Astyanax powelli, Terán & Butí & Mirande, 2017

Terán, Guillermo E., Butí, Cristina I. & Mirande, J. Marcos, 2017, A new species of Astyanax (Ostariophysi: Characidae) from the headwaters of the arheic Río Sucuma, Catamarca, Northwestern Argentina, Neotropical Ichthyology 15 (2), No. e 160165, pp. 1-10 : 2-6

Astyanax powelli , new species

Figs. 1-2; Tab. 1

urn:lsid:zoobank.org:act:7A84C73C-9F0C-428F-B778-9F5170B54584

Holotype. CI-FML 6797 , 52.3 mm SL, male, Argentina, Catamarca Province, El Alto, Río Sucuma, tributary of the arheic Río Las Tunas , 28°14’21”S 65°22’45”W, ca. 800 meters above sea level, 22 Jun 2015, C. I. Butí.

Paratypes. CI-FML 6798 , 40 , 35.5-60.2 mm SL, (5 cs, 36.0- 56.8 mm SL) collected with the holotype .

Non-types (inadequate fixing process). CI- FML 6799, 11, 37.5-55.1 mm SL, (2, 41.6-46.6 mm SL), 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 (46.8-51.8 vs. 42.6-45.8% of SL), longer preanal distance (64.3-69.9 vs. 57.6-63.3% of SL), and shorter anal-fin base length (24.4-29.7 vs. 32.3-36.7% of SL). 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).

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.

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.

Dorsal-fin rays iii,8(2), 9(39*); first unbranched dorsal-fin ray mostly visible in cs specimens; distal margin of dorsal fin straight, with last unbranched and first branched dorsal fin rays longest. Anal-fin rays iv-v, 20(3), 21(2), 22(10), 23(16*), 24(5), 25(4), or 26(1). Males with bony hooks on distal half of last unbranched anal-fin ray and posterior branch of first 5-9 branched anal-fin rays; usually one pair of hooks per segment. Caudal-fin rays: i,16,i(1); i,17i(39*); or i,19,i(1). Pectoral-fin rays i,11(4), 12(20), 13(14*), or 14(3). Pelvic-fin rays i,7(41*); males bearing bony hooks on posterior branch of pelvic-fin rays 2 to 7, one pair of hooks per segment. Hooks restricted to medial branches of pelvic-fin rays.

Scales cycloid, without circuli on posterior field. Lateral

line complete, with 34(4), 35(10), 36(17), 37(4*), or 38(1) perforated scales. Scales rows between dorsal-fin origin and lateral line 6(24) or 7(12*); scales rows between lateral line and pelvic-fin origin 5(36*). Scales rows around caudal peduncle 14(15), 15(10), 16(8*), or 17(3). Predorsal scales 10-14*, forming relative regular row. One row of scales forming a sheath, covering base of unbranched and first 8-14 branched anal-fin rays. Few scales covering base of caudalfin lobes.

In cs specimens (5), first gill arch with 20-22 rakers: 7-8 on epibranchial, 1 on cartilage, 9-11 on ceratobranchial, and 2-3 on hypobranchial; posterior margin of first epibranchial with a second row of 4-6 gill rakers. Thirty-four total vertebrae (17 precaudal and 17 caudal). Five supraneurals, 11 pairs of ribs. Caudal fin with 8 or 9 dorsal and 9 or 10 ventral procurrent rays.

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).

Sexual dimorphism. Males 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. (2006) mentioned the presence of breeding tubercles in head and scales in mature males of A. aramburui . These tubercles were not found in this species, but they were found in some specimens of A. eremus Ingenito & Duboc ( Ingenito, Duboc, 2014), A. gymnodontus (Eigenmann) (CI-FML 7138), A. ojiara (CI-FML 6779), A. parahybae (Eigenmann) (CI-FML 7174), and A. troya (CI-FML 7175) and may have a wider distribution in the genus. These tubercles are probably related with the sexual maturity and their presence in A. powelli cannot be discarded.

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.

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, 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. e igenmanniorum and A. puka ). The new taxon was not obtained as sister group of those species in any of the analyses performed herein.