A new species of Astyanax (Characiformes: Characidae) from the rio de Contas basin, Bahia, Brazil

A new species of Astyanax from tributaries of the rio de Contas, Bahia, Brazil, is described. The new species differs from congeners by having three horizontal series of scales from lateral line to pelvic-fin origin and the distal margin of third infraorbital distinctly separated from vertical and horizontal limbs of preopercle, leaving a broad area not covered by superficial bones. The new species further differs from most congeners by the presence of bony hooks on all fins of mature males. Particularly from congeners occurring in rivers of the Northeastern Mata Atlântica freshwater ecoregion, it further differs by having the highest body depth just anterior to the dorsal-fin origin, 34–37 pored lateral line scales, a vertically elongated conspicuous dark humeral blotch reaching below the lateral line and a conspicuous dark wide midlateral stripe extending from the clear area on the rear of the humeral blotch to the end of middle caudal-fin rays and forming an inconspicuous blotch on caudal peduncle.


Introduction
Astyanax Baird & Girard is one of the most species-rich genera within Characidae, with 176 valid species (Fricke et al., 2019). Furthermore, possibly it is among the genera with higher number of species being described lately, with approximately 80 new species in the last 20 years. Particularly to drainages inserted in the Northeastern Mata Atlântica freshwater ecoregion (sensu Abell et al., 2008; NMAF), 11 species were described in that period (e.g., A. brucutu Zanata, Lima, Di Dario & Gerhard, A. epiagos Zanata & Camelier, A. hamatilis Camelier & Zanata, A. lorien Zanata, Burger & Camelier, A. pelecus Bertaco & Lucena, A. sincora Burger, Carvalho & Zanata). All of them are apparently endemic to their respective river basin and none of them or other known species of Astyanax was described from the rio de Contas basin. Taxonomic (Birindelli, Britski & Garavello), Nematocharax varii Barreto, Silva, Batalha-Filho, Affonso & Zanata]. Some of these studies represent the few citations regarding species of Astyanax to the rio de Contas basin, usually solely as syntopic fauna to their new species. Other relevant studies including species of Astyanax from the rio de Contas have citogenetic or molecular approaches (e.g., Affonso et al., 2007;Medrado et al., 2008Medrado et al., , 2015Pamponet et al., 2008), or are represented by not published thesis (e.g., Silva, 2015). Recent ichthyological surveys in the rio de Contas basin yielded a new species of Astyanax apparently endemic to this basin that is described herein.

Color in alcohol.
Overall ground color pale yellow or light brown (Fig. 1a). Guanine restricted to infraorbitals, preopercle, and opercle. Dorsal part of head moderately dark anteriorly and usually darker on posterior half; presence of two large black rounded blotch on posterior part of head in some specimens. Small melanophores sparsely distributed throughout maxilla. Infraorbitals poorly pigmented, with few melanophores close to orbit; infraorbitals four to six more pigmented, with large melanophores sparsely distributed. Opercle with sparse melanophores, usually more concentrated on its dorsal half; ventral third usually 5 e190061[5] without dark pigmentation. Concentration of melanophores on opercle usually resembling a vertically elongated blotch, somewhat similar to the humeral blotch. Ventral portion of head pale or with a few diminute scattered melanophores on anteriormost portion. Middorsal line of body distinctly darkened. Humeral region with a conspicuous vertically elongated humeral blotch, formed by underlying and superficial melanophores; blotch over two or three scales on horizontal series immediately above lateral line, tapering ventrally and occupying one scale below lateral line. Humeral blotch bordered anteriorly and posteriorly by clearer areas. Dark broad midlateral stripe extending from the rear of clear area posterior to humeral blotch to caudal peduncle. A dark rounded blotch, with inconspicuous borders, present on caudal peduncle in most specimens; blotch when present, partially merged with the stripe. Two or three dorsalmost longitudinal scale series of flank usually with dark small chromatophores concentrated along their posterior margins, resulting in reticulate pattern; center of scales clearer, with few sparse larger melanophores; some specimens darker overall and reticulate pattern substituted by a more homogeneous dark pigmentation on scales. In some specimens with more defined reticulate pattern, the dark margins of scales are narrower along lateral line and one to three horizontal series of scales below it. Remaining scales along flank with sparse melanophores; dark lines usually present along myosepts above anal-fin base. Abdominal region clear. All fins darkened in some degree, with sparse melanophores concentrated on margins of rays; dorsal, anal, and caudal fins somewhat darker than pectoral and pelvic fins. Adipose fin with scattered small melanophores.

