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New small-sized species of Astyanax (Characiformes: Characidae) from the upper rio Paraguai basin, Brazil, with discussion on its generic allocation

Abstract

A new species of Astyanax is described from the rio Salobra, tributary of rio Cuiabá, rio Paraguai basin. The new taxon can be distinguished from its congeners by having a well-defined dark midlateral stripe on body extending from the posterior margin of the opercle to the base of middle caudal-fin rays and a single vertical elongate humeral blotch. Although the new species is described in Astyanax, some specimens present an incomplete or a discontinuous series of perforated scales in the lateral line. Therefore, a discussion on its generic allocation is presented. Comments on different patterns of coloration among dark-striped species of Astyanax are also provided. The discovery of a new species in an underwater tourist point relatively near a large urban center underscores that even fish species daily observed by hundreds of people in limpid waters may lack a formal taxonomic identity. Such finding also highlights how the megadiverse Brazilian freshwater ichthyofauna still needs efforts and investments to identify and describe new taxa.

Keywords:
Lateral line; Nobres; Longitudinal stripe; Taxonomy; Tourist destination

Resumo

Uma nova espécie de Astyanax é descrita do rio Salobra, afluente do rio Cuiabá, bacia do rio Paraguai. O táxon novo pode ser diferenciado de seus congêneres por apresentar uma faixa médio-lateral escura bem definida no corpo, se estendendo da margem posterior do opérculo até a base dos raios medianos da nadadeira caudal e por possuir uma mancha umeral verticalmente alongada. Apesar da espécie nova ser descrita em Astyanax, alguns exemplares apresentam uma série incompleta ou descontínua de escamas perfuradas na linha lateral. Assim, uma discussão sobre sua alocação genérica é apresentada. Comentários sobre os diferentes padrões de coloração de espécies de Astyanax com faixa escura também são fornecidos. A descoberta de uma espécie nova em um ponto turístico subaquático relativamente próximo a um grande centro urbano ressalta que mesmo as espécies de peixes observadas diariamente por centenas de pessoas em águas límpidas podem não ter uma identidade taxonômica formal. Tal achado também evidencia o quanto a megadiversa ictiofauna de água doce brasileira ainda precisa de esforços de coleta adicionais e investimentos para identificar e descrever os táxons novos.

Palavras-chave:
Linha lateral; Nobres; Faixa longitudinal; Taxonomia; Ponto turístico

INTRODUCTION

Astyanax Baird & Girard, 1854, as defined by Eigenmann (1917Eigenmann CH. The American Characidae (Part 1). Mem Mus Comp Zool. 1917; 43:1–102., 1921Eigenmann CH. The American Characidae (Part 3). Mem Mus Comp Zool. 1921; 43:209–310.), is one the most species-rich genera of characids, currently comprising 125 valid species, widely distributed on the Neotropical region from southern United States to central Argentina (Fricke et al., 2022Fricke R, Eschmeyer WN, Van der Laan R. Eschmeyer’s catalog of fishes: Genera, species, references [Internet]. San Francisco: California Academy of Sciences; 2022. Available from: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp
http://researcharchive.calacademy.org/re...
). Unlike other highly diverse groups of characids (e.g., Hemigrammus Gill, 1858, Hyphessobrycon Durbin, 1908, and Moenkhausia Eigenmann, 1903) which have their greatest diversity occurring in the Amazon basin, only 20% of the Astyanax diversity occurs in that region (see Dagosta, de Pinna, 2019Dagosta FCP, de Pinna M. The fishes of the Amazon: distribution and biogeographical patterns, with a comprehensive list of species. Bull Am Mus Nat Hist. 2019; (431):1–163. Available from: http://digitallibrary.amnh.org/handle/2246/6940
http://digitallibrary.amnh.org/handle/22...
). In turn, most species are found in rio Paraná-Paraguai basin, Laguna dos Patos system, and Atlantic coastal rivers of southeastern Brazil. Also differing from other species-rich genera of Characidae, species of Astyanax typically have relatively low variety of body shapes and colors, unexpected patterns for a megadiverse and widely distributed group of Neotropical fishes.

A new species of Characidae was collected in a recent expedition to the headwaters of rio Paraguai after being recognized during underwater observations in the crystal clear waters of an ecotourism destination in the central Brazil. The generic allocation of the new species is problematic due to two factors: the variable morphology regarding trunk lateral-line canals that challenges the traditional classification of Eigenmann (1917Eigenmann CH. The American Characidae (Part 1). Mem Mus Comp Zool. 1917; 43:1–102., 1921Eigenmann CH. The American Characidae (Part 3). Mem Mus Comp Zool. 1921; 43:209–310.); and the inconsistency of the current diagnosis of Astyanax and related genera provided by a recent phylogeny. Therefore, the generic assignment of the new species is discussed.

MATERIAL AND METHODS

Counts and measurements follow Fink, Weitzman (1974)Fink WL, Weitzman, SH. The so called Cheirodontin fishes of Central America with description of two new species (Pisces, Characidae). Smithson Contrib Zool. 1974; 72:1–46. http://dx.doi.org/10.5479/si.00810282.172
http://dx.doi.org/10.5479/si.00810282.17...
and Menezes, Weitzman, (1990)Menezes NA, Weitzman SH. Two new species of Mimagoniates (Teleostei: Characidae: Glandulocaudinae), their phylogeny and biogeography and a key to the glandulocaudin fishes of Brazil and Paraguay. Proc Biol Soc Wash. 1990; 103(2):380–426. , except for the number of horizontal scale rows below the lateral line counted to the pelvic-fin insertion, but not including the axillary scale, and with the addition of the pelvic-fin origin to anal-fin origin distance. Measurements were taken with a digital caliper to the nearest 0.1 mm. Standard length (SL) is expressed in millimeters (mm) and all other measurements are expressed as percentage of SL, except for subunits of head, which are expressed as percentage of head length (HL). In the description, counts are followed by their frequency of occurrence in parentheses. Asterisk indicates the counts of the holotype. Counts of supraneurals, tooth cusps, small dentary teeth, unbranched anal-fin rays, procurrent caudal-fin rays, and the position of the pterygiophores were taken from cleared and stained (c&s) specimens prepared according to Taylor, Van Dyke, (1985)Taylor WR, Van Dyke GC. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium. 1985; 9(2):107–19. Available from: https://sfi-cybium.fr/en/node/2423
https://sfi-cybium.fr/en/node/2423...
. Vertebrae of the Weberian apparatus were counted as four elements and the compound caudal centra (PU1+U1) as a single element. Abdominal vertebrae include the Weberian apparatus and the vertebrae associated with ribs or hemal arches without hemal spine. Caudal vertebrae are vertebra associated with hemal spine. Circuli and radii counts were taken from scale row immediately above the lateral line. The sex of specimens was confirmed by dissection of four specimens (MZUSP 118302). Catalog numbers are followed by the number of specimens in alcohol, number of specimens measured and counted in parentheses, SL range of all specimens of the lot, and if any, the number of c&s specimens and their respective SL range. Institutional abbreviations follow Sabaj, (2019)Sabaj MH. Standard symbolic codes for institutional resource collections in herpetology and ichthyology. Version 7.1 [Internet]. Washington, D.C.; 2019. Available from: http://www.asih.org/standard-symbolic-codes/about-symboliccodes
http://www.asih.org/standard-symbolic-co...
.

