertilized eggs in water hyacinth leaf bracts above the surface. Here trapped pools of rain water presumably form a favorable, predator-free environment for the larva. Parental care of eggs or larvae is unknown in both males and females (Miranda et al., 2008Miranda, M., A. C. Silva & P. K. Stoddard. 2008. Use of space as an indicator of social behavior and breeding systems in the gymnotiform electric fish Brachyhypopomus pinnicaudatus. Environmental Biology of Fishes, 83: 379-389.), although see Giora et al. (2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.). As in B. occidentalis, adult size classes of B. gauderio more or less disappear subsequent to the breeding season, a pattern consistent with an annual life cycle (Silva et al., 2003Silva, A., L. Quintana, M. Galeano & P. Errandonea. 2003. Biogeography and breeding in Gymnotiformes from Uruguay. Environmental Biology of Fishes, 66: 329-338.).

The diet of B. gauderio is dominated by small aquatic insect larvae and microcrustacea, with some (likely incidental) consumption of vegetable matter (Giora et al., 2014Giora, J., H. M. Tarasconi & C. B. Fialho. 2014. Reproduction and feeding of the electric fish Brachyhypopomus gauderio (Gymnotiformes: Hypopomidae) and the discussion of a life history pattern for gymnotiforms from high latitudes. PLoS One, 9 (e106515): 1-11.).

Co-occurring congeners: Through most of its range, B. gauderio occurs in geographical sympatry and in ecological syntopy with B. bombilla and B. gauderio. Brachyhypopomus gauderio also co-occurs with B. brevirostris and B. walteri in the upper río Paraguay.

Local names. Argentina, Paraguay: morenita; Bolivia: cuchillo; Brazil: tuvira, moreninha, tuvira-de-sela (Malabarba et al., 2013Malabarba, L. R., P. C. Neto, V. A. Bertaco, T. P. Carvalho, J. F. dos Santos & L. G. S. Artioli. 2013. Guia de identificação dos peixes da bacia do rio Tramandaí. Porto Alegre, Editora Via Sapiens, 140 pp.) (south), sarapó (north); Uruguay: morenita, limpiavidrio.

Remarks: Identity of the neurobiology model species: B. gauderio is a model species for studies of the electrosensory system, and is the subject of multiple papers on neurobiology, neuroethology, EOD plasticity, and ecology - many of which stem from research at the laboratories of Angel Caputi, Omar Macadar, and Ana Silva (Instituto de Investigaciones Biológicas Clemente Estable, Uruguay), Carl Hopkins (Cornell University), Michael Markham (University of Oklahoma), and Philip Stoddard (Florida International University) (see Introduction). Laboratory studies of B. gauderio at the Hopkins and Stoddard labs have been based on captive populations that derive from Uruguayan stock (pers. comm., P. Stoddard). We confirmed from cleared and stained specimens that populations from the Stoddard Lab exhibit the osteological characters diagnostic of B. gauderio. Multiple studies prior to ca. 2010 refer to B. gauderio as B. pinnicaudatus (or Hypopomus pinnicaudatus). Prior to Giora & Malabarba's (2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.) description of B. gauderio, which we confirm here as a valid species, B. pinnicaudatus was thought to constitute a single species distributed through much of northern and southern South America.

Invasive populations: We examined three MZUSP lots of B. gauderio collected at sites in the upper Paraná drainage, well upstream of the former Guaíra Falls (drowned by the Itaipu hydroelectric dam since 1982), and also upstream of additional hydroelectric dams (see 'Suspected introduced records' in Material examined). These were collected in 1995 and 2003. Graça & Pavanelli (2007Graça, W. J. & C. S. Pavanelli. 2007. Peixes da planície de inundação do alto rio Paraná e áreas adjacentes. Maringá, Universidade de Maringá, 241p.) and Meschiatti & Arcifa (2009Meschiatti, A. J. & M. S. Arcifa. 2009. A review on the fishfauna of Mogi-Guaçu River basin: a century of studies. Acta Limnologica Brasileira, 21: 135-159.) list B. gauderio (therein listed as B. pinnicaudatus) as an introduced species in the upper Paraná. Citing R. Campos-da-Paz of the Universidade Federal do Rio de Janeiro by personal communication, Graça & Pavanelli (Graça & Pavanelli, 2007Graça, W. J. & C. S. Pavanelli. 2007. Peixes da planície de inundação do alto rio Paraná e áreas adjacentes. Maringá, Universidade de Maringá, 241p.) suggest that B. gauderio was likely introduced by sport fishermen, who use the species as live bait. They also report that B. gauderio is now common in various floodplain lakes in the upper Paraná basin. The sale of live B. pinnicaudatus and species of Gymnotus for sport fishing is very common throughout southern Brazil (pers. comm., F. C. T. Lima, ZUEC), and is also common in the lower Paraguay basin (WGRC pers. obs. from Entre Ríos, Argentina) and upper rio Xingu (pers. comm., R. E. Reis, MCP). Galves et al. (2009Galves, W., O. A. Shibatta & F. C. Jerep. 2009. Estudos sobre diversidade de peixes da bacia do alto rio Paraná: uma revisão histórica. Semina: Ciências Biológicas e da Saúde, Londrina, 30: 141-154.), and Meschiatti & Arcifa (2009Meschiatti, A. J. & M. S. Arcifa. 2009. A review on the fishfauna of Mogi-Guaçu River basin: a century of studies. Acta Limnologica Brasileira, 21: 135-159.) comment on the prevalence of introduced fish species in the upper Paraná. We illustrate the occurrence of these introductions in Fig. 27 (with grey circles) but omit them from the range of the genus presented in Fig. 2.

Material examined. 753 specimens. Argentina (localities from Paraná dr.). Chaco. MSNG 27458, 2, 98-102 mm LEA, Resistencia, Paraná dr., ca. 27°27'S, 058°59'W (from photograph). Corrientes. MACN-ict 9459, 9, 109-134 mm, Iberá wetlands, Laguna Galarza, Paraná dr., 28°04'56"S, 056°42'04"W. Entre Ríos. MACN-ict 9460, 1, 92 mm, Pre-Delta National Park, Arroyo Los Dorados, río Paraná floodplain, Paraná dr. 32°08'08"S, 060°37'26"W. UF 177364, 5 (1CS), 135-175 mm, nr. La Paz, río Paraná floodplain, Paraná dr., ca. 30°42'S, 059°39'W. Bolivia. Santa Cruz. FMNH 54542, 1, 77 mm, Puerto Suárez, río Paraguay, Paraná dr., ca. 18°55'S, 057°47'W. Brazil. Mato Grosso (localities from rio Paraguai [Paraguay] dr., Paraná dr.). AMNH 97895, 2, 55-117 mm, rio Pixaim [Pixaime], ca. 16°44'S, 056°51'W. BMNH 1895.5.17.265-268 (part), 1, 64 mm, mun. Cácares, Descalvados, 16°43'59"S, 057°44'54"W. BMNH 1900.4.14.91-94 (part), 2, 75-79 mm, mun. Carandàzinho, rio Cuiabá, ca. 16°27'S, 056°08'W. CAS 72225, 1, 82 mm, "Mato Grosso, Brazil or Asunción, Paraguay [or río Paraguay], no coordinates. FMNH 86684, 5, 79-127 mm, Porto Cercado, side of Poconé-Porto Cercado rd., rio Cuiabá, affl. rio Piquiri, 16°30'S, 056°22'W. FMNH 108541, 12, 55-100 mm, mun. Corumbá, on hwy. MS-184, swamp, lower rio Negro, 19°20'17"S, 056°57'42"W. FMNH 120674, 1, 115 mm, mun. Cáceres, nr. Cáceres, ca. 16°05'S, 057°41'W. MZUSP 4460, 1, 45 mm, mun. Santo Antônio de Leverger, lake nr. Santo Antônio de Leverger, rio Cuiabá, ca. 15°51'S, 056°04'W. MZUSP 19224, 1, Poconé, rio Cuiabá, ca. 16°15'S, 056°37'W. MZUSP 25149, 2, 67-70 mm, mun. Cáceres, Ilha da Taiamã [Estação Ecológica Taiamã], 16°53'S, 057°27'W [coordinates from center of island]. MZUSP 35910, 1, 67 mm, mun. Itiquira, Fazenda Santo Antônio do Paraíso, lakes between rio Piquiri and rio Itiquiri, ca. 17°12'S, 054°09'W. MZUSP 77202, 5, 25-134 mm, Nobres Paraguai, Represa da Fazenda Pé de Serra, rio Cuiabá, 14°45'S, 056°40'W. MZUSP 83562, 3, immature, 55-67 mm, MZUSP 83603, 1, 124 mm, temporary lake, rio Itiquira/Piquiri, 17°28'13"S, 055°14'46"W. MZUSP 83607 (part), 3, immature, 50-76 mm, mun. Coxim, Paraguai Lagoa, source of Ribeirao dos Veados, affl. rio Coxim (rio Taquari), 18°25'21"S, 054°50'06"W. MZUSP 96652, 2, 66-67 mm, Pantanal de Paiaguás, swamp 1 km Vila de Mimoso, 16°17'S, 055°48'W. MZUSP 96703, 2, immature, 63-69 mm, mun. Barão de Melgaço, Pantanal de Paiaguás, rio Mutum, between Vila de Mimoso and Joselândia, 16°19'30"S, 055°49'59"W. ZUEC 3697, 2, 86-101 mm, ZUEC 5146, 3, 74-106 mm, ZUEC 5726, 15, 80-115 mm, mun. Poconé, Porto Cercado, rio Cuiabá, 16°31'S, 056°23'W. ZUEC 4473, 2, 42-49 mm, mun. Poconé, Transpantaneira hwy, km 24, rio Claro, 16°33'S, 056°42'W. ZUEC 5466, 1, 74 mm, mun. Poconé, rio Piraputanga, affl. rio Vermelho, affl. rio Cuiabá, ca. 16°20'S, 053°56'W. Mato Grosso do Sul. MUSM 17129, 2 (1 immature, 80 mm, 1 female, 101 mm), rio Negro on rd. between "NHE Colandia and Brazcs", 19°12'09"S, 055°03'23"W [longitude reported incorrectly on label as 052°03'23"W]. MZUSP 36386, 5, 36-98 mm, mun. Corumbá, Fazenda Nhumirim, Nhecolândia, 19°15'S, 057°02'W. MZUSP 59442 (part), 10 (4 immature, 67-92 mm, 6 female, 62-113 mm), rio Vermelho, rio Miranda, 19°37'22"S, 056°57'27"W. MZUSP 59646, 29 (1CS), 45-172 mm (14 sexed: 2 immature, 67-81 mm, 5 female, 108-172 mm, 7 male, 96-168 mm), Baía da Passagem, at Fazenda Caceres, Nhecolândia, 19°08'17"S, 056°49'14"W. Rio Grande do Sul. FMNH 54538, 1, 101 mm, Cacequy [Cacequi], rio Ibicuí, Uruguay dr., ca. 29°53'S, 054°49'W. FMNH 54546, 1, male, 180 mm, Uruguiana, rio Uruguai, Uruguay dr., ca. 29°45'S, 057°05'W. MCP 9710, 1, male, 164 mm, mouth of the arroio da Faxina, affl. rio Guaíba, Patos-Mirim dr., no coordinates. MCP 11135, 1, male, 144 mm, mun. Santo Angelo, Fazenda dos Hinz, rio Piratini, Uruguay dr., ca. 28°42'S, 054°25'W. MCP 13956, 2, 83-94 mm, hwy. BR-290, ca. 10 km BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°03'13"S, 051°26'17"W. MCP 14177, 1, 168 mm, channel, hwy. BR-290, ca. 12 km BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°03'19"S, 051°27'17"W. MCP 14459, 2 (1 female, 138 mm, 1 male, 140 mm), BR-290, channel, ca. 2 km BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'39"S, 051°21'20"W. MCP 14606, 5 (1 CS) (2 female, 139-147 mm, 3 male, 128-156 mm), channel, hwy. BR-290, ca. 2 km BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'46"S, 051°21'07"W. MCP 14775, 2, male, 142-178 mm, mun. Uruguaiana, Sanga Bárbara, Uruguaiana, affl. rio Uruguai, Uruguay dr., 29°48'00"S, 057°06'00"W. MCP 15326 (part), 2, 101-114, canals along hwy. BR-290 between 1 and 6 km junction with hwy. BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., between 30°02'39"S, 051°21'20"W and 30°02'48"S, 051°23'27"W. MCP 19547, 2, 140-200 mm, bridge on São Gabriel-Tiaraju hwy., affl. rio Vacacaí, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°17'29"S, 054°20'18"W. MCP 19549, 6, 48-156 mm, MCP 19553, 2, 35-60 mm, bridge over Banhado do Inhatium, hwy. BR-290, 21 km São Gabriel, affl. rio Ibicuí, Uruguay dr., 30°15'43"S, 054°31'33"W. MCP 20216, 3, 70-100 mm, mun. Eldorado do Sul, on hwy. BR-290, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'36"S, 051°20'56"W. MCP 20218, 3, 109-157 mm, arroio Passos dos Carros, on rd. linking hwy. BR-116 to Guaíba, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°05'55"S, 051°23'15"W. MCP 21168, 1, female, 104 mm, MCP 21169, 1, 115 mm, channel on margin hwy. BR-290, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., 30°02'36"S, 051°20'56"W. MCP 21726, 5, 87-134 mm, mun. Eldorado do Sul, channel on margin hwy. BR-290 ca. 5 km junction with BR-116, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., ca. 30°03'S, 051°24'W. MCP 37086, 1, 100 mm, mun. Cerro Largo, arroio Brum Lageado, affl. rio Ijuí, Uruguay dr., 28°12'50"S, 054°49'36"W. MCP 37580, 1, 131 mm, mun. Pelotas, nr. bridge to Pelotas, rio São Gonçalo, Patos-Mirim dr., 31°46'19"S, 52°20'33"W. MCP 43280, 1 (holotype), male, 180 mm TL, 149 mm LEA, mun. Palmares do Sul, channel connecting Lagoa do Casamento and Lagoa dos Gateados, Patos-Mirim dr., ca. 30°28'S, 050°40'W. MCP 43281, 1 (paratype), female, 124 mm LEA, MCP 43282, 1 (paratype), female, 133 mm LEA, mun. Viamão, Lagoa Negra, Parque Estadual de Itapuã, Patos-Mirim dr. MCP 43283, 2 (paratypes) (1 female, 83 mm LEA, 1 male, 92 mm LEA), mun. Capão da Canoa, Lagoa dos Quadros, rio Tramandaí dr., ca. 29°42'S, 050°06'W. MNRJ 30915, 2 (paratypes) (1 female, 85 mm LEA, 1 male, 70 mm LEA), UFRGS 8874, 1, 154 mm, mun. Cidreira, Lagoa Fortaleza, rio Tramandaí dr., 30°08'58"S, 050°14'30"W. MNRJ 32792, 5 (paratypes) (2 female, 75-78 mm LEA, 3 male, 74-97 mm LEA), UFRGS 4240, 10, 42-134 mm, mun. Barra do Ribeiro, lake on hwy. linking BR-116 to Barra do Ribeiro, Patos Mirim dr., ca. 30°17'S, 051°21'W. MNRJ 32793, 1 (paratype) male, 136 mm LEA, MCP 43284, 1 (paratype) male, 123 mm LEA, MZUSP 100309, 15 (paratypes) (7 female, 78-127 mm, 8 male, 60-127 mm), UFRGS 6499, 1 (paratype), male, 123 mm, UFRGS 6500, 1, female, 123 mm, UFGRS 6501, 1, female, 125 mm, UFRGS 6502, 1, female, 162 mm, UFRGS 6503, 1, (paratype), male, 103 mm, UFRGS 6504, 1, male, 152 mm, UFGRS 6505, 1, male, 178 mm, UFRGS 6506, 1, male, 185 mm, UFRGS 6512, 1, female, 131 mm, mun. São Gabriel, stream, affl. arroio Piraí, on margin hwy. BR-290, affl. rio Cacequí, affl. rio Santa Maria, affl. rio Ibicuí, Uruguay dr., 30°18'57"S, 054°24'23"W. MZUSP 100308, 1 male (paratype), 140 mm LEA, UFRGS 9581, 2 (paratypes) (1 female, 126 mm LEA, 1 male, 129 mm LEA), UFRGS 10032, 1 (paratype), female, 102 mm LEA, UFRGS 10035, 1 (paratype), female, 106 mm LEA, UFRGS 10042, 1 (paratype), male (CS), 120 mm LEA, UFRGS 10048, 1 (paratype), male (CS), 118 mm LEA, mun. Charqueadas, flooded area nr. Arroio dos Ratos, rio Jacuí, Patos-Mirim dr., 29°57'32"S, 051°33'10"W. MZUSP 23167, 1, 52 mm, km 124, Camaquá-Pelotas hwy. BR-116, Patos-Mirim dr., ca. 31°45'S, 052°20'W. MZUSP 23169, 1, 43 mm, Porto Alegre, rio Jacuí, Patos-Mirim dr., ca. 30°02'S, 051°13'W. MZUSP 23630, 3 (1 immature, 87 mm, 1 female, 127 mm, 1 male, 118 mm), São Leopoldo, Banhado Schreck, affl. rio dos Sinos, affl. rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., ca. 29°45'S, 051°09'W. MZUSP 25165 (part), 3, 97-132 mm, Camaquã, rio Jacuí, affl. rio Guaíba, Patos-Mirim dr., ca. 30°50'S, 051°49'W. NRM 27641, 2, 75-103 mm, stream, affl. Lagoa dos Quadros, nr. Praia do Barco, rio Tramandaí dr., ca. 29°42'S, 050°05'W. UFRGS 187, 1, 97 mm, UFRGS 719, 2, 137-141 mm, mun. Guaíba, Praia de Sans-Souci, rio Guaíba, Patos-Mirim dr., 30°03'05"S, 051°18'35"W. UFRGS 733, 1, 53 mm, mun. Guaíba, stream on hwy. BR-290, 2 km junction with BR-116, affl. rio Guaíba, Patos-Mirim dr., 30°03'00"S, 051°20'59"W. UFRGS 2219, 2 (paratypes), 100-152 mm, mun. Santo Antônio da Patrulha, creek between BR-290 and Santo Antônio da Patrulha, Patos-Mirim dr., ca. 29°52'S, 050°35'W. UFRGS 5641, 3 (paratypes), 101-158 mm, mun. Viamão, Lagoa do Palácio, Patos-Mirim dr., 30°24'10"S, 050°57'25"W. UFRGS 3845, 1, 84 mm, mun. Palmares do Sul, Lagoa dos Barros, 1st canal, hwy. to Capivarí, Patos-Mirim dr., ca. 29°53'S, 050°18'W. UFRGS 3895, 2, 78-86 mm, mun. Guaíba, mun. Barra do Ribeiro, arroio Ribeirinho, affl. rio Guaíba, Patos-Mirim dr., 30°21'00"S, 051°24'59"W. UFRGS 4003, 3, 51-72 mm, mun. Cidreira, Lagoa do Lessa, at bridge, rio Tramandaí dr., 29°50'00"S, 050°10'00"W. UFRGS 4061, 2, 26-85 mm, 2nd canal to Lagoa dos Índios, km 10, rio Tramandaí dr., ca. 29°59'S, 050°17'W. UFRGS 5015, 1, 132mm, mun. Arambaré, Patos-Mirim dr., no coordinates. UFRGS 6516, 1, female, 132 mm, UFRGS 6517, 1, female, 143 mm, UFRGS 6518, 1, female, 151 mm, UFRGS 6519, 1, female, 136 mm, UFRGS 6520, 1, female, 144 mm, UFRGS 6524, 1 (paratype) male, 160 mm, UFRGS 10036, 1 (paratype), male (CS), 133 mm LEA, mun. Viamão, Lagoa Negra, Parque Estadual de Itapuã, Patos-Mirim dr., 30°22'52"S, 051°01'25"W. UFRGS 6765, 1, 141 mm, UFRGS 6768, 1, 149 mm, mun. Uruguiana, stream, affl. Uruguay dr., 29°45'56"S, 057°02'01"W. UFRGS 8933, 1 (paratype), female, 102 mm LEA, arroio do Sal, creek on Estrada do Mar rd., rio Tramandaí dr., 29°30'33"S, 049°53'34"W. UFRGS 14563, 1, 88 mm, mun. Maquiné, mouth of rio Maquiné, Lagoa dos Quadros, rio Tramandaí dr., 29°43'38"S, 050°08'36"W.UFRGS 14963, 6, 92-135 mm, mun. Tramandaí, Lagoa do Passo, rio Tramandaí dr., 29°52'01"S, 050°06'00"W. USNM 191645, 1, 77 mm, Porto Alegre, rio Guaíba, Patos-Mirim dr., ca. 30°02'S, 051°07'W. Paraguay (localities from Paraná dr.). Alto Paraguay (localities from río Paraguay dr.). FMNH 108059, 3, 93-130 mm, lagoon nr. Estância Cerrito, 21°27'S, 057°55'W. FMNH 108060, 1, 140 mm, flooded palm forest, riacho Coeyú, affl. río Paraguayin, ca. 21°26'S, 057°58'W. FMNH 117751, 1, 59 mm, río Negro, at confl. with río Paraguay, ca. 20°09'S, 058°10'W. MZUSP 54332, 1, female, 104 mm, Puerto 14 de Maio, ca. 20°18'S, 058°06'W. Boquerón (localities from río Paraguay dr.). ANSP 185115, 1, 132 mm, pond, N side TransChaco hwy. at km 464.1, ca. 22°15'S, 060°30'W. ANSP 185116, 5, 84-134 mm, marsh at Mariscal Estigarribia, ca. 22°00'S, 060°37'W. NRM 35483, 1, 181 mm, Estancia Água de Sidia, ca. km 100 on Filadelfia-Madrejon hwy. (5.2 km off rd.), ca. 21°27'S, 059°53'W. Caaguazú. NRM 42920, 1, 47 mm, stream crossing Colonia Sommerfeld-Repatriación rd., affl. río Paraguay, 25°36'02"S, 055°47'11"W. Central (localities from río Paraguay dr.). AMNH 1009, 1, CAS 72215, 2, 143-152 mm, Campo Grande, lagoons 5 km Asunción, ca. 25°19'S, 057°31'W. MZUSP 77990, 1, 34 mm, Balneário Joly, Zona de Pirayú, ca. 25°29'S, 057°14'W. NRM 42400, 1, 123 mm, swamp nr. lago Ypacaraí, N Areguá, 25°16'16"S, 057°23'51"W. UMMZ 205591, 2, 102-103 mm, ca. 1 km S Puente Remanso, E shore río Paraguay, 25°12'30"S, 057°33'00"W. UMMZ 205874, 11, 41-125 mm, ca. 1 km S Puente Remanso, flooded pasture at margin río Paraguay, 25°12'30"S, 057°33'00"W. UMMZ 205912, 5, 27-78 mm, Arroyo Pirayú, 13 km W Caacupe, affl. lago Yparcaraí, río Salado, 25°23'12"S, 057°14'42"W. UMMZ 206001, 4 (part), 97-144 mm, río Salado (nr. mouth) at bridges 5.4-5.85 km N Limpio, ca. 25°08'S, 057°25'W. Concepción (localities from río Paraguay dr.). NRM 43362, 1, 90 mm, NRM 44254, 3, 19-31 mm, NRM 44259, 23, 30-140 mm, Isla Peña Hermosa, río Paraguay, S mouth riacho La Paz, 22°24'09"S, 057°51'13"W. UMMZ 207817, 1, 126 mm, Paso Horqueta, río Aquidabán, 23°03'48"S, 057°23'24"W. ZMH 11631, 1, 113 mm, Puerto Max, Arroyo Postillón, ca. 22°41'S, 057°44'W. Misiones. ANSP 175178, 3, 110-149 mm, pool (rd. to Ayolas?), affl. río Paraná, 27°19'40"S, 056°43'54"W. ANSP 185118, 2, 32-79 mm, marshes on rd. from Ayolas to main Asunción-Encarnación hwy. (Ruta 1), 200 m S km 18/A276, affl. río Paraná, ca. 27°23'S, 056°47'W. UMMZ 207463, 1, 151 mm, río Paraná ca. 2 km E Ayolas, río Paraná, 27°24'00"S, 056°46'12"W. Ñeembucú (localities from río Paraguay dr.). NRM 32801, 1, 48 mm, NRM 32829, 9, 53-102 mm, NRM 32852, 1, 42 mm, Paso Cornelio, swamp, Pilar-Humaitá rd., nr. Humaitá, 27°03'09"S, 058°25'39"W. NRM 32870, 1, 103 mm, km 17 on Pilar-Humaitá rd., 26°58'44"S, 058°18'00"W. Presidente Hayes (localities from río Paraguay dr.). AMNH 99960, 50, 51-130 mm, AMNH 99977, 1, 154 mm, Estancia la Golondrina, 140 km NW Asunción, marshlands affl. río Confuso, ca. 24°36'S, 058°07'W. ANSP 170413, 3, 85-96 mm, pool, km 15, Ruta General Bruguez, ca. 24°45'S, 058'49'W [coordinates for Fortín General Bruguez]. ANSP 185114, 1, 63 mm, pools on Rancho Salmo 23, ca. 8 km towards Clorinda from Puente Remanso, affl. río Negro, ca. 25°11'S, 057'34'W. ANSP 185117, 1, 129 mm, pools nr. Puente Remanso, ca. 25°10'S, 057°33'W. FMNH 54540, 2, 66-125 mm, Villa Hayes, ca. 25°05'S, 057°31'W. NRM 22601, 1, 32 mm, military post at General Bruguez, río Pilcomayo, 24°44'33"S, 058°50'07"W. NRM 27919, 1, 140 mm, NRM 32525, 4, 61-135 mm, infantry regiment Pedro Juan Caballero, río Pilcomayo, 24°38'56"S, 058°48'18"W. NRM 32524, 10, 81-105 mm, General Bruguez, ca. 1 km N military camp, río Pilcomayo, 24°43'38"S, 058°49'10"W. NRM 32526, 11, 57-156 mm, military post at general Bruguez, río Pilcomayo, 24°44'43"S, 058°50'10"W. NRM 32528, 6, 69-104 mm, Estancia la Rural, pool nr. río Confuso, 24°50'47"S, 057°46'44"W. NRM 35257, 39, 92-144 mm, Tajamar, km 78, trans-Chaco rd., 24°48'32"S, 057°46'57"W. NRM 35349, 101, 21-172 mm (1 sexed: 1 male, 172 mm), Estero Guazú at Estancia Loma Verde, ca. 10 km Concepción-Pozo Colorado rd., 23°34'53"S, 058°01'53"W. NRM 35447, 5, 26-117 mm, NRM 35830, 8, 38-106 mm, N branch riacho Negro at Makthlawayia, 23°15'58"S, 057°37'42"W. NRM 35668, 7, 58-106 mm, km 37, Pozo Colorado-Concepción rd., riacho Negro, 23°30'53"S, 057°49'17"W. UMMZ 206972, 3, 95-120 mm, Puente Remanso bridge [nr. Remansito], ca. 25°10'S, 057°32'W. UMMZ 207026, 24, 45-145, marsh, 34.3 km NW toll booth on puente Remanso, río Confuso, 25°04'54"S, 057°36'00"W. UMMZ 207098, 4, 106-138 mm, small stream ca. 33.7 km NW toll booth on Puente Remanso bridge (Estancia La Golondrina), affl. río Confuso, 25°04'54"S, 057°36'00"W. UMMZ 207369, 6, 127-154 mm, Trans-Chaco hwy., E side, 0.2 km, 1.0 km SE entrance to Estancia Juan de Zalazar, riacho San Carlos, 23°01'36"S, 059°15'00"W. UMMZ 207381, 11, 118-171 mm, pond E rd. ca. 6.6 km N Trans-Chaco hwy., ca. 46 km SE Filadelfia, ca. 22°38'S, 059°43'W. UMMZ 207565, 4, 151-188 mm, UMMZ 207598, 9, 55-140 mm, pools at bridge (Puerto Falcón to Argentina), ca. 12 km WSW Chaco-I, río Pilcomayo, 25°15'48"S, 057°42'36"W. UMMZ 207588, 1, 88 mm, pools ca. 83.2 km Puerto Falcon, 24°52'54"S, 058°18'36"W. UMMZ 207620, 1, 120 mm LEA, riacho Pilco, ca. 25°06'S, 057°46'W. UMMZ 216612, 4, 72-93 mm, Estancia La Golondrina, marshlands, affl. río Confuso, ca. 24°36'S, 058°07'W. USNM 232235, 4, 78-106 mm, río Confusa [Confuso], ca. 25 km E Trans-Chaco, ca. 25°06'S, 057°34'W. San Pedro (localities from río Paraguay dr.). NRM 33612, 1, 48 mm, km 20 on San Pedro-Nuevo Germania rd., 23°59'23"S, 056°57'13"W. UMMZ 206572, 1, 122 mm, río Corrientes, affl. río Jejuí Guazú, 24°22'54"S, 055°56'24"W. Region not specified. BMNH 1927.11.23.31, 1, 117 mm, swamp at Makthalawaiya, Paraguayan Chaco, no coordinates. CAS 72224, 2, 38-56 mm, FMNH 52591, 1, 140 mm, Arroyo Chagalalina, affl. río Aquido Canigi, no coordinates. NRM 33632, 1, 132 mm, NRM 33634, 1, 27 mm, listed "labels lost, but known to come from S. Kullander's or B. Delling's collection efforts [in Paraguay]". Uruguay. Artigas (localities from Uruguay dr.). MNHN-Uruguay 1746, 1, río Cuareim, Laguna de las Lavanderas, 30º23'34"S, 056º27'33"W. MNHN-Uruguay 2823, 1, Arrocera Conti, island in río Uruguay, 30º29'27"S, 057º51'55"W. NRM 56105, 5, 55-79 mm, NRM 56106, 1, 95 mm, N Bella Unión, lagoon on río Uruguay, 30º13'03"S, 057º37'18"W. ZVC-P 19, 4, ZVC-P 2925, 14, ZVC-P 3518, 1, ZVC-P 7984, 2, Estancia El Ombú, Barra del Yucutuyá, río Cuareim, 30º18'09"S, 057º23'21"W. ZVC-P 2923, 1, ZVC-P 7983, 1, Franquia, Bella Unión, Laguna Redonda, 30º14'46"S, 057º36'22"W. Cerro Largo. ZVC-P 5002, 1, Paso Mazangano, Route 44, río Negro, Uruguay dr., 32º06'36"S, 054º40'06"W. Durazno. UF 183774, 2 (CS), 118-155 mm, Laguna Lavalle, río Negro, Uruguay dr., 33°01'16"S, 055°22'30"W. Paysandú. USNM 86173, 1, 101 mm, Paysandú, Uruguay dr., ca. 32°19'S, 58°03'W. Río Negro (localities from Uruguay dr.). ZVC-P 4658, 1, Estero de Farrapos S side San Javier, 32º40'34"S, 058º07'49"W. ZVC-P 4696, 1, Estero de Farrapos, mouth of Arroyo Román Grande, 32º50'35"S, 058º05'05"W. Rocha (localities from Patos-Mirim dr.). CU 77186, 1, bañado, Route 19, no coordinates. CU 77187, 1, cañada, Route 19, no coordinates. ZVC-P 5917, 1, Potrerillo, Laguna Negra, 33º58'39"S, 053º38'29"W. ZVC-P 5919, 1, Arroyo de las Negras, Route 19, km 22, Laguna Mirín, 33º35'53"S, 053º41'00"W. ZVC-P 5920, 2, río San Luis, Route 19, km 30.65, affl. Laguna Merín, 33º36'06"S, 053º43'32"W. Salto (localities from Uruguay dr.). NRM 52215, 6, 106-144 mm, embayment of río Uruguay, Constitución, 31º03'57"S, 057º50'20"W. NRM 56068, 1, 141 mm, Constitución, río Uruguay, 31º04'03"S, 057º50'45"W. Tacuarembó. ZVC-P 1992, 4, Paso del Sauce above Arroyo Yaguarí, 29 km S Pueblo Ansina, affl. río Negro, Uruguay dr., 32º02'00"S, 055º22'01"W. Treinta y Tres (localities from Patos-Mirim dr.). NRM 61393, 1, 86 mm, affl. Arroyo del Parao, Ruta 18, W Vergara, río Olimar Grande, 32º55'12"S, 053º55'18"W. NRM 61473, 3, 49-63 mm, Arroyo Corrales del Parao, Ruta 91, S Vergara, río Olimar Grande, 33º01'46"S, 053º52'57"W. ZVC-P 5918, 2, Arroyo El Tigre, Ruta 17, km 322, affl. río Olimar, affl. río Cebollati, affl. Laguna Mirim, 33º14'50"S, 053º54'40"W. Region not specified. UF 183779, 1 (CS), 153 mm, aquarium specimen bred in captivity by P. Stoddard, Florida International University, from specimens exported from Uruguay. Suspected introduced records (15 specimens, grey circles in Fig. 27). Brazil. São Paulo (localities from rio Tietê dr., Paraná dr.). MZUSP 49201, 9, mun. Americana, Represa Santa Maria da Serra, ca. 22°45'S, 047°19'W [coordinates for town of Americana], coll. 7 Feb 1995, museum record states: "purchased from fishermen that sell bait in Praia Azul, Americana". MZUSP 53862, 4, 121-176 mm, mun. Santa Maria da Serra, Represa de Barra Bonita, nr. Santa Maria da Serra, rio Piracicaba, ca. 22°34'S, 048°08'W, coll. 1995. MZUSP 83410, 2, 175-175, mun. Bariri, downstream of hydroelectric barrage UHE Bariri, margin rio Tietê, ca. 22°08'S, 048°45'W, coll. 4 Apr 2003.

Brachyhypopomus hamiltoni, new species

urn:lsid:zoobank.org:act:F8BA1881-ABCE-4E3C-A39C-09C20739E83E

(Figs. 1g, 28; Tables 2 -5, 13)

Brachyhypopomus sp. G and sp. H. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus sp. "ayr" and sp. "ham". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "hamiltoni". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 45482, female, 97 mm TL, 80 mm LEA, Brazil, Amazonas, mun. Alvarães, Mamirauá Reserve (Reserva de Desenvolvimento Sustentável), Ressaca da Vila Alencar, rio Solimões-Japurá floodplain, Amazonas dr., 03º07'41"S, 064°48'04"W, 8 Mar 2001, W. Crampton & J. Oliveira.

Paratypes. 19 specimens, localities from Amazonas dr., collected by W. Crampton & J. Oliveira unless otherwise stated; localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). Brazil. Amazonas. MCP 45250, 1 (CS), immature, 80 mm, 26 Nov 1998, MCP 45303, 1, immature, 82 mm, 3 Dec 1998, mun. Maraã, Boca do igarapé Juá Grande, lago Amanã, affl. rio Japurá, 02°27'14"S, 064°48'26"W. MCP 45269, 1, male, 104 mm, Mamirauá Reserve, Ressaca do Pau, 03º02'03"S, 064º52'13"W, 17 Apr 2001. MCP 45302, 11 (3 CS, 2 with gills and brain removed), 75-89 mm (9 immature, 64-89 mm, 1 female, 84 mm, 1 male, 93 mm), 2 Dec 1998, MCP 45307, 1, female, 93 mm, 16 Feb 1993, mun. Maraã, igarapé Juá Grande, lago Amanã, affl. rio Japurá, 02°28'50"S, 064°48'50"W. MCP 45407, 1, immature, 56 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11'11"S, 064°43'05"W, 18 Aug 1998. MPEG 27114, 1, 97 mm, lago do Içé, Ilha do Içé, rio Solimões, 6 km NW Tefé, Amazonas dr., 03°16'02"S, 064°40'50"W, 18 May 2012, A. Cardoso & J. Oliveira. MPEG 27115, 2, 78-78 mm, Mamirauá Reserve, Paraná do Mamirauá, 03º02'58"S, 064°50'57"W, 18 May 2012, A. Cardoso & J. Oliveira.