Color in life.
Color pattern similar to the described in alcohol (Fig. 1b). Overall ground color yellow. Iris, infraorbitals, and opercle silvery. Humeral blotch faint or not discernible. Dark midlateral stripe more conspicuous on posterior half of body, extending to middle caudalfin rays. Unpaired fins yellowish at least on its proximal half. Pectoral and pelvic fins hyaline or poorly pigmented. Adipose fin yellowish.
Sexual dimorphism. Mature males of Astyanax varii have variable presence of hooks on fins and the examined mature females have no bony hooks on any of the fins. Some mature males possess tiny bony hooks on all fins (e.g., UFBA 4515, 29.1-34.3 mm SL), but most mature males have hooks restricted to the pectoral, pelvic, and anal fins. Anal fin of mature males with one to six hooks distributed up to the tenth first branched ray; hooks more numerous and larger on the anterior branched rays and always distally located on the posterior branch of rays. When present in the dorsal fin, up to six small hooks distributed on the first eight branched rays; hooks always distally located on the posterior branch of ray. Pectoral fins of mature males with up to six tiny hooks on the distal portion of up to the seventh branched ray. Pelvic fins with two or three small hooks on the distal portion of third to the sixth branched rays. When present in the caudal fin, very small hooks restricted to the four centralmost caudalfin rays. No other dimorphic morphological character was observed externally in the specimens examined, except by the body size. Females apparently reach larger body sizes than males (largest female observed 53.3 mm SL vs. largest male 37.9 mm SL). Males are completely mature around 29.0 mm SL and females at the same size are completely immature. The smallest mature female examined had 35.0 mm SL.
The analysis of stomach contents of two specimens of A. varii revealed the presence of allochthonous and autochthonous items, composed predominantly by filamentous algae and fragments of vascular plants and seeds, organic debris, insect aquatic larvae (Diptera: Chironomidae and Simuliidae) and fragments of unidentified insects. Etymology. The specific name varii is in honor to the ichthyologist Richard P. Vari for his friendship, mentoring, and outstanding contribution to the systematic of South American freshwater fishes.
Conservation status. Astyanax varii had been collected in six localities in the upper and lower rio de Contas basin. The main locality sampled in the upper rio de Contas, the Balneário Rio da Barra, is an artificial reservoir continually exploited for tourism as a bathing place (Barreto et al., 2018). Permanent anthropic perturbation such as loss of riparian vegetation and dams occurs in the main channel and some tributaries of rio de Contas (Cetra et al., 2010;Sarmento-Soares et al., 2016). Despite some records of threats for the region, such as deforestation, water pollution, and erosion, there are no data about the direct effects of these threats to the populations of A. varii so far. Therefore, with the currently available data, and according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2017), A. varii should be classified as Least Concern (LC).