RESULTS

Astyanax nobre, new species

urn:lsid:zoobank.org:act:60528808-774C-4C73-91C1-D7AD3C45D435

(Figs. 14; Tab. 1)

Astyanax sp. —Marinho et al., 2021Marinho MMF, Ohara WM, Dagosta FCP. A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids. Neotrop Ichthyol. 2021; 19(2):e200118. https://doi.org/10.1590/1982-0224-2020-0118
https://doi.org/10.1590/1982-0224-2020-0...
: tab. 2 (listed as having intraspecific variation in the lateral line trunk morphology).

Holotype. MZUSP 125905, 25.6 mm SL, Brazil, Mato Groso State, Municipality of Nobres, rio Salobra at Recanto Ecológico Lagoa Azul, Bom Jardim district, tributary of rio Cuiabá, rio Paraguai basin, 14º35’43.2”S 55º58’09.6”W, F. C. P. Dagosta & W. M. Ohara, 18 Nov 2014.

Paratypes. All from Brazil, Mato Grosso State, Municipality of Nobres, Lagoa Azul, rio Paraguai basin: MZUSP 110406, 11, 23.8–30.0 mm SL, I. K. Ribeiro, 23 July 2011; MZUSP 118302, 154, 11.9–27.0 mm SL, 3 c&s; UFPB 12087, 10, 15.4–23.8 mm SL, same data as holotype.

Diagnosis.Astyanax nobre can be distinguished from its congeners, except A. joaovitori Oliveira, Pavanelli & Bertaco, 2017 and A. scintillansMyers, 1928Myers GS. 1928. New fresh-water fishes from Peru, Venezuela, and Brazil. Ann Mag Nat Hist. 1928; 2(7):83–90., by the presence of a well-defined, dark midlateral stripe on body extending from opercle to middle caudal-fin rays (vs. longitudinal stripe absent; stripe starting posterior the anterior humeral and never connected to it; stripe starting immediately posterior to the humeral blotch; narrower stripe starting at posterior margin of the opercle, becoming blurred posteriorly and not reaching the caudal fin). The new species can be clearly distinguished from A. scintillans by the presence of a vertical humeral blotch (vs. absence). Astyanax nobre can be distinguished from A. joaovitori by having the dark midlateral stripe ending at the base of the middle caudal-fin rays (vs. reaching the distal tip of the middle caudal-fin rays) and three scale series below the lateral line (vs. five or six). Another remarkable difference between these species is the body size. Astyanax nobre has mature individuals at about 25 mm SL and reaching up to 30 mm SL whereas A. joaovitori reaches a much larger body size, with up to 77 mm SL (see Oliveira et al., 2017Oliveira CAM, Pavanelli CS, Bertaco VA. A new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Araguaia, Central Brazil. Zootaxa. 2017; 4320(1):173–82. https://doi.org/10.11646/zootaxa.4320.1.10
https://doi.org/10.11646/zootaxa.4320.1....
). Astyanax nobre fits within the A. scabripinnis species complex sensuBertaco, Lucena, (2006)Bertaco VA, Lucena CAS. Two new species of Astyanax (Ostariophysi: Characiformes: Characidae) from eastern Brazil, with a synopsis of the Astyanax scabripinnis species complex. Neotrop Ichthyol. 2006; 4(1):53–60. https://doi.org/10.1590/S1679-62252006000100004
https://doi.org/10.1590/S1679-6225200600...
. According to the authors, the group is characterized by species with body deepest and heaviest in area close to middle of pectoral fins, head heavy, snout short and abrupt by tapering, body depth smaller than 41% of SL (mean 30–33% of SL), reduced number of branched anal-fin rays (13–21, usually 17–18, rarely 22 or 23), presence of one or two humeral spots, and a dark, midlateral, body stripe extending to the tip of the middle caudal-fin rays. Except for the midlateral dark stripe that does not reach the tip of the middle caudal-fin rays, all characteristics are found in Astyanax nobre. According to Oliveira et al., (2017)Oliveira CAM, Pavanelli CS, Bertaco VA. A new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Araguaia, Central Brazil. Zootaxa. 2017; 4320(1):173–82. https://doi.org/10.11646/zootaxa.4320.1.10
https://doi.org/10.11646/zootaxa.4320.1....
, it is impossible to infer about the dark midlateral stripe of A. scabripinnis (Jenyns, 1842) due to the loss of coloration in the holotype. Astyanax nobre differs from the holotype of A. scabripinnis by having 32–36 lateral line scales (vs. 38).

Description. Morphometric data presented in Tab. 1. Body compressed, moderately elongate. Greatest body depth at dorsal-fin origin. Dorsal profile of head convex from upper lip to vertical through posterior nostril; slightly convex from that point to tip of supraoccipital spine. Dorsal profile of body slightly convex along predorsal region, straight to slightly convex along dorsal-fin base, slightly convex from terminus of dorsal-fin base to adipose-fin origin, and slightly concave from that point to origin of anteriormost dorsal procurrent caudal-fin ray. Ventral profile of head and body convex from tip of lower lip to pelvic-fin origin, straight to slightly concave between latter point to anal-fin origin, straight to slightly convex along anal-fin base, and slightly concave from that point to origin of anteriormost ventral procurrent caudal-fin ray.

TABLE 1 |
Morphometric data of Astyanax nobre. Range includes the holotype and 30 paratypes. SD = Standard deviation.

FIGURE 1 |
Holotype of Astyanax nobre, MZUSP 125905, 25.6 mm SL, Brazil, Mato Grosso State, Municipality of Nobres, rio Paraguai basin, upper rio Salobra drainage.

Upper and lower jaws equal lenght, mouth terminal. Upper lip slightly anteriorly positioned than lower lip in some specimens. Premaxillary teeth in two distinct rows. Outer row with 2(1), 3*(27), or 4(2) tricuspid teeth. Inner row with 5*(30) teeth with 7–9 cusps (Fig. 2). Posterior tip of maxilla at vertical through posterior half of second infraorbital. Maxilla with 1(4) or 2*(26) tri- to pentacuspid teeth. Dentary with 4*(30) larger penta- to heptacuspid teeth, followed by one small tricuspid tooth and a series of five to eight diminute conical teeth. Central median cusp in all teeth longer than lateral cusps. Branchiostegal rays four (3). First gill arch with two (3) gill rakers on hypobranchial, seven (1) or eight (2) rakers on ceratobranchial, one (3) raker on intermediate cartilage, and four (1) or five (2) rakers on epibranchial.

