Holotype. ILPLA 1712, male, 61.1 mm SL; Villaguay Creek at Balneario (31º55’S 59º03’W), Gualeguay River basin, Entre Ríos Province, Argentina; coll.: A. Miquelarena, et al., November 2004.
Paratypes. ILPLA 569, (13), 7 males, 6 females, 59.2-78.9 mm SL; Brazo Chico Creek, 10 km from Uruguay River (33°45’S 58°32’W), Entre Ríos Province, Argentina, coll: N. Landoni, January 1985; ILPLA 1709, (4) 2 males, 2 females (c&s), 60.2-80.9 mm SL; same locality as previous specimen; ILPLA 1710, (7) males, 55.0-60.6 mm SL; ILPLA 1711, (5) 4 males, 1 juv. (c&s), 41.0-74.2 mm SL; ILPLA 1713, (4) males, 57.7-66.0 mm SL, MLP 9672, male, 55.0 mm SL, collected with holotype.
Diagnosis: Astyanax aramburui is distinguished from all congeners by the following unique combination of characters: round or trapezoidal black humeral spot, dorsal to the lateral line; a branch of the infraorbital sensory canal directed ventrally, continued as a series of pores totally or partially traversing the third infraorbital; body relatively slender (31.8-37.4 % SL); eye large (41.1-45.8 % HL); snout short (15.5-20.9 % HL); caudal peduncle relatively slender (10.3-12.0 % SL); one pentacuspid maxillary tooth; 38-42 perforated scales in lateral line; and v -vi, 23-29 anal-fin rays. In addition, the species is characterized by the presence, in males, of breeding tubercles on the head and scales, and bony hooks on all fins.
Description: Morphometric data appear in table 1. Body elongate, with maximum body depth at dorsal-fin origin (31.8-37.4% SL). Dorsal body profile convex, slightly concave between eye and supraoccipital process, relatively straight from that point to dorsal-fin origin and descending slightly to adipose-fin origin. Dorsal and ventral margins of caudal peduncle slightly concave. Caudal peduncle relatively slender (10.3-12.0% SL). Ventral body profile convex between tip of snout and pelvic-fin origin, nearly straight between that point and anal-fin origin. Body compressed posteriorly from anal-fin origin. Head short (22.6-25.2% SL). Snout short (15.5-20.9% HL). Eye large (41.1-45.8% HL). Interorbital less than eye diameter (30.3-35.3% HL). Mouth terminal or slightly superior, lower jaw included. Maxilla relatively long, extending slightly beyond anterior edge of orbit.
Dorsal-fin origin almost equidistant between tip of snout and base of caudal-fin. Tip of pectoral fin surpassing pelvic-fin origin in both males and females. Tip of pelvic fin almost never reaching anal-fin origin in most females (except in one specimen). Tip of pelvic fin of males either falling short of, reaching or surpassing anal-fin origin. Bony hooks present on rays of all fins in matures males. Hooks mostly present on posterior branches of rays. Usually one pair of bony hooks per ray segment.
Dorsal-fin rays ii,9 (6*); iii,9 (4); posterior margin of dorsal fin typically straight, the last unbranched ray and first two branched rays longest. Bony hooks of males small, scattered on branches of first to eighth fin rays.
Pectoral-fin rays i,12 (3); i,13 (6); i,14 (1*). Bony hooks of large specimens small and scarce, 4-6 hooks on a few branched rays.
Pelvic-fin rays i,7 (10*). Bony hooks numerous, more developed on first to fourth branched rays. Origin of pelvic fin anterior to dorsal-fin origin. Pelvic axillary scale without hooks. Posterior margin of pectoral and pelvic fins rounded.
Anal-fin rays v,23 (1); v,24 (1); vi,25 (1*); v,25 (3); v,26 (2); v,27 (1); vi,29 (1). Bony hooks conspicuous, curved, distributed from last unbranched ray to, usually, 15th branched ray. Minute hooks distributed along distal third of some remaining rays. Origin of anal fin anterior to posteriormost dorsal fin ray insertion. Posterior margin of anal fin nearly straight in males, and with anterior one-third slightly falcate in females. Caudal-fin forked, with lobes of similar size. Principal caudal-fin rays i,17,i. Dorsal procurrent rays 11 (1) or 12 (6). Ventral procurrent rays 8 (1), 10 (5), 11(1). Caudal fin with only few bony hooks on principal rays.
Cycloid scales large, deeply striated, regularly distributed on body. Lateral line complete, perforated scales 38 (1), 39 (5), 40 (13), 41 (1*), 42 (1). Scale rows between dorsal-fin origin and lateral line 7 (19*); 8 (2). Scale rows between lateral line and anal-fin origin 6 (5), 7 (16*). Predorsal scales 11 (6), 12 (13*), 13 (2), usually in a regular series. Single row of scales at base of anal fin, 12 (1), 14 (4), 15 (6), 16 (3*), 17 (2), 18 (2), 19 (1), 20 (1), 22 (1). Preventral scales large. Pelvic-fin axillary scale with evident grooves. Males with small regularly-arranged tubercles on posterior edge of scales (see remarks below).