Non-types. 44 specimens, localities from Amazonas dr. Brazil. Amazonas (localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). IDSM 460, 1, 67 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. MCP 45268, 1, immature, 84 mm, Mamirauá Reserve, Paraná Maiana, 03º06'50"S, 064°47'48"W. MCP 45681, 5, immature, 34-56 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11'11"S, 064°43'05"W. MPEG 22744, 2, 54-66 mm, Mamirauá Reserve, lago Bolsinho, 03º03'47"S, 064°49'59"W. MZUSP 7352 (part), 2, 65-93 mm, mun. Maués, igarapé Limãozinho, affl. rio Maués Açu, ca. 03°24'S, 057°42'W. MZUSP 30058 (part), 1, immature, 60 mm, lago Amanã, affl. rio Japurá, ca. 02°30'S, 064°42'W. MZUSP 55112, 1, 65 mm, mun. Santa Isabel do rio Negro, igarapé São João, nr. Santa Isabel do rio Negro (Tapurucuara), affl. rio Negro, ca. 00°24'S, 065°02'W. MZUSP 79663, 1, 79 mm, mun. Presidente Figueiredo, rd. branch nr. Marcus Freire, km 13 on AM-240 hwy., affl. rio Preto da Eva, 02°04'06"S, 059°54'33"W. MZUSP 95226 (part), 1, 77 mm, mun. Santa Isabel do rio Negro, Paricatuba, lake, margin of rio Negro, ca. 00°31'S, 065°01'W. Ecuador (localities from río Napo dr.). Napo. MUSM 5693 (part), 1, 120 mm, río Aguarico, R. bank, temporary lake, ca. 00°38'S, 075°21'W [coordinates for mouth of río Aguarico]. Sucumbios. FMNH 102282, 2, 72-84 mm, Laguna Zancudococha, affl. río Aguarico, ca. 00°35'S, 075°29'W. FMNH 102285, 2, 73-90 mm, affl. to río Cuyabeno, N bank ca. 3 km upstream Laguna Grande de Cuyabeno, affl. río Aguarico, ca. 00°01'S, 076°10'W. FMNH 102291, 2, 63-68 mm, N bank affl. to río Aguarico, 2nd affl. downstream from Zancudo, no coordinates. FMNH 121058, 8, 21-73 mm, small stream between Laguna Zancudo and Laguna Zancudococha, affl. quebrada Zancudococha, affl. río Aguarico, 00°33'42"S, 075°30'00"W. Peru. Amazonas (localities from río Marañón, affl. río Amazonas). LACM 41774-1, 6, 66-109 mm, Caterpiza, río Santiago, ca. 03°55'S, 077°44'W. LACM 41931-3, 2, 82-91 mm, downstream from Caterpiza, río Santiago, ca. 03°55'S, 077°44'W. LACM 42012-4, 2, male, 107-125 mm, 1 km downstream from Caterpiza, río Santiago, ca. 03°55'S, 077°44'W. Loreto. MUSM 44704, 2, (1 immature, 91 mm, 1 female, 75 mm), stream nr. cocha Capite, nr. Jenaro Herrera, affl. río Ucayali, 04°52'03"S, 073°40'39"W. NRM 27758, 2, 59-62 mm, El Estrecho, quebrada de las Granjas, affl. río Putumayo, 02°28'00"S, 072°42'00"W.

Diagnosis. Brachyhypopomus hamiltoni is diagnosed from congeners by the following combination of characters: precaudal vertebrae 19-21, vs. 15-18 in B. batesi, B. benjamini, B. bullocki, B. cunia, B. hendersoni, B. menezesi, B. provenzanoi, B. regani, and B. sullivani, and vs. 24-26 in B. belindae and B. verdii; pale stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament in B. arrayae, B. beebei, B. gauderio, and B. pinnicaudatus; bilateral columns of electrocytes at the anal-fin terminus 3, vs. 4-6 in B. bennetti, B. diazi and B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis), and B. palenque; dark vertical or diagonally oriented stripes or saddles present, vs. absent in B. bombilla, B. draco, and B. jureiae; anal-fin rays 163-208, vs. 226-293 in B. brevirostris; absence of conspicuous patches of shiny yellow guanine on the operculum and anterior to pectoral-fin base in live individuals, vs. presence in B. flavipomus; caudal filament length 18.6-30.0% LEA, vs. 31.3-59.1% in B. janeiroensis; dark suborbital stripe absent, vs. present in B. walteri. B. hamiltoni can be distinguished from B. alberti by a lower number of pectoral-fin rays, 12-15 (mode, 13), vs. 15-16 (mode 16) in B. alberti (only 2 of 18 measured specimens of B. hamiltoni exhibited an overlapping number of pectoral-fin rays with B. alberti). Brachyhypopomus hamiltoni can be further distinguished from B. alberti by the presence of the first of five branchiostegal rays, vs. absence in B. alberti.

Description. Head and body shape, and pigmentation illustrated in Figs. 1g and 28. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 13. Body moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight to slightly convex from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout triangular to rounded. Eye moderate to large in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 30-39 (median 33, n = 10). Pectoral fin narrow to moderate in width, pectoral-fin rays 12-15 (mode 13). Precaudal vertebrae 19-21 (mode 20), with 1-3 (mode 1) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 163-208 (median 180). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 5). Lateral line continuous. Depigmented epidermal canals present; as an irregular interrupted single groove either side of dorsal midline along most of posterior half body; and as crisscrossing network of grooves parallel to and dorsal to lateral line, reaching about one third of distance from lateral line to dorsal midline, and mostly restricted to posterior third of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at or near a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens, and in populations from both low-conductivity and high-conductivity systems. Caudal filament of moderate length.

Coloration. (Figs. 1g, 28). Background pale tan to dark brown. Dorsal region without prominent depigmented stripe extending along midline from occipital region to base of caudal filament. Dorsal region with irregular dark patches of dark chromatophores which extend into diffuse, narrow, vertical dark bands which extend across lateral line. Some diffuse bands reach ventral midline or anal-fin margin over body cavity. Vertical bands less distinctive in posterior portion of body and mostly do not cross lateral line. Some diffuse vertically-elongated patches of chromatophores extend dorsally from anal-fin margin over anal-fin pterygiophores. Vertical dark bands much less distinct than in most congeners that possess dark vertical or diagonally oriented stripes or saddles on body surface dorsal to lateral line. Series of elongated diffuse horizontal dash-like dark markings present along lateral line in posterior third of body, anterior to anal-fin terminus. Caudal filament darker than body, with irregular dark markings or bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Anal-fin rays with light scattering of brown chromatophores, usually anal-fin rays darker than pectoral-fin rays. Color in live individuals similar to preserved ones, with opercular region usually rosy due to underlying gills. Individuals from blackwater habitats usually exhibit a darker overall coloration than those in whitewater habitats. Individuals from whitewater habitats often with yellowish tinge to background body color in live individuals.

Fig. 28
Brachyhypopomus hamiltoni. MCP 45482 (WC05.080301), holotype, female, 97 mm TL (head in lateral view, body in lateral and dorsal view); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Specimen fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 125 mm TL, 100 mm LEA (n = 61). Largest male specimen examined 125 mm TL, 100 mm LEA (n = 4). Largest female specimen examined 97 mm TL, 80 mm LEA (n = 4).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil, Ecuador, and Peru (Fig. 29). Widely distributed in the upper, central, and lower Amazon, and from the middle Negro, but with sporadic collection records.

Fig. 29
Collection records for Brachyhypopomus hamiltoni (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. In the region of the type locality B. hamiltoni is uncommon. It is known from floating macrophytes in whitewater floodplains at the confluence of rio Solimões and Japurá (see description of B. belindae for water quality parameters in this area), and from the large low-conductivity (usually <30 μScm-1) blackwater floodplain ria lake, lago Amanã; see Crampton (2008) for notes on the water chemistry of lago Amanã. Specimens in reproductive condition were found during the rising and high water period, which is consistent with the reproductive seasonality of sympatric congeners. Stomach contents of specimens from the type locality comprise aquatic insect larvae (primarily Chironomidae), and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: Brachyhypopomus hamiltoni is known to co-occur in geographical sympatry and ecological syntopy with B. beebei, B. belindae, B. bennetti, B. brevirostris, B. flavipomus, B. hendersoni, B. pinnicaudatus, B. regani, and B. walteri. It also exhibits an allotopic distribution across parts of its range with: B. batesi, B. benjamini¸ B. sullivani, and B. verdii.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of William D. Hamilton (1936-2000), British evolutionary biologist, and doctoral advisor of WGRC; for his contributions to Amazonian ecology.

Local names. Brazil: sarapó; Ecuador: cuchillo, yayo; Peru: macana.

Brachyhypopomus hendersoni, new species

urn:lsid:zoobank.org:act:A0D96996-8B4E-4001-A700-64F9093BFA4F

(Figs. 1h, 30; Tables 2-5, 13)

Brachyhypopomus beebei ('H2'). -Heiligenberg & Bastian, 1980Heiligenberg, W. & J. Bastian. 1980. Species specificity of electric organ discharges in sympatric gymnotoid fish of the Rio Negro. Acta Biológica Venezuélica, 10: 187-203.: 197, fig. 1, black and white photograph (Brazil, Amazonas, rio Negro, gymnotiform species and EOD diversity).

Brachyhypopomus sp. 8. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 30-31, color photographs; 85, fig. 6.2; 88: fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats (Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus sp. 4. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, list of Brachyhypopomus (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998b: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance).

Brachyhypopomus sp. D. -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.: 231, fig. 6, black and white photograph of head of live individual (Brazil, Amazonas, adaptations to hypoxia).

Brachyhypopomus sp. 'basepreta'. -Ferreira et al., 2007Ferreira, E. J. G., J. Zuanon, B. Forsberg, M. Goulding & Briglia-Ferreira, S. R.. 2007. Rio Branco: peixes, ecologia e conservação de Roraima. Manaus, Amazon Conservation Association, Instituto Nacional de Pesquisas da Amazônia, Sociedade Civil Mamirauá, 201pp.: 164, bottom left photograph, live individual (Brazil, Roraima, rio Branco, photographic album of fishes).

Brachyhypopomus sp. "hen". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "hendersoni". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 12, 13, 15, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 45305, male, 146 mm TL, 98 mm LEA, Brazil, Amazonas, mun. Maraã, lago Amanã, Igarapé Juá Grande, rio Japurá, Amazonas dr., 02°28'50"S, 064°48'50"W, 3 Dec 1998, W. Crampton & J. Oliveira.

Paratypes. 47 specimens, localities from Amazonas dr., collected by W. Crampton & J. Oliveira unless otherwise stated. Brazil. Amazonas. BMNH 1998.3.12.22-24, 3, immature, 122-140 mm, 7-10 Jan 1997, MCP 45483, 3, 142-142 mm, 1997, mun. Tefé, Ressaca do Socorro, lago Tefé, rio Tefé, 03°18'45"S, 64°41'50"W. BMNH 1998.3.12.175, 1, female, 159 mm, 27 May 1994, BMNH 1998.3.12.176-177, 2 (1 immature, 132 mm, 1 male, 171 mm), 27 Jan 1995, mun. Tefé, Ressaca do Cachorro, lago Tefé, rio Tefé, 03°19'50"S, 64°42'15"W. INPA 9950, 10, 125-154 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, ca. 03°34'S, 064°58'W, 11 Jan 1995. MCP 45272, 1, female, 174 mm, mun. Tefé, Ilha do Martelo, rio Tefé, 03°46'56"S, 064°59'39"W, 22 Jan 1999. MCP 45273, 1, male, 121 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°38'01"S, 064°57'59"W, 22 Jun 1999. MCP 45274, 1, female, 143 mm, mun. Tefé, rio Tefé, 03°41'23"S, 064°59'08"W, 16 Feb 2001. MCP 45309, 1, immature, 69 mm, mun. Maraã, igarapé São Sebastião, affl. rio Baré, affl. lago Amanã, affl. rio Japurá, 02°17'05"S, 064°41'25"W, 17 Feb 1993. MCP 45369, 3 (2 immature, 144-147 mm, 1 female, 175 mm), mun. Tefé, mouth of igarapé Açu, Lago Tefé, rio Tefé, 03°25'00"S, 064°48'23"W, 26-28 Jun 1998. MCP 45397, 13 (3 immature, 158-183 mm, 6 female, 140-203 mm, 4 male, 125-190 mm), mun. Tefé, lago Caiambé, rio Caiambé, 03º35'40"S, 064º26'54"W, 28 Dec 1998. MCP 45408, 1, female, 162 mm, mun. Tefé, Ressaca do Socorro, lago Tefé, rio Tefé, 03°18'45"S, 064°41'50"W, 11 Aug 1998. MPEG 973, 2, 109-110 mm, MPEG 974, 1, 127 mm, mun. Tefé, lago Jurupari, rio Tefé, ca. 03°48'S, 065°00'W, 1 Jul 1979, M. Goulding. MPEG 976, 1, 102 mm, mun. Tefé, Arana-tuba, rio Tefé, ca. 04°02'S, 065°01'W, 8 Jul 1979, M. Goulding. MZUSP 99170, 2, 96-130 mm, canal do lago Amanã, affl. rio Japurá, ca. 02°44'S, 064°39'W, 30 Sep 1979, R. Barthem.

Non-types. 103 specimens. Brazil. Amazonas (localities from Amazonas dr.). BMNH 1998.3.12.08-10, 3 (2 immature, 153-167 mm, 1 female, 167 mm), BMNH 1998.3.12.13-14, 2, female, 155-167 mm, MCP 45271, 26 (10 immature [1CS], 120-170 mm, 8 female, 145-172 mm, 8 male, 148-180 mm), mun. Tefé, lago Tefé, rio Tefé, 03°18'45"S, 064°41'50"W. BMNH 1998.3.12.159-174, 16 unsexed, 108-193 mm, BMNH 1998.3.12.178-182, 5, immature, 102-135 mm, MCP 45270, 3 (2 immature, 130-142 mm, 1 male, 195 mm), mun. Tefé, Ressaca do Cachorro, lago Tefé, rio Tefé, 03°19'50"S, 064°42'15"W. IDSM 456, 1, immature, 130 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°35'41"S, 064°58'05"W. INPA 9781, 2, 79-140 mm, rio Jaú, affl. rio Negro, ca. 01°57'S, 061°28'W. MCP 45304, 1, immature (CS), 100 mm, mun. Maraã, lago Amanã, mouth of igarapé Uxi, affl. rio Japurá, 02°32'41"S, 064°40'12"W. MCP 45454, 4 (3 female [1CS], 127-153mm, 1 male [CS], 175 mm), mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°38'01"S, 064°57'59"W. MCP 45426, 1, female (CS), 166 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°38'01"S, 064°57'59"W. MCP 45432, 6 (3 immature [1CS], 134-146 mm, 2 female, 143-163 mm, 1 male [CS], 161 mm), mun. Tefé, rio Tefé, 03º37'43"S, 064°59'03"W. MCP 45489, 2, female, 164-166 mm, mun. Tefé, Ilha do Martelo, rio Tefé, 03°46'56"S, 064°59'39"W. MCP 45491, 5 (4 immature, 128-148 mm, 1 female, 120 mm), mun. Tefé, rio Tefé, 03°41'23"S, 064°59'08"W. MCP 45682, 4, 123-152 mm, mun. Tefé, Ressaca do Socorro, lago Tefé, rio Tefé, 03°18'45"S, 64°41'50"W. MPEG 979, 5 (part), 65-147 mm, mun. Tefé, Ipanema da Baixa, rio Tefé, ca. 03°53'S, 065°00'W. MPEG 1125, 1, 81 mm, mun. Novo Airão, Anavilhanas archipelago, rio Negro, ca. 02°40'S, 060°44'W. MZUSP 30044 (part), 1, 127 mm, mun. Tefé, lago Jurupari, rio Tefé, ca. 03°48'S, 065°00'W. MZUSP 30050, 1, 106 mm, mun. Tefé, Mastro, rio Tefé, no coordinates. MZUSP 78032 (part), 1, 110 mm, mun. Maraã, Paraná do Castanho, lago Amanã, affl. rio Japurá, ca. 02°44'S, 064°39'W. Guyana. Upper Demerara-Berbice. INHS 49276, 1, 112 mm, 1.54 mi. SW Rockstone, Essequibo River (Long Lake), Essequibo River dr., ca. 05°58'N, 058°32'W. Upper Tukutu-Upper Essequibo. ANSP 179500, 2, 70-113 mm, AUM 35818, 2, 84-118 mm, stream at crossing on Massara-Karanambo rd., 10.3 km NW Karanambo, affl. Rupununi River, Essequibo River dr., 03°48'27"N, 059°23'06"W. AUM 48815, 1, 80 mm, Rupununi River at Massara landing, Essequibo River dr., 03°53'42"N, 059°17'37"W. BMNH 1972.7.519-525, 7, 34-109 mm, Rupununi River, Essequibo River dr., no coordinates.

Diagnosis. Brachyhypopomus hendersoni is diagnosed from congeners by the following combination of characters: caudal filament length 32.3-64.5% LEA, vs. 7.4-31.6% in B. alberti, B. arrayae, B. batesi, B. belindae, B. benjamini, B. bennetti, B. bombilla, B. hamiltoni, B. occidentalis, B. palenque, B. provenzanoi, B. regani, B. sullivani, and B. verdii; precaudal vertebrae 15-17, vs. 18-25 in B. beebei, B. brevirostris, B. draco, B. flavipomus, B. gauderio, B. janeiroensis, B. jureiae, and B. pinnicaudatus; head width at occiput 39.2-47.8% HL, vs. 49.5-70.4% in B. bullocki, B. diazi, and B. menezesi; dorsal rami of the recurrent branch of the anterior lateral line nerve not visible, vs. visible in B. cunia and B. walteri.

Description. Head and body shape, and pigmentation illustrated in Figs. 1h and 30. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 13. Body shallow to moderate in depth. Head short and shallow to moderate in depth. Dorsal profile of head convex from occiput to snout, ventral profile of head with areas of convexity near mouth and areas of concavity under eye, snout truncate to rounded. Eye moderate to large in size. No accessory electric organ over operculum. Gill filaments on first gill arch 32-34 (median 33, n = 4). Pectoral fin moderate in width, pectoral-fin rays 12-16 (mode 13). Precaudal vertebrae 15-17 (mode 16), with 1-2 (mode 1) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 192-210 (median 200). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Sparse depigmented epidermal canals in posterior two thirds of body, present in three series: as an irregular, interrupted, single groove either side of dorsal midline along most of posterior two thirds of body, as a meandering sometimes bifurcating single groove on each dorsal flank approximately midway from lateral line to dorsal midline, and in posterior third of body as sparse scratch like marks dorsal to and near lateral line. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament moderate in length to long.

Coloration. (Figs. 1h, 30). Background color tan or light grey to dark brown. Dorsal region with uniform speckling of dark chromatophores, and often with a thin pale line extending along midline from occipital region to deep into caudal filament, but without a prominent depigmented stripe. Flank with narrow diffuse, vague vertical stripes dorsal to lateral line, extending to but not crossing lateral line. Flank in region of body cavity ventral to lateral line with irregular dark flecks and patches, not forming vertical stripes. Prominent horizontal dark band extends from anal-fin margin to near dorsal margin of anal-fin pterygiophores along entire length of anal fin, darkening ventrally and posteriorly. This dark band along anal-fin base is more conspicuous in some specimens than others. Dark spots and diffuse vertically elongated stripes also present over anal-fin pterygiophores, extending dorsally towards lateral line. Caudal filament very dark, with irregular lighter markings, often with black tip; darkened tip resembles root tips of water hyacinths when viewed underwater. Head with evenly scattered dark chromatophores, darker dorsally. Eye with suborbital patch or stripe of chromatophores and subcutaneous pigmentation (more conspicuous in some specimens than others). Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline with light scattering of melanophores. Anal-fin rays with scattered or dark chromatophores, mostly concentrated near anal-fin margin. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills and flank over body cavity whitish.

Fig. 30
Brachyhypopomus hendersoni. a. MCP 45408 (WC07.110898b), paratype, female, 162 mm TL, (head, and body in lateral and dorsal view, specimen fixed in formalin); Brazil, rio Tefé, Amazonas dr. b. MCP 45305 (WC13.031298), holotype, male, 146 mm TL (head in lateral view, body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Japurá, Amazonas dr. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 203 mm TL, 130 mm LEA (n = 150). Largest male specimen examined 195 mm TL, 123 mm LEA (n = 18). Largest female specimen examined 203 mm TL, 130 mm LEA (n = 31).

Sexual dimorphism. Breeding males exhibit slightly enlarged electrocytes relative to immature specimens and females. No other secondary sexually dimorphic characters known.

Geographic distribution. Brazil and Guyana (Fig. 31). Known from the central Amazon from blackwater ria lakes near Tefé, from the lower Negro, and from the Essequibo drainage.

Fig. 31
Collection records for Brachyhypopomus hendersoni (circles) and B. provenzanoi (squares). Holotype locations are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. In the region of the type locality B. hendersoni is common in marginal emergent plants (mainly wild rices, Oryza spp.), rafts of floating macrophytes (including grasses, e.g., Paspalum, and water hyacinths, Eichhornia spp.), and decaying plant matter along the edges of low-conductivity blackwater floodplain ria lakes (e.g., lago Tefé, lago Amanã, and lago Caiambé), and along river and oxbow lake margins (e.g., in the rio Tefé floodplain). The following water parameters were recorded in the rio Tefé floodplain: conductivity 7-18 µScm-1, dissolved oxygen 3.0-6.7 mgl-1, temperature 29.0-33.3°C, and pH 5.3-6.7. Brachyhypopomus hendersoni occurs in habitats that are not typically exposed to protracted and severe seasonal hypoxia. Crampton et al. (2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.) documented the relatively small gill sizes of B. hendersoni relative to congeners that occur in seasonally hypoxic whitewater floodplain systems. Breeding occurs in floating macrophytes during the rising and high water period (WGRC unpublished data). Stomach contents of specimens from the type locality comprise aquatic insect larvae (primarily Chironomidae), and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the region of the type locality Brachyhypopomus hendersoni commonly co-occurs in geographical sympatry and ecological syntopy with B. brevirostris, and B. walteri, and sometimes with B. beebei. It exhibits an allotopic distribution with B. batesi, B. belindae, B. bennetti, B. flavipomus, B. hamiltoni, B. pinnicaudatus, B. regani, and B. sullivani. In the middle rio Negro B. hendersoni co-occurs in geographical sympatry with B. batesi, B. bullocki, B. beebei, B. brevirostris, B. hamiltoni, B. regani, B. sullivani, and B. walteri. In the Essequibo River B. hendersoni co-occurs in geographical sympatry with B. bullocki, B. beebei, B. brevirostris, B. regani, B. sullivani, and B. walteri.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Peter A. Henderson, British fish biologist, and doctoral co-advisor of WGRC; for his contributions to Amazonian aquatic ecology.

Local names. Brazil: sarapó; Guyana: knifefish.

Brachyhypopomus janeiroensis (Costa & Campos-da-Paz, 1992Costa, W. J. E. M. & R. Campos-da-Paz. 1992. Description d'une nouvelle espèce de poisson électrique du genre néotropical Hypopomus (Siluriformes : Gymnotoidei : Hypopomidae) du Sud-Est du Brésil. Revue Française d'Aquariologie-Herpétologie, 18: 117-120.)

(Fig. 32; Tables 2-5, 15)

Hypopomus janeiroensisCosta & Campos-da-Paz, 1992Costa, W. J. E. M. & R. Campos-da-Paz. 1992. Description d'une nouvelle espèce de poisson électrique du genre néotropical Hypopomus (Siluriformes : Gymnotoidei : Hypopomidae) du Sud-Est du Brésil. Revue Française d'Aquariologie-Herpétologie, 18: 117-120.: 118, fig. 2, black and white photograph of holotype, fig. 3, color photograph of live paratype (original description, type locality - Brazil, Rio de Janeiro, rio São João dr.).

Brachyhypopomus janeiroensis. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48 (listing of Brachyhypopomus). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p., 118 (redescription). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 495 (Brazil, catalog of hypopomids). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672 fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 15
Morphometrics for Brachyhypopomus janeiroensis, Brachyhypopomus jureiae, and Brachyhypopomus menezesi. HT, holotype; SD, standard deviation. Data for holotype of Brachyhypopomus janeiroensis (Rio de Janeiro, Brazil) are from Costa & Campos-da-Paz (1992Costa, W. J. E. M. & R. Campos-da-Paz. 1992. Description d'une nouvelle espèce de poisson électrique du genre néotropical Hypopomus (Siluriformes : Gymnotoidei : Hypopomidae) du Sud-Est du Brésil. Revue Française d'Aquariologie-Herpétologie, 18: 117-120.). Data for holotype of Brachyhypopomus jureiae (São Paulo, Brazil) are from Triques & Khamis (2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.). Ranges for Brachyhypopomus janeiroensis and Brachyhypopomus jureiae refer to non-type specimens from the type region (holotype data not included except for caudal filament length as % TL and LEA in B. jureiae). Ranges for Brachyhypopomus menezesi refer to the holotype and to paratypes from the type region.

Diagnosis. Brachyhypopomus janeiroensis is diagnosed from congeners by the following combination of characters: bilateral columns of electrocytes at the anal-fin terminus 4, vs. 6 in B. bennetti and vs. 3 in all other congeners except B. belindae, B. diazi, B. jureiae, B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis), and B. palenque; caudal filament length 31.3-59.1% LEA, vs. 7.4-30.7% in B. belindae, B. occidentalis, and B. palenque; dorsal rami of the recurrent branch of the anterior lateral line nerve visible, vs. not visible in B. diazi; snout to pectoral-fin base 10.7-12.3% LEA, vs. 12.3-15.7% in B. jureiae.

Description. Head and body shape, and pigmentation illustrated in Fig. 32. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 15. Body shallow to moderate in depth. Head short and shallow to moderate in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head straight between operculum and snout, snout truncate to rounded. Eye moderate in size. Upper jaw with moderate to acute sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 44-51 (median 48, n = 4). Pectoral fin narrow to moderate in width, pectoral-fin rays 13-16 (mode 15). Precaudal vertebrae 19-20 (mode 20), with 1-2 (mode 1) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, posterior to, or near, tip of pectoral fin. Anal-fin rays 181-223 (median 203). Dorsal rami of recurrent branch of anterior lateral line nerve visible. Middorsal region of body scaled. Rows of scales above lateral line 4-6 (mode 5). Lateral line continuous. Very sparse and irregular presence of depigmented epidermal canal; restricted mostly to posterior half of body, as parallel striations flanking lateral line, and as single irregular meandering lines around midway from lateral line to dorsal midline, or near edges of dorsal surface. Four bilateral columns of electrocytes at anal-fin terminus, and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament moderate in length to long.

Coloration. (Fig. 32). Background pale tan to brown. Dorsal region with irregular dark markings, without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Diffuse, narrow vertical bands extend from dorsal region to lateral line in some specimens, mainly in anterior third of body. Irregular series of dark spots often present along lateral line. Ventral flank without vertical bands, with irregular dark spots in region of body cavity and over anal-fin pterygiophores. Caudal filament slightly darker than body, usually relatively free of dark markings. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays with light, even scattering of dark chromatophores. Anal-fin rays with light scattering of dark chromatophores, which fuse in proximal part of rays. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 32
Brachyhypopomus janeiroensis. MZUSP 80122; male, 174 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH). Brazil, rio São João dr. Scale bars = 5mm.

Size. Moderate adult size. Largest specimen examined 230 mm TL, 148 mm LEA (n = 227). Largest male specimen examined 199 mm TL, 135 mm LEA (n = 15). Largest female specimen examined 230 mm TL, 148 mm LEA (n = 13).

Sexual dimorphism. Breeding male specimens develop somewhat elongated caudal filaments in comparison to immature individuals and breeding females, but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Males not known to reach greater average lengths than females, despite elongated caudal filaments. Tip of caudal filament in large males does not exhibit a paddle-like lateral compression. No sexual differences in pigmentation.

Geographic distribution. Brazil (Fig. 23). Known from the rio São João, rio Paraíba do Sul, and small intervening coastal drainages (e.g., rio Ururaí-Lago Feia dr.), in the state of Rio de Janeiro. Brachyhypopomus janeiroensis was also collected from the area now comprising urban Rio de Janeiro during the 1865-1866 Thayer Expedition, in the presence of the Emperor of Brazil Dom Pedro II (MCZ 9457 and 165863).

Ecological notes. Throughout its range B. janeiroensis occurs in the aquatic vegetation of normoxic, slow-flowing streams, and also lentic, swampy, and periodically hypoxic habitats (pers. comm., R. Campos-da-Paz, UFRJ). The type locality of B. janeiroensis is a narrow slow-flowing stream with a sandy bottom and heavily vegetated banks, which traverses forest fragments and pastureland (Costa & Campos-da-Paz, 1992Costa, W. J. E. M. & R. Campos-da-Paz. 1992. Description d'une nouvelle espèce de poisson électrique du genre néotropical Hypopomus (Siluriformes : Gymnotoidei : Hypopomidae) du Sud-Est du Brésil. Revue Française d'Aquariologie-Herpétologie, 18: 117-120.). In April 2006 the following water parameters were recorded at this site: conductivity 38 μScm-1, dissolved oxygen 5.0 mgl-1, temperature 23.9 C, transparency slightly silted (WGRC & R. Campos-da-Paz, unpublished data). Reproductive biology is unknown. Stomach contents of specimens from the type locality comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: None.

Local names. Brazil: tuvira.

Material examined. 227 specimens. Brazil. Rio de Janeiro. FMNH 15201, 6, 125-165 mm, FMNH 54545, 27, 83-210 mm (11 sexed, 3 immature, 148-156 mm, 3 female, 122-157 mm, 5 male, 126-199 mm), Campos, rio Paraíba do Sul dr., ca. 21°45'S, 041°18'W. FMNH 54547, 4, 131-184 mm (2 sexed: 1 female, 150 mm, 1 male, 184 mm), Lagoa Feia, Tocas [Caxia de Tocos?], rio Ururaí-Lagoa Feia dr., ca. 22°00'S, 041°20'W. MCZ 9457, 25, 105-216 mm, MCZ 165863, 72 (30 examined), 104-202 mm, mun. Rio de Janeiro, Santa Cruz, rio Grande (arroio Fundo), in urban Rio de Janeiro, coastal drainage of urban Rio de Janeiro, ca. 22°56'S, 043°12'W. MNRJ 12127, 1 (paratype), 166 mm, mun. Silva Jardim, affl. rio Maratuan, rio São João dr., ca. 22°39'S, 042°24'W. MNRJ 13503, 1, 195 mm, MNRJ 14634, 2, 34-176 mm, mun. São Fidelis, Fazenda Poço d'Antas, rio Dois Rios, aff (R bank), rio Piraíba do Sul dr., ca. 21°38'S, 041°51'W. MNRJ 15593, 1, 134 mm, mun. Campos dos Goytacazes, Lagoa Feia at Ponta Grossa dos Fidalgos, rio Ururaí-Lago Feia dr., ca. 21°57'S, 041°20'W. MNRJ 17509, 1, 64 mm, mun. Macaé, Lagoa Preta (restinga de Quissamã), boundary of Macaé with Campos, Lagoa Preta dr., ca. 22°08'S, 041°25'W. MNRJ 38510, 12 (10 immature, 99-162 mm, 1 female, 153 mm, 1 male, 111 mm), mun. Silva Jardim, ca. 5 km NNW Silva Jardim, bridge over small creek, affl. rio São João dr., 22°35'46"S, 042°24'52"W. MZUSP 22702, 5 (3 immature, 72-85 mm, 1 female, 121 mm, 1 male, 149 mm), MZUSP 22703, 1, female, 114 mm, São João da Barra, rio Paraíba do Sul dr., ca. 21°39'S, 041°03'W. MZUSP 23013, 1, São Fidelis, rio Paraíba do Sul dr., ca. 21°38'S, 041°44'W. MZUSP 43130, 1 (holotype), 124 mm, MZUSP 43131, 7 (paratypes), 75-129 mm LEA, UFRJ 598, 4 (paratypes), 76-131 mm LEA, UFRJ 599, 2 (paratypes), 80-80 mm LEA, collected with holotype. UFRJ 529, 3, 79-91 mm LEA, córrego Salto d'Água 6 km N Silva Jardim (rd. from Gaviões), rio São João dr., ca. 22°39'S, 042°23'W. MZUSP 45880, 20, mun. Silva Jardim, riacho Fazenda Nova, 5 km road to Bananeiras, rio São João dr., ca. 22°40'S, 042°22'W. MZUSP 80122, 2, male (1 CS), 174-176 mm, mun. Silva Jardim, 28 km N by Boqueirão-Japuiba rd., at Gaviões, rio São João dr., ca. 22°34'S, 042°34'W. NRM 22480, 2, 123-151 mm, mun. Silva Jardim, Japuiba, Gaviões, rio São João dr., ca. 22°33'S, 042°31'W. SU 36964, 1, 98 mm, USNM 129915, 6, 85-230 mm (3 sexed: 1 immature, 148 mm, 2 female, 138-230 mm), Rio de Janeiro and its vicinity, ca. 22°55'S, 043°09'W. SU 62742, 4, 44-87 mm, Rio de Janeiro, old Petrópolis rd., no coordinates. UF 183780, 2 (1CS), 120-130 mm, mun. Casimiro de Abreu, rio São João dr., ca. 22°29'S, 042°12'W. ZMH 11627, 18 (14 measured and sexed: 5 immature, 112-129 mm, 4 female, 120-159 mm, 5 male, 152-185 mm), prov. Rio de Janeiro, no coordinates.

Brachyhypopomus jureiae Triques & Khamis, 2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.

(Fig. 33; Tables 2-5, 15)

Brachyhypopomus jureiaeTriques & Khamis, 2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.: 62, fig. 1, color photograph of paratype (original description, type locality - Brazil, São Paulo, rio Una do Prelado, Juréia Ecological Station). -Oyakawa et al., 2006Oyakawa, O. T., A. Akama, K. C. Mautari & J. C. Nolasco. 2006. Peixes de riachos da mata atlântica nas unidades de conservação do vale do rio Ribeira de Iguape no Estado de São Paulo. São Paulo, Editora Neotrópica, 201pp.: 74, color photograph of live individual (Brazil, São Paulo, catalog of fishes from Atlantic forest streams). -Menezes et al., 2007Menezes, N. A., S. H. Weitzman, O. T. Oyakawa, F. C. T. Lima, R. M. C. Castro & M. J. Weitzman. 2007. Peixes de água doce da mata atlântica: lista preliminar das espécies e comentários sobre conservação de peixes de água doce neotropicais. São Paulo, Museu de Zoologia da Universidade de São Paulo, 407 pp.: 319 (reproduction of photograph from Oyakawa et al., 2006Oyakawa, O. T., A. Akama, K. C. Mautari & J. C. Nolasco. 2006. Peixes de riachos da mata atlântica nas unidades de conservação do vale do rio Ribeira de Iguape no Estado de São Paulo. São Paulo, Editora Neotrópica, 201pp.). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Diagnosis. Brachyhypopomus jureiae is diagnosed from congeners by the following combination of characters: bilateral columns of electrocytes at the anal-fin terminus 4, vs. 6 in B. bennetti and vs. 3 in all other congeners except B. belindae, B. diazi, B. janeiroensis, B. occidentalis (except some populations in Colombia and Venezuela, see redescription of B. occidentalis), and B. palenque; precaudal vertebrae 20, vs. 16-19 in B. diazi and vs. 24-26 in B. belindae; snout to pectoral-fin base 12.3-15.7% LEA, vs. 10.7-12.3% in B. janeiroensis; pectoral-fin rays 14-16, vs. 17-21 in B. palenque. Brachyhypopomus jureiae exhibits similar pigmentation and overlapping meristic counts and morphometric proportions with B. occidentalis but can be distinguished by absence of the lateral ethmoid absent, vs. presence (Mago-Leccia, 1978Mago-Leccia, F. 1978. Los peces de la familia Sternopygidae de Venezuela. Acta Científica Venezolana, 29: 1-89.: 58, fig. 11) in B. occidentalis.

Description. Head and body shape, and pigmentation illustrated in Fig. 33. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 15. Body moderate in depth. Head moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Pectoral fin moderate in width, pectoral-fin rays 14-16 (mode 16). Precaudal vertebrae 20, with 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) posterior to, or near, tip of pectoral fin. Anal-fin rays 188-220 rays (197-220, median 205 in specimens we examined). Dorsal rami of recurrent branch of anterior lateral line nerve visible. Middorsal region of body scaled. Rows of scales above lateral line 6-7 (mode 6). Lateral line continuous. Many specimens with complete absence of groove-like depigmented epidermal canals. Some specimens with very sparse depigmented canals bordered by dark pigment, forming parallel wavy scratch-like marks either side of and near (1-2 scales distance from) lateral line in posterior half of body only (mostly dorsal to lateral line), and some single meandering canals in upper dorsum. Four bilateral horizontal columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament moderate to long in length.

Coloration. (Fig. 33). Background pale to dark brown, much darker dorsal to lateral line. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal surface speckled with dark pigment and irregular dark flecks or patches over background. Vertical stripes and saddles absent on flank. Dorsal and ventral flank with light, even scattering of chromatophores and with irregular dark brown or charcoal spots. Caudal filament darker dorsally and with irregular dark patches. Head with very pale background color ventrally, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 33
Brachyhypopomus jureiae. MZUSP 100268, female, 170 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Bateçaria, rio Ribeira de Iguape dr. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 292 mm TL, 194 mm LEA (n = 14). Largest male specimen examined 170 mm TL, 125 mm LEA (n = 1). Largest female specimen examined 169 mm TL, 116 mm LEA (n = 4).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil (Fig. 23). Known only from the rio Una do Prelado and rio Ribeira de Iguape, coastal drainages in southeast São Paulo state.

Ecological notes. Brachyhypopomus jureiae is known from small Atlantic forest and coastal lowland streams. Triques & Khamis (2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.) provide some notes on the ecology of the type locality: "specimens were collected in the rio do Descalvado, a blackwater river of muddy bottom with surface partially covered by water-hyacinth (Eichhornia sp.); grasses are occasionally present on the margins. Water pH 6.0." One of us (WGRC) collected B. jureiae from small very slow-flowing blackwater streams of the rio Ribeira de Iguape drainage in July 2006 and July 2008. The streams traversed forest fragments and pastureland, were 0.5- 2 m in width, up to 0.5 m deep, and had clay or sandy beds. All specimens were collected from submerged leaf litter or marginal vegetation. The following water parameters were recorded: conductivity 55-62 µScm-1, dissolved oxygen 2.5-3.0 mgl-1, temperature 15-23°C, pH 6.4. Reproductive biology is unknown. Stomach contents of specimens from the rio Ribeira de Iguape drainage comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: None.

Local names. Brazil: tuvira.