Lateral line straight to slightly curved ventrally, with total of 32(1), 33*(11), 34(12), 35(5), or 36(1) scales. Scales on lateral line series variably perforated. Five specimens with completely perforated lateral line, with 33*(4) or 34(1) perforated scales; 20 specimens with incomplete lateral line, with 31(4), 32(11), or 33(5) perforated scales followed by 1(5), 2(12), or 3(3) non-perforated ones, and five specimens with discontinuous lateral line, with perforated scales interspersed with non-perforated ones of variable pattern. Longitudinal scale rows between dorsal-fin origin and lateral line 5*(30). Longitudinal scale rows between lateral line and pelvic-fin origin 3*(30). Scales along middorsal line between posterior tip of supraoccipital process and dorsal-fin origin 9*(3), 10(21), or 11(6). Horizontal scale rows around caudal peduncle 14*(30). Base of anteriormost anal-fin rays covered by a series of 3 or 4 scales. Caudal fin not scaled.

Supraneurals five (3). Dorsal-fin rays ii*(30), 9*(29) or 8+i(1). First dorsal-fin pterygiophore inserted posterior to neural spine of nineth (3) vertebra. Base of last dorsal-fin ray at vertical through base of first branched anal-fin ray. Pectoral-fin rays i*(30), 9(2), 10*(20), or 11(8). Pelvic-fin rays i*(30), 7*(30). Adipose fin present. Analfin, with iv(2) or v(1) 18(4), 19*(16), 20(9), or 21(1) rays. First anal-fin pterygiophore inserted posterior to haemal spine of 16th(3) vertebra. Principal caudal-fin rays i,9,8,i*(30); caudal fin forked, lobes somewhat rounded and small, of similar size. Dorsal procurrent caudal-fin rays 11(1) or 12(2); ventral procurrent caudal-fin rays 9(1) or 10(2). Total vertebrae 34(3): precaudal vertebrae 15(2) or 16(1) and caudal vertebrae 18(1) or 19(2).

FIGURE 2 |
Lateral view of right side, premaxillary, maxillary, and dentary of Astyanax nobre, MZUSP 118302, paratype. Scale bar = 0.5 mm.

Coloration in alcohol. Overall ground coloration pale (Fig. 1). Some specimens retaining guanine on opercular and gular areas. Dorsal portion of head and body dark. Dark chromatophores concentrated at jaws and opercle. Dark chromatophores scattered at infraorbital series. Humeral blotch present. Humeral blotch roughly rectangular, vertically oriented, extending vertically five scale rows and encompassing two scales horizontally. Conspicuous dark midlateral stripe on body, extending from upper half of opercule to base of middle caudal-fin rays. Dark midlateral stripe expanded at caudal-peduncle region forming a roughly oval caudal-peduncle blotch ending onto base of middle caudal-fin rays. Scattered dark chromatophores above anal fin, especially along margins of myosepta. Abdominal region with sparse chromatophores. Dorsal-fin rays and anteriormost anal-fin rays with dark chromatophores along edge of lepidotrichias. Pectoral and pelvic fins and distal portion of dorsal and anal fins with sparse pigmentation on interadial membranes. Adipose fin with concentration of dark chromatophores in its proximal and middle portions, distal margin hyaline.

Coloration in life. Dorsal portion of body light tan, ventral portion with silvery hue (Figs. 34). Dorsal and middorsal area with dark pigmentation. Infraorbitals, preopercle, and opercle silvery. Jaws and gular area light yellow to silver. Dorsal portion of eye orange to red; ventral portion silvery. Greenish iridescent pigmentation bordering above and below the longitudinal dark stripe, less evident in region posterior to adipose fin. Paired fins hyaline. Adipose, base of dorsal and of caudal fin orange. Anal fin slightly orange anteriorly, posterior portion nearly hyaline.

Sexual dimorphism. Males with distal margin of anal fin nearly straight (Figs. 1, 3A, 4A) (vs. anal fin falcate in females, distal margin anteriorly concave, Figs. 3B, 4B). Dorsal and caudal fins shorter and rounder in males (Figs. 1, 3A, 4A) than females (Figs. 3B, 4B). Unpaired fins coloration more intense in males (Figs. 3A, 4A). No bony hooks were found.

FIGURE 3 |
Live coloration of Astyanax nobre, paratypes, MZUSP 118302: A. Male; B. Female. Specimens not measured. Photo by W. Ohara.

FIGURE 4 |
Underwater photographs of wild specimens of Astyanax nobre at its type locality Recanto Ecológico Lagoa Azul, Bom Jardim district, Municipality of Nobres, Mato Grosso State, rio Salobra drainage, rio Paraguai basin: A. Pair of males; B. Pair of females. Details about differences between sexes can be found in Sexual dimorphism section. Photo by M. Melo.

Geographical distribution.Astyanax nobre is so far known only from the rio Salobra, tributary of rio Cuiabá, rio Paraguai basin (Fig. 5).

Ecological notes.Astyanax nobre was collected in clear water river, with moderate water flow, over bottoms typically composed of rock and sand (Fig. 6). Vegetation includes areas with dense aquatic macrophytes and well preserved riparian forest. The species is one of the most abundant fish species in the locality. Individuals are very used to the human presence; frequently approaching the swimmers to nibble skin from the legs and arms.

Etymology. The specific name nobre refers to the municipality of Nobres (Mato Grosso State, Brazil) where the species occurs. Additionally, “nobre” means noble in Portuguese, in allusion to the beauty of the type locality and of being a noteworthy species of Astyanax. A noun in apposition.

Conservation status.Astyanax nobre is endemic to Brazil and is a restricted-range species. The new species is known by only the type locality, but its EOO (Extent of occurrence) is likely underestimated since the region is poorly sampled. The species is so far only known from a tourist site, but with apparently low environmental impact since only snorkeling is allowed. The headwaters of the rio Cuiabá are relatively well protected, with part of it inside of the Parque Estadual Águas do Cuiabá. Therefore, given that no significant threats were identified for this species, it is assessed as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019International Union for Conservation of Nature (IUCN). Standards and petitions committee. Guidelines for using the IUCN Red List categories and criteria. Version 14 [Internet]. Prepared by the Standards and Petitions Committee; 2019. Available from: https://www.iucnredlist.org/resources/redlistguidelines
https://www.iucnredlist.org/resources/re...
).

FIGURE 5 |
Distribution map of Astyanax nobre in the rio Salobra, upper rio Paraguai basin, Brazil. Brown star (type locality).

FIGURE 6 |
Type locality of Astyanax nobre, rio Salobra at Lago Azul, tributary of rio Cuiabá, rio Paraguai basin, 14º35’43.2”S 55º58’09.6”W, Nobres, Mato Grosso State, Brazil. Photo by M. A. Junghans.

DISCUSSION

Variation of lateral-line perforation and generic assignment of the new species. A recent cladistic study focused on the genus Astyanax was performed by Téran et al., (2020)Téran GE, Benites MF, Mirande JM. Opening the Trojan horse: phylogeny of Astyanax, two new genera and resurrection of Psalidodon (Teleostei: Characidae). Zool J Linn Soc. 2020; 109(4):1217–34. https://doi.org/10.1093/zoolinnean/zlaa019
https://doi.org/10.1093/zoolinnean/zlaa0...
using integrative phylogeny of molecular and morphological characters combined. The study efficiently corroborated the non-monophyletic nature of the genus, but failed in providing a reliable and consistent diagnosis for the proposed clades, making the taxonomic practice even more problematical.

