Astyanax taurorum a new species from dos Touros River , Pelotas River drainage , an upland southern Brazilian river ( Characiformes : Characidae )

A new species of Astyanax belonging to the Astyanax scabripinnis complex is described from dos Touros River, tributary of the Pelotas River, Uruguay River basin. Astyanax taurorum sp. nov. is distinguished from other species of the Astyanax scabripinnis species complex by having two humeral spots, the first vertically elongated; teeth of inner row of premaxilla with three to five cusps; 2–3 (modes 2 or 3) maxillary teeth; 20–23 (mode 22) branched anal-fin rays; 13–15 (mode 14) gill rakers on lower branch of the first branchial arch; 20–23 (mode 21) total gill rakers in first branchial arch; 33–36 (mode 35) perforated lateral line scales. Astyanax taurorum sp. nov. is similar to Astyanax paris; nevertheless, it can be readily distinguished from it by having a smaller head depth (73.6-83.1% vs. 86.4–95.6%) and smaller interorbital width (24.1–28.0% vs. 30.8–32.8%). In addition, it differs from A. paris by the presence a posttemporal hook-shaped posterodorsal margin.


INTRODUCTION
The fishes of the genus Astyanax Baird & Girard, 1854 inhabit Neotropical drainages from the Colorado River in Texas and New Mexico in the United States to Northern Patagonia, Argentina (Menni 2004, López et al. 2008, Ornelas-Garcia et al. 2008).As suggested by phylogenetic analyses based on morphological (Mirande 2010) and molecular evidence (Javonillo et al. 2010, Oliveira et al. 2011), Astyanax is not monophyletic.The genus comprises 150 valid species (Eschmeyer et al. 2016), and it is still defined as in Eigenmann (1921Eigenmann ( , 1927) ) (for the characters, see Marinho and Ohara 2013).The Astyanax scabripinnis complex is a non-monophyletic group with 29 species (Ingenito and Duboc 2014: tab. 1).It is characterized, according to Bertaco and Lucena (2006), by possessing the deepest and most robust body area close to the middle length of the pectoral fins, a robust head, snout short and abrupt, body depth smaller than 41% of SL, reduced number of branched anal-fin rays (13-23, rarely 22 or 23 rays), presence of one or two humeral spots, and a dark mid-lateral body stripe extending to the tip of the middle caudal-fin rays.
Counts and measurements follow Fink and Weitzman (1974) and Bertaco and Lucena (2006) with the addition of the head depth, measured at the vertical through posterior margin of the orbit.Measurements were preferentially taken on the left side of specimens using callipers (0.1 mm approximation).Counts of vertebrae, supraneurals, teeth of dentary, unbranched dorsal, and anal-fin rays taken from cleared and stained (c&s) specimens prepared according to the protocol of Taylor and van Dyke (1985).Vertebral counts included the four vertebrae of the Weberian apparatus, and the terminal centrum counted as a single element.In the description, the frequency of each count is given in parentheses after the respective value.In the material examined, the total number of specimens in the lot follows each catalogue number, and in parentheses is the number of specimens measured and counted with their respective standard length range.HL stands for head length throughout.
Within the Astyanax scabripinnis complex, Astyanax taurorum sp.nov. is most similar to A. paris Azpelicueta, Almirón & Casciotta, 2002 -species known from the type locality, Arroio Fortaleza, tributary of upper Uruguay River, Argentina -with which most counts and morphometric percentages overlap.Nevertheless, Astyanax taurorum sp.nov.differs from A. paris by the presence of hooks on branched anal-fin rays (vs.secondary sexual dimorphism absent in A. paris), interorbital width 24.7-28.0%HL (vs.28.4-32.8%HL) and head depth 73.6-86.7%HL (vs.86.4-96.6%HL) (Fig. 2) (Table 2), and by having posterodorsal margin of the posttemporal hook-shaped (Fig. 3) (see Discussion  1. Body compressed and moderately elongate, greatest body depth at vertical through near middle length of pectoral fin.Dorsal profile of head convex from tip of snout to vertical through nostrils, straight from that point to vertical through posterior border of orbital, slanted until tip of supraoccipital spine.Snout relatively slender.Dorsal profile of body convex from tip of supraoccipital bone to dorsal-fin origin; straight from that point to end of caudal peduncle.Ventral body profile convex from mandibular symphysis to pelvic-fin origin, nearly straight from that point to anal-fin origin, and slanted along anal-fin base.Dorsal and ventral profiles of caudal peduncle nearly straight. Mouth terminal or slightly subterminal, slit below horizontal passing through middle of eye.Posterior tip of maxilla extending between vertical through anterior margin of orbit and the vertical through middle of orbit.Two tooth rows in premaxilla; outer row with 3*(2), 4(13), or 5(5) tricuspid teeth; inner row with five teeth, usually bearing four cusps on first tooth, five cusps on second to fourth tooth, three cusps on fifth tooth.Maxilla with 2(8) or 3(8) tricuspid teeth.Dentary with four large pentacuspid teeth, followed by seven small tricuspid teeth and one conical tooth (two c&s).Median cusp in all cuspidate teeth longer than remaining cusps; cusp tips slightly curved inwardly on dentary (Fig. 4).
Color in alcohol.Dorsal and dorsolateral portions of head and body dark brown.Scales on lateral of body with dark brown chromatophores sometimes concentrated on anterior border.Two conspicuous humeral spots.Anterior humeral spot vertically elongate with upper portion wider, located on second to third or fourth scale vertical series, extending three horizontal scale series above lateral line; lower portion narrow, extending on the lateral line and one or two horizontal scale series below it.Posterior humeral spot large, absent in small specimens (22.8-29.4mm SL), reaching but not surpassing lateral line ventrally, extending on two or three horizontal scale series and three vertical scale series.Humeral spots separated by a clear area occupying two or three vertical scale series.Dark midlateral strip inconspicuous anteriorly, but conspicuous posteriorly from about vertical through middle of dorsal-fin base to caudal peduncle; absent in small specimens .Caudal peduncle spot triangular, extending over median caudal-fin rays.Scattered dark chromatophores on dorsal, anal, and caudal fins.Pectoral and pelvic-fins hyaline or covered by sparse dark chromatophores.
Color in life.Overall body olive green, silvery below lateral line.Humeral spots and caudal peduncle spot conspicuous.Dorsal, anal, pelvic and caudal fins reddish.Pectoral-fin yellowish.Dark brown blotches located on anterior portion of scales.
Sexual dimorphism.Hooks on anal-fin rays of four specimens with 75.4 to 80.6 mm SL (MCP 14370).Hooks short, conical or slightly retrorse found on the first or third to eighth branched rays, along the posterolateral margin of the posterior branch.One pair on each segment.One specimen with a single hook on the third branched anal-fin ray and another specimen with a very small hook on the first branched ray and small protuberances on other rays.
Distribution and habitat.Astyanax taurorum sp.nov. is known from the dos Touros River drainage, tributary of Pelotas River, which in turn is a tributary of Uruguay River (Fig. 5).The Pelotas River drainage is located in the region named "Campos de Altitude do Planalto das Araucárias (= Araucaria Plateau in Bertaco et al. 2016)" or "Campos de Cima da Serra", which has a high level of endemism of fishes (Malabarba et al. 2009, Bertaco et al. 2016: 430) and other groups of animals (for example: sponges, Ribeiro et. al. 2009;crustaceans, Bond-Buckup et al. 2009).The dos Touros River tributary, type locality of Astyanax taurorum sp.nov., has a low to medium flow, transparent waters with stones and rocks on the bottom and moderate emergent marginal vegetation (Fig. 6).Four characid species were caught along with Astyanax taurorum sp.nov.: Bryconamericus patriciae Silva, 2004, B. iheringi Boulenger, 1887, Cheirodon interruptus Jenyns, 1842, and Oligosarcus brevioris Menezes, 1987.
Etymology.The specific name taurorum, is derived from the Latin masculine noun taurus (second declension, meaning bull) inflected in the plural and genitive case.Therefore taurorum means "of the bulls" in reference to "rio dos Touros" (= Portuguese, which means "river of the bulls") the type locality.
Conservation status.Astyanax taurorum sp.nov. is likely rare and occurs in low densities.All type specimens were collected in the dos Touros River drainage, during two field trips in 1989 and 2016.Over the last four decades (from 1980 to 2016), six field trips to the dos Touros River system have been conducted by the MCP team, two of which with the sole purpose of collecting specimens of A. taurorum.Unfortunately, no specimens were collected in 2015, and only two were found in 2016.The Museu de Ciências Naturais (FZB, Porto Alegre) and Universidade Federal do Rio Grande do Sul also conducted field surveys in that region, but no specimens of A. taurorum sp.nov.were obtained.Despite the reduced number of specimens collected and the apparently restricted geographical distribution of the new species, we did not assign Astyanax taurorum sp.nov. to any threat category because we the lack biology data for it.Instead, we considered