Material examined. 14 specimens. Brazil. São Paulo. DZUFMG 010, 1 (holotype), 292 mm TL, 194 mm LEA, examined from photographs, DZUFMG 011, 2 (paratypes), 142-147 mm LEA, examined from photograph, MZUSP 67491, 1 (paratype), MZUSP 70004, 1 (paratype), 141 mm, Estação Ecológica Juréia, rio do Descalvado, rio Una do Prelado dr., ca. 24°29'S, 047°14'W. FMNH 54543, 1, 153 mm, Iguape, rio Ribeira de Iguape dr., ca. 24°40'S, 047°32'W. MZUSP 83020, 2, immature, 60-65 mm, nr. Vila de Momuna, stream affl. rio Momuna, rio Ribeira de Iguape dr., 24°42'57"S, 47°41'27"W. MZUSP 93118, 1, male (CS), 170 mm, stream, affl. rio Momuna, ca. 1.5 km Vila de Momuna, rio Ribeira de Iguape dr., 24°42'29"S, 47°40'53"W. MZUSP 100268, 5, (1 immature, 100 mm, 4 female, 149-169 mm), nr. Vila de Momuna, rio Bateçaria, affl. rio Momuna, rio Ribeira de Iguape dr., 24°42'56"S, 047°41'28"W.

Brachyhypopomus menezesi, new species

urn:lsid:zoobank.org:act:5C81E7C7-4DCE-4EEA-A56F-D0533ACF70E2

(Fig. 34; Tables 2-5, 15)

Brachyhypopomus sp. "men". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus electropomus. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 122 (description in unpublished thesis with disclaimer stating that nomenclatural acts not available, a nomen nudum, name refers also to B. bombilla and B. regani).

Brachyhypopomus sp. "menezesi". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MZUSP 87147, male, 100 mm TL, 75 mm LEA, Brazil, Bahia, 1 km São Marcelo, rio Sapão, affl. rio Preto, rio São Francisco dr., 11°01'02"S, 045°31'50"W, 11 Nov 2002, C. Moreira & J. Nolasco.

Paratypes. 6 specimens, localities from rio São Francisco dr. Brazil. Bahia. MZUSP 40190, 1 (CS), 111 mm, mun. Ibiraba, nr. mouth of rio Icatú, ca. 10°33'S, 043°06'W, Sep 1988, M. Rodrigues. Minas Gerais. MCZ 52124, 5 (2 female, 111-112 mm, 3 male, 112-119 mm), rio Pandeiros, ca. 15°42'S, 044°36'W, 1938, W. Schroeder.

Non-types. 7 specimens. Brazil. Minas Gerais (localities from rio São Francisco dr.). MCP 28255, 5, 35-56 mm, mun. Claro de Minas, stream at entrance of Claro de Minas, hwy. Guarda-Mor-Vazante, affl. rio Claro, affl. rio Escuro, affl. rio Paracatu, 17°56'07"S, 046°58'28"W. MZUSP 39420, 2, 68-71 mm LEA, Lagoa do Tacho [nr. Pirapora], L margin rio São Francisco, ca. 17°20'S, 044°56'W.

Diagnosis. Brachyhypopomus menezesi is diagnosed from congeners by the following combination of characters: accessory electric organ over the opercular region present, vs. absent in all congeners except B. bombilla and B. regani; dorsal surface with large dark blotches against a lighter background, vs. dorsal surface speckled with small brown chromatophores on a pale background in B. bombilla; caudal filament length 24.7-33.3% LEA, vs. 11.1-17.9% in B. regani.

Description. Head and body shape, and pigmentation illustrated in Fig. 34. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 15. Body moderate in depth. Head moderate in length and shallow to moderate in depth. Dorsal profile of head straight to slightly concave from occiput to snout, ventral profile of head approximately straight to slightly concave between operculum and snout, snout truncate to rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum present and very prominent; skin over AEO completely depigmented; border rounded and very conspicuous. Pectoral fin narrow to moderate in width, pectoral-fin rays 14-16 (no mode, median 15). Precaudal vertebrae 16-17 (mode 16), with 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) posterior to, or near, tip of pectoral fin. Rows of scales above lateral line 6-7 (mode 6). Lateral line continuous. Multiple groove-like depigmented and darkly pigmented epidermal canals form parallel striations either side of lateral line in posterior third of body; striations reaching 1-4 scales (including lateral line series) dorsally, and 1-2 scales ventrally. Epidermal canals flanking lateral line not present in anterior portion of body, do not form a pair of long irregular lines either side of dorsal surface in dorsal portion of flank, and do not form isolated horizontal wavy line midway from lateral line to dorsal midline in midbody or anterior portion of body. Additional multiple parallel fine depigmented epidermal canals running in an anterodorsal to posteroventral direction over body cavity, some of which converge posteriorly to two or three canals running posteriorly for approximately third anal-fin base distance approximately half way from lateral line to proximal edge of anal-fin pterygiophores before fading. Three bilateral columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Electrocytes of hypaxial electric organ extend anterior to anal and urogenital pores and extend into opercular area to form paired accessory electric organ. Caudal filament of moderate length.

Coloration. (Fig. 34). Background light tan to brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal region mottled with irregular pattern of small, well demarcated, interconnected dark blotches against a homogenous lighter background (contrasting with a uniform speckling of small brown chromatophores against a lighter background in B. bombilla). Dark mottling extends ventrally across dorsal and ventral flank, with highest density in dorsal portions of flank. Caudal filament darker than body, with some irregular dark markings. Head with evenly scattered dark chromatophores, darker dorsally. Region over accessory electric organ completely depigmented. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline. Anal-fin rays hyaline with light scattering of brown chromatophores. Color in live individuals never observed, but likely similar to preserved specimens.

Fig. 34
Brachyhypopomus menezesi. MZUSP 87147, holotype, male, 100 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Sapão, rio São Francisco dr. Note prominent opercular accessory electric organ (pale structure). Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 119 mm TL, 83 mm LEA (n = 14). Largest male specimen examined 119 mm TL, 83 mm LEA (n = 4). Largest female specimen examined 112 mm TL, 88 mm LEA (n = 2).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil (Fig. 27). Known only from the middle and upper rio São Francisco drainage, in the states of Bahia and Minas Gerais.

Ecological notes. Geographical coordinates and labels accompanying the examined museum specimens indicate that B. menezesi occurs in small rivers and streams, and also lacustrine environments. Stomach contents of one examined specimen comprised aquatic insect larvae - mostly Chironomidae. The ecology of B. menezesi is otherwise unknown.

Co-occurring congeners: None.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Naércio Aquino Menezes, Brazilian ichthyologist, for his important contributions to Neotropical fish systematics.

Local names. Brazil: tuvira.

Brachyhypopomus occidentalis (Regan, 1914)

(Fig. 35; Tables 2-5, 16)

Rhamphichthys (Brachyrhamphichthys) brevirostris. -Steindachner, 1880Steindachner, F. 1880. Zur Fisch-fauna des Cauca und der Flüsse bei Guayaquil. Denkschriften der Kaiserlichen Akademie der Wissenschaften in Wien, Mathematisch-Naturwissenschaftliche Classe, 42: 55-104, pls. 1-9. [Also published as a separate (1880), pp. 1-51, pls. 1-9.].: 89 (Colombia, Cauca dr., catalog of fishes).

Brachyrhamphichthys brevirostris. -Eigenmann & Eigenmann, 1891Eigenmann, C. H. & R. S. Eigenmann. 1891. A catalogue of the freshwater fishes of South America. Proceedings of the United States National Museum, 14: 1-81.: 62 (Colombia, Cauca dr., catalog of South American fishes).

Hypopomus brevirostris. -Eigenmann & Ward, 1905Eigenmann, C. H. & D. P. Ward. 1905. The Gymnotidae. Proceedings of the Washington Academy of Sciences, 7: 158-188.: 170, 186. pl. 10, fig. 13, black and white photograph without locality data, photograph is not of B. brevirostris; it resembles B. occidentalis (Colombia, Cauca dr., listing of gymnotiform species). -Eigenmann, 1910Eigenmann, C. H. 1910. Catalogue of the freshwater fishes of tropical and south temperate America. Pp. 375-511. In: Scott W. B. (Ed.) Reports of the Princeton University expeditions to Patagonia 1896-1899, Volume III, Part IV. Princeton, University of Princeton.: 449 (Cauca dr., catalog of fishes). -Eigenmann & Fisher, 1914Eigenmann, C. H. & H. G. Fisher. 1914. The Gymnotidae of Trans-Andean Colombia and Ecuador (Contributions from the Zoological Laboratory of Indiana University, No. 141). Indiana University Studies, 25: 235-237.: 236 (Colombia - Soplaviento [Magdalena dr.], Managru, Truando, Raspadura, Quibdó [Atrato dr.]; Calima [San Juan dr.], Gymnotiformes of trans-Andean Colombia and Ecuador). -Meek & Hildebrand, 1916Meek, S. E. & S. F. Hildebrand. 1916. The fishes of the fresh-waters of Panama. Field Museum Natural History Publications, Zoölogical Series, 10: 1-374, pls. 376-332.: 310 (Panama, río Chagres basin, río Bayano basin, Atlantic and Pacific drainages of Panama and Colombia, catalog of fishes). -Eigenmann, 1922Eigenmann, C. H. 1922. The fishes of western South America. Part I: The fresh-water fishes of northwestern South America, including Colombia, Panama, and the Pacific slopes of Ecuador and Peru, together with an appendix upon the fishes of the Rio Meta in Colombia. Memoirs of the Carnegie Museum, 9: 1-346, pls. 341-338.: 174 (Atlantic and Pacific drainages of Panama, Atrato, San Juan and Magdalena drs., catalog of fishes in NW South America). -Eigenmann & Allen, 1942Eigenmann, C. H. & W. R. Allen. 1942. Fishes of western South America. Lexington, University of Kentucky, 494 pp.: 314 (Panama, Chagres, listing of gymnotiforms). -Fowler, 1945Fowler, H. W. 1945. Colombian Zoological Survey. Part I. The freshwater fishes obtained in 1945. Proceedings of the Academy of Natural Sciences of Philadelpia, 97: 93-135.: 179 (Panama, catalog of fishes).

Hypopomus occidentalisRegan, 1914Regan, C. T. 1914. Fishes from the Condoto river, Colombia collected by Dr. H.G.F. Spurrell. Annals and Magazine of Natural History, (8) 14: 13-32.: 32 (original description, type locality - Colombia, Chocó, río Condoto, río San Juan dr.). -Eigenmann, 1922Eigenmann, C. H. 1922. The fishes of western South America. Part I: The fresh-water fishes of northwestern South America, including Colombia, Panama, and the Pacific slopes of Ecuador and Peru, together with an appendix upon the fishes of the Rio Meta in Colombia. Memoirs of the Carnegie Museum, 9: 1-346, pls. 341-338.: 175 (Colombia, río Condoto, catalog of fishes in NW South America). -Bussing, 1987Bussing, W. A. 1987. Peces de las aguas continentales de Costa Rica. San José, Editorial de la Universidad de Costa Rica, 271 pp.: 99, fig. 37, black and white photograph (Costa Rica, catalog of fishes). -Schultz, 1944Schultz, L. P. 1944. Two new species of fishes (Gymnotidae, Loricariidae) from Caripito, Venezuela. Zoologica, Scientific Contributions of the New York Zoological Society, 29: 39-44.: 40 (diagnosis against B. beebei). -Schultz, 1949Schultz, L. P. 1949. A further contribution to the ichthyology of Venezuela. Proceedings of the United States National Museum, 99: 1-211.: 66, key to hypopomids; fig. 9a., illustration of arrangement of cephalic pores (Venezuela, listings from Motatán and Maracaibo drs.). -Hagedorn & Carr, 1985Hagedorn, M. & C. Carr. 1985. Single electrocytes produce a sexually dimorphic signal in South American electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae). Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 156: 511-523.: 513, fig. 1, drawing of breeding male and female, with sexual dimorphism of caudal filament (Panama, reproductive ecology - image reprinted in Hagedorn, 1986Hagedorn, M. 1986. The ecology, courtship and mating of gymnotiform electric fish. Pp. 495-525. In: Bullock T. H. & W. Heiligenberg (Eds.). Electroreception. New York, John Wiley and Sons.: 512, fig. 4; Hagedorn: 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335., 330, fig. 2; Kramer: 1990Kramer, B. 1990. Electro-communication in teleost fishes: behaviour and experiments. New York, Springer, 240p., 14, fig. 1.6). -Galvis et al., 1997Galvis, G., J. I. Mojica & M. Camargo. 1997. Peces del Catatumbo. Bogotá, Asociación Cravo Norte, 118 pp.: 102, color photograph of live individual (Colombia, río Catatumbo dr., fish list for NW South America). -Bussing, 1998Bussing, W. A. 1998. Peces de las aguas continentales de Costa Rica/Freshwater fishes of Costa Rica, 2nd. edition. San José, Editorial Universidad de Costa Rica, 468 pp.: 134, black and white photograph, note on diet (Costa Rica, catalog of fishes).

Brachyhypopomus occidentalis. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48, 170, fig. 70, line drawing of head and anterior portion of body of specimen MBUCV-V 14112, río Guaco, Maracaibo dr., Venezuela (in listing of Brachyhypopomus). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 133 (redescription). -Bermingham & Martin, 1998Bermingham, E. & E. P. Martins. 1998. Comparative mtDNA phylogeography of neotropical freshwater fishes: Testing shared history to infer the evolutionary landscape of lower Central America. Molecular Ecology, 7: 499-517.: 502, 505 (Panama - Atlantic and Pacific drs.; Colombia - Atrato and Magdalena drs., molecular phylogeography). -Hopkins, 1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.: 1218, fig. 1, black and white photographs of breeding male and female, reproduced from Hagedorn, 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.: 330, fig. 2 (electric organ morphology and impedance matching). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 495 (Colombia, Panama, catalog of hypopomids). -Crampton & Albert 2006: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Maldonado-Ocampo et al., 2012Maldonado-Ocampo, J. A., J. S. U. Oviedo, F. A. Vila-Navarro, A. Ortega-Lara, S. Prada-Pedreros, L. F. Jiménez S, U. Jaramillo-Villa, A. Arango, T. S. Rivas & G. C. S. Garcés. 2012. Peces dulceacuícolas del Chocó biogeográfico de Colombia. Bogotá, World Wide Fund for Nature, Colombia, 400p.: 323, color photograph of live individual (Colombia - Atrato, San Juan, Baudó, Calima, Anchicayá, Dagua, Mira drs., listing of fish in Chocó, Colombia). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 147, fig. 3D, outline of head; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Picq et al., 2014Picq, S., F. Alda, R. Krahe & E. Bermingham. 2014. Miocene and Pliocene colonization of the Central American isthmus by the weakly electric fish Brachyhypopomus occidentalis (Hypopomidae, Gymnotiformes). Journal of Biogeography, 41: 1520-1532.: 1520-1532 (Panama and Colombia, phylogeography). -Elbassiouny et al., 2016Elbassiouny, A. A., R. K. Schottt, J. C. Waddell, M. A. Kolmann, E. S. Lehmberg, A. Van Nyatten, W. G. R. Crampton, B. S. W. Chang & N. R. Lovejoy. 2016. Mitochondrial genomes of the South American electric knifefishes (Order Gymnotiformes). Mitochondrial DNA. Part B: Resources, 1: 401-403.: 402-403, fig. 1 (position in phylogeny of Ostariophysi, based on mitochondrial genomes). -Picq et al., 2016Picq, S., F. Alda, E. Bermingham & R. Krahe. 2016. Drift-driven evolution of electric signals in Neotropical knifefish. Evolution, doi: 10.1111/evo.13010.
https://doi.org/10.1111/evo.13010...
(EOD evolution). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 13, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 16
Morphometrics for Brachyhypopomus occidentalis. ST., largest syntype specimen; SD, standard deviation; drs., drainages. Ranges for the type region refer to syntype and non-type specimens from Pacific drs. of Colombia (río San Juan and Baudó drs., Chocó). Ranges for Panama populations refer to non-type specimens grouped into four regions: Atlantic - East = río Mandinga and Cartí drs.; Atlantic - West = río Cricamola dr. (and río Carbón dr. of Costa Rica); Pacific - East = río Bayano, río Mamoni and adjacent drs. Ranges for the populations grouped under lago Maracaibo drainages refer to non-type specimens from the río El Quebradón, Motatán, and San Juan drs. of Venezuela.

Diagnosis. Brachyhypopomus occidentalis is diagnosed from congeners by the following combination of characters: absence of series of diffuse horizontal dash-like dark markings along lateral line in posterior third of body, anterior to anal-fin terminus, vs. presence in B. alberti, B. arrayae, B. hamiltoni, and B. draco; pale stripe along middorsal region of body absent, vs. prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament in B. beebei, B. belindae, B. gauderio, B. pinnicaudatus, and B. verdii; anal-fin rays 191-254, vs. 155-225 in B. batesi, B. flavipomus, B. menezesi, and B. sullivani; pectoral-fin rays 15-20, vs. 10-13 in B. benjamini and B. cunia; bilateral columns of electrocytes at anal-fin terminus 4-5 (or 3 in some populations in Colombia and Venezuela, see below), vs. 6 in B. bennetti; accessory electric organ over opercular region absent, vs. present in B. bombilla and B. regani; caudal filament short, 11.5-30.7% LEA, vs. 31.3-64.5% in B. bullocki, B. hendersoni, and B. janeiroensis; diagonally oriented bars on flank diffuse and mostly break up ventral to lateral line, vs. vertical bars form distinct saddles which extend across lateral line in B. brevirostris; continuous or discontinuous dark vertical or diagonally oriented stripes or saddles present on body surface dorsal to lateral line, vs. absent in B. jureiae, B. palenque, and B. provenzanoi; dark suborbital stripe absent, vs. present in B. walteri. Brachyhypopomus occidentalis exhibits similar pigmentation and overlapping meristic counts and morphometric proportions with B. diazi. These two species can be distinguished by the more extensive network of depigmented and dark-margin epidermal canals in B. diazi (including in the anterior half of the body) than in B. occidentalis, and by the first branchiostegal ray is approximately as wide as the third branchiostegal ray in B. occidentalis, vs. the first branchiostegal ray is distinctly narrower than the third in B. diazi.

Description. Head and body shape, and pigmentation illustrated in Fig. 35. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 16. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head straight to gently convex from occiput to snout, ventral profile of head slightly concave between operculum and snout, snout rounded. Eye small to moderate in size. Upper jaw slightly to moderately prognathous. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 35-54 (median 48, n = 10). Pectoral fin narrow to broad in width, pectoral-fin rays 15-20. Modes and ranges similar for specimens from Pacific coastal drainages of Colombia (16-18, mode 17), Maracaibo drainage (15-18, mode 17), eastern Atlantic drainages of Panama (16-18, mode 17), and eastern pacific drainages of Panama (15-18, mode 17), but slightly higher for specimens from western Atlantic drainages of Panama (río Cricamola) (18-21, mode 18). Precaudal vertebrae 17-20. Modes and ranges similar for specimens from Pacific coastal drainages of Colombia (19-21, mode 19), eastern Atlantic drainages of Panama (18-19, mode 19), western Atlantic drainages of Panama (18-20, mode 19), and eastern pacific drainages of Panama (18-20, mode 19), but slightly lower for specimens from the Maracaibo drainage (17-19, mode 18). 1-3 transitional vertebrae (mode 2 in all examined populations). Anal-fin origin slightly (< 0.25 HL distance) anterior to, or posterior to, or near, tip of pectoral fin. Anal-fin rays 194-254. Ranges and medians for specimens are similar for specimens from the following three regions: eastern Atlantic drainages of Panama, 194-234 (216); western Atlantic drainages of Panama, 199-228 (216); eastern Pacific drainages of Panama, 212-229 (216). Ranges and medians are slightly lower for specimens from the Maracaibo drainage, 201-213 (203), and slightly higher for specimens from the Pacific coast of Colombia 207-254 (222). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 7). Lateral line continuous. Depigmented epidermal canals sparse, and mostly restricted to posterior half of body. In anterior half of body canals occur in low density in upper portions of flank, usually as single meandering lines in dorsal flank around midway between lateral line and dorsal midline, nearer to lateral line posteriorly. In second half of body canals occur as multiple parallel wavy lines in dorsal and (less commonly) in ventral flank, approximately parallel to lateral line. Density of epidermal canals somewhat higher in populations from the Maracaibo basin, but in all populations considerably less extensive and conspicuous than in B. diazi. Number of bilateral electrocyte columns: in populations from region of type locality (río Condoto): 4 columns at anal-fin terminus in immature specimens and 4-5 (mode 4) in mature females and males, and 4-5 (mode 4) columns at a midpoint from anal-fin terminus to tip of caudal filament in immature specimens, mature females and males. In some specimens extra electrocyte columns appear posterior to mid-point between anal-fin terminus and tip of caudal filament - especially in laterally-compressed paddle-like tip - bringing maximum number of columns to 5-6 (in both males and females). Specimens with regenerated caudal filaments often have more columns of electrocytes in regenerated portions. We noted population-level variation in number of bilateral columns of electrocytes in B. occidentalis. For example, number measured at anal-fin terminus was: río Atrato, Colombia (3-4, mode 3, n = 9); río Magdalena, Colombia (3, n = 9); río Sinú, Colombia (3, n = 1), río Motatan, lago Maracaibo, Venezuela (3-4, mode 3, n = 22); río Chagres, Panama (4-6, mode 5; increasing to 6-7 columns in laterally compressed caudal filament tip, n = 12), río Mandingá, Panama (3, n =5); río Cricamola, Panama (4, n = 12), río Sixaola, Costa Rica (4-5, mode 4, n = 9). More work is needed to fully characterize population-variation in gross anatomy of the electric organ of B. occidentalis, much of which may be explained by impedance matching to ambient conductivity. Caudal filament short to moderate in length.

Coloration. (Fig. 35). Pigmentation highly variable within and between regions. Eigenmann (1922Eigenmann, C. H. 1922. The fishes of western South America. Part I: The fresh-water fishes of northwestern South America, including Colombia, Panama, and the Pacific slopes of Ecuador and Peru, together with an appendix upon the fishes of the Rio Meta in Colombia. Memoirs of the Carnegie Museum, 9: 1-346, pls. 341-338., 174-175), discussed variation in pigmentation among populations of B. occidentalis from the Magdalena, Atrato, and San Juan drainages of Colombia. Background pale tan to dark brown, usually considerably darker dorsally. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal surface with speckling of lighter pigment on dark background, and sometimes with irregular dark patches which may extend into thin vertically oriented or diagonal incomplete bands that extend across flank; banding if present is usually more conspicuous in anterior third of body. Ventral flank over anal-fin pterygiophores with irregular dark patches forming a marbled pattern. Caudal filament darker than body. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral-fin rays hyaline with light scattering of dark chromatophores. Color in live individuals similar to preserved specimens, often with olive green tinge, opercular region usually rosy due to underlying gills, body cavity of gravid females often yellow due to underlying ripe eggs (Fig. 35d).

Fig. 35
Brachyhypopomus occidentalis. a. NRM 27736, immature, 131 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Colombia, rio Baudó dr. b. BMNH 2012.6.13.1, largest syntype specimen, sex not determined, 147 mm TL (body in lateral view, specimen preserved in EtOH, note damage and subsequent regeneration to caudal filament); Colombia, río San Juan dr. c. IAVHP 7022 (WC04.230905), male, 162 mm TL. d. IAvHP 7022 (WC03.230905), female, 112 mm TL, non-type (bodies in lateral view, live individuals); Colombia, río Atrato dr. Note sexual dimorphism in caudal-filament length and height in c (male) & d (female). Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 278 mm, 216 mm TL (n = 892). Largest male specimen examined 278 mm TL, 216 mm LEA (n = 18). Largest female specimen examined 162 mm TL, 144 mm LEA (n = 33).

Sexual dimorphism. We observed population variation in the degree to which caudal morphology differs between breeding males and females, which may be correlated to electrical conductivity. Conductivity varies considerably among drainages occupied by B. occidentalis, including low-conductivity systems (ca. 5-60 μScm-1) and high-conductivity systems (ca. 100-450 μScm-1). In low-conductivity systems (e.g. streams of the río Cricamola, río Atrato, conductivity 5-30 μScm-1, NRL, WGRC pers. obs.), breeding males appear to develop longer and marginally widened caudal filaments. In contrast, in very high conductivity systems (conductivity 300-450 μScm-1 in some streams of the río San Juan, río Bayano listed in 'Material examined', and parts of Panama, NRL pers. obs.), breeding males develop very wide but not very elongated caudal filaments. These observations suggest population-level variation in caudal filament morphology associated with impedance matching sensu Hopkins (1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.) and merit a more detailed quantitative study.

In addition to exhibiting enlarged caudal filaments, the number of bilateral columns of electrocytes at the anal-fin terminus increases slightly, from invariably 4 in immature specimens and females to 4-5 (mode 4) in breeding males. Breeding males also exhibit clearly enlarged electrocytes relative to immature specimens and females. Large breeding males commonly with paddle-like lateral compression at caudal filament tip (Figs. 35c-d). No known sexual dimorphism in pigmentation.

We noted population variation in the maximum size attained by males. Breeding males in museum collections from two drainages, the río San Juan and río Cricamola, were considerably larger than females (ca. 260-278 mm in fully mature males, vs. ca. 103-153 mm in fully mature females). In contrast, mature males were only marginally larger than females in other drainages, including the río Atrato, Atlantic and Pacific drainages of eastern Panama, and Maracaibo drainages. Based on the phylogeny of Picq et al. (2014Picq, S., F. Alda, R. Krahe & E. Bermingham. 2014. Miocene and Pliocene colonization of the Central American isthmus by the weakly electric fish Brachyhypopomus occidentalis (Hypopomidae, Gymnotiformes). Journal of Biogeography, 41: 1520-1532.), these observations suggest multiple independent origins of a prominent secondary sexual dimorphism of body size.

Geographic distribution. Colombia, Costa Rica, Panama, and Venezuela (Fig. 36). Westernmost records from the río Sixaola drainage, an Atlantic drainage of Costa Rica. Known from multiple Atlantic and Pacific drainages throughout Panama, but note gaps in collecting records in Fig. 36. Widespread through Pacific coast of Colombia, including the río Atrato (Atlantic drainage), río San Juan, río Baudó, río San Cipriano and rio Anchicayá (Pacific drainages). Isolated records from the río Sinú (Atlantic drainage) and lower and middle río Magdalena (Atlantic drainage). Widespread in lowland drainages around the entire perimeter of lago de Maracaibo.

Fig. 36
Collection records for Brachyhypopomus occidentalis (circles) and B. palenque (squares). The lectotype location for B. occidentalis and holotype location for B. palenque are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found complete overlap in the range of meristic counts (Tables 2-5) and morphometric proportions (Table 16), and observed similar pigmentation among specimens from five geographical regions. Specimens from no single region exhibited consistently divergent meristic counts or morphometric proportions (see 'Description', and 'Sexual dimorphism'). These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. occidentalis are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners.

Mirroring the results of an earlier study by Birmingham & Martin (1998), Picq et al. (2014Picq, S., F. Alda, R. Krahe & E. Bermingham. 2014. Miocene and Pliocene colonization of the Central American isthmus by the weakly electric fish Brachyhypopomus occidentalis (Hypopomidae, Gymnotiformes). Journal of Biogeography, 41: 1520-1532.), presented a population level phylogeny of B. occidentalis in which populations from west Panamanian Atlantic drainages (Cricamola, Sixaola, Changuinola, Calovébora) form the sister taxon to populations from all other regions of Panama and northwestern Colombia (including Pacific and Atlantic drainages); both studies also concluded that populations from lago Maracaibo drainages constitute the sister taxon to all Panama-Colombia lineages. Picq et al. (2013Picq, S., F. Alda, E. Bermingham & R. Krahe. 2013. Phylogeny and geographical variation in the electric signals of the primary neotropical knifefish Brachyhypopomus occidentalis. Frontiers in Behavioral Neuroscience Conference. Abstract: Tenth International Congress of Neuroethology: doi: 10.3389/conf.fnbeh.2012.3327.00283.
https://doi.org/10.3389/conf.fnbeh.2012....
; 2016Picq, S., F. Alda, E. Bermingham & R. Krahe. 2016. Drift-driven evolution of electric signals in Neotropical knifefish. Evolution, doi: 10.1111/evo.13010.
https://doi.org/10.1111/evo.13010...
) noted EOD divergences between populations in independent drainages consistent with non-adaptive drift, and observed an unusual divergence of the EOD waveforms of breeding males in the río Cricamola relative to other Panamanian populations. Although we did not note salient morphometric and meristic differences between specimens of B. occidentalis from the río Cricamola versus other populations of B. occidentalis, we did observe a more extreme form of sexual size dimorphism and larger maximum body sizes in río Cricamola specimens than in populations from other Panamanian drainages, the río Atrato, and lago Maracaibo (see 'Sexual dimorphism').

Ecological notes. Brachyhypopomus occidentalis is common in small, gently-flowing streams and shallow swamps and lagoons throughout its range (Bussing, 1987Bussing, W. A. 1987. Peces de las aguas continentales de Costa Rica. San José, Editorial de la Universidad de Costa Rica, 271 pp.; Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; Hagedorn, 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.). Water parameters, including pH, conductivity (see 'Sexual dimorphism'), dissolved oxygen, and turbidity are highly variable in the systems inhabited by this species. The reproductive ecology and mating behavior of Panamanian B. occidentalis have been documented in detail by M. Hagedorn and co-authors (Hagedorn, 1986Hagedorn, M. 1986. The ecology, courtship and mating of gymnotiform electric fish. Pp. 495-525. In: Bullock T. H. & W. Heiligenberg (Eds.). Electroreception. New York, John Wiley and Sons.; 1988Hagedorn, M. 1988. Ecology and behaviour of a pulse-type electric fish, Hypopomus occidentalis (Gymnotiformes, Hypopomidae), in a fresh-water stream in Panama. Copeia, 1988: 324-335.; Hagedorn & Zelick, 1989Hagedorn, M. & R. Zelick. 1989. Relative dominance among males is expressed in the electric organ discharge characteristics of a weakly electric fish. Animal Behavior, 38: 520-525.; Kawasaki & Heiligenberg, 1989Kawasaki, M. & W. Heiligenberg. 1989. Distinct mechanisms of modulation in a neuronal oscillator generate different social signals in the electric fish Hypopomus. Journal of Comparative Physiology a-Neuroethology Sensory Neural and Behavioral Physiology, 165: 731-741.). Brachyhypopomus occidentalis breeds through the dry season, reaching maturity in its first year and exhibiting post-reproductive mortality indicative of an annual lifecycle. Individuals exhibit a high degree of site fidelity.

Stomach contents of B. occidentalis from the Atrato drainage of Colombia comprise aquatic insect larvae (especially Chironomidae) and other small aquatic invertebrates (WGRC unpublished data). Bussing (1987Bussing, W. A. 1987. Peces de las aguas continentales de Costa Rica. San José, Editorial de la Universidad de Costa Rica, 271 pp.; 1998Bussing, W. A. 1998. Peces de las aguas continentales de Costa Rica/Freshwater fishes of Costa Rica, 2nd. edition. San José, Editorial Universidad de Costa Rica, 468 pp.) also reported a diet of aquatic invertebrates, especially Diptera, in populations from Costa Rica. Dunlap et al. (2016Dunlap, K. D., A. Tran, M. A. Ragazzi & R. Krahe. 2016. Predators inhibit brain cell proliferation in natural populations of electric fish Brachyhypopomus occidentalis. Proceedings of the Royal Society B-Biological Sciences, 283: 283 20152113; DOI: 10.1098/rspb.2015.2113
https://doi.org/10.1098/rspb.2015.2113...
) infer predation of Panamanian B. occidentalis by the heptapterid catfish Rhamdia - based on correlations between caudal filament damage and the density of Rhamdia.

Co-occurring congeners: None.

Local names. Colombia: cuchillo, beringo culebra (Atrato), mayupita (Catatumbo) (Galvis et al., 1997Galvis, G., J. I. Mojica & M. Camargo. 1997. Peces del Catatumbo. Bogotá, Asociación Cravo Norte, 118 pp.); Costa Rica: madre de barbudo (Bussing, 1987Bussing, W. A. 1987. Peces de las aguas continentales de Costa Rica. San José, Editorial de la Universidad de Costa Rica, 271 pp.); Panama: cuchillo.