In that paper, Astyanax, as traditionally defined, was recovered as a polyphyletic group, with some species more closely related to other genera (e.g., Deuterodon Eigenmann, 1907, Tetragonopterus Cuvier, 1816, Eretmobrycon Fink, 1976). Most species, although closely related, were divided into three large clades supported solely by molecular synapomorphies (e.g., Andromakhe Terán, Benitez & Mirande, 2020), or on highly homoplastic characters such as the presence of five or more cusps on teeth in the outer premaxillary row and in the maxilla (e.g., Psalidodon Eigenmann, 1911). The authors additionally presented a non-phylogenetic diagnosis for these genera, based on a combination of non-exclusive characters. However, the characters presented are, in practice, not useful for the distinction between Andromakhe, Astyanax, and Psalidodon since all have the same condition (e.g., rhinosphenoid lacking a dorsal expansion between olfactory nerves; presence of an anterior branch of the tubule for passage of blood vessels on lamellar portion of maxilla; naked caudal fin; presence of a complete lateral line; two series of teeth in the premaxilla, etc.). The only exception is the presence of circuli on posterior field of scales in Astyanax (vs. absent in Andromakhe and Psalidodon). Yet, it is a highly homoplastic character as authors themselves report its presence in species of Psalidodon. In view of that, and in the absence of molecular data for the new species, the new species is herein assigned in Astyanax.

The pre-cladistic concepts proposed by Eigenmann (1917Eigenmann CH. The American Characidae (Part 1). Mem Mus Comp Zool. 1917; 43:1–102., 1921Eigenmann CH. The American Characidae (Part 3). Mem Mus Comp Zool. 1921; 43:209–310.), based on a combination of characters, are still used to define many characids (i.e., Bryconamericus Eigenmann, 1907, Hemigrammus, Hyphessobrycon, Knodus Eigenmann, 1911, Moenkhausia). According to such classification, the only feature to distinguish Astyanax from Hyphessobrycon is the extension of the lateral-line perforation, which is completely pored in Astyanax vs. incompletely pored in Hyphessobrycon. The new species present a variable condition regarding lateral-line perforation. Of 30 examined specimens, only five have fully developed tubes in all scales of the lateral-line series. Most specimens analyzed (n = 20) has most lateral line scales perforated but not all (31 to 33 perforated scales plus 1 to 3 non-perforated scales at the end of the lateral-line series), and five specimens have discontinuous lateral line, i.e., perforated scales interspersed with non-perforated ones.

Intraspecific variation of lateral-line perforation was documented for several characids (see Dagosta et al., 2014Dagosta FCP, Marinho MMF, Camelier P. A new species of Hyphessobrycon Durbin (Characiformes: Characidae) from the middle rio São Francisco and upper and middle rio Tocantins basins, Brazil, with comments on its biogeographic history. Neotrop Ichthyol. 2014; 12(2):365–75. http://dx.doi.org/10.1590/1982-0224-20130179
http://dx.doi.org/10.1590/1982-0224-2013...
; Marinho et al., 2014Marinho MMF, Dagosta FCP, Birindelli JLO. Hemigrammus ataktos: a new species from the rio Tocantins basin, central Brazil (Characiformes: Characidae). Neotrop Ichthyol. 2014; 12(2):257–64. https://doi.org/10.1590/1982-0224-20130091
https://doi.org/10.1590/1982-0224-201300...
, 2021Marinho MMF, Ohara WM, Dagosta FCP. A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids. Neotrop Ichthyol. 2021; 19(2):e200118. https://doi.org/10.1590/1982-0224-2020-0118
https://doi.org/10.1590/1982-0224-2020-0...
), and its evolutionary significance in the family was discussed in Marinho et al., (2021)Marinho MMF, Ohara WM, Dagosta FCP. A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids. Neotrop Ichthyol. 2021; 19(2):e200118. https://doi.org/10.1590/1982-0224-2020-0118
https://doi.org/10.1590/1982-0224-2020-0...
. For more than a century after Eigenmann’s legacy, the generic allocation of new species in Characidae was indisputably based on his proposal. This scenario only began to change in the last decade with the implementation of cladistic analyses revaluating the traditional morphological characters in a phylogenetic framework.

Many characters once used to delimit genera are now hypothesized to have been independently acquired within the family. Interruption of lateral-line perforation is one of them (Mirande, 2010Mirande JM. Phylogeny of the Family Characidae (Teleostei: Characiformes): from characters to taxonomy. Neotrop Ichthyol. 2010; 8(3):385–568. https://doi.org/10.1590/S1679-62252010000300001
https://doi.org/10.1590/S1679-6225201000...
, 2019Mirande JM. Morphology, molecules and the phylogeny of Characidae (Teleostei, Characiformes). Cladistics. 2019; 35(3):282–300. https://doi.org/10.1111/cla.12345
https://doi.org/10.1111/cla.12345...
) and is probably related to the loss of terminal stages in the development, a common trend in the evolution of miniaturization process (Weitzman, Vari, 1988Weitzman SH, Vari RP. Miniaturization in South American freshwater fishes: An overview and discussion. Proc Biol Soc Wash. 1988; 101(2):444–65. Available from: https://repository.si.edu/handle/10088/901
https://repository.si.edu/handle/10088/9...
; Hanken, Wake, 1993Hanken J, Wake DB. Miniaturization of body size: organismal consequences and evolutionary significance. Annu Rev Ecol Syst. 1993; 24:501–19. https://doi.org/10.1146/annurev.es.24.110193.002441
https://doi.org/10.1146/annurev.es.24.11...
; Marinho, 2017Marinho MMF. Comparative development in Moenkhausia pittieri and Paracheirodon innesi (Ostariophysi: Characiformes) with comments on heterochrony and miniaturization in the Characidae. J Fish Biol. 2017; 91(3):851–65. https://doi.org/10.1111/jfb.13384
https://doi.org/10.1111/jfb.13384...
). Compared to other characids, A. nobre is a very small-sized species, of maximum known length of 30 mm SL. Dissection of four specimens confirmed maturation at 25 mm SL (MZUSP 118302), indicating that A. nobre may not grow much longer. Therefore, it is possible that such variation in the length perforation of lateral line may be related to the evolutionary reduction of body size in the species (see discussion in Marinho et al., 2021Marinho MMF, Ohara WM, Dagosta FCP. A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids. Neotrop Ichthyol. 2021; 19(2):e200118. https://doi.org/10.1590/1982-0224-2020-0118
https://doi.org/10.1590/1982-0224-2020-0...
).

The lateral line of A. nobre is mostly perforated along its extension (see Description), differing from the “typical” interrupted lateral line found in most species of Hemigrammus or Hyphessobrycon, in which only few scales are perforated. Therefore, the new species is provisionally assigned to Astyanax, aware that further phylogenetic studies need to be conducted for its proper allocation, along with studies on the evolution of miniaturization to evaluate questions related to the homology of lateral-line interruption.