Premaxilla with short ascending process and relatively elongated lateral process, with two series of teeth (Fig. 2a -b). Outer row with 4 to 6 teeth, somewhat irregularly arranged, with 3 to 5 (typically 3) cusps. Inner row with 5 broader teeth, a symphysial tooth, narrowest and highest, with 4 or 5 (typically 5) cusps; the second and third with 6 or 7 cusps; the fourth with 4 to 7 (typically 6) cusps. Fifth tooth smallest and situated internally with respect to fourth, with 4 to 6 cusps (single specimen with only 3). Maxilla (Fig. 2c) with one pentacuspid tooth on upper third (one tricuspid tooth in only two individuals). Dentary with 3 or 4 large teeth with 5-7 cusps, followed by a middle-sized tooth with 4 or 5 cusps, and 3-6 smaller teeth, monocuspid or tricuspid (Fig. 2d).
Vertebrae 36 (6), 37 (2). Supraneurals 5 or 6, typically 5. Infraorbitals 6. A branch of infraorbital sensory canal directed ventrally, continued as a series of pores totally or partially traversing third infraorbital (Fig. 3). Upper gill rakers 9(1), 10(2), 11(3), 12 (2); lower gill rakers 13 (1), 14 (1), 15 (4), 16 (2).
Color in alcohol: Background light yellowish. Dorsum of head and body darker. Bones in infraorbital series and operculum silvery. Small dark humeral spot, round or trapezoidal, often with diffuse margins, centered on third and fourth scales of scale row just dorsal to lateral line. Lateral body stripe broad and dark, extending from behind humeral spot, and ending as a black rhombic caudal spot on middle caudal-fin rays. Lateral body stripe silvery in some specimens. Ventrolateral region of body uniformly colored. Dorsal, anal and caudal fins with scattered dark chromatophores. Pectoral and pelvic fins hyaline.
Color in life: Body silvery white, iridescent with yellowish hues. Dorsum of head and body with dark chromatophores. Lateral surface of head silvery. Lateral stripe silvery, terminating in black caudal spot continued on to middle caudal-fin rays. Dorsal and anal fins covered with scattered dark chromatophores. Pectoral fin hyaline, except for dark first unbranched ray. Pelvic fin hyaline. Caudal fin grayish, with black distal margin (Fig. 4).
Etymology: Named after Prof. Raúl H. Arámburu (1924-2004), researcher and professor of the Museo de La Plata, Buenos Aires, founder of the first chair of Ichthyology in Argentina.
Distribution and habitat: Astyanax aramburui is known from Villaguay Creek and Brazo Chico Creek, which flow into the Paraná and Uruguay Rivers, respectively, in Entre Ríos Province, Argentina (Fig. 5).
Villaguay creek is a relatively extensive watercourse, with sections about 50 m wide and pools over 2 m deep. The banks are vegetated with grasses and other plants, and the bottom consists of mud and clay (Fig. 6). Brazo Chico creek is a watercourse situated in the deltaic area known as Islas del Ibicuy.
Remarks: Of all the families of Neotropical Characiformes, only the Characidae, Parodontidae and Lebiasinidae are known to develop true nuptial tubercles (Wiley & Collette, 1970:164-167; Collette, 1977: 236-241). Those authors state that breeding tubercles are probably present in all species of Parodontidae and at least five species of Lebiasinidae. Within the Characidae, similar structures have been reported in Bryconamericus emperador (Eigenmann & Ogle), by Meek & Hildebrand (1916:284); for an unidentified BryconamericusZBK species from Panama by Fink (1976:342); in two species of MonotocheirodonZBK by Collette (1977:238); and in two Brazilian species, Myxiops aphos Zanata & AkamaZBK, and an undescribed species of AstyanaxZBK by Zanata & Akama (2004:50-51). We were able to observe small tubercles on the dorsal part of the head, as well as on the snout, infraorbital, and opercular region in males of Parodon carrikeri FowlerZBK. These structures are irregularly distributed on the scales, particularly in the predorsal area (Figs. 7a -d). In mature males of A. aramburui, the tubercles are arranged as in P. carrikeriZBK in the cephalic region, but they are distributed regularly on the posterior edge of the scales over most of the body (Figs. 8a -d). Mature male specimens of Astyanax aeneus ( Guenther) and Bryconamericus thomasi FowlerZBK also show breeding tubercles arranged as in A. aramburui. Histological examination confirmed that they are of epitelial origin, and formed by cells distributed in a concentric manner. In all the above species the breeding tubercles were more noticeable in the specimens collected during October, November and March. Zanata & Akama (2004), in their discussion of characters that distinguish the genus MyxiopsZBK, state that these structures are located along the posterior border of the scales, thus delineating the scale outline; this agrees with our observations of A. aeneus, A. aramburui and B. thomasiZBK. However, in contrast with the condition in the above-mentioned species, the accumulation of epithelial cells of MyxiopsZBK is more conspicuous in juveniles, and occurs both in males and females (Zanata & Akama, 2004).