Discussion
A total of 79 species of Astyanax was described in the last 20 years (Fricke et al., 2019), being one of the fish genera with higher expansion on its richness knowledge. Advances in alpha taxonomy of the ichthyofauna of the Brazilian coastal drainages contributed with 21 of those descriptions, being 11 from the Northeastern Mata Atlântica freshwater ecoregion (e.g., Rangel-Pereira, 2012;Birindelli et al., 2013;Lima et al., 2013;Mattos, Costa, 2018;Barreto et al., 2018;Burger et al., 2019); seven from rivers draining the Laguna dos Patos freshwater ecoregion (e.g., Lucena et al., 2013;Bertaco, Vigo, 2015), one species from the Tramandaí-Mampituba freshwater ecoregion (Bertaco, 2014), one species from the Ribeira de Iguape freshwater ecoregion (Silva et al., 2019), and one from the Southeastern Mata Atlântica freshwater ecoregion (Oliveira et al., 2013). Particularly to the NMAF, nine of the 11 species mentioned are from river basins inserted in the Bahia State, highlighting the rio Paraguaçu basin, with six described species, all of them apparently endemic to this basin (A. brucutu, A. epiagos, A. hamatilis, A. lorien, A. rupestris, and A. sincora). Conversely, Astyanax is poorly documented to the rio de Contas basin in the taxonomic literature, being usually not identified confidently at specific level [e.g., Astyanax gr. bimaculatus (Linnaeus) in Cetra et al., 2010;A. aff. lacustris (Lütken) in Zanata, Camelier, 2010; A. gr. fasciatus and A. gr. lacustris in Barreto et al., 2018] or identified as Astyanax sp. (e.g., Camelier, Zanata, 2014;Sarmento-Soares et al., 2016). Similarly, species of Astyanax are alternately confidently identified at specific level or not in cytogenetics or molecular studies (e.g., A. fasciatus in Medrado et al., 2008;A. aff A. bimaculatus in Lima et al., 2013). Such taxonomic difficulties corroborate the poor geographical and taxonomic species delimitation of the species complexes in which the species cited above are included. Also, the cited shortcomings confirm the need of comparative taxonomic studies, including populations of Astyanax from the rio de Contas basin, to check for the presence of A. fasciatus, A. bimaculatus, or A. lacustris in this basin.
Astyanax varii is the first species of the genus described from the rio de Contas and the species does not fit in any of the species groups, traditionally used to the genus. In addition to the diagnosis given previously, the new species can be differentiated from congeners surely identified at specific level, inhabiting rivers comprised in the NMAF, by a series of characters. The species differs from A. bahiensis (Steindachner), A. brevirhinus Eigenmann, A. brucutu, A. burgerai Zanata & Camelier, A. epiagos, A. hamatilis, A. lorien, A. jacobinae Zanata & Camelier, A. pelecus, A. rupestris, A. sincora, A. turmalinensis Triques, Vono & Caiafa, and A. vermilion Zanata & Camelier by having a conspicuous dark wide midlateral stripe extending from the rear of the clear area posterior to the humeral blotch to the end of middle caudal fin rays, not forming a conspicuous blotch on the caudal peduncle (vs. absence of conspicuous lateral stripe and/or presence of a conspicuous caudal blotch), from A. burgerai, A. epiagos, A. jacobinae, A. lorien, A. microschemos Bertaco & Lucena, A. rupestris, A. sincora, and A. turmalinensis by having the highest body depth approximately at vertical through the dorsal-fin origin (vs. body deepest on a vertical approximately at midlength or posterior portion of pectoral fin), from A. brevirhinus by the presence of a vertically elongated conspicuous dark humeral blotch (vs. presence of horizontally elongate black humeral blotch), and from A. pelecus by having 34-37 pored lateral line scales and humeral blotch with its ventral portion located ventrally to the lateral line series (vs. 38-39 pored lateral line scales and humeral blotch limited to the region above lateral line).
The endemic nature of the fish fauna of the rio de Contas is exemplified by eight endemic species, including Cyphocharax pinnilepis, Hasemania piatan, Hyphessobrycon brumado, Ituglanis agreste, Megaleporinus brinco, Nematocharax varii, Parotocinclus jimi Garavello, and the new species described herein. The rio de Contas basin ranks second in number of endemic fish species after the rio Paraguaçu basin, among river basins completely included in the Bahia State. Thus, the fish fauna of the rio de Contas, known up to date, is in agreement with the statement of previous authors about coastal drainages of eastern Brazil being recognized as a very distinct area in terms of their ichthyofauna, mainly expressed by the high endemism at species and genus level (e.g., Bizerril, 1994;Camelier, Zanata, 2014). Appart from endemicities restrict to the basin itself, according to Camelier, Zanata (2014), one of the few publications with somewhat broader taxonomic information on its fish fauna,