Given the unsolved systematic situation of several genera of Characidae discussed above and the similarity of A. nobre with species of Hyphessobrycon, a brief diagnosis from all species of Hyphessobrycon is necessary. The new species can be distinguished from most species of Hyphessobrycon, except H. cachimbensis Travassos, 1964, H. fernandezi Fernández-Yépez, 1972, H. melanostichos Carvalho & Bertaco, 2006, H. nigricinctus Zarske & Géry, 2004, H. paucilepis García-Alzate, Román-Valencia & Taphorn, 2008, H. petricolus Ohara, Lima & Barros, 2017, H. piranga Camelier, Dagosta, Marinho & Oyakawa, 2018, H. psittacus Dagosta, Marinho, Camelier & Lima, 2016, H. scholzei Ahl, 1937, H. sovichthys Schultz, 1944, H. stegemanni Géry, 1961, H. taphorni García-Alzate, Román-Valencia & Ortega, 2013, H. tuyensis García-Alzate, Román-Valencia & Taphorn, 2008, and H. vilmae Géry, 1966, by the presence of a well-defined, relatively narrow dark midlateral stripe on body extending from opercle to base of middle caudal-fin rays (vs. absence of a well-defined longitudinal stripe, stripe starting approximately at vertical through the dorsal-fin origin, or midlateral dark stripe that becomes blurred towards the caudal peduncle). It differs from H. fernandezi, H. paucilepis, H. piranga, H. psittacus, H. sovichthys, H. scholzei, H. stegemanni, H. taphorni, H. tuyensis, and H. vilmae by the presence of a humeral blotch (vs. absence), from H. cachimbensis, H. cyanotaenia, and H. petricolus by having 14 horizontal scale rows around caudal peduncle (vs. 12) and by H. melanostichos and H. nigricinctus by the presence of 3 longitudinal scale rows between lateral line and pelvic-fin origin (vs. 4–5).

Patterns of dark midlateral stripe in Astyanax. The most remarkable morphological character of A. nobre is the presence of a conspicuous, straight, and relatively narrow dark midlateral stripe on body. Despite being a highly homoplastic feature found in phylogenetic distant groups of characids such as Astyanax (Oliveira et al., 2017Oliveira CAM, Pavanelli CS, Bertaco VA. A new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Araguaia, Central Brazil. Zootaxa. 2017; 4320(1):173–82. https://doi.org/10.11646/zootaxa.4320.1.10
https://doi.org/10.11646/zootaxa.4320.1....
), Caiapobrycon Malabarba & Vari, 2000 (Malabarba, Vari, 2000Malabarba LR, Vari RP. Caiapobrycon tucurui, a new genus and species of characid from the rio Tocantins basin, Brazil (Characiformes: Characidae). Ichthyol Explor Freshw. 2000; 11(4):315–26.), Creagrutus Günther, 1864 (Dagosta, Pastana, 2014Dagosta FCP, Pastana MNL. New species of Creagrutus Günther (Characiformes: Characidae) from rio Tapajós basin, Brazil, with comments on its phylogenetic position. Zootaxa. 2014; 3765(6):571–82. https://doi.org/10.11646/zootaxa.3765.6.5
https://doi.org/10.11646/zootaxa.3765.6....
), Erythrocharax Netto-Ferreira, Birindelli, Sousa, Mariguela & Oliveira, 2013 (Netto-Ferreira et al., 2013Netto-Ferreira AL, Birindelli JLO, Sousa LM, Mariguela TC, Oliveira C. A new miniature characid (Ostariophysi: Characiformes: Characidae), with phylogenetic position inferred from morphological and molecular data. PLoS ONE. 2013; 8(1):1–07. https://doi.org/10.1371/journal.pone.0052098
https://doi.org/10.1371/journal.pone.005...
), Hemigrammus (Marinho et al., 2014Marinho MMF, Dagosta FCP, Birindelli JLO. Hemigrammus ataktos: a new species from the rio Tocantins basin, central Brazil (Characiformes: Characidae). Neotrop Ichthyol. 2014; 12(2):257–64. https://doi.org/10.1590/1982-0224-20130091
https://doi.org/10.1590/1982-0224-201300...
), Hyphessobrycon (Camelier et al., 2018Camelier P, Dagosta FCP, Marinho MMF. New remarkable sexually dimorphic miniature species of Hyphessobrycon (Characiformes: Characidae) from the upper Rio Tapajós basin. J Fish Biol. 2018; 92(4):1149–62. https://doi.org/10.1111/jfb.13579
https://doi.org/10.1111/jfb.13579...
), Moenkhausia (Petrolli et al., 2016Petrolli MG, Azevedo-Santos VM, Benine RC. Moenkhausia venerei (Characiformes: Characidae), a new species from the rio Araguaia, central Brazil. Zootaxa. 2016; 4105(2):159–70. https://doi.org/10.11646/zootaxa.4105.2.4
https://doi.org/10.11646/zootaxa.4105.2....
), Serrapinnus Malabarba, 1998 (Jerep et al., 2018Jerep FC, Dagosta FCP, Ohara WM. A new miniature species of Serrapinnus (Characiformes: Characidae) from the upper Rio Araguaia, Brazil. Copeia. 2018; 106(1):180–87. https://doi.org/10.1643/CI-17-653
https://doi.org/10.1643/CI-17-653...
), Thayeria Eigenmann, 1908 (Moreira, Lima, 2017Moreira CR, Lima FCT. Thayeria tapajonica (Characiformes: Characidae), a new species from rio Tapajós basin, Brazil. Zootaxa. 2017; 4344(1):137–46. https://doi.org/10.11646/zootaxa.4344.1.5
https://doi.org/10.11646/zootaxa.4344.1....
), Varicharax Vanegas-Ríos, Faustino-Fuster, Meza-Vargas & Ortega, 2020 (Vanegas-Ríos et al., 2020Vanegas-Ríos JA, Faustino-Fuster DR, Meza-Vargas V, Ortega H. Phylogenetic relationships of a new genus and species of stevardiine fish (Characiformes: Characidae: Stevardiinae) from the Río Amazonas basin, Peru. J Zool Syst Evol Res. 2020; 58(1):387–407. https://doi.org/10.1111/jzs.12346
https://doi.org/10.1111/jzs.12346...
), it is taxonomically informative when details of the pigmentation pattern are considered. Species of Astyanax with a dark-stripe differ from the condition found in A. nobre mainly concerning the starting and the ending point of the stripe.