Material examined. 773 specimens. Colombia. Antioquia (localities from Atlantic drainages). CAS 72231, 1, 65 mm, quebrada Cristalina at Cristalina, 28 km above Puerto Berrio, río Magdalena dr., ca. 06°16'N, 074°32'W. IAVH-P 7278, 4, mun. Turbo, caño Tumarado, last 'cienaga' [swamp], Puerto Plata Vereda, El Cuarenta, río Atrato dr., 07°42'34"N, 077°01'46"W. IAVH-P 7411, 1, caño Muerto, last "cienaga" [swamp], Vereda [village] El Cuarenta, río Atrato dr., 07°42'31"N, 077°01'56"W. Bolívar. FMNH 56788, 5, 88-142 mm, SU 63675, 5, 88-142 mm, Canal de Dique between Cartagena and Calamar, at Soplaviento, affl. río Magdalena, río Magdalena dr. (Atlantic), ca. 10°23'N, 075°08'W. Chocó. BMNH 1910.7.11.217, 1, 99 mm, río Condoto, río San Juan dr. (Pacific), ca. 05°04'N, 076°40'W. BMNH 1914.5.18.94-98, 6 (syntypes), 41-105 mm, río Condoto, río San Juan dr. (Pacific), ca. 05°04'N, 076°40'W, 1914, H. Spurrell. BMNH 1915.10.1.10, 1, 123 mm, Andagoya, río San Juan, río San Juan dr. (Pacific), ca. 05°05'N, 076°43'W. BMNH 2012.6.13.1, 1 (syntype), 147 mm (see Fig. 35b), same collection data as BMNH 1914.5.18.94-98. CAS 72219, 3, 85-132 mm, Managru, upper río Quito, río Atrato dr. (Atlantic), ca. 05°20'N, 076°43'W. CAS 72227, 3, río Truando, río Atrato dr. (Atlantic), ca. 07°09'N, 077°12'W. CAS 72229, 2, FMNH 56792, 1, 121 mm, creek nr. mouth of río Guineo, affl. río Calima, río San Juan dr. (Pacific), ca. 04°04'30"N, 077°02'50"W. FMNH 56779, 3, 80-163 mm, Managrú, rio Atrato dr. (Atlantic), ca. 05°20'N, 076°43'W. FMNH 56787, 2, 86-128 mm, Truando [río Truando], rio Atrato dr. (Atlantic), ca. 07°09'N, 077°12'W. FMNH 56789, 2, 90-98 mm, Raspadura [probably Boca de Raspadura and not Raspadura, Nariño because C. E. Wilson 1913-1914 collections were all in vicinity of Quibdó, Chocó], affl. río Paimado, río Atrato dr. (Atlantic), ca. 05°16'N, 076°42'W. FMNH 56790, 1, 92 mm, Quibdó, río Atrato dr. (Atlantic), ca. 05°41'N, 076°39'W. FMNH 70885, 1, 117 mm, Pangala, ca. 40 km N Palestina, río San Juan dr. (Pacific), ca. 04°31'N, 076°59'W. IAVH-P 6812, 2, IAVH-P 6814, 2, IAVH-P 6816, 1, IAVH-P 6817, 1, IAVH-P 6820, 1, IAVH-P 7019, 1, immature, 80 mm, IAVH-P 7020, 13 (8 immature, 38-131 mm, 3 female, 105-134 mm, 2 male, 93-140 mm), mun. Yuto, quebrada Josefa 0.5 km Yuto, río Atrato dr. (Atlantic), 05°31'58"N, 076°38'04"W. IAVH-P 6813, 3, IAVH-P 6815, 1, IAVH-P 6818, 3, IAVH-P 6819, 4, IAVH-P 6821, 1, mun. Yuto, río Yuto, río Atrato dr., ca. 05°30'N, 076°39'W. IAVH-P 7017, 13 (11 immature, 41-120 mm, 1 female, 146 mm, 1 male, 144 mm), mun. Quibdó, quebrada Samurindó, 0-0.5 km upstream bridge on Quibdó-Yuto rd., río Atrato dr. (Atlantic), 05°34'24"N, 076°37'13"W. IAVH-P 7021, 27 (13 immature, 31-98 mm, 10 female, 90-134 mm, 5 male, 105-140 mm), IAVH-P 7022, 12 (9 immature, 46-102 mm, 2 female, 112-160 mm, 1 male, 162 mm), quebrada Jigudat, 5 km S Yuto on Quibdó- Certegui rd., río Atrato dr. (Atlantic), 05°30'57"N, 076°37'48"W. IAVH-P 7410, 1, mun. Riosucio, caño Sautata, río Atrato dr. (Atlantic), ca. 07°50'N, 077°04'W. IAVH-P uncat. Ict-1.1.18, 6, 99-142 mm, IAVH-P uncat. Ict-1.1.19, 2, 130-131 mm, IAVH-P uncat. Ict-1.3.1, 1, 162 mm, IAVH-P uncat. Ict-1.3.2, 9, 95-162 mm, IAVH-P uncat. Ict-1.3.3, 3, 104-173 mm, nr. Yuto, río Atrato dr. (Atlantic), ca. 05°31'N, 076'38"W. IAVH-P uncat. 12, 155-270 mm, río San Juan dr. (Pacific), no coordinates. NRM 10699, 2, 75-194 mm, headwaters of río San Juan, río San Juan dr. (Pacific), ca. 05°15'N, 076°39'W. NRM 27728, 4, 74-123 mm, quebrada Tuaró, close to La Victoria on Pan-American hwy., río Baudó dr. (Pacific), no coordinates [listed coordinates 05°32'N, 076°00'W, not located in río Baudó dr.]. NRM 27729, 1, 126 mm, NRM 27736, 5, 63-137 mm, NRM 30659, 2, 52-78 mm, Pie de Pepé, río Pepé, affl. río Baudó, río Baudó dr. (Pacific), 05°08'59"N, 076°47'00"W. NRM 27735, 5, 56-130 mm, Chaparra Idó, beneath waterfall, Tutunendo-San Francisco de Ichó rd., río Atrato dr. (Atlantic), 05°46'58"N, 076°32'02"W. NRM 27747, 2, 58-70 mm, Condoto, quebrada on rd. Condoto-Soledad, 5 min from airport rd., río San Juan dr. (Pacific), ca. 05°06'N, 076°40'W. Córdoba. NRM 46106, 1, 153 mm, 3 km E Urrá Hydropower Station, quebrada Santa Ana, río Sinú dr. (Atlantic), 08°00'40"N, 076°10'48"W. Santander. CAC-CDMB 129, 1, 132 mm, mun. Barrancabermeja, río Sogamoso, río Magdalena dr. (Atlantic), ca. 07°13'N, 073°55'W [coordinate for mouth of río Sogamoso]. Valle del Cauca (localities from Pacific drainages). CAS 72223, 3, río Calima, río San Juan dr., no coordinates. FMNH 56791, 2, 140-174 mm, creek nr. mouth of río Calima, río San Juan dr., ca. 04°08'N, 077°08'W. IMCN 2248, 2, 132-158 mm, quebrada La Sardiña, affl. río Dagua, río San Cipriano dr., ca. 03°51'N, 076°52'W. IMCN 4523, 5, quebrada El Venado at Cordoba, río San Cipriano dr., 03°52'28"N, 076°55'33"W. NRM 27751, 1, 90 mm, Sabaletas, río Sabaletas and streams upstream Sabaletas, rio Anchicayá dr., 03°44'N, 076°58'W. Region not specified. CU 71934, 4, no locality, no coordinates. Costa Rica (localities from Atlantic drainages). Limón. ANSP 163126, 4, 125-164 mm, creek on rd. from Bribri to Suretka, 6.0 km W Bribri, río Sixaola dr., 09°37'36"N, 082°52'44"W. ANSP 163170, 4, 103-131 mm, río Carbón, at Sixaola-Limon rd. 7.0 km NE Bribri, río Carbón dr., 09°39'45"N, 082°48'15"W. ANSP 163176, 10 (5 measured, 107-211 mm), ANSP 163760, 2, 134-156 mm, ANSP 163762, 1, 133 mm, creek crossing rd. 0.9 km W Shiroles, affl. río Telire, río Sixaola dr. (Atlantic), 09°33'56"N, 082°55'59"W. ANSP 163190, 6, 154-183 mm, ANSP 163205, 1, 129 mm, Suretka, creek crossing old Bribri-Suretka rd., río Sixaola dr., ca. 09°37'N, 082°51'W. ANSP 163761, 3, 113-154 mm, stream at Suretka rd., 1.4 km W Bambu, no coordinates. NCSM 44973, 2, Canton Talamanca, nr. Bratsi, affl. río Telire, río Sixaola dr. (Atlantic), 09°33'41"N, 082°53'27"W. Panama. Bocas del Toro. UF 19727, 2, female, 121-134 mm, unknown river entering Almirante Bay, mi. 5 along rd. from Almirante (Atlantic), ca. 09°15'N, 082°21'W. Bocas del Toro: Comarca Ngobe-Buglé (localities from Atlantic drainages). BMNH 1925.3.6.229.238, 10 (3 immature, 137-176 mm, 4 female, 103-153 mm, 3 male, 159-278 mm), FMNH 59196, 5, 109-155 mm, UMMZ 145687, 2, 125-170 mm, UMMZ 145688, 4, 97-200, UMMZ 145689, 4, 105-200 mm, creek nr. Konkintu, río Cricamola dr., ca. 08°51'N, 081°49'W. CAS 67704, 4, 116-225 mm, Guibari creek, below Konkintu, río Cricamola dr., ca. 08°51'N, 081°49'W. CAS 67721, 1, CAS 72230, 7, "Nomormen [label unclear] creek" above Konkintu, Cricamola dr., ca. 08°51'N, 081°49'W. CAS 67722, 1, CAS 67723, 2, creeks nr. Konkintu, Cricamola dr., ca. 08°51'N, 081°49'W. ROM 89751, 2, 206-214 mm, STRI 7724, 3, 152-203 mm, caño Chalite, stream at mouth of Poman Creek, río Cricamola dr., 08°54'13"N, 081°52'53"W. ROM 89752, 3, 139-207 mm, ROM 89754, 8, 119-222 mm, STRI 7725, 9, 80-202 mm, stream nr. Bisira, río Cricamola dr., 08°54'14"N, 081°51'27"W. ROM 89755, 1, 203 mm, ROM 89756, 2, 72-175 mm, STRI 7727, 2, 118-183 mm, small stream affl. río Uyama, río Uyama dr., 09°08'58"N, 082°19'33"W. ROM 89757, 3, 102-188 mm, STRI 7728, 4, 55-131 mm (09°08'21"N, 082°18'26"W), ROM 89758, 3, 64-142 mm (09°08'17"N, 082°18'31"W), stream at village (Baisiro?), off rd. from Almirante to Punta Peña, río Uyama dr. ROM 89759, 5, 83-231 mm, STRI 7729, 5, 98-195 mm, stream affl., río Robalo, río Robalo dr., 09°00'27"N, 082°18'49"W. ROM 89760, 4, 119-241 mm, ROM 89786, 1, 182 mm, small creek, N Almirante, río Changuinola dr., 09°20'04"N, 082°28'56"W. STRI 7730, 4, 81-195 mm, stream on Almirante to Punta Peña rd., 08°58'24"N, 082°12'23"W. UF 183793, 10, 58-163 mm, Reserva Indígena de Cricamola, río Cricamola dr., 08°56'18"N, 081°54'15"W. USNM 302016, 1, 187 mm, río Changuinola dr., ca. 09°24' N, 082°26'W. Chiriquí (localities from Pacific drainages). AUM 32356, 1, 202 mm, 10 km ESE Tolé on Pan American hwy., río Tabascara, río Vigui dr., 08°12'27"N, 081°35'07"W. Coclé. ANSP 151058, 1, 127 mm, río Chorrera at Inter-American hwy., between Penonome and Anton, río Chorrera dr., ca. 08°26'N, 080°19'W. AUM 31594, 2, 130-146 mm, Pan American hwy., 3 km SSE Chorrerita, río Hondo dr., Bahia de Parito (Pacific), 08°28'18"N, 080°19'25"W. Colón. ANSP 99880, 1, 75 mm, Canal Zone, río Agua Salud, creek on pipeline rd. nr. Gamboa, río Gatun dr. (Atlantic), ca. 09°11'N, 079°47'W. ANSP 104216, 1, 115 mm, coastal stream at Lagarto (Palma Nueva [Palmas Bellas]), W Canal Zone, río Lagarto dr. (Pacific), ca. 09°13'N, 080°04'W. ANSP 147048, 1, 163 mm, brook 7 km inland from Portobelo, Pacific coastal dr., ca. 09°31'N, 079°37'W. AUM 32118, 9, 132-170 mm, Pipeline rd. at km 4.6, Colón, río Frijoles, río Chagres dr. (Atlantic), 09°09'08"N, 079°44'06"W. FMNH 32034, 1, 69 mm, creek above Monte Líria, río Gatún dr. (Atlantic), ca. 09°16'N, 079°47'W. INHS 68132, 6, 69-99 mm, Parque Nacional Soberania, Tower Creek, río Chagres dr. (Atlantic), ca. 09°08'N, 079°41'W. INHS 68142, 1, 68 mm, INHS 68152, 8, Parque Nacional Soberania, río Frijolito, río Chagres dr. (Atlantic), ca. 09°09'N, 079°44'W. INHS 68180, 17, 33-135 mm, Parque Nacional Soberania, Tayra creek, río Chagres dr. (Atlantic), ca. 09°08'N, 079°41'W. MCP 27107, 5, 40-131 mm, río Frijoles, N Gamboa on pipeline rd., río Chagres dr. (Atlantic), ca. 09°12'N, 079°33'W. MPEG 1103, 7, to 170 mm, MPEG 1104, 13, 85-160 mm, MPEG 1106, 7, to 150 mm, Canal Zone, Gamboa hwy., nr. "2nd" bridge, no coordinates. USNM 293085, 7, 55-121 mm, río Pingandi, 1km above Pueblo Mandinga, río Mandinga dr. (Atlantic), ca. 09°28'N, 079°06'W. Darién. INHS 36100, 1, 120 mm, río Iglesia, Gulf of San Miguel (Pacific), 08°25'23"N, 078°00'05"W. SU 54431, 1, Pito, coastal stream (Atlantic), ca. 08°41'N, 077°31'W. USNM 293202, 1, 171 mm, rio Tuira 0.5 km above community Boca de Cupe, río Tuira dr. (Pacific), ca. 08°02'N, 077°34'W. Panamá. ANSP 104116, 1, 104 mm, creek at bridge on Interamerican hwy., ca. 9 mi. E río Pacora dr. (Pacific), ca. 09°08'N, 079°09'W. ANSP 104239, 1, 134 mm, creek (río Cristal) on bridge on Inter-American hwy. between Chorrera and Arraijan (Pacific), ca. 08°54'N, 079°44'W. ANSP 104436, 1, 142 mm, creek ca. 5 mi. W El Llano rd., río Bayano dr. (Pacific), ca. 09°12'N, 078°51'W [coordinates for El Llano]. ANSP 151021, 1, 191 mm, río Canitas at Inter-American hwy., ca. 10.4 km W Bayano bridge, río Chepes dr. (Pacific), 09°13'05"N, 078°52'38"W. FMNH 32033, 1, 162 mm, El Capital, río Mamoni, río Mamoni dr. (Pacific), ca. 09°07'N, 079°04'W. MCZ 45816, 10 (2 immature, 150-164 mm, 2 female, 154-162 mm, 6 male, 148-209 mm), quebrada Jesus Cristo, affl. río Chagres, at Prince Philip rd. río Chagres dr. (Atlantic - now drains to Panama Canal), ca. 09°07'N, 079°42'W. ROM 89765, 2, 69-192 mm, STRI 7741, 2, 71-75 mm, río Terable, upstream from Inter-American hwy., río Bayano dr. (Pacific), 09°13'34"N, 078°58'26"W. ROM 89768, 2, 54-58 mm, STRI 7743, 2, 63-66 mm, río Terable, upstream from Inter-American hwy., río Bayano dr. (Pacific), 09°13'34"N, 078°58'27"W. ROM 89769, 4, 65-179 mm, STRI 7745, 2, 83-169 mm, río Cañita, upstream from Inter-American hwy., río Bayano dr. (Pacific), 09°13'10"N, 078°50'54"W. ROM 89771, 3, 82-186 mm, STRI 7747, 4, 78-110 mm, stream crossing rd. through Tecal forest, off Inter-American hwy., affl. río Chachare, río Bayano dr. (Pacific), 09°12'41"N, 079°03'14"W. ROM 89772, 1, 84 mm, small stream crossing rd. to río Mamoni off Inter-American hwy., affl. río Mamoni, río Bayano dr. (Pacific), 09°11'55"N, 079°04'19"W. ROM 89773, 5, 113-146 mm, STRI 7749, 5, 111-132 mm, quebrada Tapagrilla, río Bayano dr. (Pacific), 09°09'00"N, 079°10'48"W. STRI 7744, 1, 88 mm, río Cañita below dam, río Bayano dr., 09°12'35"N, 078°53'55"W. SU 24769, 6, Canal Zone, Three Rivers Plantation, Gatun Lake, río Chagres dr. (Atlantic - now drains to Panama Canal), ca. 09°10'N, 079°51'W. UF 12979, 3, female, 74-109 mm, creek 11 mi. S Chepo, on rd. to El Llano [río Pacora dr.?], (Pacific), ca. 09°08'N, 079°12'W. UF 12995, 1, female, 135 mm, creek 5 mi. S Tocumen Airport on Inter-American hwy., small coastal dr. (Pacific), ca. 09°02'N, 079°24'W. USNM 78764, 1, 150 mm, El Capitán, río Mamoni, río Bayano dr. (Pacific), ca. 09°12'N, 079°03'W. USNM 78765, 1, 145 mm, Largataria, rio Chagres dr. (Atlantic), ca. 09°12'N, 079°39'W. USNM 293144, 3, 44-140 mm, small stream, Cartí rd., 15 km N Pan-American [Inter-American hwy.], río Bayano dr. (Pacific), ca. 09°17'N, 078°58'W. USNM 302009, 4, 82-174 mm, creek about 2 mi. E El Llano rd., río Chepo dr. (Pacific), ca. 09°13'N, 078°56'W. USNM 302012, 2, 70-117 mm, Canal Zone, creeks of río Cocoli, W Canal, río Cocoli dr. (Pacific), ca. 08°59'N, 079°36'W. USNM 302018, 3, 92-109 mm, creek at bridge on Inter-American hwy., ca. 9 mi. E río Pacora, ca. 09°09'N, 079°09'W. USNM 302019, 1, 120 mm, creek 1 mi. W El Llano, río Bayano dr. (Pacific), ca. 09°12'50"N, 078°59'20"W. San Blas - Comarca Guna Yala (locations from Atlantic drainages). ANSP 151073, 1, 91 mm, stream on El Llano-Cartí rd., 15.9 km Inter-American hwy., no coordinates. INHS 36074, 2, 110-125 mm, Western San Blas Mountains, río Azucar dr., 09°24'N, 078°38'W. MCZ 88603, 1, 110 mm, quebrada Sigdi at Pingandi, río Mandinga dr., ca. 09°27´N, 079°05´W. MCZ 88604, 2, 105-110 mm, marsh, río Mandinga, 4-5 km above mouth, río Mandinga dr., ca. 09°28'N, 079°03'W. USNM 293152, 5 (1CS), 77-160 mm, río Cartí, 3 km Cartí, río Cartí dr. (Atlantic), ca. 09°26'N, 078°58'W. USNM 293154, 7, 58-114 mm, río Cangandi, ca. 3 km above confl. with río Mandinga, río Mandinga dr., ca. 09°26'N, 079°05'W. USNM 293155, 2, 130-145 mm, 2 km. E Cangandi village, quebrada Dolati, affl. río Cangandi, río Mandinga dr. ca. 09°26'N, 079°05'W. USNM 302001, 7 (1CS), 102-135 mm, río Chucubti, nr. Obaldía [Puerto Obaldía], río Chucubti dr. ca. 08°39'N, 077°25'W. Veraguas (locations from Pacific drainages). ANSP 99922, 2, 73-80 mm, creek at bridge ca. 9 mi. W El Maria on Sona-Remedios rd., río Tabasara dr., ca. 08°01'N, 081°32'W. ANSP 104031, 1, bridge ca. 17 mi. W Santiago on rd. to Sona, río San Pablo dr., ca. 08°03'N, 081°10'W. ANSP 104087, 1, 215 mm, stream on Sona-Remedios rd., ca. 2 mi. W El Maria, río Tabasara dr., ca. 08°01'N, 081°27'W. ANSP 104173, 1, 120 mm, creek at bridge ca. 9 mi. from Santiago on rd. to San Francisco, río Santa Maria dr., ca. 08°12'N, 080°57'W. AUM 32145, 1, 174 mm, 1 km SE Sona on rd. to Santiago, affl. río San Pablo, río San Pablo dr., Golfo de Montijo, 08°00'15"N, 081°17'09"W. USNM 302000, 1, 217 mm, no coordinates (Pacific dr.). USNM 302010, 1, 170 mm, ca. 7 mi. S Santiago de Veraguas, bridge on Ontijo rd., río San Martin Chiquito, río San Pedro dr., ca. 07°59'N, 080°58'W. USNM 302020, 4 (2 measured), 183-208 mm, creek 1 mile S Santa Fé, río Santa Maria dr., 08°29'40"N, 081°04'33"W. USNM 302023, 1, 157 mm, creek 20 mi. W Santiago de Veraguas, on Inter-American hwy., río San Pablo dr., 08°11'55"N, 081°13'50"W. USNM 302024, 2, 120-131 mm, río Conaco, ca. 16 mi. E Santiago, río Santa Marta dr., ca. 08°06'N, 080°44'W. Region not specified. CAS 50274, 1, 53 mm, no locality/coordinates. CU 71935, 7, no locality/coordinates. CU 71936, 27, no locality/coordinates. MZF-Manitoba 499, 4, 104-110 mm, no locality/coordinates. Venezuela (localities from Atlantic drainages). Mérida. MBUCV-V 8991, 2, female, 144-146 mm, mun. Alberto Adrianis, río Guayabones, affl. río Chama, lago de Maracaibo dr., ca. 08°34'N, 071°41'W. Táchira (localities from lago de Maracaibo drainages). MBUCV-V 10877, 2, 90-97 mm, stream between El Vigía and La Fría, affl. río Zulia, affl. río Catatumbo, ca. 08°12'N, 072°15'W [coordinates for La Fría]. MHNLS 1866, 4, 47-105 mm LEA, MHNLS 1867, 4, 62-100 mm LEA, MHNLS 1868, 4, El Vigía hwy., at La Fria, río Zulia, affl. río Catatumbo, ca. 08°12'N, 072°15'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Trujillo. INHS 59921, 1, 92 mm, 2 km S La Victoria on hwy. 1, río Caus, lago de Maracaibo dr., ca. 09°19'N, 070°51'W. MBLUZ 3766, 1, Pan American hwy., río Villegas at Puente Villegas, affl. río Bucare, río Tocuyo dr., ca. 09°45'N, 070°14'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MCNG 24898, 1, 136 mm LEA, quebrada Catalina, stream in Flor de Pátria, lago de Maracaibo dr., ca. 09°27', 070°28'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Zulia (localites from lago de Maracaibo drainages). INHS 34708, 1, 103 mm, stream S Machiques, 09°45'00"S, 072°30'42"W. INHS 35365, 2, 108-114 mm, 18 km. N Puerto Catatumbo at hwy. 6, bridge over caño Taguara, affl. río Santa Ana, 09°17'22"N, 072°32'49'W. INHS 60283, 1, 98 mm, 12 km intersection hwy. 6 and hwy. 2, río Zulia, ca. 08°23'N, 072°23'W. MBLUZ 2645, 1, Mara District, nr. El Sargento, flooded area of río Limon, no coordinates (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MBLUZ 3937, 3, caño Ictobogui at Aragtoba, Sierra de Perija, no coordinates, ca. 09°44'N, 072°52'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MBLUZ 4274, 2, unnamed stream, Parque Sierra de Perija, ca. 09°44'N, 072°52'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MBUCV-V 2935, 3, female, 155-160 mm, río El Quebradón, between Caja Seca and Aguas Calientes, ca. 09°04'N, 071°10'W. MBUCV-V 9328, 2, 75-150 mm, mun. Jesús María Semprún, Hacienda El Encantado, stream affl. río Zulia, ca. 08°45'N, 072°20'W. MBUCV-V 14046, 7, 68-161 mm, Catatumbo region, base of Sierra Azul, río Catatumbo, ca. 08°54'N, 072°26'W. MBUCV-V 14112, 59, 38-93 mm, MBUCV-V 15067, 18, 33-68 mm, District of Perijá, Cañada Riecito, río Guaco, ca. 09°48'N, 072°12'W. MCNG 24884, 1, 125 mm LEA, río Chiquito, ca. 10°13'N, 071°02'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). UF 21796, 1 (CS), 120 mm, stream about 10 km N Mene Grande, ca. 09°55'N, 070°55'W. UF 25444, 1, 179 mm, prov. Libertad, stream, path to La Misión de los Ángeles, ca. 10°32'N, 071°27'W. UMMZ 56099, 2, 124-176 mm, La Fría, Pueblo Nuevo, ca. 08°57'N, 071°36'W. USNM 121584, 8, 50-115 mm, 12 km S Rosário, río San Juan, ca. 10°12'N, 072°19'W. USNM 121585, 11 (2 lost during CS), 69-177 mm, río San Juan at bridge, affl. rio Motatán [presumably río Motatán de los Negros, not río Motatán, listed in Trujillo State], no coordinates. USNM 121586, 17, 62-143 mm, USNM 348532, 15, 93-165 mm, río San Pedro at bridge, affl. río Motatán, no coordinates. Country not specified. ANSP 22980, 2, 118-178 mm, New Grenada [Colombia, Panama and parts of Ecuador and Venezuela prior to 1858], no coordinates.

Brachyhypopomus palenque, new species

urn:lsid:zoobank.org:act:BA8EFB5D-A00F-42A9-BB1C-F7750BCBDF79

(Fig. 37; Tables 2-5, 17)

Brachyhypopomus occidentalis. -Barriga, 1994Barriga, R. 1994. Peces del noroeste del Ecuador. Politécnica, 19: 43-154.: 84, note on diet (NW Ecuador, catalog of fishes). -Jiménez-Prado et al., 2015Jiménez-Prado, P., W. Aguirre, R. Laaz-Moncayo, R. Navarette-Amaya, F. Nugra-Salazar, E. Rebolledo-Monsalve, E. Zárate-Hugo, A. Torres-Noboa & J. Valdiviezo-Rivera. 2015. Gúia de peces para aguas continentales en la vertiente occidental del Ecuador. Esmeraldas, Ecuador, PUCESE, UDA, MECN, 416p.: 283, color photograph (Ecuador, Pacific drainages - Santiago-Cayapas, Esmeraldas, Guayas, Daule, Cóngoma, Güijas, and Baba).

Brachyhypopomus sp. M. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree, 681; notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus sp. 'pal'/PAL. -Lovejoy et al., 2010Lovejoy, N. R., K. Lester, W. G. R. Crampton, F. P. L. Marques & J. S. Albert. 2010. Phylogeny, biogeography, and electric signal evolution of Neotropical knifefishes of the genus Gymnotus (Osteichthyes: Gymnotidae). Molecular Phylogeny and Evolution, 54: 278-290.: 281, table 1; 283, figs. 2-3 (outgroup in phylogenetic analysis of Gymnotus). -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes).

Brachyhypopomus sp. PALE. -Maldonado-Ocampo et al., 2014Maldonado-Ocampo, J. A., H. López-Fernández, D. C. Taphorn, C. B. Bernard, W. G. R. Crampton & N. R. Lovejoy. 2014. Akawaio penak, a new genus and species of Neotropical electric fish (Gymnotiformes, Hypopomidae) endemic to the upper Mazaruni River in the Guiana Shield. Zoologica Scripta, 43: 24-33.: 8, fig. 6, position in phylogeny (phylogeny of Rhamphichthyoidea).

Brachyhypopomus sp. "palenque". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. UF 180270, female, 149 mm TL, 135 mm LEA, Ecuador, Los Ríos, mun. Buena Fé, Parroquia Patricia Pilar, Centro Científico río Palenque, 45 km S Santo Domingo, small forest stream, affl. río Palenque, río Guayas dr., 00°35'01"S, 079°22'13"W, 16 Apr 2004, W. Crampton, J. Albert, F. Villao, R. Navarrete.

Paratypes. 31 specimens. Ecuador. Los Ríos. FMNH 79125, 3, 56-97 mm, FMNH 79126, 1, 84 mm, FMNH 79209, 1, 114 mm, FMNH 79210, 1, 97 mm, FMNH 79211, 1, 104 mm, FMNH 93123, 13, 62-196 mm, FMNH 93133, 7, 86-150 mm, FMNH 93142, 2, 77-83 mm, FMNH 93143, 2, 107-115 mm, Estación Biológica río Palenque, series of small pools at bottom of old rd. to station, and pools nr. the station, affl. río Palenque, affl. río Quevedo, affl. río Babahoyo, río Guayas dr., ca. 00°35'S, 079°22'W, 31 Jul 1974, G. Glodek, G. Whitmire & J. Dryan.

Non-types. 74 specimens. Ecuador. Azuay. ZOOA, FR-PE-003, 1, Ponce Enrique (Cantón), río Fermín, affl. río Siete, río Siete dr. (Gulf of Guayaquil), 03º03'26"S, 079º44'11"W. Cotopaxi. USNM 270692, 5 (2 CS), 115-203 mm, "río Sigchos, affl. río Esmeraldo" [interpreted as río Toachi nr. town Sigchos, Cotopaxi, affl. río Esmeraldas], río Esmaraldas dr., no coordinates. Esmeraldas. SU 54426, 2, 142-150 mm, río Cupa confl. with río Blanco at the Guaillabamba junction, río Esmeraldas dr., ca. 00°27'N, 079°24'W. USNM 270695, 2, 99-116 mm, río Bogotá, río Santiago dr., ca. 01°02'N, 078°50'W. Guayas. UF 35330, 1, 150 mm, 6.7 km S Nobol, río Daule, rio Guayas dr., ca. 01°58'S, 080°00'W. Los Ríos (localities from río Guayas dr.). ROM 93742, 1, 123 mm, Babahoyo (Cantón), Caracol (Sector), río Clara at La Clara, 01°40'30"S, 079°23'14"W. ROM 93755, 3, 145-181 mm, Montalvo (Cantón and Sector), creek on San José del Tambo-Juan Montalvo rd., 01°50'16"S, 079°16'14"W. UF 148572, 4 (3 female, 143-157 mm, 1 male, 203 mm), UF 180271, 5, immature (1 CS), 19-40 mm, collected with holotype. FMNH 79122, 9, 74-110 mm, FMNH 79124, 9, 55-101 mm, Estación Biológica río Palenque, affl. río Palenque, affl. río Quevedo, affl. río Babahoyo, ca. 00°35'S, 079°22'W. Pichincha. CAS 72214, 3, 138-170 mm, río Toachi, affl. río Blanco, nr. Santo Domingo de los Colorados, río Esmeraldas dr., ca. 00°14'S, 079°03'W. KU 20008, 6, 76-119 mm, affl. río Baba at Hotel Zaracoyat, E edge Santo Domingo de los Colorados, affl. río Quevedo, río Babahoyo, río Guayas dr., ca. 00°15'S, 079°09'W. KU 20020, 1, 93 mm, rio Verde, 2 km SE Santo Domingo, río Baba, affl. río Quevedo, río Babahoyo, río Guayas dr., ca. 00°16'S, 079°09'W. ROM 93681, 6, 97-173 mm, San Miguel de los Bancos (Cantón), Puerto Quito (Sector), río Silanchi downstream of community of Silanchi, río Esmeraldas dr., 00°09'32"N, 079°14'36"W. ROM 93671, 4, 132-153 mm, San Miguel de los Bancos (Cantón), Puerto Quito (Sector), W Puerto Quito, río Blanco W Puerto Quito, río Esmeraldas dr., 00°07'12"N, 079°14'09"W. ROM 93707, 5, 128-160 mm, Santo Domingo de los Colorados (Cantón), Santo Domingo (Sector), río Chiguilpe nr. bridge, affl. río Quevedo, río Babahoyo, río Guayas dr., 00°19'21"S, 079°13'00"W. SU 54435, 3, 115-121 mm, río Toachi, affl. río Blanco, río Esmeraldas dr., ca. 00°06'S, 079°13'W. USNM 247230, 1, male, 168 mm, 5 km Santo Domingo de los Colorados, río Quinindé, affl. río Esmeraldas, río Esmeraldas dr., ca. 00°14'S, 079°13'W. USNM 270694, 2, 90-111 mm, río Mindó, río Esmeraldas dr., ca. 00°00'N, 078°49'W. Santo Domingo de los Tsáchilas. ZOOA WAM-14-05, 1, Santo Domingo (Cantón), Mimo Chico, nr. Santo Domingo, affl. río Blanco, affl. río Esmeraldas, río Esmeraldas dr., 00°13'26"S, 079°04'20"W.

Table 17
Morphometrics for Brachyhypopomus palenque, Brachyhypopomus provenzanoi, and Brachyhypopomus regani.HT, holotype; SD, standard deviation. Ranges for Brachyhypopomus palenque and Brachyhypopomus regani refer to the holotype and to paratype and non-type specimens from the type region. Ranges for Brachyhypopomus provenzano i refer to the holotype and to paratype specimens from the type region.

Diagnosis. Brachyhypopomus palenque is diagnosed from congeners by the following combination of characters: caudal filament length 7.4-14.0% LEA, vs. 14.1-83.1% in B. alberti, B. batesi, B. benjamini, B. brevirostris, B. bullocki, B. cunia, B. draco, B. gauderio, B. hamiltoni, B. hendersoni, B. janeiroensis, B. jureiae, B. menezesi, B. pinnicaudatus, B. provenzanoi, B. sullivani, and B. walteri; absence of pale stripe along middorsal region, vs. presence of prominent pale uninterrupted middorsal stripe from occipital region to base of caudal filament in B. arrayae, B. beebei, and B. belindae; mouth width 25.1-37.8% HL, vs. 15.9-23.2% in B. bennetti and B. flavipomus; absence of accessory electric organ over the opercular region, vs. presence in B. bombilla and B. regani; precaudal vertebrae 19-22, vs. 24-26 in B. verdii; absence of continuous or discontinuous dark vertical or diagonally oriented bars or saddles on body surface dorsal to lateral line, vs. presence in B. diazi and B. palenque.

Description. Head and body shape, and pigmentation illustrated in Fig. 37. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 17. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout bulbous and rounded. Eye small to moderate in size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 28-48 (median 38, n = 8). Pectoral fin broad, pectoral-fin rays 17-21 (no mode, median 18). Precaudal vertebrae 19-22 (mode 21), with 1-3 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) to substantially (0.33-0.5 HL distance) posterior to tip of pectoral fin. Anal-fin rays 180-229 (median 206). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-6 (mode 6). Lateral line continuous. Very sparse depigmented epidermal canals; as irregular short curved scratch-mark like grooves in mid dorsal flank in anterior half of body, and sporadically as short scratch marks close to and parallel to lateral line along much of body, but no dense crisscrossing pattern of epidermal canals in posterior third of body as present in many congeners. 4-5 columns (mode 5) bilateral columns of electrocytes at anal-fin terminus, and 4-6 columns (mode 5) at or near a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Number of electrocyte columns tapers rapidly to 2-3 at caudal filament tip. Caudal filament very short.

Coloration. (Fig. 37). Background light to dark brown, fading ventrally. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal region very dark, with irregular mottling of lighter background pigmentation, no prominent vertically oriented stripes or bands. Ventral flank over body cavity and anal-fin pterygiophores with distinctive irregular marbled pattern of fused dark brown patches over lighter background. Caudal filament darker than body, with or without irregular light patches. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of melanophores. Color in live individuals similar to preserved specimens, with opercular region slightly rosy due to underlying gills.

Fig. 37
Brachyhypopomus palenque. a. UF 180270 (WC05.160404), holotype, female, 149 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Ecuador, río Palenque, río Guayas dr. b. USNM 247230, male, 171 mm TL (body in lateral view, specimen fixed in formalin and preserved in EtOH); Ecuador, río Quinindé, río Esmeraldas dr. Note sexual dimorphism in caudal filament height. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 203 mm TL, 184 mm LEA (n = 85). Largest male specimen examined 203 mm TL, 184 mm LEA (n = 2). Largest female specimen examined 157 mm TL, 151 mm LEA (n = 4).

Sexual dimorphism. Sexually mature males attain larger sizes than females, and exhibit substantially deeper caudal filaments than immature individuals and breeding females (Figs. 37a-b), but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Large males often with slight paddle-like lateral compression at caudal filament tip (Fig. 37b), which is sometimes free of electrocytes distally. No known sexual dimorphism in pigmentation.

Geographic distribution. Ecuador (Fig. 36). Known from two large Pacific drainages, the río Esmeraldas and río Guayas. Known also from the río Santiago, a smaller Pacific drainage in northern Ecuador, and from the río Siete, a small drainage of the Gulf of Guayaquil.

Ecological notes. Known from small streams and rivers to an altitude of ca. 650m. The type series of B. palenque was collected in a small clearwater streams (up to about 1m wide and 20-30 cm deep) in protected secondary rainforest. The substrate of these streams comprised clay, pebbles, rocks up to about 30 cm in diameter, leaf litter, and decaying logs. The following water parameters were recorded: conductivity 52 μScm-1, dissolved oxygen 6.8 mgl-1, temperature 23.6-23.8°C, pH 6.5, and flow 0.05-0.2 ms-1. All specimens were collected from leaf litter or submerged root mats; usually up against or under logs or large rocks. Several fully mature male and female specimens were collected, and all were spaced at least 0.5 m apart except for a large male and female which were located in very close proximity (ca. 10 cm) and captured in the same net. Scattered along a 10-15 m stretch of stream were many (ca. 20 or more estimated from a fish-finder survey) very small specimens in the size range 19-40 mm (5 vouchered in UF 180271), which were difficult to collect because they passed through the mesh of the dip net. There was no sign of aggregations of post-larval specimens, as observed for B. beebei by Westby (1988Westby, G. W. M. 1988. The ecology, discharge diversity and predatory behaviour of gymnotiform electric fish in the coastal streams of French Guiana. Behavioral Ecology and Sociobiology, 22: 341-354.). The population at the río Palenque Scientific Center was evidently breeding in mid-April 2004, when the type series was collected. However, the full extent of the breeding season is unknown. Stomach contents of specimens from the type locality comprise aquatic invertebrates, predominantly larval Chironomidae and Coleoptera (WGRC unpublished data). Barriga (1994Barriga, R. 1994. Peces del noroeste del Ecuador. Politécnica, 19: 43-154.) reports an omnivorous diet.

Co-occurring congeners: None.

Etymology. The specific name derives from the río Palenque, a Pacific Ocean drainage of Ecuador, where the type series was collected. A noun in apposition.

Local names. Ecuador: Cuchillo, bío-bío, anguila (Barriga, 1991Barriga, R. 1991. Peces de agua dulce. Politécnica, 16: 7-88.).

Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.)

(Figs. 1i, 38; Tables 2-5, 18)

Hypopomus pinnicaudatusHopkins et al., 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.: 352, fig. 1, illustration of breeding male and female, showing sexual dimorphism of caudal filament morphology; 360, fig. 9, illustrations of caudal filament with damage and regeneration (original description, type locality - French Guiana, coastal swamp, 'Grand Pripris' [see 'Remarks'], sexual dimorphism of electric organ and EOD). -Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.: 153-154, figs. 1-2, drawings of holotype, black and white photographs of preserved specimens (French Guyana, description of type locality and type series, invalid as original description but includes nomination of holotype, see 'Remarks'). -Costa & Campos-da-Paz, 1992Costa, W. J. E. M. & R. Campos-da-Paz. 1992. Description d'une nouvelle espèce de poisson électrique du genre néotropical Hypopomus (Siluriformes : Gymnotoidei : Hypopomidae) du Sud-Est du Brésil. Revue Française d'Aquariologie-Herpétologie, 18: 117-120.: 117 (listing in description of B. janeiroensis).

