A new species of Astyanax ( Ostariophysi : Characidae ) from the headwaters of the arheic Río Sucuma , Catamarca , Northwestern Argentina

A new species of Astyanax is described from the arheic system of Río Sucuma, in Catamarca, Northwestern Argentina. The new species is distinguished from its congeners by a combination of characters including the presence of a broad vertical humeral spot, absence of maxillary teeth, and absence of circuli in posterior field of scales. Furthermore, this species is distinguished by the orbital diameter, head length, branched anal-fin rays, perforated lateral-line scales, transverse scales, dentary teeth with abrupt decrease in size. This species is, to date, the single known fish endemic of Río Sucuma basin.


Introduction
Astyanax Baird & Girard includes almost 150 valid species (Eschmeyer et al., 2016).According to Eigenmann (1917Eigenmann ( , 1921)), this genus is diagnosed by the presence of two series of teeth in the premaxilla: the first series with a variable number of teeth and the second series with usually five, crowns of premaxillary and mandibulary teeth usually ridged and denticulated, maxilla with 0-9 teeth, a complete lateral line, absence of a predorsal spine, and naked caudalfin.Most of these characters are broadly distributed among characids, evidencing that a definition of the genus is necessary (Marinho, Lima, 2009;Mirande et al., 2004Mirande et al., , 2006aMirande et al., , 2007)).As currently defined, Astyanax is the most diverse genus of Characidae and also the most widely distributed, inhabiting from Texas, with A. mexicanus (De Filippi), to the north of Argentine Patagonia, with A. pampa Casciotta, Almirón & Azpelicueta (Casciotta et al., 2005;Pérez, 2008).

Material and Methods
Counts were taken as described by Fink, Weitzman (1974) and Bertaco, Lucena (2006).Counts of vertebrae, supraneurals, procurrent caudal-fin rays, gill rakers, ribs, and caudal-fin rays were taken from cleared and stained (cs) specimens prepared according to Taylor, Van Dyke (1985).Tooth counts were taken in all specimens, including cs specimens.In the descriptions, an asterisk indicates counts of the holotype and the frequency of each count is provided in parentheses.
Measurements were taken as point-to-point linear distances measured with digital caliper with a precision of 0.01 mm, on the left side of the specimen.Measurements are expressed as percent of standard length (SL) except for subunits of the head, which are recorded as percent of head length (HL) and follow Fink, Weitzman (1974).Maxillary and postorbital lengths are measured as in Mirande et al. (2004Mirande et al. ( , 2006aMirande et al. ( , 2006bMirande et al. ( , 2007)).Maxillary length is measured from its articulation with the premaxilla to the maxillary tip.Postorbital distance is measured from the posterior margin of the orbit to posteriormost point of the opercular flap.
The diagnosis is presented according to the procedures described by Lucena et al. (2013) and followed by Bertaco, Vigo (2015).
The new taxon is herein added to the character matrix of Mirande (2010) and its phylogenetic relationships evaluated through a parsimony analysis.The analysis is done under extended implied weighting (Goloboff, 1993(Goloboff, , 2014)), following the procedures described by Mirande (2009) and Mirande et al. (2013).Support measures were calculated through symmetric resampling and expressed as GC values (Goloboff et al., 2003) and Bremer supports (Bremer, 1994).As absolute Bremer supports values are not much intuitive in analyses under implied weighting, they have been rescaled from 0 to 1000 using as limits the fit of the most parsimonious trees and those of the best of 100 Wagner trees (from different random addition sequences).Therefore, clades that collapse in most parsimonious trees will have a value of 0, while those that are monophyletic in trees which are as suboptimal as the used Wagner tree, will have a value of 1000.Those values have been calculated only for the clade of Astyanax.All searches have been done with TNT (Goloboff et al., 2008).Paratypes.40,(5 cs, mm SL) collected with the holotype.