Without implying homologies, four different types of dark midlateral stripes can be recognized in Astyanax: 1) stripe of variously shapes and pigmentation, starting posterior to the anterior humeral blotch and never connected to it (Fig. 7A; e.g., A. bagual Bertaco & Vigo, 2015, A. eremus Ingenito & Duboc, 2014); 2) stripe starting immediately posterior to the humeral blotch and usually ending at the tip of middle caudal-fin rays (Fig. 7B; e.g., species typically assigned to the Astyanax bimaculatus-group such as A. argyrimarginatus Garutti, 1999, A. clavitaeniatus Garutti, 2003, A. novae Eigenmann, 1911, A. saltor Travassos, 1960, A. unitaeniatus Garutti, 1998, and A. utiariti Bertaco & Garutti, 2007); 3) narrower stripe starting at posterior margin of the opercle, becoming blurred posteriorly and not reaching the caudal fin (Fig. 7C; e.g., Astyanax myersi (Fernández-Yépez, 1950), Jupiaba anterior (Eigenmann, 1908), and J. ajuricaba (Marinho & Lima, 2009)); 4) stripe starting immediately posterior to the opercle (Fig. 7D; e.g., A. joaovitori and A. scintillans).

Among all species of Astyanax, the stripe of A. nobre is more similar to that of A. joaovitori and A. scintillans. The former is discussed in details in the diagnose section. The latter was described by Myers, (1928)Myers GS. 1928. New fresh-water fishes from Peru, Venezuela, and Brazil. Ann Mag Nat Hist. 1928; 2(7):83–90., without illustrations – a usual practice of the author – and, up to date, it is a poorly known species, only known by the type-material, in which the dark pigmentation is today completely faded. Therefore, similarities between the stripe of A. scintillans and that of A. nobre are only based on the textual description of the original description: “there is a darker, wide, plumbeous lateral bland, from upper end of gill-slit to caudal base…” (Myers, 1928Myers GS. 1928. New fresh-water fishes from Peru, Venezuela, and Brazil. Ann Mag Nat Hist. 1928; 2(7):83–90.:29). Nonetheless, following words in the same sentence leaves no doubt that it is distinct from A. nobre: “…but no humeral or caudal spots are discernible” (Myers, 1928Myers GS. 1928. New fresh-water fishes from Peru, Venezuela, and Brazil. Ann Mag Nat Hist. 1928; 2(7):83–90.:29).

FIGURE 7 |
Different types of dark midlateral stripes in Astyanax: A. Stripe of variously shapes and pigmentation starting posterior to the humeral blotch and never connected to it (e.g., A. bagual and A. eremus); B. Stripe starting immediately posterior to the humeral blotch and usually ending at the tip of middle caudal-fin rays (e.g., species typically assigned to the Astyanax bimaculatus-group); C. Narrower stripe starting at posterior margin of the opercle, becoming blurred posteriorly and not reaching the caudal fin (e.g., Jupiaba anterior and J. ajuricaba); D. Stripe starting immediately posterior to the opercle (e.g., A. joaovitori and A. scintillans). See discussion for further details. Fish layout modified from Van der Sleen, Albert (2018)Van der Sleen P, Albert JS, editors. Field Guide to the fishes of the Amazon, Orinoco & Guianas. Princeton: Princeton University Press; 2018..

The megadiverse but still poorly known Brazilian freshwater ichthyofauna. The region where the new species was collected is relatively near to the municipality of Cuiabá, Mato Grosso State, a large urban area in Central Brazil. This discovery, in proximity of a large urban center that have been repeatedly explored for fish diversity, further underscores the fact that major elements of tropical biodiversity remain unknown. The region surrounding Cuiabá, mainly to the North, has attracted attention of ichthyologists in recent years where many species have been recently described. Most species are restricted to the headwaters of the Cuiabá and Sepotuba rivers, both tributaries of the Paraguai River, such as the following examples Astyanax dolinae da Graça, Oliveira, Lima, da Silva & Fernandes, 2017 (da Graça et al., 2017da Graça WJ, Oliveira CAM, Lima FCT, da Silva HP, Fernandes IM. A new species of Astyanax (Characiformes: Characidae) from Dolina Água Milagrosa, Rio Paraguai basin, Mato Grosso, Brazil. J Fish Biol. 2017; 91(4):1123–38. https://doi.org/10.1111/jfb.13405
https://doi.org/10.1111/jfb.13405...
), A. pirapuan Tagliacollo, Britzke, Silva & Benine, 2011 (Tagliacollo et al., 2011Tagliacollo VA, Britzke R, Silva GSC, Benine RC. Astyanax pirapuan: a new characid species from the upper Rio Paraguay system, Mato Grosso, central Brazil (Characiformes, Characidae). Zootaxa. 2011; 2749(1):40–46. https://doi.org/10.11646/zootaxa.2749.1.3
https://doi.org/10.11646/zootaxa.2749.1....
), Characidium nupelia da Graça, Pavanelli & Buckup, 2008 (da Graça et al., 2008da Graça WJ, Pavanelli CS, Buckup PA. Two new species of Characidium (Characiformes: Crenuchidae) from Paraguay and Xingu basins, state of Mato Grosso, Brazil. Copeia. 2008; 2008(2):326–32. https://doi.org/10.1643/CI-06-167
https://doi.org/10.1643/CI-06-167...
), Crenicichla ploegi Varella, Loeb, Lima & Kullander, 2018 (also in the rio Juruena basin) (Varella et al., 2018Varella HR, Loeb M, Lima FCT, Kullander SO. Crenicichla ploegi, a new species of pike–cichlid of the C. saxatilis group from the Rio Juruena and upper Rio Paraguai basins in Brazil, with an updated diagnosis and biogeographical comments on the group (Teleostei: Cichlidae). Zootaxa. 2018; 4377(3):361–86. https://doi.org/10.11646/zootaxa.4377.3.3
https://doi.org/10.11646/zootaxa.4377.3....
), Curculionichthys coxipone Roxo, Silva, Ochoa & Oliveira, 2015 (Roxo et al., 2015Roxo FF, Silva GS, Ochoa LE, Oliveira C. Description of a new genus and three new species of Otothyrinae (Siluriformes, Loricariidae). ZooKeys. 2015; 534:103–34. http://doi.org/10.3897/zookeys.534.6169
http://doi.org/10.3897/zookeys.534.6169...
), Curculionichthys paresi (Roxo, Zawadzki & Troy, 2014) (Roxo et al., 2014Roxo FF, Zawadzki CH, Troy WP. Description of two new species of Hisonotus Eigenmann & Eigenmann, 1889 (Ostariophysi, Loricariidae) from the rio Paraná–Paraguay basin, Brazil. ZooKeys. 2014; 395:57–78. http://doi.org/10.3897/zookeys.395.6910
http://doi.org/10.3897/zookeys.395.6910...
), Gephyrocharax machadoi Ferreira, Faria, Ribeiro, Santana, Quagio-Grassioto & Menezes, 2018 (Ferreira et al., 2018Ferreira KM, de Faria É, Ribeiro AC, Santana JCO, Quagio–Grassioto I, Menezes NA. Gephyrocharax machadoi, a new species of Stevardiinae (Characiformes: Characidae) from the Rio Paraguai basin, central Brazil. Zootaxa. 2018; 4415(1):161–72. https://doi.org/10.11646/zootaxa.4415.1.8
https://doi.org/10.11646/zootaxa.4415.1....
), Hyphessobrycon rutiliflavidus Carvalho, Langeani, Miyazawa & Troy, 2008 (Carvalho et al., 2008Carvalho FR, Langeani F, Miyazawa CS, Troy WP. Hyphessobrycon rutiliflavidus n. sp., a new characid fish from the upper rio Paraguai, State of Mato Grosso, Brazil (Characiformes: Characidae). Zootaxa. 2008; 1674(1):39–49. https://doi.org/10.11646/zootaxa.1674.1.3
https://doi.org/10.11646/zootaxa.1674.1....
), Hypostomus renestoi Zawadzki, da Silva & Troy, 2018 (Zawadzki et al., 2018Zawadzki CH, da Silva HP, Troy WP. Redescription of Hypostomus latirostris (Regan, 1904) with the recognition of a new species of Hypostomus (Siluriformes: Loricariidae) from the upper rio Paraguay basin, Brazil. Ichthyol Explor Freshw. 2018; 28(3):253–70. https://doi.org/10.23788/IEF-1079
https://doi.org/10.23788/IEF-1079...
), Knodus geryi Lima, Britski & Machado, 2004 (Lima et al., 2004Lima FCT, Britski HA, Machado FA. New Knodus (Ostariophysi: Characiformes: Characidae) from the upper Rio Paraguay basin, Brazil. Copeia. 2004; 2004(3):577–82. http://doi.org/10.1643/CI-03-297R1
http://doi.org/10.1643/CI-03-297R1...
), and Moenkhausia flava Britzke, Troy, Oliveira & Benine, 2018 (Britzke et al., 2018Britzke R, Troy WP, Oliveira C, Benine RC. Description of a new species of Moenkhausia (Characiformes: Characidae) from the upper Paraguay basin, Central Brazil, with comments on its phylogenetic relationships. Neotrop Ichthyol. 2018; 16(2):1–11. https://doi.org/10.1590/1982-0224-20170086
https://doi.org/10.1590/1982-0224-201700...
).

