Corydoras tukano , a new species of corydoradine catfish from the rio Tiquié , upper rio Negro basin , Brazil ( Ostariophysi : Siluriformes : Callichthyidae )

83 * Departamento de Vertebrados, Museu Nacional da Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, 20940-040 Rio de Janeiro, RJ, Brazil. e-mail: mrbritto2002@yahoo.com.br ** Museu de Zoologia da Universidade de São Paulo, Caixa Postal 42594, 04299-970 São Paulo, SP, Brazil. e-mail: fctlima@usp.br Corydoras tukano, a new species of corydoradine catfish from the rio Tiquié, upper rio Negro basin, Brazil (Ostariophysi: Siluriformes: Callichthyidae)


Introduction
Corydoras Lacepède is one of the most speciose catfish genera, currently comprising 176 nominal species, of which 143 species are presently considered valid (Reis, 2003).The genus is widely distributed in Cis-andean South America, occurring in a variety of habitats, such as shallow, marginal areas of rivers and associated flooded areas, and smaller streams.Despite several significant contributions during the course of the extensive taxonomic history of Corydoras (e.g.Gosline, 1940;Nijssen, 1970;Nijssen & Isbrücker, 1980, 1983a, 1986), and recent attempts to define its limits (Reis, 1998;Britto & Castro, 2002), the status of most species as well as their phylogenetic relationships are still poorly understood.
between the material collected in the rio Tiquié and paratypes of Corydoras reynoldsi revealed that it is, in fact, a distinct species, that is described below.

Material and Methods
Morphometric and meristic data were taken following Reis (1997).Length of the ossified portion of pectoral spine was measured from the spine-pectoral girdle articulation to distal tip of spine.Length of the soft portion of the dorsal fin was taken from the dorsal spine base to the fin distalmost tip.Measurements were obtained with 0.1 mm precision calipers.Teeth and vertebral counts were taken only from clearedand-stained (cs) specimens, prepared according to Taylor & Van Dyke (1985).Vertebral counts include only free centra, with the compound caudal centra (preural 1 + ural 1) counted as a single element.In the description, numbers assigned with an asterisk represent counts from the holotype.Nomenclature of latero-sensory canals follows Schaefer & Aquino (2000), and that of preopercular pores follows Schaefer (1988).Osteological terminology follows Reis (1998), except by "parieto-supraoccipital" instead of "supraoccipital" (Arratia & Gayet, 1995), "compound pterotic" instead of "pteroticsupracleithrum" (Aquino & Schaefer, 2002), and "scapulocoracoid" instead of "coracoid" (Lundberg, 1970).In the present study, the term "maxillary barbel" (previously named "upper maxillary barbel" or "dorsal maxillary barbel"; e.g.Britto et al., 2002) refers only to the sensorial structure with its core linked to the maxilla.The so-called "ventral maxillary barbel" or "rictal barbel" has its core extended to the dentary symphysis, corresponding, in fact, to a modified mental barbel (Baskin, 1973;de Pinna, 1998).Thus, this structure is named herein as "outer mental barbel", differing from the inner one.The term "Corydoras" refers to those species closer to Aspidoras than to Brochis, as briefly explained in Britto & Castro (2002)
Description.Morphometric data presented in Table 1.Head compressed with slightly convex dorsal profile; roughly triangular in dorsal view (Fig. 4).Snout rounded.Head profile convex from upper lip to horizontal through the anterior nares; slightly convex from that point to tip of parieto-supraoccipital expansion.Dorsal profile of body slightly convex from tip of parieto-supraoccipital expansion to last dorsal-fin ray.Postdorsal-fin body profile slightly concave to adipose-fin spine; markedly concave from this point to caudal-fin base.Ventral profile of body slightly convex from isthmus to analfin origin.Profile markedly concave from first anal-fin ray to caudal-fin base.Body roughly cylindrical in cross section at pectoral girdle, gradually becoming more compressed toward caudal fin.
Nasal, frontal, sphenotic, compound pterotic, and parietosupraoccipital visible externally, all covered by thin layer of skin and bearing minute scattered odontodes.Frontal fontanel elongate, ellipsoid, covered by thin layer of skin; posterior tip extending into parieto-supraoccipital.Nasal slender, slightly curved laterally, mesial border contacting frontal.Frontal quadrangular; anterior expansion in contact with nasal bone, posterior portion contacting sphenotic and parietosupraoccipital.Sphenotic trapezoid in shape, contacting parieto-supraoccipital dorsally, compound pterotic posteriorly, second infraorbital ventrally.Compound pterotic roughly pipe-shaped, with slender posterior expansion contacting first dorsal body plate and first lateral-line ossicle.Contact region between compound pterotic and first dorsal body plate covered by area of thick skin.Ventral margin of compound pterotic contacting infraorbital 2 and cleithrum.Parietosupraoccipital quadrangular with posterior expansion notched at its tip, sutured with nuchal plate.