Brachyhypopomus pinnicaudatus. -Mago-Leccia, 1994Mago-Leccia, F. 1994. Electric fishes of the continental waters of America. Caracas, Biblioteca de la Academia de Ciencias Fisicas, Matematicas y Naturales, Caracas, 206p.: 48 (listing of Brachyhypopomus). -Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.: 398, color photograph of live individual (French Guiana, listing of Brachyhypopomus). -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 25-26, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1 reproductive biology (Brazil, central Amazon, ecology and signal diversity). -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 114 (redescription). -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; 821, table 4, 834, fig. 9, illustration of specimen, with EOD (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998b: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance). -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Hopkins, 1999Hopkins, C. D. 1999. Design features for electric communication. Journal of Experimental Biology, 202: 1217-1228.: 1218, fig. 1, drawings of breeding male and female, showing sexual dimorphism of caudal filament morphology (electric organ morphology and impedance matching). -Albert & Crampton, 2003Albert, J. S . & W. G. R. Crampton. 2003. Family Hypopomidae (bluntnose knifefishes). Pp. 494-496. In: Reis R. E., S. O. Kullander & C. J. Ferraris (Eds.). Checklist of the freshwater fishes of South and Central America. Porto Alegre, Edipucrs .: 495 (Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, catalog of hypopomids). -Goulding et al., 2003Goulding, M., C. Cañas, B. R. B. Forsberg & H. Ortega. 2003. Amazon headwaters: rivers, life and conservation of the Madre de Dios river basin. Lima, Asociación para la Conservación de la Cuenca Amazónica, Amazon Conservation Association, Gráfica Biblos S.A., 198p.: 177, color photograph of live individual (Peru, río Madre de Dios; catalog of fishes). -Triques & Khamis, 2003Triques, M. L. & D. K. Khamis. 2003. Brachyhypopomus jureiae, a new species of freshwater Neotropical electric fish (Teleostei: Gymnotiformes: Hypopomidae) from a coastal stream of Southeastern Brazil. Lundiana, 4: 61-64.: 63 (diagnosis against, in description of B. jureiae). -Loureiro & Silva, 2006Loureiro, M. & A. Silva. 2006. A new species of Brachyhypopomus (Gymnotiformes, Hypopomidae) from northeastern Uruguay. Copeia, 2006: 665-673.: 667 (diagnosis against, in description of B. bombilla). -Giora et al., 2008Giora, J., L. R. Malabarba & W. Crampton. 2008. Brachyhypopomus draco, a new sexually dimorphic species of neotropical electric fish from southern South America (Gymnotiformes: Hypopomidae). Neotropical Ichthyology, 6: 159-168.: 162 (diagnosis against, in description of B. draco). -Giora & Malabarba, 2009Giora, J. & L. R. Malabarba. 2009. Brachyhypopomus gauderio, new species, a new example of underestimated species diversity of electric fishes in the southern South America (Gymnotiformes: Hypopomidae). Zootaxa: 60-68.: 63 (diagnosis against, in description of B. gauderio). -Sullivan & Hopkins, 2009Sullivan, J. P. & C. D. Hopkins. 2009. Brachyhypopomus bullocki, a new species of electric knifefish (Gymnotiformes: Hypopomidae) from northern South America. Proceedings of the Academy of Natural Sciences of Philadelphia, 158: 18392.: 183 (listing in description of B. bullocki). -Kirschbaum & Schugardt, 2002Kirschbaum, F. & C. Schugardt. 2002. Reproductive strategies and developmental aspects in mormyrid and gymnotiform fishes. Journal of Physiology-Paris, 96: 557-566.: 562, figs. 3-4, black and white photographs of free embryo after hatching, larva at beginning of exogenous feeding, juvenile, and adult (gymnotiform reproduction). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8 (inset 10), color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EODs [survey of gymnotiform species and EOD diversity]. -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology). -Mol, 2012: 598 (Suriname, catalog of fishes). -de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.: 545, table 1 (Brazil, rio Madeira, lago Cuniã, listing of fish species). -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 238, color photograph of live individual (Brazil, rio Madeira, listing of hypopomids). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.: 27, fig. 10, color photograph of preserved intact and damaged/regenerated specimen (comparison to B. bennetti and B. walteri). -Cardoso et al., 2015Cardoso, A., J. C. Pieczarka & C. Y. Nagamachi. 2015. X1X1X2X2/X1X2Y sex chromosome systems in the Neotropical Gymnotiformes electric fish of the genus Brachyhypopomus. Genetics and Molecular Biology, 38: 213-219.: 214 (Brazil, Amazonas, cytogenetics). -Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Table 18
Morphometrics for Brachyhypopomus pinnicaudatu s. LT, lectotype; SD, standard deviation. Data for lectotype, ANSP 163463 (Cayenne, French Guiana) are from Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.). Ranges for the type region refer to type specimens from the "Grand Pripris", French Guiana (lectotype not included in ranges). Ranges for the other population refer to non-type specimens from the vicinity of Tefé, Amazonas, Brazil (Central Amazon basin).

Diagnosis. Brachyhypopomus pinnicaudatus is diagnosed from congeners by the following combination of characters: prominent pale stripe along middorsal region present, vs. absent in all congeners except B. arrayae, B. beebei, B. belindae, B. gauderio, and B. verdii); anal-fin rays 176-196, vs. 200-230 in B. beebei and B. belindae; precaudal vertebrae 18-21, vs. 24-26 in B. verdii. Brachyhypopomus pinnicaudatus exhibits similar pigmentation and overlapping meristic counts and morphometric proportions with some populations of B. arrayae and B. gauderio. Brachyhypopomus pinnicaudatus can be distinguished from B. arrayae by the absence of a contact between a small ascending process on the endopterygoid and the orbitosphenoid vs. a contact between these two bones in B. arrayae (see diagnosis for B. arrayae for further details). Brachyhypopomus pinnicaudatus can be distinguished from B. gauderio by the presence of a medial bridge on the posterior portion of the basihyal, vs. absence in B. gauderio (see diagnosis for B. gauderio for further details).

Description. Head and body shape, and pigmentation illustrated in Figs. 1i and 38. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 18. Body moderate to deep in depth. Head short to moderate in length and moderate to deep in depth. Dorsal profile of head straight to slightly convex from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with slight to moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Pectoral fin of moderate width, pectoral-fin rays 13-16 (median of 15 in populations from coastal drainages of French Guiana; mode of 14 in population from rio Amazon of Brazil). Precaudal vertebrae 18-22 (mode of 20 in populations from coastal drainages of French Guiana; mode of 19 in population from rio Amazon of Brazil), including 1-2 transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to, or near, tip of pectoral fin. Anal-fin rays 177-196 (median of 184 in populations from coastal drainages of French Guiana; mode of 190 in population from rio Amazon of Brazil). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 4-6 (mode 5). Lateral line continuous. Epidermal canals almost entirely absent; present in posterior half of body in form of an irregular, meandering, and sometimes bifurcating horizontal depigmented groove, on either side of dorsal surface in dorsal portions of flank; and as very sparse single or sometimes parallel double depigmented grooves either side of, but mostly dorsal to, lateral line. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Coloration. (Figs. 1i, 38). Background pale tan to dark brown. Pigmentation highly variable. Dorsal region with prominent depigmented or lightly pigmented stripe extending along midline from occipital region to base of caudal filament, or deep into caudal filament, bordered by prominent dark horizontal wavy reticulated lines from which short irregular patches extend ventrally. Dorsal pigmentation pattern strongly resembles that of B. gauderio, but pale depigmented stripe is more conspicuous. Irregular small dark patches or horizontally elongated spots often extend along lateral line. Ventral flank usually without irregular broken vertical bands and vertically elongated spots, especially over anal-fin pterygiophores, as often present in B. gauderio. Caudal filament darker than body, with irregular dark markings or bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays with light scattering of brown chromatophores, especially in posterior portion of anal-fin. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 38
Brachyhypopomus pinnicaudatus. a. MCP 45469 (WC13.310701b), female, 143 mm (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin); b. MCP 45278 (WC13020698), male, 167 mm TL (body in lateral view, specimen fixed in formalin and preserved in EtOH). Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note sexual dimorphism in caudal-filament length and height, and feather-like structure at caudal filament terminus in male. Scale bars = 5 mm.

Size. Moderate adult size, largest specimen examined 208 mm TL, 142 mm LEA (n = 993). Largest male specimen examined 208 mm TL, 142 mm LEA (n = 23). Largest female specimen examined 156 mm TL, 118 mm LEA (n = 32).

Sexual dimorphism. Sexually mature males attain slightly larger sizes, and develop much broader caudal filaments than immature individuals and breeding females (Figs. 38a-b), but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Tip of caudal filament in breeding males often with paddle-like compression, commonly with end free of electrocytes (in some cases with electrocyte-free portion extending anteriorly for up to 20% of caudal-filament length). Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.) and Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.) provide detailed notes on secondary sexual dimorphism of EO, electrocyte anatomy, and the EOD. No known sexual dimorphism in pigmentation.

Geographic distribution. Bolivia, Brazil, Peru, and French Guiana (Fig. 39). Brachyhypopomus pinnicaudatus is widespread in eastern portions of the lowland Amazon, as far west as the confluence of the rio Japurá and rio Solimões near Tefé, and throughout the rio Madeira drainage. Specimens have also been collected from the rio Mearim drainage of Maranhão, Brazil, some 700 km SE of the mouth of the Amazon, and (based on photographs from Matavelli et al. 2015Matavelli, R., A. M. Campos, J. do Vale, N. M. Piorski & P. dos Santos Pompeu. 2015. Ichthyofauna sampled with tadpoles in northeastern Maranhão state, Brazil. Check List: Journal of Species Lists and Distribution, 11: 1-16.), from unspecified localities in the rio Munim basin, further SE (identified incorrectly as Rhabdolichops sp.). Populations are also known from freshwater systems along much of the coast of French Guiana. Museum lots from localities further west along the northern coast of South America are not known although Mol (2012) reports B. pinnicaudatus from the Commewijne River in eastern Suriname.

Fig. 39
Collection records for Brachyhypopomus pinnicaudatus (circles) and B. verdii (squares). Holotype locations are marked with open symbols. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found complete overlap in the range of meristic counts (Tables 2-5) and morphometric measurements (Table 18), and observed similar pigmentation among populations of B. pinnicaudatus from the eastern portions of the Amazon basin, and from the region of the type locality in coastal swamps of French Guiana. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. pinnicaudatus are members of a single geographically widespread species, which is morphologically and genetically distinct from its allopatric sister species, B. gauderio, and from all other congeners.

Ecological notes. In the Amazon basin Brachyhypopomus pinnicaudatus occurs primarily in floodplain systems of intermediate conductivity (30-90μScm-1) and high conductivity (90-250μScm1), especially those with turbid water. Records for low-conductivity (5-30μScm-1) clearwater and blackwater rivers are mostly confined to near their confluence with major whitewater rivers (e.g. at the confluence of the rio Negro and rio Tefé with the Amazon River), although specimens are known from the rio Tapajós upstream of its mouthbay (ria) lake. Throughout its range B. pinnicaudatus is usually encountered in floating or rooted macrophytes along the margins of lakes, channels and swamps (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.; 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.; Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.; Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.; de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.; Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.). Brachyhypopomus pinnicaudatus is able to tolerate seasonal or intermittent hypoxia by undertaking aerial gill respiration (Crampton, 1998b; Hopkins, 1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.). Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.) describes the nature of aerial gill respiration of B. pinnicaudatus: "We noted in containers not oxygenated by bubbling, H. pinnicaudatus would rise to the surface every few minutes, take bubbles of air and lodge them in the gill chamber, which became noticeably flared as a result, and return to the bottom. Gentle pressure to the sides of the head would cause the release of several bubbles of air.". Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.) also describes the expanded size of the gill chamber in B. pinnicaudatus relative to congeners from normoxic systems, which "extends far toward the ventral midline where the two chambers meet at a septum. The secondary lamellae of the respiratory gill are well developed; the respiratory folds are very broad and thin, making them highly efficient in the uptake of oxygen from water". Breeding occurs during the rising and high water period in populations from Amazonian floodplain floating macrophytes (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p., 165), and during the rainy seasons in populations from coastal French Guiana (Hopkins et al., 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.). Stomach contents in populations from the central Amazon comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136).

Co-occurring congeners: In the region of the type locality in coastal French Guiana, B. pinnicaudatus occurs in sympatry with B. beebei, B. brevirostris, and B. regani. In the Amazon basin (excluding the rio Madeira), B. pinnicaudatus occurs in sympatry and ecological syntopy with B. belindae, B. beebei, B. bennetti, B. brevirostris, B. flavipomus, B. hamiltoni, B. regani, and B. walteri, and in allotopy with B. batesi, B. hendersoni, and B. sullivani (except in terra firme-floodplain ecotones). In the rio Madeira basin B. pinnicaudatus is known to occur in sympatry and syntopy with B. arrayae, B. beebei, B. bombilla, B. brevirostris, B. cunia, and B. walteri, and in allotopy with B. alberti and B. sullivani.

Local names. Bolivia: cuchillo; Brazil: sarapó; French Guiana: poisson couteau (French) and multiple creole/Amerindian names (Planquette et al., 1996Planquette, P., P. Keith & P. Y. Le Bail. 1996. Atlas des poissons d'eau douce de Guyane. Vol. I. Paris, Muséum National d'Histoire Naturelle, 431pp.); Peru: macana.

Remarks. Comments on original description:Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.), in the journal Copeia, provided a description of B. pinnicaudatus (as Hypopomus pinnicaudatus). However, this description was preceded by a paper in the journal Brain, Behavior and Evolution (Hopkins et al., 1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.), which uses the name H. pinnicaudatus, comments that it is a "new species" (p. 350), specifies a type locality and type series (including repository information) (p. 351), provides an illustration (p. 352), and includes diagnostic notes by way of a comparison of sexual dimorphism to congeners (p. 365). Consequently, Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.), must be considered the valid authority (ICZN, 1999ICZN. 1999. International Code of Zoological Nomenclature. London, U.K., The International Trust for Zoological Nomenclature, 306p., paragraphs 11.5.1, 13.1.1, and 16.1). Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.) evidently intended the Copeia paper to also be published in 1990 and provided a statement on p. 350: "A formal species description can be found in Hopkins [1990]." (Hopkins [1990] is cited "in press" in Copeia in the bibliography). This statement does not in itself constitute a valid disclaimer to availability of the name, but rather makes the name H. pinnicaudatus available by indication (ICZN, 1999ICZN. 1999. International Code of Zoological Nomenclature. London, U.K., The International Trust for Zoological Nomenclature, 306p., paragraph 13.1.2). No holotype was nominated by Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.) from a list of what must be considered syntypes. The "holotype" listed by Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.) (ANSP 163463) is hereby designated as lectotype. Further, several "paratypes" lots listed by Hopkins (1991Hopkins, C. D. 1991. Hypopomus pinnicaudatus (Hypopomidae), a new species of gymnotiform fish from French Guiana. Copeia, 1: 151-161.) that are not listed among the syntypes listed in Hopkins et al. (1990Hopkins, C. D., N. C. Comfort, J. Bastian & A. H. Bass. 1990. Functional analysis of sexual dimorphism in an electric fish, Hypopomus pinnicaudatus, order Gymnotiformes. Brain Behavior and Evolution, 35: 350-367.) must be excluded from the type series.

Material examined. 1,154 specimens. Bolivia. Beni (localities from rio Madeira dr., Amazonas dr.). AMNH 39848, 7, 68-103 mm, Pampa de Meio, ca. 12 km SE Costa Marques, affl. rio Guaporé, affl. río Mamoré, 12°34'00"S, 064°12'42"W. AUM 23504, 1, 85 mm, AUM 23643, 3, 124-127 mm, mun. Vaca Díez, affl. lago Tumi Chucua, affl. río Beni, ca. 11°07'S, 066°11'W. CAS 72216, 3, 112-165 mm, Reyes, 24 mi. NE Rurrenabaque, río Beni, 14°17'42"S, 067°20'27"W. CBF 10260, 1, immature, 102 mm, CBF 10261, 1, immature, 100 mm, mun. Riberalta, stream nr. lago de San José, floodplain of río Beni, 10°54'47"S, 065°59'49"W. CBF 10262, 1, male, 157 mm, CBF 10263, 1, female, 115 mm, CBF 10264, 1, immature, 115 mm, CBF 10265, 1, immature, 101 mm, CBF 10266, 1, female, 111 mm, CBF 10267, 1, immature, 125 mm, UF 177343, 1, immature, 111 mm, UMSS 7025, 1, male, 119 mm, UMSS 7026, 1, female, 81 mm, UMSS 7027, 1, male, 106 mm, UMSS 7028, 1, female, 108 mm, UMSS 7029, 1, immature, 78 mm, UMSS 7030, 1, female, 95 mm, UMSS 7031, 1, female, 70 mm, UMSS 7032, 1, immature, 86 mm, mun. Riberalta, swamp nr. lago de San José, floodplain of río Beni, 10°54'45"S, 065°59'46"W. INHS 37118, 1, 97 mm, borrow pit, río Apere, aff río Mamoré, ca. 14°29'S, 065°40'W. INHS 37244, 1, 67 mm, 41 km E Estación Biológica del Beni, on rd. to San Ignacio de Moxos, río Chevejecure, affl. río Apere, affl. río Mamoré, ca. 14°22'S, 065°29'W. MNHN 1998-1047, 2 (of 5), 123-142 mm, Trinidad, río Beni, ca. 14°50'S, 064°54'W. NMW 65039, 1, 102 mm TL, 80 mm LEA (paralectotype of B. brevirostris), rio Guaporé, affl. río Mamoré, no coordinates. UF 81877, 1, 54 mm, Renez prov., stream, 1 km S Magdalena, río Itonomas, affl. río Machupo, affl. río Guaporé, affl. río Mamoré, ca. 13°16'S, 064°04'W. UF 82508, 4, 44-108 mm, pond 25 km N San Javier, río Mamoré, ca. 14°24'S, 064°56'W. UF 148445, 1, 100 mm, prov. Iténez, río Blanco, nr. Bella Vista, affl. rio Guaporé, affl. río Mamoré, ca. 13°16'S, 063°41'W. UMMZ 66417, 2, 128-139 mm, Reyes and lagoons nr. Reyes, 24 mi. NE Rurrenabaque, affl. río Beni, ca. 14°17'S, 067°20'W. UMMZ 204434, 13, 52-90 mm, pool, Pampa do Meio, ca. 12 km SE Costa Marques (Brazil), río Iténez (río Guaporé), affl. río Mamoré, 12°34'00"S, 064°12'42"W. UMMZ 205102, 1, 158 mm, Arroyo Grande at mouth, ca. 1 km N Guayaramerín, affl. río Mamore, 10°48'00"S, 065°24'36"W. USNM 305593, 1, 85 mm, prov. Ballivia, lago Normandia, 40 km E San Borja, río Matos, affl. río Apere, affl. río Mamoré, ca. 14°55'S, 066°18'W. Pando. FMNH 106648, 1, 75 mm, río Manuripi, ca. 12 km upstream Puerto Rico, río Manuripi, affl. río Orthon, affl. río Madre de Dios, affl. río Beni, affl. rio Madeira, Amazonas dr., ca.11°09'06"S, 067°33'41"W. Santa Cruz (localities from río Mamoré, affl. rio Madeira, Amazonas dr.). UF 82159, 11, 66-139 mm, 41 km SSE Concepción, affl. río San Martin, affl. rio Guaporé, ca. 16°37'S, 061°47'W. UF 82171, 1, 88 mm, prov. Velasco, 5.5 km N San Miguel, affl. río Paraguas, affl. río Iténez (río Guaporé), ca. 16°45'S, 060°59'W. UF 82189, 1, 75 mm, prov. Velasco, 71 km N San Jose de Chiquitos, río San Diablo, affl. río Itonam, affl. río San Martín, affl. río Guaporé, ca. 17°18'S, 060°35'W. ZUEC 7100, 1, 114 mm, Quimone, 45.4 km W San José de Chiquitos, río Quimone, affl. río San Pablo, 17°42'48"S, 062°08'56"W. Brazil. Amapá. MNRJ 12175, 3, 83-191 mm, mun. Mazagão, rio Miri nr. Mazagão-Macapá, rio Amazonas estuary, Amazonas dr., ca. 00°06'S, 051°17'W. MNRJ 12176, 1, 165 mm, mun. Amapá, Fazenda Modelo do Aporema, rio Aporema, L bank, rio Araguari dr., ca. 01°03'N, 050°40'W. NRM 32240, 39, 38-85 mm, stream at Aldeia Cunene, rio Oiapoque dr., 04°01'08"N, 051°37'06"W. Amazonas (localities from Amazonas dr., localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1998.3.12.108-116, 9 (1 female, 110 mm, 8 immature), mun. Tefé, Ilha Panamim, rio Solimões nr. Tefé, 03º17'38"S, 64º41'16"W. BMNH 1998.3.12.117-118, 2, immature, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12.119, 1, immature, 120 mm, MCP 45398, 1, female (CS), 116 mm, Mamirauá Reserve, lago Juruá Grande, 03º01'51"S, 064º51'07"W. BMNH 1998.3.12.120-122, 3, immature, 111-118 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º03'51"S, 64º51'05"W. BMNH 1998.3.12.123-124, 2 (1 female, 134 mm, 1 male, 163 mm), Mamirauá Reserve, lago Pirarara, 02º57'04"S, 64º50'04"W. BMNH 1998.3.12.125-126, 2, immature, 150-178 mm, Mamirauá Reserve, lago Saracura, 02º58'34"S, 64º55'34"W. BMNH 1998.3.12.127, 1, male, 158 mm, Mamirauá Reserve, cano dos Lago Curuçá, 03º04'31"S, 64º48'52"W. BMNH 1998.3.12.128, 1, immature, 153 mm, Mamirauá Reserve, Ressaca do Pau, 03º02'03"S, 64º52'13"W. BMNH 1998.3.12.129, 1, male, 169 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 64°48'32"W. BMNH 1998.3.12.130-132, 3 male, 154-159 mm, MCP 45328, 1, immature, 89 mm, Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. IDSM 445, 1, 116 mm, Mamirauá Reserve, lago Sumaumeirinha I, 02º48'27"S, 065º04'37"W. IDSM 446, 4, 82-133 mm, MCP 45275, 2 (1 female, 148 mm, 1 male, 208 mm), MCP 45437, 3 (1 female, 144 mm, 2 male, 139-143 mm), Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. INHS 67200, 1, lago Canta Galos, lago Janauari, ca. 03°13'S, 060°00'W. INHS 70412, 1, 98 mm, INHS 71295, 1, 141 mm, lago Janauari, 03°13'S, 060°00'W. INPA 4389, 4, 92-135 mm, INPA 9119, 8, INPA 19939, 39, 23-141 mm, Paraná do Rei, Ilha Careiro, rio Amazonas floodplain, 03°12'W, 059°44'W. INPA 4738, 1, 113 mm, INPA 4806, 25, 76-142 mm, INPA 4871, 35, 32-135 mm, INPA 19941, 1, 77 mm, INPA 19946, 1, 84 mm, INPA 19955, 6, 75-130 mm, MZUSP 24967, 1, 147 mm, MZUSP 75572, 4, 121-142 mm, lago do Castanho, Ilha Janauacá, rio Solimões floodplain, 03°43'S, 060°26'W. INPA 9946, 24, 86-140 mm, Reserva Mamirauá, lago Caetano, 02º50'58"S, 064º55'42"W. INPA 13568, 2, 33-59 mm, INPA 15771, 2, 77-86 mm, INPA 16700, 1, 136 mm, lago Comprido, Ilha da Marchantaria, rio Amazonas floodplain, ca. 03°14'S, 059°56'W. INPA 17119, 2, 112-138 mm, lake nr. Sacado da Santa Luzía, rio Purus, 04°42'48"S, 062°22'26"W. INPA 17120, 2, 71-96 mm, Paranã 2, nr. Arumã, rio Purus, 04°46'24"S, 062°11'35"W. INPA 19942, 4, 93-147 mm, rio Negro, Amazonas dr., no coordinates. MCP 45276, 3 (1 immature, 82 mm, 1 female, 129 mm, 1 male, 110 mm), Mamirauá Reserve, lago Curuçá Redondo, 03º06'13"S, 064°49'06"W. MCP 45277, 3 (1 immature, 120 mm, 1 female, 103 mm, 1 male, 104 mm), Mamirauá Reserve, lago Curuçá Aberto, 03º06'07"S, 064°49'10"W. MCP 45278, 4 (1 immature, 120 mm, 1 female, 156 mm, 2 male, 153-177 mm), Mamirauá Reserve, lago Curuçá Comprido, 03º05'31"S, 064°48'58"W. MCP 45279, 1, immature, 134 mm, MCP 45410, 1, immature, 101 mm, MCP 45435, 66, 33-161 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º05'15"S, 064°48'03"W. MCP 45280, 2, female, 127-136 mm, MCP 45281, 1, male, 158 mm, Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45351, 2, female, 127-136 mm, Mamirauá Reserve, lago Juruazinho, 03º02.58'S, 064º51.01'W. MCP 45370, 2, female (2CS) 122-125 mm, Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. MCP 45409, 1, immature, 88 mm, Mamirauá Reserve, lago Promessa, 03º04'29"S, 064°47'02"W. MCP 45433, 2 (1 immature, 115 mm,1 female 145 mm), Mamirauá Reserve, lago Araçazinho, 02º59'35"S, 064º51'33"W. MCP 45436, 1, male, 173 mm, Mamirauá Reserve, Ressaca do Itu, 02º49'51"S, 064º57'11"W. MCP 45438, 1, immature, 113 mm, MCP 45455, 3 (1 immature, 67 mm, 1 female, 135 mm, 1 male, 147 mm), MCP 46928, 2, female (2CS), 143-148 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. MCP 45469, 12, 58-143 mm, mun. Tefé, floodplain lake, Ilha Panamim, rio Solimões, nr. Tefé, rio Solimões, 03°19'29"S, 064°38'37"W. MCZ 8354, 26, 76-83 mm, MCZ 9421, 1, 137 mm, MCZ 9424, 1, 48 mm, mun. Parintins, Villa Bella, rio Amazonas at Parintins, ca. 02°38'S, 056°54'W. MCZ 78165, 1, 95 mm, lago Jacaretinga, nr. Careiro de Várzea, rio Amazonas, 03°13'00"S, 059°49'41"W. MPEG 1110, 11, 67-147 mm, MPEG 1112, 1, 70 mm, MPEG 1117, 6, 53-115 mm, mun. Iranduba, rio Solimões, ca. 03°17'S, 060°11'W [coordinates for Iranduba]. MPEG 22740, 1, 86 mm, Mamirauá Reserve, lago do Pagão, 03º02'51"S, 064°50'23"W. MZUSP 6326 (part), 3, 83-136 mm, lago Castro, Boca do rio Purus, rio Purus, ca. 03°42'S, 061°28'W. MZUSP 6475, 1, lago Jacaré, upstream Manacapurú, rio Solimões floodplain, ca. 03°40'S, 060°48'W. MZUSP 165854, 3, 84-133 mm, mun. Manaus, lago Hyanuary [lago do Janauari], rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 229915, 2, 107-135 mm, USNM 306833, 40, 27-137 mm, USNM 306866, 4, 55-150 mm, São José, lago do Castanho, lago Janauacá, rio Amazonas floodplain, ca. 03°26'S, 060°17'W [coordinates taken from center of lago Janauacá]. USNM 306678, 1, 75 mm, USNM 306870, 3, 116-133 mm, lago Murumuru, nr. Curral, lago Janauacá, rio Amazonas floodplain, ca. 03°25'S, 060°16'W. USNM 306693, 3, 68-102 mm, USNM 306735, 3, 118-130 mm, USNM 306872, 1, 80 mm, Paraná do lago Janauacá, entrance of lago do Castanho, rio Amazonas floodplain, no coordinates. USNM 306694, 1, 87 mm, Ressaca da Ilha da Marchantaria, rio Amazonas floodplain, ca. 03°14'S, 059°56'W. USNM 306749,1, 116 mm, furo [artificial channel] between lago Murumuru and Paraná de Janauacá, rio Amazonas floodplain, ca. 03°25'S, 060°16'W. USNM 306785, 1, 116 mm, lago Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 306789, 5, 48-145 mm, USNM 306811, 7, 100-121 mm, lago Janauari, nr. entrance, rio Amazonas floodplain, ca. 03°13'S, 059°59'W. USNM 306877, 1, 36 mm, lago Canta Galos, lago Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. USNM 306948, 1, 54 mm, lago Terra Preta, lago do Janauari, rio Amazonas floodplain, ca. 03°13'S, 060°00'W. Maranhão. MNRJ 12222, 2, 77-80 mm, mun. Ararí, lago Malhada Grande, rio Mearim dr., ca. 03°27'S, 044°46'W. MNRJ 12223, 2, 98-113 mm, mun. Ararí, lago Capivara, rio Mearim dr., ca. 03°27'S, 044°46'W. Pará. (localities from Amazonas dr.). ANSP 194516, 4, 75-106 mm, mun. Porto de Moz, beach, R bank rio Xingu 3 km downstream Porto de Moz, rio Xingu, 01°43'54"S, 052°15'16"W. CAS 33502, 1, 136 mm, SU 54500, 1, 143 mm, Ajamury, lago Grande, rio Amazonas floodplain, ca. 02°16'S, 54°17'W. FMNH 54550, 3, 84-126 mm, Santarém, rio Amazonas, ca. 02°25'S, 054°42'W. INPA 19961, 7, 72-107 mm, lago Salgado, rio Cumuní, affl. rio Trombetas, ca. 01°26'S, 055°55'W. MCP 28564, 1, 64 mm, mun. São Domingos do Capim, igarapé do Onze, ca. 11 km São Domingos do Capim on Belém-Brasília hwy., affl. rio Guamá, affl. Baía de Marajó, ca. 01°45'S, 047°41'W. MCP 49403, 11, mun. Curuá, Lago Preto, Ilha São Luiz, rio Amazonas, 02°06'22"S, 055°10'17"W. MCP 49407, 15, UF 238558, 28, 116-209 mm, UF 238559, 15, 110-209 mm, UF 238560, 25, 57-155 mm, UF 238561, 1, 68 mm, UF 238562, 46, 48-142 mm, UF 238563, 36, 66-125 mm, mun. Santarém, Lago de Santana, Ilha Marimarituba, rio Amazonas, 02°11'13"S, 055°02'21"W. UF 238569, 1, 58 mm, UF 238571, 2, 49-57 mm, UF 238572, 23, 131-206, UF 238573, 4, 131-209, UF 238574, 7, 72-109, UF 238576, 9, 68-115 m, UF 238578, 1, 16 mm, UF 238579, 9, 76-91 mm, UF 238581, 19, 67-139 mm, mun. Santarém, lago Pajau, rio Amazonas, 02˚11'29"S, 054˚51'28"W. MCZ 9415, 1, 127 mm, MCZ 45095, 2, 125-132 mm, rio Xingu at Porto de Moz, ca. 01°45'S, 052°10'W. MCZ 9432, 1, 108 mm, MCZ 9435, 4, 98-137 mm, MCZ 165862, 11 (part), 40-114 mm, mun. Santarém, Santarém and environs, rio Tapajós, ca. 02°26'S, 54°41'W. MPEG 1130, 2, 97-107 mm, MPEG 2816, 2, 50-127 mm, MPEG 3723, 1, 88 mm, mun. Cachoeira do Arari, Taperebá, rio Goapi, llha de Marajó, affl. Baía do Marajó, ca. 01°00'S, 048°57'W [coordinates for Cachoeira do Arari]. MPEG 1860, 11, 37-102 mm, mun. Óbidos, rio Amazonas nr. Óbidos, ca. 01°54'S, 055°26'W. MPEG 2437, 2, 90-112 mm, mun. Cachoeira do Arari, 1 km upstream Taperebá, rio Goapi, llha de Marajó, affl. Baía do Marajó, ca. 01°00'S, 048°57'W [coordinates for Cachoeira do Arari]. MPEG 5819, 1, 97 mm, mun. Almeirim, São Raimundo, rio Amazonas, ca. 01°32'S, 052°31'W [coordinates for Almeirim]. MPEG 9942, 1, 125 mm, MPEG 9943, 1, 97 mm, MPEG 9958, 6, 47-132 mm, MPEG 9962, 1, 63 mm, MPEG 9987, 1, 125 mm, MPEG 10162, 4, 97-130 mm, mun. Portel, Floresta Nacional Caxiuanã, affl. rio Anapú, affl. rio Pará, affl. Baía de Marajó, ca. 01°44'S, 051°26'W. MUSM 565, 1, 134 mm, lago Uruira, Oriximinã, rio Trombetas-Amazonas floodplain, ca. 01°46'S, 055°51'W [coordinate for Oriximinã]. MZUSP 5033, 1, 87 mm, mun. Cachoeira do Arari, Ilha de Marajó, rio Arari, affl. Baía de Marajó, ca. 01°00'S, 048°57'W. MZUSP 22894, 1, 92 mm, igarapé Caraparú, affl. rio Guamá, aff, Baía de Marajó, ca. 01°23'S, 048°08'W. MZUSP 23216, 20, 78-108 mm LEA, lago Ururiá [ L. Urarirá], Oriximiná, rio Amazonas floodplain nr. mouth rio Trombetas, ca. 01°53'S, 055°52'W. SU 54490, 1, 57 mm, SU 54498, 1, 88 mm, Uruará brook into rio Tapajós, Santarém, ca. 02°26'S, 054°42'W [coordinates for Santarém]. SU 54493, 1, 109 mm, igarapé do Sapucua [probably affl. lago Sapucuá] at Ayereua, affl. río Trombetas, ca. 01°49'S, 056°05'W. SU 54501, 1, 130 mm, lago Grande, rio Amazonas floodplain, ca. 02°16'S, 54°17'W. SU 54614, 1, 99 mm, Alemquer [Alenquer] pond affl. rio Amazonas, ca. 01°57'30"S, 54°44'18"W [coordinates for Alenquer]. Rondônia (localities from rio Madeira dr., Amazonas dr.). INPA 9719, 2, 148-155 mm, INPA 9728, 3, 125-145 mm, ca. 15 km Guajará Mirim, rio Pacaás Novos, affl. rio Mamoré, ca. 10°51'S, 065°16'W. INPA 19943, 15, 53-92 mm, rio Mamoré, upstream Surprêsa, ca. 11°53'S, 064°59'W. INPA 19953, 3, 34-88 mm, rio Mamoré, just upstream Guajará Mirim, ca. 10°47'S, 065°20'W. INPA 19957, 1, 148 mm, Surprêsa, at rio Guaporé- Mamoré confl., ca. 11°53'S, 064°59'W. MPEG 1116, 6, 77-100 mm, rio Pacaás Novas, Guajará Mirim, affl. rio Mamoré, ca. 10°51'S, 065°16'W. MPEG 1121 (part), 1, 85 mm, rio Pacaás Novos, 20 km upstream Guajará Mirim, ca.10°56'15"S, 065°16'29"W. UFRO-I 6484, 34, 43-145 mm, UFRO-I uncat. (field number CUN2009061202), 1, 58 mm, UFRO-I uncat. (field number CUN2009072001), 1, 54 mm, Furo Variante, lago Cuniã, rio Madeira floodplain, 08°21'18"S, 063°30'11"W. UFRO-I 6486, 11, 68-144 mm, lago Cuniã, nr. ICMBio base, rio Madeira floodplain, 08°19'40"S, 063°30'11"W. UFRO-I 6489, 2, 86-161 mm, UFRO-I 6498, 1, 124 mm, lago Cuniã, nr. ICMBio base, rio Madeira floodplain, 08°19'20"S, 063°30'14"W. UFRO-I 6491, 4, 38-111 mm, lago Cuniã, nr. igarapé do Campo, rio Madeira floodplain, 08°19'09"S, 063°28'44"W. UFRO-I 6493, 3, 141-151 mm, Arrozal do lago, lago Cuniã, rio Madeira floodplain, 08°19'36"S, 063°29'59"W. UFRO-I 6500, 3, 55-148 mm, lago Cuniã, rio Madeira floodplain, 08°19'45"S, 063°28'06"W. UFRO-I 6502, 28, 78-135 mm, lago Cuniã, rio Madeira floodplain, 08°21'10"S, 063°30'26"W. UFRO-I 6510, 21, 81-180 mm, mouth of rio Cautário, affl. rio Guaporé, affl. rio Mamoré, 12°10'51"S, 064°34'04"W. UFRO-I 6511, 1, 113 mm, igarapé do Campo, lago Cuniã, rio Madeira floodplain, 08°19'14"S, 063°28'05"W. UFRO-I 7927, 8 (2 immature, 96-111 mm, 6 female, 90-107 mm), mun. Porto Velho, lago Cuniã, rio Madeira floodplain, 08°19'S, 063°28'W. USNM 348864, 1, 119 mm, Brazil-Bolivia border region between Guajará-Mirim and Mato Grosso, rio Guaporé, affl. rio Mamoré, ca. 13°46'S, 061°04'W. French Guiana. Cayenne. ANSP 163463, 1 (lectotype), male, 125 mm, ANSP 163464, 1 (paralectotype), male, 149 mm, ANSP 163465, 1 (paralectotype), female, 119 mm, ANSP 164474, 1 (paralectotype), male, 156 mm, BMNH 1990.10.23.1-3, 3), 93-108 mm, FMNH 98817, 1 (paralectotype), 116 mm, MBUCV-V 20221, 3, 82-100 mm, MNHN 1989-1209, 3 (paralectotypes), NMW 90321, 5, 115-139 mm, UMMZ 216032, 3, 48-68 mm [originally 96-106] mm, USNM 301966, 1 (paralectotype), 114 mm, USNM 301967, 1 (paralectotype), female, 114 mm, coastal swamp, 'Grand Pripris', 3.5 km NW center of old Kourou, ca. 100m N old Route Nationale 1, Kourou River dr., 05°10'45"N, 052°40'00"W. CU 71933, 1, male, 170 mm, FMNH 98818, 3, 124-161 mm, swampy border, Kaw River, ca. 3.5 km SW Kaw, River Kaw dr., ca. 04°27'N, 052°10'W. USNM 301968, 1, 64 mm, swamp, old Rn-1 Hwy., nr. city of Kourou, Kourou River dr., ca. 05°10'N, 052°39'W. Peru. Madre de Dios. (localities from río Madre de Dios, affl. río Beni, affl. rio Madeira, Amazonas dr.). MUSM 2470, 1, Parque Nacional del Manu, Pakitza, río Manu, ca. 12°52'S, 069°16'W. MUSM 2874, 2, Reserva Nacional (RN) Tambopata, cocha Redonda, no coordinates. MUSM 2981, 1, 90 mm, Planchón, N Puerto Maldonado, río Manuripi, affl. río Orthon, ca. 12°17'S, 069°09'W. MUSM 3521, 2, Reserva Nacional Tambopata, La Colpa, río Tambopata, no coordinates. MUSM 4198, 4, RN Tambopata, no coordinates. MUSM 9265, 10, 94-171 mm, MUSM 9847, 1, 170 mm, MUSM 16004, 1, 123 mm, MUSM 16169, 1, MUSM 16181, 1, 195 mm, lago Tres Chimbadas, RN Tambopata, río Tambobata, 12°47'26"S, 069°20'31"W. MUSM 16610, l, 109 mm, lago Valencia, río Madre de Dios floodplain, ca. 12°25'S, 068°46'W. MUSM 16712, 2, 142-147 mm, MUSM 16743, 1, 140 mm, Tambopata, lago Copamanu, ca. 12°50'S, 069°17'W. MUSM 19991, 1, 149 mm, Los Amigos Biostation, río Madre de Dios floodplain, ca. 12°33'S, 070°07'W. MUSM 20046, 1, 150 mm, Manu, no coordinates. MUSM 20184, 4, Mavila, río Los Amigos, no coordinates. MUSM 20588, 2, MUSM 21390, 10, MUSM 21483, 1, Tambopata, Pozo Pedro, río Los Amigos, 12°33'40"S, 070°06'36"W. MUSM 21731, 2, MUSM 21779, 3, Pozo Santa Elena, no coordinates. MUSM 22101, 1, Tambopata, Aguajal Oeste, ca. 12°00'S, 070°40'W. TCWC 13983.01, 2, 73-87 mm, lago Tres Chimbadas, río Tambopata, 12°47'29"S, 069°20'54"W. TCWS 13985.02, 2, 86-115 mm, lago Tres Chimbadas, río Tambopata, 12°47'04"S, 069°20'29"W. USNM 263859, 4, 70-135 mm, RN Tambopata, Laguna Chica, 12°50'30"S, 069°17'30"W. USNM 264110, 5, 42-102 mm, USNM 387400, 1, 91 mm, NR Tambopata, Laguna Cocococha, 5.1 km E Explorer's Inn, 12°49'00"S, 069°16'30"W.