Even more remarkable is the fact that Astyanax nobre was discovery at an underwater tourist point, which means that even species daily observed by hundreds of people in limpid waters can lack a formal taxonomic identity. Interestingly, the case of A. nobre is not exclusive. Several freshwater fish species from popular underwater tourist points in Brazil were described in the last decades (e.g., Astyanax brucutu Zanata, Lima, Di Dario & Gerhard, 2017 (Zanata et al., 2017Zanata AM, Lima FCT, Di Dario F, Gerhard P. A new remarkable and critically endangered species of Astyanax Baird & Girard (Characiformes: Characidae) from Chapada Diamantina, Bahia, Brazil, with a discussion on durophagy in the characiformes. Zootaxa. 2017; 4232(4):491–510. https://doi.org/10.11646/zootaxa.4232.4.2
https://doi.org/10.11646/zootaxa.4232.4....
), Characidium deludens Zanata & Camelier, 2015 (Zanata, Camelier, 2015Zanata AM, Camelier P. Two new species of Characidium Reinhardt (Characiformes: Crenuchidae) from northeastern Brazilian coastal drainages. Neotrop Ichthyol. 2015; 13(3):487–98. https://doi.org/10.1590/1982-0224-20140106
https://doi.org/10.1590/1982-0224-201401...
), Hyphessobrycon negodagua Lima & Gerhard, 2001 (Lima, Gerhard, 2001Lima FCT, Gerhard P. A new Hyphessobrycon (Characiformes: Characidae) from Chapada Diamantina, Bahia, Brazil, with notes on its natural history. Ichthyol Explor Freshw. 2001; 12(2):105–14.), Hypostomus jaguar Zanata, Sardeiro & Zawadzki, 2013 (Zanata et al., 2013Zanata AM, Sardeiro B, Zawadzki CH. A new dark–dotted species of Hypostomus Lacépède (Siluriformes: Loricaridae) from rio Paraguaçu, Bahia State, Brazil. Neotrop Ichthyol. 2013; 11(2):247–56. https://doi.org/10.1590/S1679-62252013000200002
https://doi.org/10.1590/S1679-6225201300...
), Kolpotocheirodon figueiredoi Malabarba, Lima & Weitzman, 2004 (Malabarba et al., 2004Malabarba LR, Lima FCT, Weitzman SH. A new species of Kolpotocheirodon (Teleostei: Characidae: Cheirodontinae: Compsurini) from Bahia, northeastern Brazil, with a new diagnosis of the genus. Proc Biol Soc Wash. 2004; 117(3):317–29.), Lepidocharax diamantina Ferreira, Menezes & Quagio-Grassiotto, 2011 in the rio Pratinha, Bahia State (Ferreira et al., 2011Ferreira KM, Menezes NA, Quagio–Grassiotto I. A new genus and two new species of Stevardiinae (Characiformes: Characidae) with a hypothesis on their relationships based on morphological and histological data. Neotrop Ichthyol. 2011; 9(2):281–98. https://doi.org/10.1590/S1679-62252011000200005
https://doi.org/10.1590/S1679-6225201100...
; Vita et al., 2020Vita GP, Camelier P, Zanata AM. Ichthyofauna of the remarkably crystalline rio Pratinha, upper rio Paraguaçu basin, Chapada Diamantina, Brazil: inventory and conservation status. Stud Neotrop Fauna Environ. 2020; 56(2):124–34. https://doi.org/10.1080/01650521.2020.1758601
https://doi.org/10.1080/01650521.2020.17...
); A. dolinae in Dolina Água Milagrosa, Mato Grosso State (da Graça et al., 2017da Graça WJ, Oliveira CAM, Lima FCT, da Silva HP, Fernandes IM. A new species of Astyanax (Characiformes: Characidae) from Dolina Água Milagrosa, Rio Paraguai basin, Mato Grosso, Brazil. J Fish Biol. 2017; 91(4):1123–38. https://doi.org/10.1111/jfb.13405
https://doi.org/10.1111/jfb.13405...
); Ancistrus formoso Sabino & Trajano, 1997 (Sabino, Trajano, 1997Sabino J, Trajano E. A new species of blind armoured catfish, genus Ancistrus, from caves of Bodoquena region, Mato Grosso do Sul, southwestern Brazil (Siluriformes, Loricariidae, Ancistrinae). Rev Fr Aquariol. 1997; 24(3–4):73–78. ), Hypostomus basilisko Tencatt, Zawadzki & Froehlich, 2014 (Tencatt et al., 2014Tencatt LFC, Zawadzki CH, Froehlich O. Two new species of the Hypostomus cochliodon group (Siluriformes: Loricariidae) from the rio Paraguay basin, with a redescription of Hypostomus cochliodon Kner, 1854. Neotrop Ichthyol. 2014; 12(3):585–602. https://doi.org/10.1590/1982-0224-20130162
https://doi.org/10.1590/1982-0224-201301...
), H. froehlichi Zawadzki, Nardi & Tencatt, 2021 (Zawadzki et al., 2021Zawadzki CH, Nardi G, Tencatt LFC. The crystalline waters of the Bodoquena Plateau revealed Hypostomus froehlichi (Siluriformes: Loricariidae), a new armored catfish from the rio Paraguay basin in Brazil. Zootaxa. 2021; 4933(1):98–112. https://doi.org/10.11646/zootaxa.4933.1.4
https://doi.org/10.11646/zootaxa.4933.1....
), Moenkhausia bonita Benine, Castro & Sabino, 2004 (Benine et al., 2004Benine RC, Castro RMC, Sabino J. Moenkhausia bonita: a new small characin fish from the Rio Paraguay basin, southwestern Brazil (Characiformes: Characidae). Copeia. 2004; 2004(1):68–73. https://doi.org/10.1643/CI-03-008R1
https://doi.org/10.1643/CI-03-008R1...
) in Serra da Bodoquena, Mato Grosso do Sul State). If fish diversity that is daily observed is barely known, what can be predicted for the ichthyofauna that inhabits turbid water rivers, or even deep channel of rivers? Definitely, there are many more species waiting to be described.