Two infraorbital bones, externally visible, covered by thin layer of skin.First infraorbital with slender anterior expansion.Minute odontodes-bearing platelets anterodorsally on orbit (Fig. 5).Presence of small, narrow, roughly triangular platelet between eye and anterior expansion of first infraorbital (Fig. 5).Opercle exposed, compact in shape, with angular free border.Preopercle externally visible, slender and covered by thin layer of skin.Interopercle triangular, covered by thin layer of skin.
Trunk lateral line with two laterosensory canals, reduced to small ossicles.Lateral-line canal entering neurocranium through compound pterotic, splitting into two branches before entering sphenotic: pterotic and preoperculomandibular, each with single pore.Sensory canal continuing through compound pterotic, entering sphenotic as temporal canal, which splits into two branches: one branch giving rise to infraorbital canal, other branch entering frontal through supraorbital canal.Supraorbital canal with two branches: epiphyseal, opening in frontal bone, and anterior, running through nasal bone.Nasal canal with single opening at each end.Infraorbital canal running through entire second infraorbital, extending to infraorbital 1 and opening into two pores.Preoperculomandibular branch giving rise to preoperculomandibular canal, which runs through entire preopercle with three openings, leading to pores 3, 4, and 5, respectively.
Body plates with minute odontodes restricted to posterior margins.Nuchal plate exposed.Cleithrum and mesial process of scapulocoracoid exposed.Minute odontodes scattered over area between scapulocoracoids.Body plates not touching counterparts in specimens up to 28.2 mm SL, leaving narrow naked area on medial dorsal and ventral surfaces.3 and "Sexual dimorphism", below).Dorsal-fin rays I,7 in all specimens examined.Adipose fin roughly triangular; its origin separated from base of last dorsal-fin ray by 7-9 dorsolateral body plates.Anal fin roughly triangular; its origin located just posterior to 13th to14th ventrolateral body plates, at vertical through anterior margin of adipose-fin spine.Analfin rays ii,5 in all specimens.Pectoral fin triangular; its origin located just posterior to gill opening.Ossified portion of pectoral spine shorter than first branched rays.Distal tip of spine with minute-segmented unossified portion.Pectoral spine with well-developed serrations along entire posterior border.Pectoral-fin rays I,8, one specimen with I,7.Pelvic fin ellipsoid; its origin just below second ventrolateral body plate, at vertical through base of second branched dorsal-fin ray.Pelvic-fin rays i,5.Caudal fin bilobed; upper lobe slightly longer.Principal caudal-fin rays i,6/6,i, one specimen i,7/6,i; upper procurrent caudal-fin rays iii; lower procurrent caudalfin rays iii.All fins with minute odontodes scattered over all rays.
Color in alcohol.Ground coloration of head gray to brown, light ventrally.Wide, slightly oblique dark vertical blotch ("mask") from top of head throughout anterior and posterior margins of eye to lower anterior opercle corner.Dark v-shaped stripe between nares, with angle directed anteriorly.Barbels cream.Opercle and preopercle with narrow, dark, oblique, vertically-elongated blotch, formed by relatively large chromatophores.
Ground color of trunk cream to light brown.Nuchal plate gray to dark brown.Large, roughly rectangular, dorsolateral dark blotch ("first trunk blotch") extending dorsally from posterior margin of second plate to fifth-eighth dorsal plate, and ventrally from posterior margin of cleithrum to fifth ventral plate.Dark blotch on dorsal portion of dorsolateral plates, just posterior to last dorsal-fin ray, extending from 9th to 13th plate; in some specimens connected to large, anterior dorsolateral blotch.Second large, roughly rectangular, dorsolateral dark blotch ("second trunk blotch") below adipose fin, extending vertically from adipose-to anal-fin base.Scattered chromatophores on margins of plates, close to midline, between the two large dorsolateral blotches.Caudal fin with four vertical, narrow dark stripes.Dorsal-and pectoral-fin spines gray; remaining rays and membrane of both fins unpigmented.Base of anterior anal-fin rays dark, remaining rays and membrane unpigmented.