Astyanax powelli, new species
Non-types (inadequate fixing process).11,(2,, Argentina, Catamarca Province, Río Sucuma, tributary of the arheic Río Las Tunas, 24 Jun 2015, C. I. Butí. Diagnosis.Astyanax powelli can be distinguished from its congeners of the Astyanax bimaculatus group (e.g. A. abramis and A. lacustris) by the vertical humeral spot (vs.horizontally oval) and the absence of circuli on posterior field of scales (vs.presence).The new taxon differs from the remaining species of Astyanax by the absence of maxillary teeth (vs.presence, in a variable number).Astyanax powelli bears few denticles on the base of the first ceratobranchial gill rakers (vs.broad denticles on anterior, lateral, and posterior edges of first ceratobranchial gill rakers in A. puka).Also, the dentary teeth decrease abruptly posterior to the fourth tooth in A. powelli (Fig. 2b) (vs.decreasing gradually in A. puka and A. cf.eigenmanniorum).Astyanax powelli bears two humeral spots (vs.one in A. rutilus (Jenyns)).In addition, males of A. powelli have bony hooks restricted to anal and pelvic-fins (vs.bony hooks in all fins in A. chico, A. tumbayaensis, and A. hermosus).Additionally, A. powelli is distinguished from A. latens Mirande, Aguilera & Azpelicueta by the longer prepelvic distance , longer preanal distance (64.3-69.9 vs. 57.6-63.3% of SL), and shorter anal-fin base length .Furthermore A. powelli differs from A. hermosus and A. tumbayaensis by the relatively longer head (27.9-31.0 vs. 23.5-27.1% of SL and 24.0-26.7% of SL).Also, in Astyanax powelli the snout is relatively straight (vs.markedly convex in A. endy and A. tumbayaensis).Astyanax tumbayaensis has a reticulated pigmentation pattern formed by finely dotted scales, especially in its posterior border, which is not evident in A. powelli.Astyanax powelli can be easily distinguished from A. lineatus (Perugia) by the absence of circuli on posterior field of scales (vs.presence) and the lack of lateral stripes on the flanks (present in A. lineatus).The possession of 34-38 perforated scales of the lateral line distinguishes the new species from A. abramis and A. cordovae (Günther) (vs. 42-48 and 43-45).Astyanax tupi Azpelicueta, Mirande, Almirón & Casciotta and A. stenohalinus Messner, possess 2-4 maxillary teeth (vs.absent in A. powelli).The new species can be further distinguished from A. tupi and A. stenohalinus by the anal-fin origin located posterior to the vertical through last dorsal-fin ray insertion (vs.anal-fin origin located anterior to the vertical through last dorsal-fin ray insertion).Astyanax tupi also possesses a supraopercular spot that is absent in A. powelli.Astyanax stenohalinus is further distinguished by the possession of bony hooks on all fins of males (vs.bony hooks present only in anal and pelvic-fins).Astyanax pynandi, A. ita, and A. correntinus (Holmberg) may be distinguished from the new taxon by the possession of one distally expanded maxillary tooth with 5-9 cusps (vs.tooth absent).Also, A. pynandi bears hooks on all fins of males (vs.bony hooks present only in anal and pelvic fins).The relatively low number of branched analfin rays (20-26) allows the distinction of the new species from A. correntinus (29-33), A. pelegrini Eigenmann (41-47), and A. erythropterus (Holmberg) (38-45).Also, Astyanax powelli has fewer perforated scales in the lateral line (34-38 vs. 39-42, 46-52, and 47-54, respectively).Astyanax leonidas and A. troya have been described for the headwaters of streams that drain in the upper portion of the Río Parana in Argentina.Those species bear a maxillary tooth and a horizontally shaped humeral spot superimposed to a vertically elongated one (vs.tooth absent and a vertically elongated spot in A. powelli).Astyanax aramburui Protogino, Miquelarena & Lopez can be distinguished from the new taxon by the presence of a maxillary tooth (vs.absent in A. powelli).As well, A. aramburui bears one humeral spot (vs.two in A. powelli) and has hooks in all fins of mature males (vs.hooks restricted to anal and pelvic fins).Mouth terminal; placed at level of inferior half of eye.Premaxilla bearing two series of teeth; outer row with 2 to 5 penta-to hexacuspidate teeth; inner row with 4(3) or 5(27*) teeth; 11 specimens with 4 teeth on one side and five on other (four specimens with 4 teeth on the left side, 7 specimens with 4 teeth on the right side).Distally expanded teeth, slightly concave anteriorly; first tooth slender with 5 cusps, second to fourth teeth with 5 or 6 cusps and fifth tooth, when present, with 3 cusps.Ascending process of maxilla broad, expanded over distal part of premaxillary alveolar ramus; laminar process of maxilla short, without teeth.Dentary with 8-10 abruptly decreasing teeth, first 4 large hexa-to heptacuspidate and posterior ones tricuspidate or conical.
Eye moderately small.Third infraorbital not contacting laterosensory canal of preopercle either ventrally or posteriorly, leaving small space.
Color in alcohol.Uniformly yellowish, darker dorsally.Two humeral spots.Anterior one conspicuous, black, vertically elongated, upper portion wider and darker; extended from third row over the lateral line to second row under lateral line.Second spot large, diffuse, and dark, continuous with dark lateral stripe.Lateral stripe silvery in specimens with less time in formaldehyde.Lateral stripe limited posteriorly by a black, triangular, caudal spot extended, although not conspicuously, to tip of middle caudal-fin rays.Dorsal, anal, pelvic, and adipose fins hyaline (Fig. 1).
Tab. 1. Morphometric data for holotype and paratypes of Astyanax powelli, n = 41 (including holotype) from Río Sucuma basin, Catamarca, Argentina.SD = standard deviation.Astyanax powelli is confined to the arheic system of the Río Sucuma.This area belongs to the ecorregion of Mar Chiquita -Salinas Grandes, according to Hales, Petry (2015), which comprises several arheic and endorheic basins.Even though the upper portion of the river does not present mayor threats, the lower portion of this river system is under strong anthropic pressure, with the whole river outrageously channeled to satisfy demands from agriculture and population.
Etymology.The species name, powelli is in honor and memory to the late Dr. Jaime Eduardo Powell; prominent paleontologist, dear friend, and colleague.A noun in genitive case.
Conservation status.Even though the known geographic distribution of A. powelli is restricted and that the lower portion of the basin is entirely channeled for agriculture, no threats to the species were detected in the upper portion of the basin.Therefore, Astyanax powelli can be classified as Least Concern (LC), according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2016).
Remarks.All the analyses performed, see coding in Appendix 1 (S1 -Available only as online supplementary file accessed with the online version of the article at http://www.scielo.br/ni),with values of K ranging from 5.26 to 47.35 (see Mirande, 2009 for details), agree in the monophyly of a clade composed of all the analyzed species of Astyanax and including also Astyanacinus Eigenmann, Markiana Eigenmann, Psellogrammus Eigenmann, and Hyphessobrycon anisitsi (Eigenmann), in a result similar to that obtained by Mirande et al. (2011).Relationships within this clade are stable in the most parsimonious trees obtained in the 11 lower (stronger) values of K, ranging from 5.26 to 13.53 (Fig. 5), although most clades are weakly supported, as in previously published phylogenetic hypotheses (Mirande, 2009(Mirande, , 2010)).In these analyses, Astyanax powelli is the sister group of all the remaining species of the clade, excepting A. latens and A. paris.In higher (milder) values of K, A. powelli is obtained as the sister group of a clade composed of Astyanacinus moorii (Boulenger), Astyanax abramis, A. lacustris, A. lineatus, A. pelegrini Eigenmann, Markiana nigripinnis (Perugia), and Psellogrammus kennedyi (Eigenmann), in a rather odd result that is also weakly supported.
The aim of this phylogenetic analysis is not to resolve the relationships of Astyanax, which is far beyond the scope of this paper, but to obtain some idea about the phylogenetic relationships of A. powelli and the cryptic species with which the new taxon is sympatric (A.cf.eigenmanniorum and A. puka).The new taxon was not obtained as sister group of those species in any of the analyses performed herein.

