(Figs. 1-3, Table 1)
Additional material (not designated as paratypes): CI-FML 3850 , 3 ex. (C&S), 42.7-50.0 mm SL, collected with the holotype .
Diagnosis: Astyanax puka is distinguished from the remaining species of the genus by the following combination of characters: shallow body (33.5-39.8 % SL), 36-38 perforated scales in lateral line, 6/5 transverse scales, 9-10 gradually decreasing dentary teeth, distally expanded premaxillary teeth, one distally expanded maxillary tooth with 7-9 cusps, short upper-jaw length (34.5-37.8 % HL), short maxilla (20.7-23.3 % HL) expanded abruptly under maxillary tooth position, short postorbital distance (36.6-46.9 % HL), short pelvic to anal-fin origin distance (17.1-20.6 % SL), 22-27 branched anal-fin rays, long caudal peduncle (13.3-16.5 % SL), bony hooks restricted to pelvic-fin rays 2 to 6 and anterior 6-13 branched anal-fin rays on mature males, and the presence of broad denticles on anterior, lateral, and posterior edges of first ceratobranchial gill rakers. A detailed comparison of Astyanax puka with the other species of Astyanax appears in the “Discussion” section below in this paper.
Description: Morphometrics of the holotype, and 19 paratypes are presented in Table 1. Body rather slender(33.5-39.8 % SL), with maximum depth at dorsal-fin origin. Dorsal profile slightly convex over snout and straight from interorbital area to tip of supraoccipital process; slightly convex to dorsal-fin origin; straight from this point to caudal peduncle; gently concave along caudal peduncle to base of caudal-fin rays. Ventral profile of body convex from lower-jaw tip to anal-fin origin; straight to anal-fin origin; slanted dorsally to end of anal fin, and almost straight under caudal peduncle. Ventral portion of body between bases of pectoral and pelvic fins transversally rounded; ventral portion of body between origins of pelvic and anal fins more compressed laterally.
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 located just behind vertical line through base of posteriormost dorsal-fin rays. Tip of pectoral fin reaching pelvic-fin origin, and tip of pelvic fin reaching anal-fin origin in males and some females.
Mouth terminal, placed at level of inferior third of eye. Premaxilla bearing two series of teeth; ascending process with rather broad base and acute tip, less developed than alveolar ramus. Outer row with 2(2), 3(18*), or 4(2) pentacuspidate teeth, with slender base and slightly expanded distally; inner row with 5 distally expanded teeth, slightly concave anteriorly; symphysial tooth slender with 5 cusps, second to fourth teeth with 7-9 cusps and fifth tooth with 5-6 cusps (Fig. 2). Ascending process of maxilla broad, expanded over distal part of premaxillary alveolar ramus; laminar process of maxilla short, with 1(22*) tooth with 7-9 cusps, abruptly expanded under maxillary tooth position; ligamentum primordiale attached over horizontal line through maxillary tooth base (Fig. 2). Dentary moderately deep (aproximately 45 % of its length), with its maximum depth approximately in middle of its length; dentary with 9-10 gradually decreasing teeth, first 4 or 5 heptacuspidate, sixth and seventh penta or tricuspidate, and posterior ones tricuspidate or conical (Fig. 2).
Eye moderately large, longer than snout. Third infraorbital not contacting latero-sensory canal of preopercle either ventrally or posteriorly.
Dorsal fin with iii, 9 rays; distal margin of dorsal fin straight, with last unbranched and first branched dorsal fin rays longest. First unbranched dorsal-fin ray mostly visible in cleared and stained specimens. Anal fin with iv-v, 22(1), 23(2), 24(7), 25(8*), 26(2), or 27(2) rays; small lobe formed by last unbranched and first 5-6 rays in both sexes, pointed in females and rounded in males. Males with hooks on distal half of last unbranched anal-fin ray and posterior branch of first 6-13 branched anal-fin rays; usually one pair of hooks per segment. Caudal fin with principal rays i,17,i. Pectoral fin with i,11-12 rays. Pelvic fin with i,7 rays; males bearing hooks on posterior branch of pelvic-fin rays 2 to 7, one pair of hooks per segment.