Sexual dimorphism.We have not dissected any specimens to confirm their sex, but aquarists who have bred the species in captivity (e.g.James, 2003a, b) mentioned that specimens with elongated dorsal fins are mature males.Presumably mature males examined (MZUSP 64096, 1 of 4; MZUSP 81179, 2) possess the soft portion of the dorsal spine, and the first two dorsal-fin branched rays very elongate.The first branched ray is the longest, followed by the soft portion of the dorsal spine.This results in an anteriorly elongated dorsal fin (see Fig. 3; Table 1).See the "Discussion", for comparisons with another Corydoras that possess elongated dorsal fins.

Popular name. "Waipotá" (both in Tukano and Tuyuka languages).
Habitat and ecological notes.The rio Tiquié, type-locality of C. tukano, is a blackwater river.At the exact type locality the bottom is sandy, with a moderate amount of vegetal debris.Corydoras tukano also was collected at sites with predominantly clay substrates.James (2003a,b) related that in captivity specimens of this species (identified by him as Corydoras sp.cf.reynoldsi) lay several scattered clutches of large eggs (2.2 mm in size).See also "Discussion", below.
Distribution.Known only from the rio Tiquié and its tributaries, as the igarapé Cabari.Rio Tiquié is a tributary of the rio Uaupés, in the upper rio Negro basin, Amazonas, Brazil, near the Brazilian/Colombian border (Fig. 6).Most of the specimens studied were collected in the upper rio Tiquié, in the area between Pari-Cachoeira (0°15'N, 69°46'W) and Caruru (0°16'N, 69°54'W).One sample (MZUSP 65689) was collected near Cunuri (0°12'N, 69°22'W), a downstream locality not intensively sampled by the second author or associates.According to Tukano and Tuyuka fishermen, Corydoras tukano occurs thorough the rio Tiquié basin, from its lower course upstream to Caruru, where a major waterfall about 8 m high, the Cachoeira do Caruru, effectively separates the downstream ichthyofauna from the upper section of this river.Again according to Tukano and Tuyuka fishermen, C. tukano is absent upstream of this waterfall.In fact, despite considerable time and effort spent in apparently suitable sites, the second author was unable to collect any C. tukano upstream of the Cachoeira do Caruru.
Etymology.After the Tukano, an Amerindian group from the upper rio Negro and Japurá/Caquetá basins in Brazil, Colombia, and Venezuela.Main cultural features displayed by this ethnic group are the Tukanoan language, the patrilineal clans system, and a diet having as staple foods manioc and fish (Chernella, 1989;Ribeiro, 1995).The presently known range of C. tukano is entirely within the Tukano territory.

Discussion
As noted above, Corydoras tukano recently appeared in the aquarist hobby tentatively identified as C. reynoldsi (Finley, 1998;Lucanus, 1998;James, 2003a,b).Both Finley (1998) and James (2003a,b) expressed doubts concerning the assignment of specimens of this species as C. reynoldsi.They correctly noticed differences in color pattern, which are detailed in the "Diagnosis", above.James (2003a) remarked that C. tukano (Corydoras sp.cf.reynoldsi of that author) differs from C. reynoldsi by the sexually dimorphic, elongate dorsal fin, and in the breeding biology in aquarium.According to him, C. reynoldsi deposited a mass of eggs, while C. tukano deposited several scattered small batches of eggs.Whether or not that author had correctly identified C. reynoldsi is something that cannot be verified.
Comparisons between C. tukano and two paratypes of C. reynoldsi (CAS-SU 50702) revealed an interesting feature concerning the development of body plates.In C. tukano, specimens up to 28.2 mm SL (MZUSP 64069) had the body plates not yet fully formed, leaving naked areas in both the medial dorsal and ventral regions, while in C. reynoldsi, specimens as small as 22.3 mm SL already have the body plates fully formed, i.e. meeting their counterparts.
The new species also possesses minute odontode-bearing platelets in the anterodorsal area of the orbit (Fig. 5).Comparisons with some other corydoradine catfishes revealed that this character may be unique to C. tukano.Interestingly, the development of small platelets in different regions of body seems to be a trend in some species of Corydoradinae, as reported in the literature (e.g.Fraser-Brunner, 1947;Britto et al., 2002).