Discussion
The new species shares most of the meristic data with Astyanax eigenmanniorum.That species was described from laguna dos Patos system, Rio Grande do Sul, Brazil, but it has a broad distribution and may actually represent a complex of species that should be carefully revised, as noted by Malabarba (1989) and Vari, Castro (2007).
Species of Astyanax with similar counts than A. eigenmanniorum have been recorded in several basins of Argentina.Astyanax powelli can be easily distinguished from all those species by the absence of maxillary teeth.Also, the holotype of A. eigenmanniorum has a shorter snout, of 16.2% (Vari, Castro, 2007) vs. 20.1-24.8 % HL in A. powelli.
The species of Astyanax known to lack maxillary teeth belong to the A. bimaculatus-group (as A. abramis and A. lacustris), which share the presence of an ovate humeral spot and circuli on posterior field of scales (e.g.Mirande, 2010).Astyanax powelli clearly does not belong to the Astyanax bimaculatus species complex (Garutti, Britski, 2000), having a vertical humeral spot and lacking circuli on posterior field of scales.The new taxon, also, was not found as closely-related to A. abramis and A. lacustris in the phylogenetic analysis herein performed.The lack of a maxillary tooth in A. powelli is an autapomorphy that readily distinguishes it from closely related species.
Astyanax powelli can be easily distinguished from the remaining species of Astyanax that occur in the lower Río Uruguay basin.Astyanax saguazu Casciotta,Almirón & Azpelicueta,.The new species can be further distinguished from A. saguazu by the anal-fin origin located posterior to the vertical through last dorsal-fin ray insertion (vs.anal-fin origin located anterior to a vertical through last dorsal-fin ray insertion).In addition, A. paris possesses a supraopercular spot that is absent in A. powelli.The large eye of A. saguazu (41.1-45.5% of HL) allows its distinction from .Astyanax ojiara and A. dissensus Lucena & Thofehrn may be distinguished from the new taxon by the possession of one distally expanded maxillary tooth with 7-9 cusps (vs.tooth absent).Also, A. ojiara possesses hooks on all fins of males (vs.bony hooks present in anal and pelvic-fins).
Astyanax xiru Lucena, Castro & Bertaco is distributed in the upper Río Uruguay basin (Casciotta et al., 2016;Lucena et al., 2013).This species can be easily distinguished from A. powelli by the shape of the first humeral spot: upper portion horizontally elongate and lower portion vertically narrow (vs.vertically elongated).
Astyanax pampa is one of the species of Characiformes with the southernmost distribution in South America, inhabiting Las Mostazas stream, the lower Río Colorado basin (southern Buenos Aires Province), and Río Negro drainage (Río Negro Province) (Casciotta et al., 2005;Pérez, 2008).This species is mainly distinguished from A. powelli by the presence of one maxillary teeth (vs.absent) and a lower number of branched anal fin rays (17-20 vs. 20-26 in A. powelli); some specimens of A. pampa have 5 scales rows between the lateral line and the dorsal-fin origin, while this condition was not found in A. powelli, and all the examined specimens have 6 or 7 rows instead.
The Río Sucuma flows northward to Río Las Tunas, forming together an arheic basin.The closest river drainage is the Río Salí basin.The type locality of Astyanax puka is in the Río Salí basin and the presence of this species living sympatrically with A. powelli at the Río Sucuma may evidence some historical and/or occasional connection between these two basins, as previously noted by Azpelicueta et al. (2010).Species with restricted ranges of distribution, especially those inhabiting arheic systems (e.g.Astyanax powelli in the Río Sucuma-Las Tunas basin), may be considered as more susceptible to environmental impacts.Therefore, such basins and their faunas should receive special attention in the research efforts and planning of conservation strategies.