These perceptions agree with the suspicious that the number of South American species is, in fact, much greater than we know today (Reis et al., 2016Reis RE, Albert JS, Di Dario F, Mincarone MM, P Petry, Rocha LA. Fish biodiversity and conservation in South America. J Fish Biol. 2016; 89(1):12–47. https://doi.org/10.1111/jfb.13016
https://doi.org/10.1111/jfb.13016...
). Unfortunately, such incipient knowledge has disastrous consequences for the conservation of aquatic diversity. As highlighted by Heilpern (2015)Heilpern S. Biodiversity: Include freshwater species. Nature. 2015; 518:167. https://doi.org/10.1038/518167d
https://doi.org/10.1038/518167d...
, freshwater biotas remain too poorly known to be integrated into conservation strategies based on terrestrial environments, despite their intrinsic importance and urgent need for protection (Amis et al., 2009Amis MA, Rouget M, Lotter M, Day J. Integrating freshwater and terrestrial priorities in conservation planning. Biol Conserv. 2009; 142(10):2217–26. https://doi.org/10.1016/j.biocon.2009.04.021
https://doi.org/10.1016/j.biocon.2009.04...
; Strayer, Dudgeon, 2010Strayer DL, Dudgeon D. Freshwater biodiversity conservation: Recent progress and future challenges. Freshw Sci. 2010; 29(1):344–58. https://doi.org/10.1899/08-171.1
https://doi.org/10.1899/08-171.1...
; Dagosta et al., 2020Dagosta FCP, de Pinna M, Peres CA, Tagliacollo VA. Existing protected areas provide a poor safetynet for threatened Amazonian fish species. Aquatic Conserv: Mar Freshw Ecosyst. 2020; 31(5):1167–89. https://doi.org/10.1002/aqc.3461
https://doi.org/10.1002/aqc.3461...
). The global-scale extinction crisis, with the current alarming rate of biodiversity loss, requires the selection of taxa to concentrate limited resources on regions of highest conservation value and with the most pressing need for conservation plans (Vane-Wright et al., 1991Vane-Wright RI, Humphries CJ, Williams PH. What to protect? – Systematics and the agony of choice. Biol Conserv. 1991; 55(3):235–54. https://doi.org/10.1016/0006-3207(91)90030-D
https://doi.org/10.1016/0006-3207(91)900...
; Margules, Pressey, 2000Margules CR, Pressey RL. Systematic conservation planning. Nature. 2000; 405:243–53. https://doi.org/10.1038/35012251
https://doi.org/10.1038/35012251...
; Myers, et al., 2000Myers N, Mittermeier RA, Mittermeier CG, da Fonseca GAB, Kent J. Biodiversity hotspots for conservation priorities. Nature. 2000; 403:853–58. https://doi.org/10.1038/35002501
https://doi.org/10.1038/35002501...
; Brooks et al., 2006Brooks TM, Mittermeier RA, da Fonseca GAB, Gerlach J, Hoffmann M, Lamoreux JF et al. Global biodiversity conservation priorities. Science. 2006; 313(5783):58–61. https://doi.org/10.1126/science.1127609
https://doi.org/10.1126/science.1127609...
; Kier et al., 2009Kier G, Kreft H, Lee TM, Jetz W, Ibisch PL, Nowicki C et al. A global assessment of endemism and species richness across island and mainland regions. Proc Natl Acad Sci USA. 2009; 106(23):9322–27. https://doi.org/10.1073/pnas.0810306106
https://doi.org/10.1073/pnas.0810306106...
). Therefore, the Brazilian freshwater ichthyofauna needs to be described as quickly as possible so that its elements may have a chance to have their conservation picture evaluated. For this, it is crucial that Brazil supports more taxonomy research and especially the training of new taxonomists to value its greatest wealth: its biodiversity.

Comparative material examined.Astyanax ajuricaba: MZUSP 18277, holotype, 65.5 mm SL, rio Negro basin, Brazil. Astyanax scintillans: CAS 39493, 2 syntypes, 27.3–29.2 mm SL, Playa Matepalma, rio Orinoco, Venezuela. Jupiaba anterior: MZUSP 18277 (53, 62.1–111.3 mm SL), rio Tapajós, Brazil. Species of Hyphessobrycon examined listed at Dagosta et al. (2016)Dagosta FCP, Marinho MMF, Camelier P, Lima FCT. A new species of Hyphessobrycon (Characiformes: Characidae) from the upper Rio Juruena basin, Central Brazil, with a redescription of H. cyanotaenia. Copeia. 2016; 104(1):250–59. https://doi.org/10.1643/CI-15-243
https://doi.org/10.1643/CI-15-243...
.

ACKNOWLEDGEMENTS

We thank Willian M. Ohara (MZUSP) for providing Fig. 3 and helping in the fieldwork. We are grateful to Marcelo Melo and Marcos A. Junghans for providing Figs. 4 and 6, respectively, and Michel Gianetti and Karolina Reis (MZUSP) for curatorial assistance. Marcelo Melo (USP) and Vinicius A. Bertaco (MCN) provided valuable commentaries that improved the manuscript. Authors also thank Anderson Ferreira and Thomaz J. Seren (UFGD) for helping in lab activities. Most specimens were collected during an expedition funded by the South American Characiformes Inventory (FAPESP 2011/50282–7). The authors were funded by FAPESP (grant # 2016/19075–9; MMFM: grant # 2017/09321–5; and by CNPq (FCPD: grant # 405643/2018–7).

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ADDITIONAL NOTES

  • HOW TO CITE THIS ARTICLE

    Dagosta FCP, Marinho MMF. New small-sized species of Astyanax (Characiformes: Characidae) from the upper rio Paraguai basin, Brazil, with discussion on its generic allocation. Neotrop Ichthyol. 2022; 20(1):e210127. https://doi.org/10.1590/1982-0224-2021-0127

Edited-by

Marcelo Melo

Publication Dates

  • Publication in this collection
    21 Mar 2022
  • Date of issue
    2022

History

  • Received
    9 Aug 2021
  • Accepted
    30 Nov 2021
Sociedade Brasileira de Ictiologia Neotropical Ichthyology, Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura, Universidade Estadual de Maringá., Av. Colombo, 5790, 87020-900, Phone number: +55 44-3011-4632 - Maringá - PR - Brazil
E-mail: neoichth@nupelia.uem.br