Brachyhypopomus provenzanoi, new species

urn:lsid:zoobank.org:act:E64D737C-8334-47FA-9598-79B4F76C89CF

(Fig. 40; Tables 2-5, 17)

Brachyhypopomus sp. "pro". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. "provenzanoi". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MBUCV-V 35650, immature, 87 mm TL, 71 mm LEA, Venezuela, Amazonas, mun. San Fernando de Atabapo, caño "CVG" (Corporacion Venezuelana Guyana), km 10.5 km on San Fernando de Atabapo-Santa Barbara rd., affl. río Orinoco, Orinoco dr., 03º58'59"N, 067º38'29"W, 11 Mar 2004, W. Crampton, N. Lovejoy, S. Willis & C. Montaña.

Paratypes. 59 specimens, all from Orinoco dr. Venezuela. Amazonas. MBUCV-V 12991, 2, 71-72 mm, MBUCV-V 12993, 4 (2 measured), 79-108 mm, Pozo de Lucas, ca. 7 km S San Fernando de Atabapo, affl. río Orinoco, ca. 04°15'N, 067°39'W, 8 Apr 1982, R. Royero & G. Pereira. MBUCV-V 35651, 16 (14 immature [1 CS], 73-93 mm, 2 male, 92-94 mm), caño Viejita, on rd. from San Fernando de Atabapo to Santa Barbara, affl. río Atabapo, 03°55'59"N, 067°36'34"W, 13-15 Mar 2004, W. Crampton, N. Lovejoy, S. Willis & C. Montaña. UF 177347 33 (19 immature [3 CS], 67-87 mm, 10 female, 69-110 mm, 4 male, 83-94 mm), collected with holotype.

Non-types. 10 specimens. Venezuela. Amazonas. MBUCV-V 11221, 1, 107 mm, caño Chola, rd. to Solano, at km 17.7 from San Carlos de rio Negro, río Negro, upper rio Negro, Amazonas dr., ca. 01°57'N, 066°59'W. UF 185344, 9, immature, collected with holotype.

Diagnosis. Brachyhypopomus provenzanoi is diagnosed from congeners by the following combination of characters: scales absent in middorsal region of anterior third of body (vs. present in all congeners except B. benjamini); dorsal surface of body with irregular pattern of distinct dark blotches on depigmented tan-colored background, vs. speckled with small brown chromatophores on light brown background in B. benjamini.

Description. Head and body shape, and pigmentation illustrated in Fig. 40. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 17. Body shallow in depth. Head short to moderate in length and shallow in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head gently convex between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with slight sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 26-32 (median 29, n = 9). Pectoral fin narrow, pectoral-fin rays 12-15 (mode 13). Precaudal vertebrae 15-17 (mode 16), with 1-2 (mode 1) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) to substantially (0.33-0.5 HL distance) posterior to tip of pectoral fin. Anal-fin rays 162-195 (median 184). Dorsal rami of recurrent branch of anterior lateral line nerve visible. Middorsal region of body without scales in anterior third of body. Middorsal region with small scales completely occluded by skin in posterior two thirds of body. Rows of scales above lateral line 4-5 (mode 4); at measuring point in mid-anal fin, scale rows do not reach dorsal midline - instead middorsal region is scaleless, as is condition anterior. Scale rows reach dorsal midline just posterior to this point. Lateral line continuous. Sparse depigmented epidermal canals present as short parallel scratch like marks dorsal to and near lateral line; mostly restricted to posterior third of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus, and at a mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Coloration. (Fig. 40). Pale straw to tan background. Dorsal region comprising irregular brown patches and a pale straw or tan background, with no pale stripe along dorsal midline from occipital region to base of caudal filament. Distinct stripes or saddles on flank absent. Region over anal-fin pterygiophores straw colored with very faint irregular markings. Caudal filament darker than body, with indistinct, disrupted vertical bars. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch, or stripe, of chromatophores/subcutaneous pigmentation. Pectoral-fin and anal-fin membranes hyaline. Pectoral-fin rays hyaline and unpigmented. Anal-fin rays with light scattering of dark chromatophores, in posterior half of fin only. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 40
Brachyhypopomus provenzanoi. MBUCV-V 35650, holotype, immature, 87 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Venezuela, río Orinoco, Orinoco dr. Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 110 mm TL, 91 mm LEA (n = 70). Largest male specimen examined 94 mm TL, 83 mm LEA (n = 6). Largest female specimen examined 110 mm TL, 91 mm LEA (n = 10).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Venezuela (Fig. 31). Known from the upper Orinoco and upper Negro (Amazonas dr.).

Ecological notes. Ecology known only for the type series. Brachyhypopomus provenzanoi was collected in small, gently flowing, low-conductivity clearwater terra firme forest and savanna streams, and from static leaf-litter choked blackwater streams and swamps in Mauritia palm swamps. Most specimens in streams were found sheltering in submerged and marginal aquatic vegetation growing in sandy beds, and those in Mauritia palm swamps were collected from dense leaf litter banks and root mats. The following water parameters were recorded at the sampling sites: conductivity 9-10 μScm-1, dissolved oxygen 1.6-3.8 mgl-1, temperature 25.8-28.2°C, pH 3.1-4.0. Reproductive biology is unknown. Stomach contents comprise aquatic insect larvae and other small aquatic invertebrates (WGRC unpublished data).

Co-occurring congeners: In the region of the type locality, Brachyhypopomus provenzanoi was found in sympatry and in ecological syntopy with B. bullocki, B. brevirostris, and B. sullivani. Its geographical range also overlaps with that of B. beebei and B. regani.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Francisco Provenzano Rizzi, Venezuelan ichthyologist, for his contributions to Neotropical ichthyology.

Local names. Venezuela: cuchillo.

Brachyhypopomus regani, new species

urn:lsid:zoobank.org:act:F537AD66-390E-4767-926E-0D18CAD199AC

(Figs. 1j, 41; Tables 2-5, 17)

Hypopomus brevirostris. -Hopkins & Heiligenberg, 1978Hopkins, C. D . & W. Heiligenberg. 1978. Evolutionary designs for electric signals and electroreceptors in gymnotoid fishes of Surinam. Behavioral Ecology and Sociobiology, 3: 113-134.: 132, fig. 10, black and white photograph of adult (Suriname, species and EOD diversity).

Hypopomus artedi. -Hopkins & Westby, 1986Hopkins, C. D. & G. W. M. Westby. 1986. Time domain processing of electric organ discharge waveforms by pulse type electric fish. Brain Behavior and Evolution, 29: 77-104.: 83, fig. 3, line drawing (Guianas, species and EOD diversity).

Hypopomidae sp. 9. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 32-33, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1 reproductive biology (Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus electropomus. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 91 (description in unpublished thesis with disclaimer stating that nomenclatural acts are not available, a nomen nudum, refers also to B. bombilla and B. menezesi).

Brachyhypopomus sp. 5. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4, 834, fig. 9, illustration of specimen, with EOD (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance). -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species).

Brachyhypopomus sp. E. -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus sp. "reg". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. 1. -Mol, 2012: 598 (Suriname, catalog of fishes). -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 238, color photograph (Brazil, rio Madeira, listing of hypopomids).

Brachyhypopomus sp. 'ele'. -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 177, fig. 37A, color photograph of head showing position of accessory electric organ; 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea).

Brachyhypopomus sp. "regani". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MCP 47022, female, 128 mm TL, 115 mm LEA, Brazil. Amazonas. Mamirauá Reserve, cano do lago Rato, rio Solimões-Japurá floodplain, Amazonas dr., 03º02'41"S, 064º51'26"W, 14 Mar 2001, W. Crampton & J. Oliveira.

Paratypes. 40 specimens. Brazil. Amazonas (collected from Amazonas dr., by W. Crampton & J. Oliveira; localities from Amazonas dr., localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). BMNH 1998.3.12.183, 1, immature, 117 mm, mun. Tefé, Ressaca do Cachorro, lago Tefé, (rio Tefé), 03°19'50"S, 64°46'15"W, 3 Feb 1995. BMNH 1998.3.12.184-188, 6, immature (1 measured, 90 mm), Mamirauá Reserve, cano do lago Mamirauá, 03º03'51"S, 64º51'05"W, 12 Apr 1994. BMNH 1998.3.12.189-190, 2 (1 female, 109 mm, 1 male, 134 mm), Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W, 20 Jan 1995. INPA 9951, 8, 70-108 mm, Mamirauá Reserve, lago Caetano, 02º50'58"S, 064º55'42"W, Oct 1993. INPA 18447, 2, immature, 66-79 mm, Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W, Jun 1998. MCP 45333, 2 (1 immature, 118 mm, 1, male, 132 mm), Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W, 2 Apr 1994. MCP 45334, 1, female, 120 mm, Mamirauá Reserve, lago Bolsinha, 03º03'47"S, 064º50'03"W, 5 Apr 1994. MCP 45335, 1, immature, 140 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º03'51"S, 064º51'05"W, 2 Oct 1994. MCP 45411, 1, female, 107 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W, 15 Apr 1998. MCP 45439, 1, immature, 107 mm, Mamirauá Reserve, Paraná do Apara, 03º06'40"S, 064°47'52"W, 23 Mar 1995. MCP 45446, 4, 57-109 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W, 1997 (no precise date). MCP 45474, 1, 107 mm, mun. Tefé, Ilha Panamim, rio Solimões floodplain, 03º19'29"S, 064º38'37"W, 31 Jul 2001. MCP 45475, 2, 76-86 mm, MCP 45476, 1, female, 141 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11'11"S, 064°43'05"W, 18 Aug 2001. MCP 45484, 8 (1 not sexed [CS], 105 mm, 2 immature [1CS], 84-90 mm, 2 female, 89-117 mm, 3 male, 104-135 mm [1 with gill and brain removed, 135 mm]), Mamirauá Reserve, cano do lago Mamirauá, 03º06'40"S, 064°47'52"W, 15 Mar 2001.

Non-types. 189 specimens. Brazil (localities from Amazonas dr.). Acre. MCP 41043, 2, mun. Brasiléia, stream, affl. small river, ca. 2 km hwy. BR-317 on branch 26, affl. rio Purus, 10°56'10"S, 068°56'01"W. Amazonas. (localities from Amazonas dr., localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). IDSM 458, 1, 67 mm, MCP 45473, 3 (1 female, 112 mm, 2 male, 104-119 mm), Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. INPA 15443, 1, 143 mm, igarapé Água Viva, nr. Presidente Figueiredo, 12 km on hwy. AM-240, igarapé Mutum, affl. igarapé Urubú, 02°15'13"S, 060°24'59"W. INPA 19945, 2, 73-88 mm, Ilha Janauacá, rio Solimões floodplain, ca. 03°43'S, 060°26'W. MCP 41036 (part), 1, 86 mm, mun. Canutama, igarapé São João on hwy. BR-319, ca. 60 km S Humaitá, affl. rio Ipixuna, affl. rio Purus, 07°56'07"S, 063°20'03"W. MCP 45282, 1, immature, 80 mm, rio Japurá, at Nova Colômbia, rio Solimões-Japurá floodplain, 02º54'47"S, 064º54'19"W. MCP 45283, 2, immature, 73-76 mm, rio Japurá, nr. Boca do lago Mamirauá, rio Solimões-Japurá floodplain, 03º07'03"S, 064º46'51"W. MCP 45284, 1, female, 133 mm, Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45285, 3 (2 female, 100-112 mm, 1 male, 123 mm), Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. MCP 45286, 2, female, 107-111 mm, Mamirauá Reserve, Ressaca do Pau, 03º02'03"S, 064º52'13"W. MCP 45456, 2 (1 immature, 103 mm, 1 female, 106 mm), Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. MCP 45457, 3 (1 not sexed [CS], 130 mm, 2 male, 96-134 mm), Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MZUSP 23403, 1, igarapé Tucuxi, Ati-Paraná, NW Fonte Boa, rio Solimões floodplain, ca. 02°14'S, 066°37'W. USNM 304962, 1, 82 mm, Paraná do Marauiá, affl. río Negro, ca. 00°23'S, 065°13'W. Goiás. MZUSP 4887, 1, 53 mm LEA, rio Araguaia at Aruanã, affl. rio Tocantins, Amazonas dr., 14°55'S, 051°04'W. Mato Grosso (localities from rio Tocantins dr., Amazonas dr.). MCP 40271, 5, mun. Vila Rica, stream on rd. Vila Rica-Confresa rd., affl. Ribeirão Gameleira, affl. rio Araguaia, 10°31'31"S, 051°24'39"W. MCP 40780, 2, 66-90 mm, mun. Confresa, Ribeirão Tucunara, hwy. MT-432 between hwy. BR-158 and Terra Indígena Urubu Branco, affl. rio Araguaia, 10°41'25"S, 051°22'52"W. MZUSP 88597, 2, 71-80 mm, Cocalinho, ca. 79 km N Cocalinho on hwy. MT-326, Ribeirão Agua Preta, affl. rio Cristalino, affl. rio Araguaia, 14°08'57"S, 051°32'21"W. Pará (localities from Amazonas dr.). MCP 23358, 3, 76-88 mm, mun. São Miguel do Guamá, stream on rd. from São Miguel do Guamá to Ourem, ca. 10 km São Miguel do Guamá, affl. rio Guamá, affl. Baía de Marajó, 01°33'18"S, 047°25'41"W. MCP 49412, 2, mun. Alenquer, small stream, affl. rio Curuá, 01°36'13"S, 054°55'10"W. MPEG 1127, 1, 115 mm, mun. Castanhal, Boa Vista do Apeú, rio Apeú, affl. rio Guamá, affl. Baía de Marajó, ca. 01°18'S, 047°59'W. MPEG 2399, 1, 97 mm, mun. Castanhal, Boa Vista do Apeú, rio Apeú, affl. rio Guamá, affl. Baía de Marajó, ca. 01°18'S, 047°59'W. MPEG 2402, 1, 103 mm, mun. Peixe-Boi, rio Peixe-Boi, affl. rio Maracanã, rio Amazonas estuary, 01°11'31"S, 047°18'14'W [coordinates rio Peixe-boi at Peixe-boi]. MPEG 15005 (part), 1, 82 mm, mun. Itaituba, stream at trail head from BR-163, affl. rio Tapajós., 04°23'41"S, 055°32'20"W. MPEG 24491, 17, 84-123 mm, mun. Capanema, igarapé Açaiteuazinho nr. Vila de Tauarí, rio Caeté dr., rio Amazonas estuary, 01°11'45"S, 047°10'51"W. MZUSP 97324, 1, 72 mm, mun. Novo Progresso, nr. Mil, rio Jamanxim, affl. rio Tapajós, 07°43'51"S, 055°16'36"W. MZUSP 97544, 1, 82 mm, mun. Novo Progresso, affl. rio Jamanxim, bridge on hwy. BR-163, affl. rio Jamanxim, affl. rio Tapajós, 07°21'08"S, 055°17'45"W. USNM 330451, 1, 90 mm, Belém, Baía de Marajó, ca. 01°27'S, 048°28'W. Tocantins (localities from rio Tocantins dr., Amazonas dr.). MZUSP 51366, 2, 75-76 mm, mun. Araguaçu, Fazenda Praia Alta 2.27 km N Araguaçu, on Araguacu-Barreira do Piqui rd., rio Agua Fria, affl. rio Javaés, affl. rio Araguaia, affl. rio Tocantins, ca. 12°45'S°, 049°55'W. MZUSP 52166, 3, 78-90 mm, mun. Araguaçu, Fazenda Praia Alta 2, on Araguaçu-Barreira do Piqui rd., rio Agua Fria, affl. rio Javaés, affl. rio Araguaia, affl. rio Tocantins, ca. 12°43'S, 049°55'W. MZUSP 52214, 1, 79 mm, mun. Sandolândia, stream on Sandolândia-Barra do rio Verde rd., ca. 5 km Sandolândia, rio Água Fria, affl. rio Javaés, affl. rio Araguaia, affl. rio Tocantins, ca. 12°32'S, 049°55'W. Ecuador (localities from río Napo dr., Amazonas dr.). Francisco de Orellana. FMNH 102289, 4, 27-91 mm, affl. río Payamino, downstream from San José de Payamino, N bank, affl. río Payamino, affl. río Napo, 00°30'S, 077°15'W. QCAZ-I 1828, 1, 134 mm, QCAZ-I 1829, 1, 132 mm, QCAZ-I 1830, 1, 132 mm, QCAZ-I 1831, 1, 148 mm, QCAZ-I 1832, 1, 136 mm, Parque Nacional Yasuní, km 39 on Pompeya-NPF (oil field) rd., río Tiputini, affl. río Napo, ca. 00°36'S, 076°28'W. Sucumbios. FMNH 102273, 1, 53 mm, affl. río Aguarico, N bank, 1-2 km upstream from mouth of río Pushino, affl. río Napo, 00°03'30"N, 076°56'00"W. FMNH 120675, 1, 43 mm, small stream between Laguna Zancudo and Laguna Zancudococha, affl. quebrada Zancudococha, affl. río Aguarico, affl. río Napo, ca. 00°26'S, 076°36'W. KU 13802, 1, 127 mm, río Conejo at Santa Cecília, affl. río Aguarico, affl. río Napo, ca. 00°06'N, 076°51'W. Guyana. Upper Takutu-Upper Essequibo (localities from Takutu River dr., affl. rio Branco, affl. rio Negro, Amazonas dr.). ANSP 179507, 1, 81 mm, 31.2 km NW Sand Creek village, Sauriwau River, 03°06'52"N, 059°46'32"W. AUM 48079, 1, 82 mm, creek, 2nd bridge from Moco-Moco power station to Lethem, 03°18'10"N, 059°39'01"W. CU 71937, 11, Moco-Moco Creek, 15 km W Lethem. ca. 03°15'N, 059°39'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). CU 71939, 3, CU 71940, 1, CU 71941, 2, USNM 209197, 1, 89 mm LEA, overflow of Moco-Moco Creek nr. Moco-Moco village, Kumaka Swamp, ca. 15 km E Lethem, ca. 03°19'N, 059°40'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). USNM 209196, 1, 135 mm, USNM 209198, 1, 105 mm, Rupununi, Moco-Moco Creek, ca. 03°15'N, 059°39'W. USNM 209200, 1, 110 mm, Rupununi, creek in swampy area, nr. Moco-Moco Creek, ca. 03°15'N, 059°39'W. Peru. Amazonas. LACM 41930-5, 1, 129 mm, LACM 41934-4, 2, 116-146 mm, LACM 41935-2, 1, 127 mm, LACM 41936-5, 1, 138 mm, 500 m upstream from Caterpiza, río Santiago, affl. río Marañón, affl. rio Amazonas, Amazonas dr., ca. 03°55'S, 077°44'W. Loreto (localities from Amazonas dr.). AMNH 78112, 1, 77 mm, río Tahuayo, ca. 04°03'S, 073°08"W. AMNH 78114, 1, 140 mm, río Yarapá, affl. río Ucayali, ca. 04°31'S, 073°22'W. INHS 43308, 2, 84-87 mm, Maynas, 11 km SSW Iquitos, río Itaya, 03°49'48"S, 073°18'03"W. INHS 52032, 1, 125 mm, Ullpa, caño Moena, nr. confl. with caño Ullpa, SE Iquitos, affl. río Itaya, 03°46'20"S, 073°14'17"W. INHS 54796, 1, 70 mm, floodplain of río Marañón, S Nauta, 04°30'36"S, 073°34'06"W. MUSM 4341, 1, 118 mm, MUSM 17308, 2, 91-93 mm, Yurimáguas, San Ramón, quebrada Simay, affl. río Huallaga, affl. río Marañón, ca. 05°56'S, 076°06'W. MUSM 14494 (part), 2 (1 immature, 104, 1 male, 156 mm), Maynas, Lagartococha, Aguas Negras, río Aguarico, affl. río Napo, 00°31'38"S, 075°15'41"W. MUSM 14497 (part), 6, 91-138 mm, Puesto de Vigiliancia area MH93LO, río Napo, 00°58'S, 075°11'W. MUSM 14498 (part), 1, 124 mm, mun. Maynas, Puesto de Vigilancia Arcadia, río Napo, 00°59'37"S, 075°18'30"W. MUSM 18538, 1, 71 mm, nr. Musha Carusha, río Pastaza, affl. río Marañón, 04°26'54"S, 076°39'28"W. MUSM 21896, 1 (not measured), MUSM 21983, 2, mun. Nauta, Reserva Nacional (RN) Pacaya Samiria, quebrada Llanchama, affl. río Yanayacu-Pucate, río Marañón, ca. 04°39'S, 073°50'W. MUSM 23141, 1, Alto Amazonas, Abanico del Pastaza, stream affl. río Platanoyacu, río Corrientes, río Tigre, río Marañón, ca. 03°07'S, 075°40'W. UF 126192, 1, 125 mm, RN Pacaya Samiria, río Pacaya, affl. río Ucayali, ca. 05°16'S, 074°27'W. UF 129816, 1, 62 mm, UF 131404, 1, immature, 100 mm, RN Pacaya Samiria, caño Yarina, río Pacaya, affl. río Ucayali, 05°25'56"S, 074°30'01"W. UF 131405, 1, immature, 94 mm, RN Pacaya Samiria, cocha Yarina, río Pacaya, affl. río Ucayali, 05°23'58"S, 074°32'05"W. Suriname. Brokopondo. UF 177362, 7 (5 female, 119-132 mm, 2 male, 133-141 mm), Affobaka rd. from Paranam bauxite refinery to Brokopondo Reservoir, bridge over Marshall kreek, Suriname River dr., 05°14'40"N, 055º 06'05"W. Marowijne. UF 177360, 12 (7 female, 105-114 mm, 5 male, 98-129 mm), small stream on rd. from Paramaribo to French Guiana, affl. Cottica River, Commewijne River dr., 05°34'51"N, 054°15'31"W. UF 177363, 2, female, 105-109 mm, small stream on rd. from Paramaribo to French Guiana, affl. Cottica River, Commewijne River dr., 05°35'11"N, 054°17'05"W. Venezuela (localities from Orinoco dr.). Anzoátegui. MHNLS 9360, 1, 83 mm LEA, río Morichal Largo, río Orinoco delta, ca. 09°26'N, 062°24'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Apure. INHS 28179, 4, 90-102 mm, 58 km SSW Bruzual, caño Guaritico, affl. río Apure, 07°33'09"N, 069°38'40"W. INHS 28360, 7, 72-91 mm, 62 km E Elorza on hwy. to La Victoria at Charal, río Orichuma, affl. río Apure, ca. 07°04'N, 070°01'W. INHS 30112, 1, 84 mm, 58 km SSW Bruzual, caño Guaritico, affl. río Apure, 07°33.24'N, 069°38.68'W. MCNG 11032 (part), 5, 79-98 mm LEA, caño Maporal, río Caicara, affl. río Apure, ca. 07°24'N, 069°32'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Barinas. MCNG 5611, 1, Reserva de Ticoporo, affl. río Suripa, affl. río Apure, ca. 08°09'N, 070°50'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Bolivar. AUM 22303, 1, 106 mm, río Chaviripa, on Caicara-Puerto Ayacucho rd., 07°07'57"N, 066°29'56"W. FMNH 109967, 1, 38 mm, caño Wani, affl. río Caura, 06°04'47"N, 064°55'20"W. MCNG 19941, 1, MCNG 19999, 1, stream affl., río Caura, no coordinates. MHNLS 8783, 1, 83 mm LEA, Raudales del Cambur [El Raudal, caño Cambur], 20 km [SE] bridge at Maripá, ca. 07°22'N, 065°18'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Monagas. MBUCV 14122, 1, 97 mm LEA, bridge over caño Piedritas on Temblador-Barrancas hwy., affl. río Urucoa, río Orinoco delta, ca. 08°49'N, 062°29'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). MHNLS 6512, 1, 76 mm LEA, inundated area, Chaguaramas, río Urucoa, ca. 08°40'N, 062°45'W (listed by Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.). Portuguesa. TNHC 12703, 2, 64-83 mm, 35 km SE Guanare, caño (río) Maraca at Urriola Ranch, affl. río Portuguesa, affl. río Apure, 08°52'30"N, 069°27'40"W. Tachira. INHS 35527, 1, 92 mm, [stream] just W junction between hwy. 5 and hwy. 19, río Caparo, affl. río Anaro, affl. río Apure, 07°32'01"N, 071°34'56"W.

Diagnosis. Brachyhypopomus regani is diagnosed from congeners by the following combination of characters: accessory electric organ over opercular region present, vs. absent in all congeners except B. bombilla, and B. menezesi; dorsal surface with large dark blotches against a lighter background, vs. dorsal surface speckled with small brown chromatophores on a pale background in B. bombilla; caudal filament length 11.1-17.9%, vs. 24.-33.3% LEA in B. menezesi.

Description. Head and body shape, and pigmentation illustrated in Figs. 1j and 41. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 17. Body moderate to broad in depth. Head moderate to long in length and shallow to moderate in depth. Dorsal profile of head approximately straight to slightly concave from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum present and very prominent; skin over AEO completely depigmented; border rounded and very conspicuous. Gill filaments on first gill arch 35-45 (median 40, n = 9). Pectoral fin narrow to moderate, pectoral-fin rays 14-16 (no mode, median 15). Precaudal vertebrae 16-18 (mode 17), with 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) anterior to tip of pectoral fin. Anal-fin rays 165-205 (median 184). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Multiple groove-like depigmented epidermal canals, some with dark borders, form parallel striations mostly dorsal to lateral line in posterior portion of body, beginning ca. two thirds of LEA; striations reaching 1-4 scales (including lateral line series) dorsally, and occasionally (with much lower density) 1-2 scales ventrally. Epidermal canals absent in anterior portion of body; never form a pair of long irregular lines either side of dorsal surface in dorsal portion of flank; do not form isolated horizontal wavy line midway from lateral line to dorsal midline in midbody or anterior portion of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Electrocytes of hypaxial electric organ extend anterior to anal and urogenital pores and appear to extend into opercular area to form paired accessory electric organ. Caudal filament short.

Coloration. (Figs. 1j, 41). Background light tan to brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament. Dorsal region mottled with irregular, indistinct dark blotches against a homogenous lighter background (contrasting to a speckling with small brown chromatophores in B. bombilla and to much more distinct dark blotches in B. menezesi). Dark mottling restricted to dorsal region, extending to around mid-distance from dorsal midline to lateral line. No vertical stripes or lines on flank, some vague irregular dark markings over anal-fin pterygiophores, flank otherwise relatively free of markings. Caudal filament darker than body, with some irregular dark markings. Head with evenly scattered dark chromatophores, darker dorsally. Eye with indistinct to very distinct suborbital patch or stripe of chromatophores and subcutaneous pigmentation. Region over AEO completely depigmented. Border of AEO often with very dark chromatophores. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline in distal third to half, with scattered or fused light brown chromatophores on proximal half. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 41
Brachyhypopomus regani. MCP 47022 (WC04.140301), holotype, female, 128 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note prominent opercular accessory electric organ (pale structure). Scale bars = 5 mm.

Size. Small adult size, largest specimen examined 156 mm TL, 130 mm LEA (n = 230). Largest male specimen examined 156 mm TL, 130 mm LEA (n = 17). Largest female specimen examined 141 mm TL, 125 mm LEA (n = 28).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Brazil, Ecuador, Guyana, Peru, Suriname, and Venezuela (Fig. 42). Widely distributed through the Amazon basin, including multiple sites in the upper Amazon, the Negro, Purus, Tapajós, and Araguaia drainages. Absent from the upper Madeira, above its major falls beginning at Porto Velho, where the closely related species B. bombilla occurs. Known also from northern portions of the Orinoco drainage, the Essequibo River, and some coastal drainages of Guyana.

Fig. 42
Collection records for Brachyhypopomus regani (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Ecological notes. In the central and upper Amazon B. regani is restricted to high-conductivity whitewater floodplains - occurring in floating rafts of macrophytes, and the leaf litter of newly-inundated forest (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.; 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.). Breeding occurs in floating macrophytes during the rising and high water period (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p., 165). Like other congeners in this habitat, B. regani is able tolerate protracted seasonal hypoxia. However, in experimental conditions it is less tolerant of anoxia than syntopic congeners (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Unlike most congeners B. regani does not undertake aerial gill respiration during experimentally-induced hypoxia. Instead it wedges itself into roots near the water surface and exhibits a variant of aquatic surface respiration in which water at the surface meniscus is passed across its gills by buccal pumping (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Populations assigned here to B. regani from the lower Amazon in the vicinity of Belém, coastal Suriname, and in the rio Negro (and possibly also the rio Tapajós and rio Araguaia) have a noticeably different ecology, occurring in constantly normoxic rainforest streams and small rivers with relatively low conductivity (10-30 μScm-1) (WGRC unpublished data). We suspect that future studies of ecological, genetic, and EOD variation in this widely distributed species may reveal additional cryptic species. Specimens from whitewater floodplain systems of the central Amazon (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136), and also terra firme stream from coastal Suriname (WGRC unpublished data), exhibit similar stomach contents, comprising aquatic insect larvae, microcrustacea, and other small aquatic invertebrates with a predominance of Chironomidae larvae.

Co-occurring congeners: In the upper, central, and lower Amazon (excluding the upper Madeira), B. regani occurs in sympatry and ecological syntopy with B. arrayae (in lower Madeira), B. beebei, B. belindae, B. bennetti, B. brevirostris, B. flavipomus, B. hamiltoni, B. pinnicaudatus, and B. walteri, and exhibits an allotopic distribution with B. alberti (in lower Madeira), B. batesi, B. benjamini, B. cunia (in lower Madeira), B. hendersoni, B. sullivani, and B. verdii. In the rio Negro B. regani occurs in sympatry (and probably in syntopy) with B. batesi, B. beebei, B. brevirostris, B. bullocki¸ B. hamiltoni, B. hendersoni¸ B. sullivani, and B. walteri. In the río Orinoco basin B. regani occurs in sympatry with B. beebei, B. brevirostris, B. bullocki, B. diazi, and B. sullivani. In the Essequibo River B. regani occurs in sympatry with B. beebei, B. brevirostris, B. bullocki¸ B. hendersoni¸ B. sullivani, and B. walteri. In Coastal Suriname and French Guiana B. regani occurs in sympatry with B. beebei, B. brevirostris, and B. pinnicaudatus.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Charles Tate Regan (1878-1943), British ichthyologist, for his contributions to Neotropical ichthyology.

Local names. Brazil: sarapó; Ecuador: cuchillo, yayo; French Guiana: poisson couteau (French) (and multiple creole/Amerindian names), Guyana: knife fish; Peru: macana; Suriname: saprapi; Venezuela: cuchillo.

Brachyhypopomus sullivani, new species

urn:lsid:zoobank.org:act:A5E0AE79-5691-4FEE-AA8B-F9BD8AE86D1C

(Figs. 1k, 43; Tables 2-5, 19)

Hypopomidae sp. 11. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 36-37, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats (Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus royeroi. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 126 (description in unpublished thesis with disclaimer stating that nomenclatural acts not available, a nomen nudum).

Brachyhypopomus sp. 6. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4 (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance).

Brachyhypopomus sp. F. -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity). -Crampton et al., 2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.: 231, fig. 6, black and white photograph of head of live individual (Brazil, Amazonas, adaptations to hypoxia).

Brachyhypopomusbeebei. -Galvis, 2006Galvis, G., J. I. Mojica, S. R. Duque, C. Castellanos, P. Sánchez-Duarte, M. Arce, Á. Gutiérrez, L. F. Jiménez, M. Santos, S. Vejerano, F. Arbelaez, E. Prieto & M. Leiva. 2006. Peces del medio Amazonas - Región de Leticia. Bogotá, Conservation International, 548p.: 528, pl. 104c, color photograph of live individual (Colombia, Amazonas, listing of Brachyhypopomus).

Brachyhypopomus sp. "roy". -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).-Tagliacollo et al., 2016Tagliacollo, V. A., M. J. Bernt, J. M. Craig, C. Oliveira & J. S. Albert. 2016. Model-based total evidence phylogeny of Neotropical electric knifefishes (Teleostei, Gymnotiformes). Molecular Phylogenetics and Evolution, 95: 20-33.: 28, fig. 5 (phylogeny of Gymnotiformes).

Brachyhypopomus sp. 2. -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 240, color photograph (Brazil, rio Madeira, listing of hypopomids).

Brachyhypopomus sp. "sullivani". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 14-15, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MUSM 39624, 108 mm TL, 91 mm LEA, Peru, Loreto. mun. Requena, stream nr. Jenaro Herrera, affl. río Ucayali, Amazonas dr., 04°54'39"S, 073°39'29"W, 21 Jul 2009, W. Crampton, E Correa Roldán, M. Aldea Guevara & J. Waddell.

Paratypes. 59 specimens. Peru. Loreto (localities are from Amazonas dr.; localities listed from nr. Jenaro Herrera are from the río Ucayali dr., mun. Requena; collected by W. Crampton, E. Correa Roldán, M. Aldea Guevara & J. Waddell unless stated otherwise). MUSM 44682, 9 (6 immature, 72-94 mm, 2, female, 96-113 mm, 1 male, 107 mm), stream nr. Jenaro Herrera, 04°53'35"S, 073°39'01"W, 11-20 Jul 2009. MUSM 44731, 1, immature, 110 mm, stream nr. Jenaro Herrera, 04°54'49"S, 073°39'43"W, 4 Aug 2009. MZUSP 91427, 2, 45-87 mm, affl. quebrada Chica, nr. Jenaro Herrera, 04º55'S, 073º40'W, Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148513, 1, female, 112 mm, quebrada Chupiai nr. Jenaro Herrera, ca. 04°53'S, 073°39'W, 9 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148515, 2 (1 immature, 87 mm, 1 male, 94 mm), quebrada Salomé nr. Jenaro Herrera, 04º54'32"S, 073º35'37"W, 13 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148516, 9, 98-120 mm, affl. quebrada Chica, nr. Jenaro Herrera, ca. 04º55'S, 073º40'W, 15 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148517, 5 (1 immature, 46 mm, 3 female, 88-105 mm, 1 male, 108 mm), affl. quebrada Chica, nr. Jenaro Herrera, 04º55'22"S, 073º39'45"W, 15 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148518, 5, 95-104 mm, quebrada Chica, nr. Jenaro Herrera, ca. 04º55'S, 073º40'W, 15 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega & B. Crampton. UF 148519, 3 (1 immature, 103 mm, 1 female, 101 mm, 1 male, 125 mm), quebrada Fierro caño, affl. quebrada Sapuenillo, nr. Jenaro Herrera, 04º51'39"S, 073º38'59"W, 16 Jan 2004, W. Crampton, R. Reis, F. Lima, H. Ortega, B. Crampton. UF 184008, 6 (5 immature, 52-118 mm, 1 female, 103 mm), stream near Jenaro Herrera, 04°52'42"S, 073°38'51"W, 12-16 Jul 2009. USNM 405575, 5, immature, 58-70 mm, stream nr. Jenaro Herrera, 04°52'24"S, 073°38'49"W, 14 Jul 2009. USNM 405576, 3 (2 immature, 89-108 mm, 1 male, 101 mm), stream nr. Jenaro Herrera, 04°54'40"S, 073°39'29"W, 21 Jul 2009. USNM 405577, 8 (4 immature, 74-94 mm, 2 female, 101-104 mm, 2 male, 114-123 mm), stream nr. Jenaro Herrera, 04°56'16"S, 073°39'20"W, 27 Jul 2009.