Corydoras tukano differs from congeners with elongated dorsal fins by having a relatively short ossified portion of its dorsal spine that is similar in size in males and females.Among  (Nijssen, 1970;Britto, 1997, in press).However, in these species, the longest dorsal-fin element is the ossified portion of the dorsal spine, with its soft portion absent or reduced to a minute remnant.In addition, we found no evidence that the condition in the above cited species is related to sexual dimorphism.Elongated dorsal fins similar to that found in Corydoras tukano (i.e. on soft portion of dorsal spine and first two branched dorsal-fin rays in males) occurs in more distantly related corydoradine catfishes, such as Aspidoras virgulatus Nijssen & Isbrücker and "Corydoras" species closer to that genus, e.g."C." barbatus (Quoy & Gaimard) and "C." macropterus Regan (Britto, 1997, in press).Nevertheless, the condition in these species is more extreme: the first two branched dorsal-fin rays and the soft portion of dorsal spine are twice as long, or more, than the ossified portion or the dorsal spine, while in C. tukano the elongated elements are not much longer than one-half the spine.Corydoras boehlkei Nijssen & Isbrücker seems to be the only Corydoras that possesses a similar condition of dorsal-fin elongation to C. tukano.It is uncertain, however, if the elongation of the dorsal fin in C. boehlkei is a sexually dimorphic character.
Concerning the phylogenetic relationships of C. tukano, the current knowledge of the group does not allow an accurate hypothesis.Examination of characters proposed by Britto (1997, in press) tentatively places the new taxon in a small assemblage composed of C. trilineatus Cope, C. baderi Geisler, and C. arcuatus Elwin.However, this tentative hypothesis is weakly corroborated, because this assemblage is situated in a large polytomy with other Corydoras, and also because it is supported by highly homoplastic characters (e.g.absence of opercular odontodes), with optimizations depending on the tree topology.Color pattern characters might relate C. tukano to C. reynoldsi and C. weitzmani, species not examined by Britto (1997, in press).Nijssen & Isbrücker (1980) included C. reynoldsi and C. weitzmani, along with some other species, in the so-called "aeneus group".However, as Nijssen & Isbrücker (1986: 2) noticed, "[...] these groups were based on several morphometric characters and on color patterns, however, without implying a reflection of their phylogenetic relationships (which are still obscure)".
Before the 1980's, only one species of Corydoras was known from the rio Negro basin, C. melini Lönnberg & Rendahl (1930).Since then, a host of Corydoras species have been described from the rio Negro basin in Brazil, almost all by aquarists: Corydoras adolfoi Burgess (1982), C. amandajanae Sands (1995), C. burgessi Axelrod (1987), C. crypticus Sands (1995), C. davidsandsi Black (1987), C. duplicareus Sands (1995), C. imitator Nijssen & Isbrücker (1983b), C. incolicana Burgess (1993), C. paralellus Burgess (1993), C. nijsseni Sands (1989), C. robineae Burgess (1983), and C. serratus Sands (1995;see Glaser et al., 1996 for pictures of most of them).Except for C. robineae, all of these species possess a dark "mask", associated either with an oblique, dark bar along the dorsal region (C. adolfoi, C. davidsandsi, C. duplicareus, C. imitator, C. melini, and C. serratus), or with a dark saddle-like blotch on dorsal-fin base, extending into the dorsolateral body plates (C. amandajanae, C. burgessi, C. crypticus, C. incolicana, C. nijsseni, and C. parallelus).Unlike C. tukano, none of them possess a "second trunk blotch" with its center at the midline of the body, or a large dark blotch at the adipose fin level.The present taxonomic status of Corydoras species from the rio Negro basin is confused, mainly because there are few specimens deposited in ichthyological collections with locality data.A proper assessment of the diversity of the genus throughout the basin requires additional sampling.
Lucanus (1998) mentioned a second "form", similar to C. tukano, in his words "a long snouted stretched [bodied] form".He noticed that it might represent a different species from the "short snouted high bodied form" (= C. tukano).We obtained through the courtesy of an aquarium fish exporter from Manaus a specimen of this "form" (MZUSP 82344).It represents in fact a distinct, undescribed Corydoras species, differing from C. tukano both in snout shape and details of color pattern.Description of this species must wait for adequate material, with precise locality data.
Corydoras tukano made its debut in the aquarium fish trade a few years ago (Anonymous, 1998;Finley, 1998;Lucanus, 1998).Judging from the amount of information on this species available on the World Wide Web (generally identified as Corydoras sp.cf.reynoldsi, Asher Cory, or Bumblebee Cory), it seems to be one of the most prized species in hobby at present.The capture of C. tukano in the rio Tiquié is done by the Tukano fishermen.They collect the fish mainly in the middle and lower portions of the river, where the species is considered to be common, and earn 150-200 Brazilian reais per one thousand specimens (about 50-67 American dollars).Corydoras species are usually only moderately abundant, and many appear to have relatively restricted distributions.Studies on the potential impacts of the aquarium trade on the natural fish populations, which are still incipient for the Amazon basin (e.g.Chao, 2001;Crampton, 1999) are clearly needed.