Fig. 2 .
Fig. 2. Astyanax powelli, paratype CI-FML 6798.a. 57.6 mm SL, maxilla and premaxilla.b.Dentary, lateral view, anterior to right.c. 45.7 mm SL, premaxilla, medial view, anterior to left.Scale bars = 1 mm.Description.Morphometric data of holotype and 35 paratypes are presented in Tab. 1. Body slender.Maximum depth at dorsal-fin origin.Dorsal profile convex from snout to dorsal-fin origin and straight from this point to caudal peduncle; gently concave from adipose fin, along caudal peduncle, to base of caudal-fin rays.Ventral profile of body convex from lower-jaw tip to pelvic-fin origin; straight to anal-fin origin; slanted dorsally to end of anal fin, and almost straight under caudal peduncle.Dorsal-fin origin equidistant from snout tip and caudal-fin origin.Pelvic-fin origin located slightly anterior to vertical through dorsal-fin origin.Anal-fin origin just behind vertical line through base of posteriormost dorsal-fin rays.Tip of pectoral fin surpassing pelvic-fin origin and tip of pelvic fin reaching anal-fin origin in most of specimens.

Fig. 5 .
Fig. 5. Detail of the Astyanax clade in the most parsimonious tree obtained from values of K between 5.26 and 13.53.Numbers above branches are rescaled Bremer supports (see material and methods section) and numbers below branches are GC values in clades having positive values.
(Terán et al., 2015)les bear hooks in the first 5 to 9 branched anal-fin rays and in all branched pelvic-fin rays excepting the last one.Fusion of the anteriormost gill filaments, as in other species of Astyanax(Terán et al., 2015)was found in mature males.Protogino et al.
Geographical distribution.Headwaters of Río Sucuma upstream of Dos Afluentes dam, in Department El Alto, Province of Catamarca (Figs.3, 4).Ecological notes.The new species inhabits mountain environments with high flow velocity and gravel substrate with clear waters.The river has abundant water vegetation such as Myriophyllum aquaticum and undetermined Poaceae and floating vegetation (Hydrocotyle ranunculoides and Azolla filiculoides).As well, the presence of green algae is common in these environments.