Non-types. 326 specimens. Bolivia. Beni (localities from rio Madeira dr., Amazonas dr.). AMNH 39824, 4, 60-71 mm LEA, 10 km SE Costa Marques (Brazil), río Iténez floodplain (río Guaporé), affl. rio Mamoré, 12°30'37"S, 064°12'59"W. CBF 10253, 1, immature, 90 mm, mun. Riberalta, stream nr. lago San José, affl. río Beni, 10°54'47"S, 065°59'49"W. CBF 10254, 1, female, 127 mm, CBF 102455, 1, female, 122 mm, UMSS 7018, 1, immature, 66 mm, mun. Riberalta, stream nr. San José, nr. Riberalta, affl. río Beni, 10°55'32"S, 066°00'36"W. UF 177341, 1, female, 105 mm, UMSS 7019, 1, female, 136 mm, mun. Riberalta, Riberalta-Guayaramerín rd., nr. km 43, affl. río Beni, 11°01'58"S, 065°44'53"W. Brazil (localities from Amazonas dr.). Acre. MCP 35527, 1, 85 mm, mun. rio Branco, igarapé Quinoa, affl. rio Acre, affl. rio Purus, ca. 10°03'S, 067°37'W. Amazonas. INPA 6611, 1, Santa Isabel do rio Negro, igarapé de Santo Antônio, nr. Nova Esperança, ca. 00°24'S, 065°01'W [coordinates for Santa Isabel do rio Negro]. BMNH 1998.3.12.193, 1, female, 84 mm, BMNH 1998.3.12.210, 1, immature, 46 mm, INPA 9954, 2 (1 immature, 78 mm, 1 female, 94 mm), MCP 45288, 1, female, 92 mm, mun. Tefé, igarapé Curupira, at bridge of Estrada Agrovila rd., affl. lago Tefé (rio Tefé), 03º25'48"S, 064º44'15"W. BMNH 1998.3.12.208-209, 1, female, 91 mm, 1 male, 97 mm, MCP 45287, 3 (2 immature, 60-84 mm, 1 female, 100 mm), MCP 45336, 16 (10 female, 81-100 mm, 6 male, 98-113 mm), MCP 45464, 1, immature, 79 mm, MCP 45486, 10 (2 immature, 84-85 mm, 3 female [1CS], 83-91 mm, 5 male [2CS], 91-101 mm), MCP 45492, 2 (1 female, 85 mm, 1 male, 99 mm), UF 177357, 2, 86-88 mm, mun. Tefé, igarapé Repartimento, 1.5 km downstream from Estrada Agrovila rd., affl. lago Tefé (rio Tefé), 03º24'25"S, 064º44'08"W. INPA 8886, 1, rio Preto da Eva, downstream rio Preta da Eva, ca. 02°40'S, 059°40'W. MCP 41032 (part), 1, mun. Humaitá, stream on BR-319, ca. 96 km S Humaitá, affl. rio Pixuna [Ipixuna], affl. rio Purus, 08°05'31"S, 063°35'47"W. MCP 41033 (part), 1, 56 mm, MCP 41036 (part), 6, 43-85 mm, mun. Canutama, igarapé São João on hwy. BR-319, ca. 60 km S Humaitá, affl. rio Ipixuna, affl. rio Purus, 07°56'07"S, 063°20'03"W. MCP 41040, 1, 59 mm, mun. Humaitá, stream ca. 43 km E rio Madeira on Transamazon hwy., affl. rio Madeira, 07°38'49"S, 062°40'57"W. MCP 41042 (part), 2, 59-69 mm, mun. Humaitá, stream ca. 68 km E rio Madeira on Transamazon hwy., affl. rio Madeira, 07°44'02"S, 062°29'40"W. MCP 41045 (part), 1, 68 mm, mun. Humaitá, rio Maicimirim, ca. 45 km rio Madeira on Transamazon hwy., affl. rio Madeira, 07°38'04"S, 062°39'44"W. MCP 45310, 5 (1 immature, 61 mm, 2 female, 65-67 mm, 2 male, 76-97 mm), mun. Maraã, lago Amanã, rio Baré, igarapé São Sebastião, rio Japurá, 02°17'05"S, 064°41'25"W. MCP 45325, 1, immature, 88 mm, mun. Alvarães, igarapé Jarauá, Nogueira-Alvarães rd., affl. Lago Tefé (rio Tefé), 03º15'06"S, 064º48'55"W. MCP 45434, 1, female, 76 mm, mun. Tefé, igarapé Xidarinini, affl. lago Tefé (rio Tefé), 03°22'46"S, 064°41'17"W. MCP 45449, 1, male, 109 mm, mun. Tefé, swamp, margin of igarapé Repartimento, at Estrada Agrovila rd., affl. lago Tefé (rio Tefé), 03º24'25"S, 064º44'08"W. MPEG 12450, 3, 79-85 mm, mun. Coari, stream in Urucu oil field, affl. rio Urucu, affl. lago de Coarí, Amazonas dr., 04°52'19"S, 065°15'02'W. MPEG 12458, 2, 73-82 mm, mun. Coari, igarapé Tartaruga, affl. rio Urucu, affl. lago de Coarí, affl. Amazonas dr., 04°53'55"S, 065°19'18'W. MPEG 12459, 2, 74-85 mm, MPEG 13110, 1, 62 mm, mun. Coari, igarapé Tamanduá, affl. rio Urucu, affl. lago de Coarí, 04°51'43"S, 065°15'54'W. MPEG 12504, 1, 74 mm, MPEG 12523, 4, 76-122 mm, mun. Coari, igarapé Lontra, affl. rio Urucu, affl. lago de Coarí, 04°52'47"S, 065°08'58'W. MCP 13670, 1, 96 mm, mun. Juriti, nr. Juriti, igarapé da Ponte, 02°10'47"S, 056°04'38"W. MZUSP 59227, 1, 41 mm, pools in beach, Tapera, rio Negro, ca. 00°12'S, 064°04'W. Mato Grosso. INPA 11585, 2, 103-119, INPA 11593, 2, 113-141 mm, INPA 11595, 5 (3CS), 85-121 mm, INPA 11606, 2, 100-104 mm, INPA 11607, 1, 98 mm, INPA 11692, 3, 88-149 mm, INPA 11693, 1, 88 mm, INPA 11722, 2, 130-130 mm, Igarapé do Aeroporto, Humboldt [Aripuanã], rio Aripuanã, affl. rio Madeira, 10°11'18"S, 059°27'47"W. MPEG 1313, 1, 74 mm, mun. Juína, Reserva Ecológica Iquê, affl. rio Iquê, on AR 1, Vilhena-Juína hwy., affl. rio Juruena, affl. rio Tapajós, 11°25'S, 058°45'W [coordinates for Juína]. Pará. FMNH 70075, 13 (2 CS), 60-112 mm, Missão do Cururu, rio Cururu, affl. rio Tapajós, 07°36'50"S, 057°38'58"W. MPEG 3039, 1, 87 mm, mun. igarapé-Açu, bridge over rio Cajueiro, affl. rio Marapanim, ca. 01°07'S, 047°36'W. MPEG 7177, 2, 68-77 mm, mun. Barcarena, igarapé Tauá, nr. hwy. PA 483, affl. Furo do Arrozal, affl. Baía de Marajó, ca. 01°34'S, 048°42'W. MPEG 7468, 1, 71 mm, MPEG 7471, 1, 73 mm, mun. Paragominas, igarapé Cachoeirinha, Fazenda Potiritá, affl. rio Potiritá, affl. rio Capim, affl. rio Guamá, affl. Baía de Marajó, 03°12'13"S, 047°39'52'W. MPEG 15623, 1, 103 mm, mun. Almeirim, rio Ipitinga, affl. rio Jari, 00°49'02"S, 053°56'27"W. UF 36599, 1, 109 mm, igarapé Pirelli, affl. rio Maguari, affl. Baía de Marajó, 01°21'24"S, 048°19'36"W. Rondônia (localities from rio Madeira dr.). FMNH 54544, 1, 59 mm LEA, Maciel, rio Guaporé, affl. rio Mamoré, ca. 12°30'S, 062°20'W. MCP 41041, 1, 77 mm, mun. rio Crespo, stream ca. 20 km E hwy. BR-364 in direction of rio Crespo, affl. rio Preto do Crespo, affl. rio Jamari, 09°42'21"S, 062°55'38"W. UFRO-I 6494, 2, 72-93 mm, stream, Estação Ecológica do Cuniã (ESEC), 08°04'30"S, 063°28'34"W. UFRO-I 6495, 1, 73 mm, stream, ESEC, 08°04'07"S, 063°28'34"W. UFRO-I 6506, 4, 62-75 mm, UFRO-I 6508, 1, 67 mm, stream, ESEC, 08°05'30"S, 063°28'35"W. UFRO-I 6509, 1, 73 mm, stream, ESEC 08°04'09"S, 063°28'34"W. Roraima. INPA 7362, 1, INPA 7363, 1, INPA 7367, 1, igarapé do Cajú, 21 km Bonfim on old rd. to Normândia, rio Tacatú, affl. rio Branco, affl. rio Negro, ca. 03°32'N, 059°53'W. Colombia. Meta (localities from Orinoco dr.). MPEG 1105, 9, 90-122 mm, 7 km SE Puerto Lopez, affl. río Meta, ca. 04°03'N, 072°54'W. SU 50348, 1, 77 mm, nr. Los Micos, N end Cordillera Macarena, río Guaviare, río Meta, ca. 03°19'N, 073°54'W. SU 53762, 1, 67 mm LEA, stream affl. río Guayabero, ca. 5 mi. below El Refugio, affl. río Guayabero, affl. río Guaviare, ca. 02°17'N, 073°44'W. UF 19472, 1, 68 mm, UF 26012, 3, 66-67 mm, UF 33466 (part), 2, 83-89 mm, UF 33467, 1, 66 mm, 4.7 km W Puerto Gaitán, affl. río Yucao, affl. río Manacacias, affl. río Meta, ca. 04°18'N, 072°07'W. UF 33373, 1, 102 mm, 47 km ENE Villavicencio, affl. río Humea, ca. 04°18'N, 073°11'W. UF 36603, 2, 93-98 mm, río Guatiguia nr. Villavicencio, affl. río Meta, ca. 04°09'N, 073°38'W. UF 80991, 1, 99 mm, small creek ca. 70 km E Villavicencio on rd. to Puerto López, ca. 04°03'N, 073°04'W. Ecuador. Sucumbios (localities from Río Napo dr.). FMNH 102278, 1, 121 mm, ca. 10 km N Marian and 1 km S río Cuyabeno below rd., affl. to río Cuyabeno, affl. río Aguarico, ca. 00°07'N, 076°17'W. FMNH 102283, 1, 103 mm, headwater río Aguas Negras, 1-2 km N Marian, affl. río Cuyabeno, affl. río Aguarico, ca. 00°46'S, 076°20'W. Guyana. Potaro-Siparuni (localities from Essequibo River dr.). ANSP 175954, 4, 57-70 mm, small creek crossing Kurupukari-Surama River rd. ca. 2.0 mi. from Kurupukari [Iwokroma] field station, 04°30'12"N, 058°42'32"W. FMNH 53323, 1, 99 mm, Chipoo Creek, affl. Ireng River, ca. 04°42'N, 059°06'W. ROM 62556, 1, 83 mm, stream affl. Siparuni River, affl. Siparuni River, 04°49'11"N, 058°51'01"W. Peru. Loreto. ANSP 178620, 4, 50-123 mm, caño Sabolito, terra firme stream, ca. 25 mi. S Iquitos, affl. río Amazonas, 04°14'45"S, 073°24'57"W. INHS 43903, 3, 64-79 mm, quebrada Shushuna, on rd. to Corrientillos, affl. rio Nanay, 03°49'48"S, 073°20'14"W. MUSM 5402, 2, 113-126 mm, stream nr. Jenaro Herrera, affl. río Ucayali, ca. 04°54'S, 073°37'W. MUSM 14494 (part), 1, 131 mm, Lagartococha, Aguas Negras, río Aguarico, affl. río Napo, 00°31'22"S, 075°15'25"W. MUSM 44695, 40 (25 immature, 62-113 mm, 13 female, 76-112 mm, 2 male, 84-112 mm), stream nr. Jenaro Herrera, 04°51'51"S, 073°38'45"W. MUSM 44752, 4 (3 immature, 17-85 mm, 1 female, 104 mm), stream nr. Jenaro Herrera, affl. río Ucayali, 04°54'54"S, 073°39'25"W. MUSM 44763, 1, immature, 55 mm, stream nr. Jenaro Herrera, affl. río Ucayali, 04°54'36"S, 073°39'58"W. UF 148514, 7 (1 immature, 92 mm, 3 female, 98-107 mm, 3 male, 103-125 mm), Quebreda Sapuena, nr. Jenaro Herrera, 04°54'49"S, 073°34'59"W. UF 183772, 4, 29-79 mm, río Nanay, 03°53'50"S, 073°40'01"W. UF 184012, 10 (8 immature, 66-118 mm, 1 female, 98 mm, 1 male, 104 mm), stream nr. Jenaro Herrera, 04°53'59"S, 073°38'51"W. UF 184019, 11 (8 immature, 62-89 mm, 2 female, 108-110 mm, 1 male, 102 mm), stream nr. Jenaro Herrera, 04°55'19"S, 073°38'57"W. UF 184024, 21 (11 immature, 56-114 mm, 6 female, 90-109 mm, 3 male, 113-116 mm), stream nr. Jenaro Herrera, 04°54'15"S, 073°36'53"W. Venezuela. Amazonas. AMNH 230873, 1, 85 mm, MBUCV-V 29177, 1, 86 mm, 1 hr. downstream Campamento Yutaje, río Coracora, affl. río Manapiari, affl. río Ventuari, Orinoco dr., 05°36'25"N, 066°07'03"W. MBUCV-V 228 (part), 2, 84-106 mm, Caños Parú and Canna, upper río Ventuari, Orinoco dr., no coordinates. MBUCV-V 3460, 3, 78-83 mm, caño Iguapo, E La Esmeralda, ca. 03°10'N, 065°33'W. MBUCV-V 12986, 1, 143 mm, Tobogan de la Selva, ca. 36 km de Puerto Ayacucho, affl. río Orinoco, Orinoco dr., 05°23'13"N, 067°37'02"W. MBUCV-V 14330, 1, 131 mm, small stream nr. Sarama Sota, upper río Cataniapo, Orinoco dr., 05°38'00"N, 067°07'40"W. MBUCV-V 14678, 1, 132 mm, 0.5-1 km upstream La Neblina basecamp, río Baria, affl. río Casiquiare, affl. rio Negro, Amazonas dr., ca. 00°50'N, 066°05'W. MBUCV-V 14713, 5 (2 measured, 120-122 mm), stream nr. La Neblina basecamp, río Baria, affl. río Casiquiare, affl. rio Negro, Amazonas dr., ca. 00°50'N, 066°05'W. MBUCV-V 14720, 1, male, 152 mm, La Neblina basecamp, río Baria, aff río Casiquiare, affl. rio Negro, Amazonas dr., ca. 00°50'N, 066°05'W. MBUCV-V 14760, 1, 82 mm, stream, 100 m before intersection of Gavilán and Las Palmas, affl. río Cataniapo, Orinoco dr., 05°32'45"N, 67°23'36"W. MBUCV-V 14768, 1, 78 mm, Raudal Yahui, 5 km upstream La Reforma, río Cataniapo, affl. río Orinoco, Orinoco dr., ca. 05°33'N, 067°31'W. UF 177354, 11 (8 immature, 73-104 mm, 4 female, 73-127 mm, 2 male, 89-117 mm, on rd. from Puerto Ayacucho to Gavilan, caño Culebra, affl. río Cataniapo, Orinoco dr., 05°32'48"N, 067°26'55"W. UF 177355, 6, 60-117 mm (3 CS), on rd. from Puerto Ayacucho to Gavilan, caño Moia, affl. río Cataniapo, Orinoco dr., 05°32'26"N, 067°23'02"W. UF 177356, 8, 61-83 mm, rd. from Puerto Ayacucho to Gavilan, caño Samaria, affl. rio Cataniapo, Orinoco dr., 05°33'52"N, 067°28'15"W. USNM 266718, 3, 80-119 mm, "Cãno Igapo" [probably río Iguapo], E La Esmeraldas [La Esmeralda], affl. upper río Orinoco, Orinoco dr., ca. 03°07'N, 065°28'W. Apure. MCNG 26553, 2, 62-63 mm LEA, stream W Parque Nacional Galeras del Cinaruco, affl. río Cinaruco, Orinoco dr., ca. 06°34'N, 067°17'W. Bolívar. SU 54492, 1, 73 mm LEA, SU 54612, 1, 65 mm LEA, mun. Caicara del Orinoco, caño de Quiribana, Orinoco dr., ca. 07°32'N, 066°08'W.

Diagnosis. Brachyhypopomus sullivani is diagnosed from congeners by the following combination of characters: precaudal vertebrae 15-18, vs. 19-26 in B. alberti, B. arrayae, B. beebei, B. belindae, B. draco, B. hamiltoni, B. janeiroensis, B. jureiae, B. palenque, and B. verdii; anal-fin rays 143-185, vs. 190-293 in B. bennetti, B. brevirostris, B. bullocki, B. diazi, B. hendersoni, B. occidentalis, and B. walteri; scales present in middorsal region, vs. absent in B. benjamini and B. provenzanoi; accessory electric organ over the opercular region absent, vs. present in B. bombilla, B. menezesi, and B. regani; head depth at eye 38.5-47.6% HL, vs. 47.8-59.9% in B. cunia, B. gauderio, and B. pinnicaudatus; presence of scattered conspicuous black or charcoal flecks on flank, vs. absence in B. batesi and B. flavipomus.

Description. Head and body shape, and pigmentation illustrated in Figs. 1k and 43. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 19. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head approximately straight between operculum and snout, snout rounded. Eye small to moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum absent. Gill filaments on first gill arch 29-33 (median 31, n = 6). Pectoral fin of moderate width, pectoral-fin rays 11-16 (median of 11 in populations from the upper Amazon of Peru; mode of 14 in populations from upper rio Madeira, and from río Orinoco). Precaudal vertebrae 15-17 (mode of 16 in all populations), including 1-2 transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) posterior to, or near, tip of pectoral fin. Anal-fin rays 143-184 (median of 171 in populations from the upper Amazon of Peru; 159 from the upper rio Madeira; and 171 from the río Orinoco). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 6). Lateral line continuous. Extensive network of epidermal canals dorsal to lateral line in posterior half of body, extending to about midway from lateral line to dorsal midline and forming a crisscrossing pattern of posteriorly converging chevrons. Groove-like canals are depigmented or almost depigmented, sometimes with chromatophores along margins, and are filled with a translucent material covered with skin (overlain by scales). Groove-like canals with apparent partitioning into rectangular segments and with pores to exterior located at posterior ends in many cases (possibly tuberous electroreceptors). Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Table 19
Morphometrics for Brachyhypopomus sullivani. HT, holotype; SD, standard deviation; dr., drainage. Ranges for the type region refer to the holotype and to paratype specimens (and also non-types for caudal filament length as % of TL). Ranges for the other populations refer to non-type specimens from the lower río Beni of Bolivia, and the upper río Orinoco of Venezuela, respectively.

Coloration. (Figs. 1k, 43). Background pale tan to dark brown. Dorsal region without prominent depigmented pale stripe extending along midline from occipital region to base of caudal filament, although in some individuals there is an indistinct lighter middorsal stripe in posterior third to half of body. Dorsal region variably pigmented, often with irregular dark blotches against a homogenous lighter background, sometimes with dark blotches forming a single intermittent series along dorsal midline. Dark blotches restricted to dorsal region, never extending far ventrally and only just visible in lateral view. No vertical stripes or lines on flank; flank with evenly scattered chromatophores, darker dorsally and lighter ventrally, especially over pterygiophores. Characteristic prominent dark brown or black flecks scattered irregularly over flank. Caudal filament darker than body, with some irregular dark markings. Head with evenly scattered dark chromatophores, darker dorsally. Eye with indistinct to very distinct suborbital patch or stripe of chromatophores and subcutaneous pigmentation. Pectoral and anal-fin membranes and rays hyaline. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 43
Brachyhypopomus sullivani. MUSM 39624 (WC48.210709), holotype, female, 108 mm TL (head in lateral view, and body in lateral and dorsal view, specimen fixed in formalin and preserved in EtOH); Peru, río Ucayali, Amazonas dr. Scale bars = 5 mm.

Size. A Brachyhypopomus of small adult size, largest specimen examined 152 mm TL, 123 mm LEA (n = 390). Largest male specimen examined 152 mm TL, 123 mm LEA (n = 36). Largest female specimen examined 127 mm TL, 100 mm LEA (n = 67).

Sexual dimorphism. No known secondary sexual dimorphism.

Geographic distribution. Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela (Fig. 44). Widely distributed through the Amazon basin including multiple sites in the upper, central, and lower Amazon, the Negro, Purus, lower and upper Madeira, and Tapajós drainages. Known from some coastal drainages in Pará state, near the mouth of the rio Tocantins. Known also from parts of the Orinoco basin, and from the Essequibo River.

Fig. 44
Collection records for Brachyhypopomus sullivani (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found overlap in the range of meristic counts (Tables 2-5) and morphometric measurements (Table 19), and observed similar pigmentation among populations of B. sullivani across its entire distribution. One meristic character, the number of pectoral-fin rays, is somewhat divergent between populations in the upper Amazon (11-13, mode 11) vs. the upper Madeira (13-14, mode 14) and Orinoco (13-15, mode 14). These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. sullivani are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners.

Ecological notes. Brachyhypopomus sullivani is restricted to gently flowing, normoxic, low-conductivity streams and small rivers in closed canopy rainforest and savanna, where it is typically encountered in or near aquatic vegetation, root mass, or leaf litter. See description of B. benjamini for water quality parameters of the area of the type locality. Crampton et al. (2008Crampton, W. G. R., L. J. Chapman & J. Bell. 2008. Interspecific variation in gill size is correlated to ambient dissolved oxygen in the Amazonian electric fish Brachyhypopomus (Gymnotiformes: Hypopomidae). Environmental Biology of Fishes, 83: 223-235.) documented the relatively small gill sizes of B. sullivani relative to congeners that occur in seasonally hypoxic whitewater floodplain systems. Breeding occurs during the rainy season; both in the type locality, and in the vicinity of Tefé, Brazil (approximately December to April in both regions) (JCW, WGRC unpublished data). Stomach contents of specimens from the type locality comprise aquatic insect larvae (primarily Chironomidae), and other small aquatic invertebrates (JCW, WGRC unpublished data).

Co-occurring congeners: In the upper, central, and lower Amazon (including lower Madeira, but excluding upper Madeira), B. sullivani occurs in sympatry and ecological syntopy with B. batesi, B. beebei, B. benjamini, B. brevirostris, B. verdii, and B. walteri, and exhibits an allotopic distribution to B. belindae, B. bennetti, B. cunia, B. flavipomus, B. hamiltoni, B. hendersoni, B. pinnicaudatus, and B. regani (note: in the lower Amazon populations of B. regani occur in low-conductivity systems in syntopy with B. sullivani). In the upper Madeira, B. sullivani is known to occur in sympatry with B. alberti, B. brevirostris, and B. walteri, and in allotopy with B. arrayae, B. bombilla, and B. cunia. In the rio Negro B. sullivani occurs in sympatry with B. batesi, B. beebei, B. brevirostris, B. bullocki, B. hendersoni, B. regani, and B. walteri (likely in syntopy with all these species except B. hendersoni, which is a floodplain species). In the río Orinoco B. sullivani occurs in sympatry and syntopy with B. beebei, B. brevirostris, B. bullocki, B. diazi, B. provenzanoi, and B. regani (likely in syntopy with all these species except B. diazi which is restricted to high-conductivity systems). In the Essequibo River, B. sullivani occurs in sympatry with B. beebei, B. brevirostris, B. bullocki, B. hendersoni, B. regani, and B. walteri (likely in syntopy with all these species except B. hendersoni, which is a floodplain endemic).

Etymology. The specific name is a patronym (noun in the genitive case) in honor of John P. Sullivan, American (USA) ichthyologist, for his contributions to gymnotiform biology.

Local names. Bolivia: cuchillo; Brazil: sarapó; Colombia: cuchillo; Ecuador: cuchillo, yayo; Guyana: knife fish; Peru: macana; Venezuela: cuchillo.

Brachyhypopomus verdii, new species

urn:lsid:zoobank.org:act:3FC61943-7A01-40A4-A5D6-C7E296167CE0

(Fig. 45; Tables 2-5, 20)

Brachyhypopomus pinnicaudatus. -Chang & Ortega, 1995Chang, F. & H. Ortega. 1995. Additions and corrections to the list of freshwater fishes of Peru. Publicaciones del Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Serie A - Zoology, 5: 1-11.: 3, (Peru, catalog of fishes).

Brachyhypopomus sp. 'ver'. -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus n. sp. VERD. -Elbassiouny et al., 2016Elbassiouny, A. A., R. K. Schottt, J. C. Waddell, M. A. Kolmann, E. S. Lehmberg, A. Van Nyatten, W. G. R. Crampton, B. S. W. Chang & N. R. Lovejoy. 2016. Mitochondrial genomes of the South American electric knifefishes (Order Gymnotiformes). Mitochondrial DNA. Part B: Resources, 1: 401-403.: 401-403, fig. 1 (description of mitogenome, position in phylogeny of Ostariophysi based on mitochondrial genomes).

Brachyhypopomus sp. "verdii". -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus).

Holotype. MUSM 35307, female, 79 mm TL, 67 mm LEA, Peru, Loreto, mun. Maynas, Jenaro Herrera, stream, nr. Jenaro Herrera-Colonia Angamos rd., affl. río Ucayali, Amazonas dr., 04º53'54"S,073º38'22"W, 16 Jan 2004, W. Crampton, H. Ortega, R. Reis, F. Lima & J. Oliveira.

Paratypes. 41 specimens, localities from Amazonas dr. Peru. Loreto (localities listed from nr. Jenaro Herrera, are from the río Ucayali dr., mun. Requena). MUSM 44683, 4 (2 immature, 89-103 mm, 1 female, 79 mm, 1 male, 107 mm), stream nr. Jenaro Herrera, 04°53'35"S, 073°39'01"W, 11-30 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. MUSM 44726, 1, female, 76 mm, forest stream 1.65 km Jenaro Herrera, affl. río Ucayali, Amazonas dr., 04°54'33"S, 073°39'26"W, 30 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. UF 148522, 2, immature, 82-106 mm, nr. Jenaro Herrera, stream in agricultural field, affl. quebrada Parnayari, ca. 04º54'S, 073º37'W, 14 Jan 2004, W. Crampton, H. Ortega, R. Reis, F. Lima & J. Oliveira. UF 148523, 7, immature, 84-109 mm, stream nr. Jenaro Herrera, 04°53'54"S, 073°38'21"W, 16 Jan 2004, W. Crampton, H. Ortega, R. Reis, F. Lima & J. Oliveira. UF 184011, 1, female, 107 mm, stream nr. Jenaro Herrera, 04°52'42"S, 073°38'51"W, 20 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. UF 184021, 1, immature, 66 mm, stream nr. Jenaro Herrera, 04°54'40"S, 073°39'29"W, 21 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. UF 184026, 19 (4 immature, 67-87 mm, 6 female, 67-100 mm, 9 male, 79-120 mm), stream nr. Jenaro Herrera, 04°54'36"S, 073°39'44"W, 31 Jul 2009. W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. USNM 405580, 3, immature, 74-78 mm, stream nr. Jenaro Herrera, 04°54'15"S, 073°36'53"W, 25 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell. USNM 405582, 3 (2 immature, 83-104 mm, 1 female, 91 mm), stream nr. Jenaro Herrera, 04°54'49"S, 073°39'43"W, 31 Jul 2009, W. Crampton, E. Correa Roldán, M. Guevara & J. Waddell.

Non-types. 185 specimens, localities from Amazonas dr. Peru. Amazonas. FMNH 96997, 1, 125 mm, Caterpiza, affl. río Santiago, affl. río Marañón, ca. 03°54'S, 077°42'W. Loreto (localities listed from nr. Jenaro Herrera, are from the río Ucayali dr., mun. Requena). ANSP 167724, 4, 65-109 mm, swamp on path from Mishana village to Nauta rd., affl. río Nanay, 03°53'12"S, 073°28'57"W. MUSM 3229, 3, stream nr. Jenaro Herrera, ca. 04°53'S, 073°39'W. MUSM 4449, 2, mun. Yurimaguas, San Ramón, río Marañón, ca. 04°54'S, 076°26'W. MUSM 44677, 30 (14 immature, 33-110 mm, 10 female, 77-104 mm, 6 male, 88-111 mm), stream nr. Jenaro Herrera, 04°53'59"S, 073°38'51"W. MUSM 44764, 27 (18 immature, 26-107 mm, 9 female, 61-109 mm), stream nr. Jenaro Herrera, 04°54'36"S, 073°39'58"W. UF 148520, 19 (16 immature [3 CS], 38-105 mm, 2 female, 83-96 mm, 1 male, 106 mm), stream nr. Jenaro Herrera, ca. 04º53'S, 073º39'W. UF 148521, 32 (28 immature, 45-109 mm, 3 female, 80-97 mm, 1 male, 109 mm), stream nr. Jenaro Herrera, 04°55'38"S, 073°39'10"W. USNM 405578, 17 (9 immature, 49-114 mm, 6 female, 82-101 mm, 2 male, 98-114 mm), stream nr. Jenaro Herrera, 04°53'54"S, 073°38'23"W. USNM 405579, 24 (14 immature, 44-100 mm, 4 female, 92-112 mm, 6 male, 92-115 mm), stream nr. Jenaro Herrera, 04°55'38"S, 073°39'14"W. USNM 405581, 25 (15 immature, 55-95 mm, 4 female, 69-95 mm, 6 male, 93-110 mm), stream nr. Jenaro Herrera, 04°55'41"S, 073°38'46"W.

Table 20
Morphometrics for Brachyhypopomus verdii. HT, holotype; SD, standard deviation. Ranges refer to the holotype and to paratype specimens from the type region.

Diagnosis. Brachyhypopomus verdii is diagnosed from congeners by the following combination of characters: precaudal vertebrae 24-26, vs. 15-23 in all congeners except B. belindae and B. draco; bilateral columns of electrocytes at the anal-fin terminus 3, vs. 4-5 in B. belindae; continuous or discontinuous dark vertical or diagonally oriented bands or saddles present on body surface dorsal to lateral line, vs. absence of oblique bands or saddles on body surface dorsal to lateral line in B. draco.

Description. Head and body shape, and pigmentation illustrated in Fig. 45. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 20. Body shallow in depth. Head short and shallow to moderate in depth. Dorsal profile of head convex from occiput to snout, ventral profile of head convex between operculum and snout, snout rounded. Eye small to moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. Accessory electric organ (AEO) over operculum absent. Gill filaments on first gill arch 35-40 (median 37, n = 6). Pectoral fin narrow to moderate, pectoral-fin rays 13-17 (mode 15). Precaudal vertebrae 24-26 (mode 25), with 1-2 (mode 2) transitional vertebrae. Anal-fin origin slightly (< 0.25 HL distance) posterior to tip of pectoral fin. Anal-fin rays 194-225 (median 208). Dorsal rami of recurrent branch of anterior lateral line nerve not visible. Middorsal region of body scaled. Rows of scales above lateral line 5-6 (mode 5). Lateral line continuous. Sparse groove-like depigmented epidermal canals - as parallel crisscrossing lines either side of lateral line (mainly in posterior third of body), or branching ventrally from lateral line (mainly in mid-third of body); and as a pair of long irregular lines either side of dorsal surface in dorsal portion of flank, along posterior two thirds of body. Three bilateral horizontal columns of electrocytes at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Caudal filament short to moderate in length.

Size. Small adult size, largest specimen examined 125 mm TL, 107 mm LEA (n = 222). Largest male specimen examined 120 mm TL, 102 mm LEA (n = 32). Largest female specimen examined 112 mm TL, 95 mm LEA (n = 52).

Coloration. (Fig. 45). Background light tan to brown. Dorsal region with prominent depigmented or lightly pigmented stripe extending along midline from occipital region to base of caudal filament, or deep into caudal filament, bordered by prominent dark horizontal wavy reticulated lines from which short irregular patches extend ventrally - reaching or traversing lateral line in anterior third of body but reaching less than half distance from dorsal midline to lateral line posteriorly. Dorsal pigmentation pattern resembles that of B. gauderio and B. pinnicaudatus, but reticulated lines extending ventrally from either side of depigmented dorsal stripe are shorter and often only faintly visible in lateral view in posterior two thirds of body. Ventral flank otherwise marked only with small irregular dark spots. Very faint short vertical dark markings sometimes present over anal-fin pterygiophores in posterior half of body. Caudal filament darker than body, with irregular dark markings or bands along entire length. Head with evenly scattered dark chromatophores, darker dorsally. Eye without prominent suborbital patch or stripe of chromatophores/subcutaneous pigmentation. Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays with light scattering of brown chromatophores, accentuated in posterior portion of anal-fin. Color in live individuals similar to preserved specimens, with opercular region usually rosy due to underlying gills.

Fig. 45
Brachyhypopomus verdii. a. UF 148520 (WC24.090104), paratype, male, 106 mm TL (head in lateral view, and body in lateral and dorsal view); b. MUSM 35307 (WC06.160104), holotype, female, 79 mm TL (body in lateral view). Peru, río Ucayali, Amazonas dr. Note sexual dimorphism in caudal-filament length and height. Specimens fixed in formalin and preserved in EtOH. Scale bars = 5 mm.

Sexual dimorphism. Sexually mature males attain slightly larger sizes. Sexually mature males develop broader caudal filaments than immature individuals and breeding females (Figs. 45a-b) but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Breeding males with paddle-like lateral compression at caudal filament tip. No known sexual dimorphism in pigmentation.

Geographic distribution. Peru (Fig. 39). Known only from tributaries of the río Marañón and río Ucayali in the upper Amazon basin.

Ecological notes. Known only from low-conductivity blackwater terra firme rainforest streams and swamps, where it is found in association with submerged roots and leaf litter. See description of B. benjamini for water quality parameters of the area of the type locality. Breeding occurs during the rainy season in the area of the type locality (approximately December to April) (JCW unpublished data). Stomach contents of specimens from the type locality comprise small aquatic invertebrates (JCW unpublished data).

Co-occurring congeners: In the region of the type locality in the lower río Ucayali, B. verdii occurs in sympatry and syntopy with B. beebei, B. benjamini, B. brevirostris, B. sullivani, and B. walteri. It exhibits an allotopic distribution to B. bennetti, B. flavipomus, B. hamiltoni, and B. regani.

Etymology. The specific name is a patronym (noun in the genitive case) in honor of Lorgio Verdi Olivares, Peruvian conservation biologist, for his support to WGRC and NRL.

Local name. Peru: macana.

Brachyhypopomus walteri Sullivan, Zuanon & Cox Fernandes, 2013

(Figs. 1l, 46; Tables 2-5, 21)

Brachyhypopomus sp. 4. -Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 77, table 6.1.a, species list; 79, fig. 6.1 inset 22-24, color photographs; 85, fig. 6.2; 88, fig. 6.3; 92-94, figs. 6.4a, 6.5; 191, fig. 11.2; 193, fig. 11.3, EOD data; 110, table 7.5, 113, table 7.7, 115, fig. 7.1, habitats; 136, table 8.2a,b, diet; 151-160, figs. 9.2-9.3, table 9.1a,b, hypoxia tolerance; 165-169, table 10.1 reproductive biology (Brazil, central Amazon, ecology and signal diversity).

Brachyhypopomus walteri. -Sullivan, 1997Sullivan, J. P. 1997 A phylogenetic study of the neotropical hypopomid electric fishes (Gymnotiformes, Rhamphichthyoidea). Unpublished Ph.D Dissertation, Duke University, Durham, NC. 335p.: 105 (description in unpublished thesis with disclaimer stating that nomenclatural acts not available, a nomen nudum).

Brachyhypopomus sp. 3. -Crampton, 1998aCrampton, W. G. R. 1998a. Electric signal design and habitat preferences in a species rich assemblage of gymnotiform fishes from the upper Amazon basin. Anais da Academia Brasileira de Ciencias, 70: 805-847.: 821, table 4, 834, fig. 9, illustration of specimen, with EOD (Brazil, Amazonas, species and EOD diversity). -Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.: 314, table 2, list of Brachyhypopomus (Brazil, Amazonas, hypoxia tolerance).

Brachyhypopomus sp. C. -Crampton, 1999Crampton, W. G. R. 1999. Os peixes da Reserva Mamirauá: diversidade e história natural na planície alagável da Amazônia. Pp. 10-36. In: Queiroz H. L. & W. G. R. Crampton (Eds.). Estratégias para manejo de recursos pesqueiros em Mamirauá. Brasília, Sociedade Civil Mamirauá/CNPq.: 17 (Brazil, Amazonas, Mamirauá Reserve, listing of species). -Crampton & Albert, 2006Crampton, W. G. R. & J. S. Albert. 2006. Evolution of electric signal diversity in gymnotiform fishes. I. Phylogenetic systematics, ecology and biogeography. Pp. 647-696; 718-731. In: Ladich F., S. P. Collin, P. Moller & B. G. Kapoor (Eds.). Communication in fishes. Enfield, NH, Science Publishers.: 672, fig. 23.8 (inset 11), color photograph of head of live individual with EOD, position in phylogenetic tree; 681, notes on EODs (gymnotiform species and EOD diversity).

Brachyhypopomus sp. 2. -Stoddard, 1999Stoddard, P. K. 1999. Predation enhances complexity in the evolution of electric fish signals. Nature, 400: 254-256.: 255, fig. 4, color photograph of live mature female specimen, with EOD (EOD evolution).

Brachyhypopomus sp. "walteri". -Stoddard et al., 1999Stoddard, P. K., B. Rasnow & C. Assad. 1999. Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus. Journal of Comparative Physiology a-Sensory Neural and Behavioral Physiology, 184: 609-630.: 610, fig. 1, black and white photograph of female specimen, with EOD (EOD evolution).

Brachyhypopomus sp. 2. -Ferreira et al., 2007Ferreira, E. J. G., J. Zuanon, B. Forsberg, M. Goulding & Briglia-Ferreira, S. R.. 2007. Rio Branco: peixes, ecologia e conservação de Roraima. Manaus, Amazon Conservation Association, Instituto Nacional de Pesquisas da Amazônia, Sociedade Civil Mamirauá, 201pp.: 164, center right and bottom right photographs, live individuals, (Brazil, Roraima, rio Branco, photographic album of fishes).