Scales cycloid, without circuli on posterior field. Lateral series with 36(3), 37(18*), or 38(1) perforated scales. Scales between dorsal-fin origin and lateral line 6(20*) or 7(2); scales between lateral line and pelvicfin origin 5(22*). Scales around caudal peduncle 13(1), 14(15*), 15(4), or 16(2). Scales between tip of supraoccipital spine and base of dorsal fin 10-11, usually forming a regular row. One row of scales forming a sheath-covering base of unbranched and first 7-12 branched anal-fin rays. Few scales covering only the base of caudal-fin lobes.
First branchial arch with 17-18 gill rakers: 6 on epibranchial, 1 on cartilage, 8-9 on ceratobranchial, and 2 on hypobranchial; posterior edge of first epibranchial with a second row of 4-5 gill rakers. Gill rakers on first ceratobranchial with broad denticles on anterior, lateral, and posterior edges (Fig. 3). Thirty-five to 36 vertebrae(15-16 precaudal and 19-20 caudal vertebrae). Four or five supraneurals, 11 pairs of ribs. Caudal fin with 10 dorsal and 8-9 ventral procurrent rays.
Colour in life: Body silvery, darker dorsally. Lateral silvery band inconspicuous. First humeral spot vertically elongated, narrow, and second one faint. Intensely red anal and caudal fins. Hyaline pectoral, pelvic and dorsal fins.
Colour in alcohol: Body yellowish, darker dorsally. Head dark dorsally, with chromatophores scattered on maxilla and anterior part of lower jaw; few chromatophores on first to third infraorbital. First humeral spot broad, vertically elongated and intensely pigmented, extended from second row of scales over lateral line to second row under lateral line. Second humeral spot rather well defined, especially over lateral line. Well defined, but rather thin, lateral stripe extended from postero-dorsal angle of opercle, through the humeral spots to end of middle caudal-fin rays; the lateral stripe is sligthly expanded vertically at caudal peduncle, although not forming a conspicuous spot. Dense chromatophores located under proximal and medial surface of scales of dorsum, leaving distal area lighter, forming thus a reticulate pattern. Scales of flanks with a thin line of melanophores in its distal border. Pectoral and pelvic fins hyaline. Dorsal, anal, and caudal fins hyaline, with chromatophores scattered on membrane, more densely concentrated distally, especially evident in membranes of caudal fin.
Distribution: Astyanax puka is known only from the Mandolo and Sall rivers, Rio Sall endorheic basin, Tucumán , northwestern Argentina (Fig. 4).
Habitat notes: The type locality is approximately one-meter deep and has a gravel bottom, with slow current.
Etymology. The specific epithet puka is a Quichua word that means red, in allusion to the intensely red anal and caudal fins of this species. A noun in apposition.
As mentioned above, Astyanax pukasp. n. shares the number of perforated lateral line scales and anal-fin rays, expanded premaxillary teeth and gradually decreasing dentary teeth with a group of species that includes A. giton and A. hastatus from eastern Brazil, A. ojiara , A. troya , A. leonidas , A. pynandi and A. ita from northeastern Argentina, and A. chico from northwestern Argentina. Some species of Deuterodon and Hyphessobrycon also shares some of these features. The genus Deuterodon was phylogenetically diagnosed by Lucena & Lucena (2002); the new species does not share the putative synapomorphies of this genus, and is readily distinguished from species of Hyphessobrycon by its complete lateral line. Reis (2003) considered “Deuterodon” parahybae Eigenmann and “ D.” pedri Eigenmann as incertae sedis within Characidae. Astyanax puka is distinguished from both species by the presence of only one maxillary tooth (vs. two or three in “Deuterodon” pedri , and two in “ D.” parahybae ).