DISCUSSION
The Astyanax scabripinnis species complex is not a monophyletic group; this clustering, however artificial, facilitates discussions and comparisons on the diversity of the genus according to Bertaco and Lucena (2006).These authors presented a series of morphological characters that delimit this complex, which are mostly found in A. taurorum sp.nov.except for the abrupt snout (slender in A. taurorum sp.nov.).Mirande (2010) presented the most encompassing, morphology-based phylogeny of Characidae.Astyanax taurorum sp.nov.has all synapomorphies that define node 201 in that analysis (sister group of Tetragonopterinae clade): dorsal expansion in the rhinosphenoid absent (character 48, state 0), and tubule with anterior branch parallel to anterior margin of maxilla, reaching a third of its length (character 98, state 1).Node 201 has two branches, the Hyphessobrycon luetkenii clade and node 200.The new species shares all synapomorphies of node 200: fourth infraorbital approximately square, or more developed longitudinally than dorsoventrally (67, state 0); coronomeckelian situated dorsal to Meckelian cartilage (character 110, state 1); 24 or less branched anal-fin rays (288, state 0).Node 200 has two branches named Astyanax paris and node 199 clades.For now, we note that A. taurorum shares, with the former clade, "the abrupt decrease in size of dentary teeth (character 148, state 1)" and not the synapomorphy of clade 199 "ventral margin of horizontal process of anguloarticular perpendicular to laterosensory canal of dentary from medial view".We have examined some species of the clade at node 199, mostly included in the Astyanax clade (node 267) (e.g., Astyanax lacustris Lutken, 1875 and A. eigenmanniorum Cope, 1894, Markiana nigripinnis Perugia, 1891, and Hyphessobrycon anisitsi Eigenmann, 1907), and other representatives of Astyanax not analyzed by Mirande (see Additional material).None of them have a posterodorsal margin with posttemporal hook-shape, as it is the case with A. taurorum, though some species have an enlarged posterodorsal margin, which is not hook-shaped (see Mirande 2010: fig.48).
Astyanax is represented in the Laguna dos Patos, Tramandaí River, and Uruguay River drainages, by 20 species, eight of which have restricted distribution within these drainages (Fig. 5 2014), with restricted distributions on the headwaters mentioned above, as well as the occurrence of 43 undescribed fish species in these drainages (Bertaco et al. 2016: 428), demonstrate the importance of conservation of this type of environment, as remarked by other authors (e.g., Ferrer andMalabarba 2011, Ferrer et al. 2015).