Brachyhypopomus sp. 'wal'. -Crampton, 2011Crampton, W. G. R. 2011. An ecological perspective on diversity and distributions Pp. 165-189. In: Albert J. S. & R. E. Reis (Eds.). Historical biogeography of neotropical freshwater fishes. Berkeley, University of California Press.: 176, table 10.2, species list; 179, figs. 10.2-10.3, phylogeny, geographical and ecological distributions (gymnotiform biology).

Brachyhypopomus sp. 4. -de Queiroz et al., 2013de Queiroz, L. J.., G. Torrente-Vilara, F. G. Vieira, W. M. Ohara, J. Zuanon & C. R. C. Doria. 2013. Fishes of Cuniã Lake, Madeira River Basin, Brazil. Check List: Journal of Species Lists and Distribution, 9: 540-548.: 545, table 1, (Brazil, rio Madeira, lago Cuniã, listing of fish species]. -Crampton & Ribeiro, 2013Crampton, W. G. R. & A. C. Ribeiro. 2013. Hypopomidae. Pp. 232-249. In: Torrente-Vilara G., L. Queiroz & J. Zuanon (Eds.). Peixes do rio Madeira. Porto Velho, Universidade Federal de Rondônia.: 242, color photograph (Brazil, rio Madeira, listing of hypopomids).

Brachyhypopomus(Odontohypopomus)walteriSullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.: 8, figs. 3-4, 8, color photographs of holotype, paratypes, backlit electric organs (original description and assignment to subgenus Odontohypopomus, type locality - Brazil, Amazonas, nr. Manaus, Amazonas dr.). -Carvalho, 2013Carvalho, T. P. 2013 Systematics and evolution of the toothless knifefishes Rhamphichthyoidea Mago-Leccia (Actinopterygii: Gymnotiformes): Diversification in South American freshwaters. Unpublished Ph.D. Dissertation, University of Louisiana at Lafayette, Lafayette, 516 pp.: 181-185, figs. 41-43, position in phylogeny (phylogenetic systematics of Rhamphichthyoidea). -Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
: 1-66, table 1, 3-4, figs. 1-7, 12, 18-20 (phylogeny, biogeography and ecology of Brachyhypopomus; Odontohypopomus not recognized).

Table 21
Morphometrics for Brachyhypopomus walteri. HT, holotype; SD, standard deviation; dr., drainage. Data for holotype (nr. Manaus, Amazonas, Brazil) from Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). Range for type region (Central Amazonas drainage) refers to non-type specimens from the vicinity of Tefé, Amazonas, Brazil. Specimens from the Upper rio Paraguay drainage are from Mato Grosso and Mato Grosso do Sul, Brazil.

Diagnosis. Brachyhypopomus walteri is diagnosed from congeners by the following combination of characters: caudal filament length 27.8-56.4% LEA, vs. 7.4-26.8% in B. batesi, B. belindae, B. bennetti, B. palenque, B. provenzanoi, B. regani, and B. verdii; distinct dark sub-orbital stripe present, vs. absent in B. alberti, B. arrayae, B. beebei, B. benjamini, B. brevirostris, B. bullocki, B. diazi, B. draco, B. flavipomus, B. gauderio, B. janeiroensis, B. jureiae, B. menezesi, B. occidentalis, and B. pinnicaudatus; accessory electric organ over the opercular region absent, vs. present in B. bombilla; absence of scattered conspicuous black or charcoal flecks on flanks, vs. presence in B. cunia, B. hendersoni, and B. sullivani.

Description. Head and body shape, and pigmentation illustrated in Figs. 1l and 46. Meristic and morphometric data for examined specimens presented in Tables 2-5 and 21. Body shallow to moderate in depth. Head short to moderate in length and shallow to moderate in depth. Dorsal profile of head approximately straight from occiput to snout, ventral profile of head gently convex between operculum and snout, snout rounded. Eye moderate in size. Upper jaw with moderate sigmoidal angle between premaxillary and maxillary portions in lateral view. No accessory electric organ over operculum. Gill filaments on first gill arch 34-48 (median 39, n = 29). Pectoral fin moderate to broad in width, pectoral-fin rays 12-17 (mode of 15 in populations from the region of the type localities in the central Amazon basin; 14 in populations from the Paraguay basin). Precaudal vertebrae 16-20 (mode of 18 in populations from the region of the type localities in the central Amazon basin, and from the Paraguay basin), including 1-2 transitional vertebrae. Anal-fin origin substantially (0.25-0.33 HL distance) anterior to tip of pectoral fin, never posterior. Anal-fin rays 192-235 (median of 210 in populations from the region of the type localities in the central Amazon basin; 226 in populations from the Paraguay basin). Dorsal rami of recurrent branch of anterior lateral line nerve usually visible. Middorsal region of body scaled. Rows of scales above lateral line 5-7 (mode 7). Lateral line continuous. Depigmented epidermal canals very sparse, almost unnoticeable, found mainly in middle section of body - as curved short lines (usually no more than one) either side of lateral line. Epidermal canals absent from either side of mid-dorsal region, and absent on flank midway from lateral line to dorsal midline. 3-4 bilateral columns at anal-fin terminus and at mid-point between anal-fin terminus and tip of caudal filament in immature, mature female, and mature male specimens. Three or four electrocyte columns sometimes alternate in middle of caudal filament. Caudal filament moderate in length to long.

Coloration. (Figs. 1l, 46). Pigmentation strongly resembles that of B. bennetti. Background pale straw to tan. Dorsal region with irregular brown blotches which extend to irregular-edged and sometimes divided brown bands which extend towards lateral line. No pale mid-dorsal stripe extending from occiput to base of caudal filament. A series of brown blotches is usually present along lateral line. Flank ventral to lateral line and pterygiophore region with very sparse and indistinct disrupted vertical bands. Caudal filament darker than body, with indistinct dark blotches and disrupted vertical bands, often with darkened tip; darkened tip of caudal filament resembles root tips of water hyacinths when viewed underwater. Head darker, especially dorsally. Eye with prominent suborbital patch of chromatophores and subcutaneous pigmentation (rarely indistinct, never absent). Pectoral and anal-fin membranes hyaline. Pectoral and anal-fin rays hyaline with light scattering of brown chromatophores. Anal-fin ray pigmentation darker in posterior half of fin. Color in live individuals similar to preserved specimens, body sometimes with yellow-green tinge in waters with high sediment load, opercular region usually very rosy due to underlying gills.

Size. A Brachyhypopomus of moderate adult size, largest specimen examined 215 mm TL, ca. 150 mm LEA (n = 1,400). Largest male specimen examined 195 mm TL, 136 mm LEA (n = 25). Largest female specimen examined 201 mm TL, 140 mm LEA (n = 55).

Fig. 46
Brachyhypopomus walteri. a. MCP 45291 (WC16.180598), female, 145 mm TL (head, and body in lateral and dorsal view); b. MCP 45292 (WC05.190598), male, 168 mm TL (body in lateral view); Brazil, rio Solimões-Japurá confluence, Amazonas dr. Note sexual dimorphism in caudal-filament length. Specimen fixed in formalin and preserved in EtOH. Scale bars = 5mm.

Sexual dimorphism. No salient sexual dimorphism in size. Breeding males develop elongated caudal filaments in comparison to immature individuals and breeding females (Fig. 46a,b), but do not exhibit an elevated number of horizontal bilateral columns or vertical rows of electrocytes. Instead breeding males exhibit clearly enlarged electrocytes relative to immature specimens and females. Tip of caudal filament in large males never exhibits a paddle-like lateral compression. No sexual differences in pigmentation.

Geographic distribution. Bolivia, Brazil, Ecuador, Guyana, Paraguay, and Peru (Fig. 47). Widely distributed through the Amazon basin, including whitewater, clearwater and blackwater systems. Also known from the middle Essequibo, and from the Paraguay-Paraná drainage. Records from the Paran á-drainage are mostly from collections in the Pantanal Matogrossense in the northern río Paraguay, but a single specimen was collected from the río Paraná of Paraguay, at a latitude of 27°17'03"S. Sullivan et al. (2013) did not report B. walteri from the Paraná-Paraguay drainage.

Fig. 47
Collection records for Brachyhypopomus walteri (circles). Holotype location is marked with an open symbol. Elevation data refers to altitude above mean sea level (see Fig. 2 for legend).

Population variation: We found overlap in the range of meristic counts (Tables 2-5) and morphometric measurements (Table 21), and observed similar pigmentation among populations of B. walteri from the central Amazon and from the upper Paraguay. These observations, in combination with molecular data (Crampton et al., 2016Crampton, W. G. R., C. D. de Santana, J. C. Waddell & N. R. Lovejoy. 2016. Phylogenetic systematics, biogeography, and ecology of the electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes). PLoS One, 11(10): 1-63: e0161680. doi: 10.1371/journal.pone.0161680.
https://doi.org/10.1371/journal.pone.016...
), support the hypothesis that all populations we have assigned to B. walteri are members of a single geographically widespread species, which is morphologically and genetically distinct from all congeners.

Ecological notes. Brachyhypopomus walteri is an ecologically cosmopolitan species that occurs in both high-conductivity and low-conductivity systems, but is usually more abundant in low-conductivity systems. It is a common component of floating meadow habitats in the high-conductivity whitewater floodplains of the Amazon River and its whitewater tributaries, and also along the margins of low-conductivity blackwater rivers such as the rio Negro, and rio Tefé. In the central and upper Amazon, in the vicinity of Tefé, Brazil, and Iquitos, Peru, B. walteri is much more common in floating meadow communities of normoxic low-conductivity blackwater systems than in seasonally hypoxic high-conductivity whitewater systems. Populations from central Amazon whitewater floodplains are able to tolerate protracted periods of experimentally induced hypoxia by undertaking aerial gill respiration (Crampton, 1998bCrampton, W. G. R. 1998b. Effects of anoxia on the distribution, respiratory strategies and electric signal diversity of gymnotiform fishes. Journal of Fish Biology, 53 (Suppl. A): 307-330.). Brachyhypopomus walteri is also abundant in small low-conductivity terra firme rivers and streams, where it is associated with aquatic vegetation and submerged root masses and leaf litter. Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.) infer, incorrectly, that B. walteri is predominantly a white-water floodplain specialist that occurs in blackwater systems only near their confluence with whitewater systems. For instance, contrary to Sullivan et al. (2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.), B. walteri is known from the rio Negro far from its confluence with the Amazon River near Manaus (Fig. 47). Breeding occurs during the rising and high water period in populations from Amazonian floodplain floating macrophytes (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 165). Stomach contents in populations from the central Amazon comprise aquatic insect larvae, microcrustacea, and other small aquatic invertebrates - with a predominance of Chironomidae larvae (Crampton, 1996aCrampton, W. G. R. 1996a The electric fish of the upper Amazon: ecology and signal diversity. Unpublished D.Phil. Dissertation, The University of Oxford, Oxford. 223p.: 136).

Co-occurring congeners: Because of its wide geographical range and occurrence in multiple habitats, B. walteri occurs in geographical sympatry and ecological syntopy with multiple congeners: in the Amazonas drainage, rio Essequibo, and coastal drainages of the Guianas: B. alberti, B. arrayae, B. batesi, B. beebei, B. belindae, B. benjamini, B. bennetti, B. bombilla, B. brevirostris, B. bullocki, B. cunia, B. flavipomus, B. hamiltoni, B. hendersoni, B. pinnicaudatus, B. regani, B. sullivani, and B. verdii; and in the río Paraná-Paraguay drainage with B. bombilla, B. brevirostris, B. draco, and B. gauderio.

Local names. Bolivia: cuchillo; Brazil: sarapó (north), tuvira (south); Ecuador: cuchillo, yayo; Guyana: knife fish; Paraguay: morenita; Peru: macana.

Material examined. 1,032 specimens. Bolivia. Beni (localities from rio Madeira dr., Amazonas dr.) AMNH 39773, 5, 96-113 mm, 6 km SW Costa Marques (Brazil), río Baures (río Blanco) at confluence with río Iténez (río Guaporé), affl. río Mamoré, 12°30'10"S, 064°16'47"W. AMNH 40086 (part), 1, 121 mm, rio Baures, 2 km above mouth, affl. rio Guaporé, affl. río Mamoré, 12°30'32"S, 064°16'46"W. CBF 10256, 1, immature, 117 mm, CBF 10257, 1, immature, 116 mm, mun. Riberalta, stream nr. lago San José, affl. río Beni, 10°54'47"S, 065°59'49"W. CBF 10258, 1, immature, 115 mm, UMSS 7020, 1, immature, 137 mm, UMSS 7021, 1, female, 201 mm, UMSS 7022, 1, immature, 102 mm, UMSS 7023, 1, immature, 126 mm, mun. Riberalta, stream nr. San José, affl. río Beni, 10°55'32"S, 066°00'36"W. INHS 37193, 1, 89 mm, 46 km E Estación Biológica del Beni on rd. to San Ignacio, río Moseruna, affl. río Apere, affl. río Mamoré, ca. 14°59'S, 065°48'W. UF 82009, 2, 96-142 mm, Bella Vista, río Blanco (río Baures), affl. río San Martín, affl. río Guaporé, affl. río Mamoré, 13°16'S, 063°42'W. UMMZ 204297, 2, 89-105 mm, 2 km SW Costa Marques (Brazil), río Iténez (río Guaporé), affl. río Mamoré, 12°29'30"S, 064°15'24"W. UMMZ 204632, 6, 90-142 mm, 5 km SW Costa Marques, río Iténez, nr. mouth of río Baures (río Blanco), affl. río Guaporé, affl. río Mamoré, 12°30'30"S, 064°19'00"W. UMMZ 204829, 1, 80 mm, UMMZ 246439, 3, 78-114 mm, río Baures (río Blanco), nr. mouth, L bank río Iténez (río Guaporé), affl. río Mamoré, 12°31'06"S, 064°19'00"W. UMMZ 205163, 3, 87-108 mm, 10 km SE Costa Marques (Brazil), backwater of río Iténez (río Guaporé), affl. río Mamoré, 12°30'37"S, 064°12'59"W. Brazil. Amazonas (localities from Amazonas dr.; localities listed from the Mamirauá Reserve [Reserva de Desenvolvimento Sustentável Mamirauá] are in rio Solimões-Japurá floodplain, mun. Alvarães). ANSP 194025, 6 (1CS), 60-126 mm LEA, INPA 30241, 8, 64-114 mm LEA, mun. São Paulo de Olivença, Monte Sinai, Rio Camatiã, affl. rio Solimões, 03°27'34"S, 068°56'00"W [coordinates for São Paulo de Olivença] (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). BMNH 1998.3.12.83-101, 19 (3 immature, 136-184 mm, 1 male, 142 mm, 15 unsexed/measured), MCP 46933, 1 (CS), 70 mm, Mamirauá Reserve, lago Rato, 03º03'01"S, 064º52'23"W. BMNH 1998.3.12.102, 1, male, 186 mm, mun. Tefé, Cabeceira do lago Tefé, rio Tefé, 03°38'01"S, 064°57'59"W. BMNH 1998.3.12.103-104, 2, female, 150-160 mm, Mamirauá Reserve, lago Bolsinha, 03º03'47"S, 064º50'03"W. BMNH 1998.3.12.105, 1, female, 166 mm, MCP 45445, 33, 79-160 mm, Mamirauá Reserve, cano do lago Rato, 03º02'41"S, 064º51'26"W. BMNH 1998.3.12.106-107, 2, female, 163-191 mm, MCP 45490, 2 (1 female, 152 mm, 1 male, 167 mm), Mamirauá Reserve, Ressaca do Caetono, 02º50'15"S, 064º55'50"W. CU 97641, 1 (paratype), 80 mm, rio Negro upstream of Manaus, rio Negro, 03°05'23"S, 060°27'01"W. CU 97642, 5 (paratypes), 95-104 mm LEA, rio Negro upstream of Manaus, rio Negro, 03°05'35"S, 060°26'50"W. IDSM 457, 6, 72-130 mm, MCP 45297, 1, female, 138 mm, mun. Tefé, lago Martelo, rio Tefé, 03°46'56"S, 064°59'39"W. INHS 44484, 4, 101-140 mm, mun. Manaus, inlet to lago Camaleão, Ilha da Marchantaria, rio Solimões floodplain, Amazonas dr., 03°14'22"S, 059°56'37"W. INHS 70542 (part), 4, 71-162 mm LEA, lago Camaleão, Ilha da Marchantaria, rio Solimões floodplain, 03°14'22"S, 059°56'37"W. INPA 8880, 3 (paratypes), 108-116 mm LEA, 1 examined from photograph in original description (164 mm), INPA 8939, 1 (paratype), 125 mm LEA, examined from photograph in original description, INPA 8941, 1 (holotype), 163 mm TL, 126 mm LEA, examined from photograph in original description, Paraná do Paracuúba, nr. mouth of rio Negro and entrance to lago Januari, rio Solimões floodplain, 03°12'36"S, 059°59'24"W. INPA 9945, 31, 51-143 mm, Mamirauá Reserve, lago Caetano, 02º50'58"S, 064º55'42"W. INPA 17112, 20, 58-132 mm, Paraná do Seixo, lago Jari, rio Purus, 04°54'41"S, 062°27'26"W. INPA 17121, 1, 92 mm, Paraná 2, nr. Arumã, rio Purus, 04°46'24"S, 062°11'35"W. INPA 17161, 2, 92-108 mm, INPA 19935, 2, 72-102 mm, lake nr. Sacado da Santa Luzia, rio Purus, 04°42'17"S, 062°22'26"W. INPA 17170, 1, 82 mm, lago Sacado, rio Purus, 04°42'49"S, 062°23'55"W. INPA 17192, 26, 72-127 mm, igarapé de Duas Bocas, Paraná do Jari, rio Purus, 04°55'33"S, 062°21'58"W. INPA 19938, 2, 70-94 mm, lago Campina, rio Purus, 04°55'59"S, 062°56'25"W. INPA 19940, 1, 58 mm, Paraná do Rei, Ilha Careiro, rio Amazonas, Amazonas dr., 03°12'S, 059°44'W. INPA 29259, 12, mun. Beruri, igarapé Ajará, lago Ayapá, affl. rio Purus, 04º25'07"S, 062°15'36"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33253, 3, mun. Manacapuru, Canaboca, rio Solimões floodplain, 03º35'33"S, 060°50'09"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33268, 3, mun. Coari, rio Solimões floodplain, 03º51'10"S, 062°28'07"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 39074, 1, mun. São Sebastião do Uatamã, São José do Jabote, rio Uatamã, 01º56'12"S, 058°17'47"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). MCP 33368, 1, 124 mm, MCP 44649, 2 (1 female [CS], 140 mm, 1 male [CS], 185 mm), Mamirauá Reserve, lago Curuçá Comprido, 03º05'31"S, 064°48'58"W. MCP 33369, 1, 141 mm, Mamirauá Reserve, lago Curuçá Redondo, 03º06'13"S, 064°49'06"W. MCP 41033 (part), 1, 109 mm, mun. Canutama, igarapé São João on hwy. BR-319, ca. 60 km S Humaitá, affl. rio Ipixuna, affl. rio Purus, 07°56'07"S, 063°20'03"W. MCP 44607, 1, female (CS), 150 mm, MCP 45488, 1, female, 116 mm, Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. MCP 44741, 2, immature (1CS), 126-146 mm, MCP 45296, 3, immature, 110-123 mm, MCP 45372, 2, male, 137-146 mm, MCP 45415, 4, 82-129 mm, MCP 45440, 2, immature, 100-136 mm, MCP 45478, 1, female, 141 mm, mun. Tefé, igarapé Repartimento, 1.5 km downstream Estrada Agrovila rd., affl. Lago Tefé (rio Tefé), 03º24'25"S, 064º44'08"W. MCP 44742, 6 (2 immature, 125-142 mm, 4 female [1CS], 104-149 mm), Mamirauá Reserve, lago Periquito Comprido, 03º04'57"S, 064°46'42"W. MCP 44743, 11 (10 immature [2CS], 86-124 mm, 1 female, 100 mm), mun. Tefé, rio Tefé, 03º37'43"S, 064°59'03"W. MCP 45289, 1, immature, 122 mm, MCP 45298, 1, female, 123 mm, MCP 45477, 1, male, 155 mm, mun. Tefé, igarapé Curupira, Estrada Agrovila rd., affl. lago Tefé (rio Tefé), 03º25'48"S, 064º43'53"W. MCP 45290, 1, male, 152 mm, MCP 45442, 1, male, 165 mm, Mamirauá Reserve, cano do lago Sapucaia, 03º04'07"S, 064°48'32"W. MCP 45292, 6 (5 female, 120-153 mm, 1 male, 168 mm), Mamirauá Reserve, lago Promessa, 03º04'29"S, 064°47'02"W. MCP 45293, 3 (2 female, 135-168 mm, 1, male, 135 mm), Mamirauá Reserve, lago Curuçá Aberto, 03º06'07"S, 064°49'10"W. MCP 45294, 1, female, 156 mm, mun. Tefé, lago Caiambé, rio Caiambé, 03º35'40"S, 064º26'58"W. MCP 45291, 1, female, 145 mm, MCP 45295, 1, female, 176 mm, MCP 45458, 1, male, 161 mm, Mamirauá Reserve, lago Secretaria, 03º07'12"S, 064°47'49"W. MCP 45306, 1, immature, 132 mm, mun. Maraã, lago Amanã, Igarapé Juá Grande, rio Japurá, 02°28'50"S, 064°48'50"W. MCP 45314, 5 (4 immature, 95-116 mm, 1 male, 138 mm), MCP 45417, 1, 98 mm, MCP 45371, 1, female, 96 mm, MCP 45373, 3 (1 immature, 94 mm, 2 male, 123-125 mm), mun. Tefé, igarapé Xidarinini, affl. lago Tefé (rio Tefé), 03°22'46"S, 064°41'17"W. MCP 45320, 1, immature, 130 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º02'41"S, 064º51'26"W. MCP 45327, 1, immature, 105 mm, Mamirauá Reserve, lago Sumaumeirinha I, 02º48'26"S, 065º04'33"W. MCP 45412, 1, female, 153 mm, MCP 45444, 2 (1 female, 166 mm, 1 male, 165 mm), Mamirauá Reserve, Ressaca da Vila Alencar, 03º07'41"S, 064°48'04"W. MCP 45413, 1, male, 181 mm, Mamirauá Reserve, cano do lago Mamirauá, 03º04'29"S, 064°48'29"W. MCP 45418, 23, 54-150 mm, mun. Tefé, lago Jacaré, rio Solimões floodplain, 03°11'11"S, 064°43'05"W. MCP 45441, 1, female, 142 mm, Mamirauá Reserve, lago Pirarara, 02º57'04"S, 064º50'04"W. MCP 45443, 1, female, 181 mm, Mamirauá Reserve, Ressaca do Itu, 02º49'51"S, 064º57'11"W. MCP 45479, 1, 124 mm, mun. Tefé, rio Solimões, nr. mouth Paraná Capivara, 03°16'37"S, 064°37'42"W. MCP 45321, 1, immature, 141 mm, MCP 45487, 1, male, 184 mm, Mamirauá Reserve, lago Bolsinha, 03º03'47"S, 064º50'03"W. MCP 45414, 1, female, 173 mm, MCP 45683, 20, 86-162 mm, mun. Tefé, Ilha Panamim, rio Solimões floodplain, 03º19'29"S, 064º38'37"W. MCZ 2769, 4, 99-160 mm, mun. Manaus, rio Negro nr. lago Alexo [lago do Aleixo, E Manaus], 03°05'28"S, 059°53'09"W. MCZ 9427 (part), 1, 85 mm, mun. Manaus, lago Hyanuary [lago do Janauari], rio Amazonas floodplain, 03°13'S, 060°00'W. MPEG 967 (part), 29, 42-137 mm, MPEG 970 (part), 3, 57-105 mm, MPEG 971 (part), 1, 47 mm, MZUSP 30063 (part), 1, 50 mm, MZUSP 30065 (part), 1, 32 mm, MZUSP 44060 (part), 3, 52-62 mm, MZUSP 85816, 4, 77-133 mm, mun. Tefé, lago Jurupari, rio Tefé, 03°48'S, 065°00'W. MPEG 1123 (part), 5, 65-85 mm, mun. Tefé, Costa Capivara, rio Solimões, ca. 03°16'38"S, 064°38'09"W. MPEG 22747, 3, 113-151 mm, Mamirauá Reserve, lago Mamirauá, 02º59'38"S, 064°54'26"W. MPEG 22748, 3, 90-145 mm, Mamirauá Reserve, lago Bolsinho, 03º03'47"S, 064°49'59"W. MZUSP 7803, 1, 123 mm, mun. Parintins, stream affl. lago José Açu, 02°40'S, 056°37'W. MZUSP 23282, 1, 107 mm, mun. Coari, Ilha Surubim, upstream Coari, branch of rio Solimões, 03°54'S, 063°19'W. MZUSP 28054 (part), 1, 78 mm, MZUSP 28055, 1, 96 mm, Moura, Pedra do Gavião, rio Negro, 01°28'S, 061°38'W. MZUSP 30049 (part), 8, 42-60 mm, MZUSP 30054, 1, 58 mm, mun. Tefé, Vista Escura, rio Tefé, no coordinates. MZUSP 30051, 1, 68 mm, MZUSP 30056, 1, 50 mm, MZUSP 30061 (part), 28, 37-103 mm, mun. Tefé, lago Mucura, rio Tefé, no coordinates. MZUSP 30052 (part), 1, 78 mm, mun. Tefé, Mastro, rio Tefé, no coordinates. MZUSP 30058 (part), 2, 114-115 mm, mun. Maraã, lago Amanã, canal do lago Amanã, affl. rio Japurá, 02°44'S, 64°41'W. MZUSP 75571 (part), 4, 106-152 mm, USNM 306903, 1, 136 mm, USNM 306919, 1, 75 mm LEA, USNM 374466, 4, 135-155 mm, lago Camaleão, Ilha da Marchantaria, rio Solimões floodplain, 03°14'22"S, 059°56'37"W. MZUSP 78032 (part), 1, 110, mun. Maraã, Paraná do Castanho, lago Amanã, affl. rio Japurá, 02°44'S, 064°39'W. MZUSP 78954 (part), 1, 92 mm, Costa do Anori, nr. mouth of rio Purus, rio Solimões, 03°46'S, 061°37'W. MZUSP 85814, 1, 55 mm, mun. Tefé, Jauari-atuba, rio Tefé, ca. 03°56'S, 065°01'W. MZUSP 94038, 1, 100 mm, MZUSP 99170, 7, 60-135 mm, canal do lago Amanã, affl. rio Japurá, ca. 02°44'S, 064°39'W. MZUSP 95226 (part), 1, 100 mm, mun. Santa Isabel do rio Negro, Paricatuba, lake on margin of rio Negro, ca. 00°31'S, 065°01'W. USNM 300978, 1, 94 mm, rio Unini, affl. rio Negro, 01°41'S, 061°31'W [coordinates for mouth of rio Unini]. USNM 306874, 2, 91-100 mm LEA, Paraná da Ilha da Marchantaria, rio Solimões floodplain, ca. 03°14'22"S, 059°56'37"W. Goiás (localities from rio Araguaia dr., affl. rio Tocantins, Amazonas dr.). AUM 45436, 9, 107-187 mm, mun. Aruanã, Fazenda Sobrado, margin Aruanã-Cocalinho rd., 14°45'51"S, 050°57'50"W. MZUSP 89218 (part), 1, 114 mm, mun. Aruanã, Fazenda Viplan, on hwy. GO 334, floodplain of rio do Peixe, 14°20'11"S, 050°46'31"W. Mato Grosso. BMNH 1900.4.14.91-94 (part), 1, 98 mm, mun. Carandàzinho, rio Cuiabá, affl. rio Paraguai, Paraná dr., ca. 16°27'S, 056°08'W. BMNH 1982.9.24.132, 1, 78 mm, Corgo do Gato [córrego do Gato], on hwy. BR-158, affl. rio Suiazinho, affl. rio Suiá Missu, affl. rio Xingu, Amazonas dr., ca. 12°56'S, 051°51'W. MCP 30786, 1, 106 mm, mun. Nova Ubiratã, rio Celeste ca. 9 km W Nova Ubiratã on rd. to Sorriso, affl. rio Tapajós, Amazonas dr., 13°03'08"S, 055°21'13"W. MCP 44451, 1, 87 mm, mun. Nova Mutum, Córrego Ranchão on Nova Mutum-Santa Rita do Trivelato hwy., MT-235, affl. rio Tapajós, Amazonas dr., 13°44'35"S, 055°50'08"W. MZUSP 25138, 2, 102-111 mm, MZUSP 25143, 1, 147 mm, mun. Cáceres, Ilha da Taiamã [Estação Ecológica Taiamã], rio Paraguai, Paraná dr., 16°53'S, 057°27'W [coordinates from center Ilha da Taiamã]. MZUSP 57478, 1, 67 mm, mun. Xavantina, rio Areões, affl. rio das Mortes, affl. rio Araguaia, affl. rio Tocantins, Amazonas dr., 14°39'S, 052°07'W. MZUSP 77724, 6, 108-147 mm, rio Juruena, ca. 1 km upstream mouth rio Arinos, affl. rio Tapajós, Amazonas dr., ca. 10°26'S, 58°20'W. MZUSP 88593, 15, 83-215 mm, mun. Cocalinho, stream, affl. Corixo da Saudade, ca. 17 km NW Cocalinho on hwy. MT-326, affl. rio Araguaia, aff rio Tocantins, Amazonas dr., 14°19'35"N, 051°06'25"W. MZUSP 95068 (part), 18, 93-155 mm, MZUSP 100307, 18, 89-152 mm, mun. Barão de Melgaço, rio Mutum, between Vila de Mimoso and Joselândia (Pantanal de Paiaguás), rio Paraguai, Paraná dr., 16°19'30"S, 055°49'59"W. MZUSP 95736, 40, 72-179 mm, stream, affl. rio Culuene, on rd. to Cachoeira do Adelino, affl. rio Xingu, Amazonas dr., 13°48'12"S, 053°13'35"W. MZUSP 96252, 3, 94-106 mm, mun. Paranaíta, rio Teles Pires, affl. rio Tapajós, Amazonas dr., 09°25'44"S, 056°32'36"W. MZUSP 96667, 1, 87 mm, mun. Barão de Melgaço, swamp, 1 km Vila de Mimoso, Pantanal de Paiaguás, affl. rio Cuiabá, affl. rio Paraguai, Paraná dr., ca. 16°17'S, 055°48'W. MZUSP 100084, 2, 75-110 mm, mun. Paranaíta, just upstream of Sete Quedas, rio Teles Pires, affl. rio Tapajós, Amazonas dr., 09°24'05"S, 056°33'49"W. USNM 301981, 2, 103-124 mm, rio Batovi, affl. rio Xingu, Amazonas dr., ca. 11°56'S, 053°36'W. Mato Grosso do Sul (localities from rio Paraguai dr., Paraná dr.). FMNH 108538, 8, 55-91 mm, Corumbá, bay on left margin rio Vermelho, affl. rio Miranda, 19°37'13"S, 056°57'16"W. MUSM 17103, 2, 84-95 mm, side channel, rio Abobral, 19°27'22"S, 057°01'38"W. MZUSP 48311 (part), 1, 98 mm, MZUSP 48312, 3, 85-95 mm, mun. Coxim, Fazenda Santo Antonio (Baía da Sede), Pantanal do Paiaguás, affl. rio Coxim (rio Taquari), ca. 18°30'S, 054°45'W. MZUSP 59443, 25, 83-133 mm, mun. Corumbá, on rd. from Nhecolândia to BR-262, rio Negro, 19°17'16"S, 057°03'39"W. MZUSP 83607 (part), 1, 87 mm, mun. Coxim, Paraguai Lagoa, source of Ribeirao dos Veados, affl. rio Coxim (rio Taquari), 18°25'21"S, 054°50'06"W. Pará (localities from Amazonas dr.). ANSP 194517, 32, 74-140 mm, mun. Porto de Moz, beach, 3 km downstream Porto de Moz, rio Xingu, 01°43'54"S, 052°15'16"W. INPA 4209, 2, 103-155, Ilha de Babaguara, rio Xingu (no coordinates). INPA 7267, 2, 108-110 mm, rio Tapajós, nr. mouth rio Cupari, ca. 03°43'S, 055°24'W. INPA 32703, 1, Jacareacanga, igarapé do Cocho, rio Crepori, affl. rio Tapajós, 06°44'54"S, 056°54'43"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). INPA 33192, 1, mun. Almeirim, Paranaguara, rio Amazonas floodplain, 01°44'29"S, 053°10'15"W (listed in Sullivan et al., 2013Sullivan, J. P., J. Zuanon & C. C. Fernandes. 2013. Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge. ZooKeys, 327: 1-34.). MCP 23359 (part), 1, 107 mm, Concórdia do Pará, rio Bujarú, affl. rio Guamá, affl. Baía de Marajó, ca. 02°06'S, 047°56'W. MCZ 9440, 1, 52 mm, Belém and environs., Báia de Marajó, ca. 01°27'S, 048°29'W. MCP 49398, 3, mun. Santarém, Cachoerinha do Mentai, rio Mentai, affl. Rio Arapiuns, affl. Rio Tapajós, 02°43'12"S, 055°36'15"W. MCP 49400, 7, mun. Curuá, Lago Preto, Ilha São Luiz, rio Amazonas floodplain, 02°06'22"S, 055°10'17"W. MCP 49411, 4, mun. Alenquer, small stream affl. rio Curuá, 01°36'13"S, 054°55'10"W. MPEG 5813, 1, 115 mm, mun. Almeirim, Pesqueiro da Ilha, no precise locality, rio Amazonas, 01°31'S, 052°35'W [coordinates for Almeirim]. MPEG 9758, 10, 46-105 mm, mun. Tomé-Açu, igarapé Arrainha, affl. rio Acará-Mirim, affl. rio Acará, affl. Baía de Marajó, 02°25'11"S, 048°12'13"W. ZUEC 12328, 1, mun. Belterra, Igarapé do Mato Grosso, nr. Jaguarari, affl. rio Tapajós, 02°55'01"S, 055°03'54"W. ZUEC 12329, 1, Igarapé Jandá, nr. Piquiatuba, affl. rio Tapajós, 03°00'37"S, 055°06'16"W. ZUEC 12330, 1, mun. Belterra, Igarapé Dominguinho, nr. Piquiatuba, affl. rio Tapajós, 03°00'48"S, 055°06'22"W. ZUEC 12336, 5, mun. Santarém, rio Mentai at Cachoeirinha do Mentai, affl. rio Arapiuns, affl. rio Tapajós, 02°43'12"S, 055°36'15"W. Rondônia (localities from rio Madeira dr., Amazonas dr.). FMNH 117760, 4, 82-104 mm, Maciel, rio Guaporé, affl. rio Mamoré, 12°30'S, 062°20'W. INPA 9721, 19, 100-146 mm, INPA 9727, 18, 56-148 mm, rio Pacaás Novos, nr. confluence with rio Mamoré, ca. 15 km Guajará Mirim, 10°51'S, 065°16'W. INPA 9724, 2, 49-131 mm, rio Mamoré, just upstream Guajará Mirim, ca. 10°47'S, 065°20'W. INPA 9729 (part) 1, 127 mm, mouth of rio Pacaás Novos, ca. 15 km Guajará Mirim, rio Mamoré, 10°51'S, 065°16'W. INPA 19958, 1, 105 mm, Surprêsa, at rio Mamoré-Madeira confl., ca. 11°53'S, 064°59'W. MPEG 1120 (part), 1, 95 mm, rio Pacaás Novos, Guajará Mirim, affl. rio Mamoré, ca. 10°51'S, 065°16'W. MPEG 1121 (part), 2, 111-120, rio Pacaás Novos, 20 km upstream Guajará Mirim, affl. rio Mamoré, ca.10°56'15"S, 065°16'29"W. UFRO-I 6463, 30, 125-160 mm, mouth rio Cautário, affl. rio Guaporé, affl. rio Mamoré, 12°10'51"S, 064°34'00"W. UFRO-I 6465, 1, 130 mm, UFRO-I uncat. (field number CAU2010010701), 2, 141-145 mm, mouth of rio Cautário, affl. rio Guaporé, affl. rio Mamoré,12°11'22"S, 064°35'20"W. UFRO-I 6466, 5, 75-112 mm, UFRO-I 6469, 5, 93-105 mm, Colocação Três Praias, rio Jaciparaná, 09°27'29"S, 064°25'22"W. UFRO-1 6468, 26, 85-155 mm, Furo Variante, lago Cuniã, rio Madeira floodplain, 08°21'17"S, 064°30'11"W. UFRO-I uncat. (field number CUN2008120102), 4, 115-153 mm, igarapé do Campo, lago Cuniã, rio Madeira floodplain, 08°19'14"S, 064°28'05"W. USNM 301980, 10, 98-132 mm, Brazil-Bolivia border, region between Guajará-Mirim and Mato Grosso, rio Guaporé, affl. rio Mamoré, affl. rio Madeira, Amazonas dr., 12°41'S, 063°07'W [coordinate taken half-way from Guajará-Mirim to Mato Grosso, listed coordinate is in Bolivian territory nr. Guayara-Mirín]. Roraima. INPA 30748, 11, INPA 30749, 8, rio Branco, near Boa Vista, affl. rio Negro, Amazonas dr., 02°47'31"N, 060°40'09"W. Tocantins (localities in rio Tocantins dr., Amazon