The new species is distinguished from the Brazilian species Astyanax giton by the presence of one maxillary tooth (vs. usually two), 22-27 branched anal-fin rays (vs. 20-22), and the interopercle extended covering anterior border of subopercle (vs. not covering anterior border of subopercle); from A. hastatus by the absence of hooks on caudal fin in mature males (vs. presence), the presence of hooks on first 6-13 branched anal-fin rays only (vs. hooks on 20 anterior branched anal-fin rays), and longer peduncle (13.3-16.5 vs. 6.7-13.0 % SL). Astyanax puka is distinguished from A. ojiara , A. troya , A. chico , and A. leonidas by the presence of 22- 27 branched anal-fin rays (vs. 20-23, 18-21, 19-24, and 17-21, respectively), and from these species plus A. pynandi by the presence of hooks only on pelvic fins and first 6-13 branched anal-fin rays (vs. presence of hooks on most anal-fin rays, and pelvic, pectoral, caudal, and excepting A. leonidas , dorsal fin). The new species is further distinguished from A. troya , A. chico , and A. leonidas by the presence of one hepta to nonacuspidate premaxillary tooth (vs. conical to pentacuspidate). Additionally, the new species is distinguished from A. ojiara by the shorter postorbital distance (36.6-46.9 vs. 50.0-57.2 % HL), from A. chico by the shallower body (33.5-39.8 vs. 37.0-43.0 % SL) and longer caudal peduncle (13.3-16.5 vs. 10.1-12.0 % SL), and is distinguished from A. pynandi by the shorter head (25.7-28.6, mean value= 26.5 % SL, vs. 27.5-30.8, mean value= 28.8 % SL), the shorter maxilla (20.7-23.3, mean value=22.0 % HL, vs. 22.8-27.5, mean value=25.2 % HL), and the abrupt expansion of the maxilla under maxillary tooth position (vs. not abruptly expanded). Astyanax puka is distinguished from A. ita by the presence of 36-38 perforated scales on lateral line (vs. 34- 36), the presence of 22-27 branched anal-fin rays (vs. 20-24), shorter distance between pelvic to anal fins (17.1-20.6 vs. 19.1-21.3 % SL), and shorter maxillary length (20.7-23.3 vs. 24.4-29.9 % HL).
The shape and denticulation of the gill-rakers were not described for all the species mentioned, but similar broad denticles on gill-rakers distributed on most of its surface, were observed in A. chico and A. troya , along with A. puka . In other species of Astyanax not sharing the expanded teeth and gradually decreasing dentary teeth, as A. abramis (Jenyns) , A. asuncionensis Géry , A. correntinus (Holmberg) , A. endy Mirande, Aguilera & Azpelicueta , A. cf. fasciatus (Cuvier) , A. latens Mirande, Aguilera & Azpelicueta , A. lineatus (Perugia) , A. pelegrini Eigenmann , A. tumbayaensis Miquelarena & Menni , and A. mexicanus (De Filippi) , the type-species of the genus, the gill-rakers have few, thin denticles located only on proximal half of anterior and, in some cases, posterior edges. Gill-rakers similar to those of A. chico , A. troya , and A. puka were observed also in species of other genera that do not share this teeth morphology, e. g., Gymnocorymbus ternetzi (Boulenger) and Tetragonopterus cf. argenteus Cuvier . Therefore, the phylogenetic information contained in the morphology of teeth and gill-rakers has to be tested in more inclusive and detailed analyses.
Astyanax puka lives in sympatry with A. abramis , A. asuncionensis , A. cf. eigenmanniorum (Cope) , and A. cf. fasciatus . The new species is readily distinguishable from all these species by the expanded premaxillary and maxillary teeth, and the gradually decreasing dentary teeth (vs. not expanded premaxillary and maxillary teeth, and the presence of 4 or 5 anterior dentary teeth conspicuously larger). The new species is further distinguished from A. abramis and A. asuncionensis by the vertical humeral spot (vs. horizontally oval) and the absence of circuli on posterior field of scales (vs. presence), and from A. cf. fasciatus by the fewer lateral-line scales (36-38 vs. usually 38-40) and fewer branched anal-fin rays (22-27 vs. usually 26-29).
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