Nineteen species of the genus AstyanaxZBK have thus far been reported from Argentina (Miquelarena & Menni, 2005). Although A. fasciatus Cuvier is indicated, in some references, to be widely distributed in Argentina, Melo & Buckup (2006) concluded that this species is restricted to the São Francisco River drainage, in Brazil. A. aramburui resembles A. fasciatus in possessing a single humeral spot, a relatively high number of anal-fin rays, and one tooth on the anterior margin of the maxilla. It differs from the São Francisco populations by usually having 5 (vs. 4) teeth in the outer row of the premaxilla [ A. aramburui 4(3), 5(17), 6(1); A. fasciatus 3(1), 4(38), 5(4), 6(1)]. Moreover, A. fasciatus is diagnosed by the presence of an elongated dorsal fin in mature males (Melo & Buckup, 2006), a character not shared by A. aramburui.
Tetragonopterus rutilus JenynsZBK, originally described from the Paraná River, was considered by Melo & Buckup (2006:49, 50; table2) as a probable valid species of AstyanaxZBK. An analysis of morphometric and meristic data of the A. rutilus holotype provided by those authors shows that A. aramburui (21 specimens analyzed unless otherwise indicated) differs from A. rutilus in several characters: lesser body depth (31.8-37.4 [mean=33.9] vs. 40% SL), shorter preanal distance (54.5-61.8 [mean=59.6] vs. 66.4% SL), shorter snout length (15.5-20.9 [mean=17.8] vs. 23.0% HL), lower vertebrae count (36-37 [mean=36.2] [8 specimens] vs. 37), lesser number of scale rows between lateral line and dorsal-fin origin (7-8 [mean=7.1] vs. 8) and lesser number of scale rows between lateral line and anal-fin origin (6-7 [mean=6.8] vs. 8). In addition, according to the original description, the fins of A. rutilus are “dirty orange or bright red in color” (vs. paired fins hyaline and unpaired fins grayish).
A. aramburui differs from A. biotae Castro & VariZBK, described from the upper Rio Paraná system in southeastern Brazil, by having a greater number of scales in the lateral line (38-42 vs. 32-35), a greater number of scales in transverse series from origin of anal fin to lateral line (6-7 vs. 4-5), and a rounded humeral spot (vs. vertically elongated spot).
A. aramburui exhibits bony hooks on all fins of mature males. This dimorphic character has also been reported in several species that have been recently described from the Paranoplatensean basin: A. chico Casciotta & AlmironZBK; A. hermosus Miquelarena, Protogino & LopezZBK; A. ojiara Azpelicueta & GarciaZBK; A. pynandi Casciotta, Almiron, Bechara, Roux & Ruiz DiazZBK; A. troya Azpelicueta, Casciotta & AlmironZBK; A. leonidas Azpelicueta, Casciotta & AlmironZBK (without bony hooks on dorsal fin); and A. tumbayaensis Miquelarena & MenniZBK (without bony hooks on pectoral fin). The new species differs from A.chicoZBK, A. leonidasZBK, A. ojiaraZBK, A. pynandiZBK, A. troyaZBK, and A. tumbayaensisZBK by having a coloration pattern that includes a single humeral spot (vs. two humeral spots). A. aramburui shares with A. hermosusZBK the presence of a single humeral spot, which, however, differs in shape (rounded vs. Y-shaped).
Other characters that distinguish A. aramburui from A.hermosusZBK, A. ojiaraZBK, A. pynandiZBK, and A. troyaZBK are: greater number of scales in lateral line series (38-42 vs. 35-38; 36-38; 34-37 and 34-37, respectively); greater number of branched rays in anal fin (23-29 vs. 17-22; 20-23; 21-26 and 18-21, respectively), and shorter snout length (15.5-20.9% HL vs. 18.3-26.6; 24.5-30.9; 22.7-26.9 and 22.9-28.9% HL, respectively). It also differs from A. hermosusZBK by the greater eye diameter (41.1-45.8% HL vs. 29.7-34.7% HL) and lesser depth of the caudal peduncle (10.3-12.0% SL vs. 12.6-14.7% SL).
A. aramburui differs from A. ojiaraZBK in having a greater eye diameter (41.1-45.8% HL vs. 29.1-37.2% HL) and by the presence of one pentacuspid (vs. heptacuspid) maxillary tooth; from A. pynandiZBK by a lesser body depth (31.8-37.4% SL vs. 35.4-42.9% SL); from A. tumbayaensisZBK by having a greater eye diameter (41.1-45.8% HL vs. 28.9-35.0% HL), lesser body depth (31.8-37.4% SL vs. 39.2-45.3% SL) and lesser depth of the caudal peduncle (10.3-12.0% SL vs. 13.6-15.0% SL); and from A. chicoZBK by a greater number of branched anal-fin-rays (23-29 vs. 19-24).
Males of A. elachylepis Bertaco & LucindaZBK, described from the Tocantins River drainage, also have bony hooks on the dorsal, anal, pectoral, and pelvic-fin rays, but that species is easily distinguished from A. aramburui by the greater number of perforated scales in the lateral line (48-53 vs. 38-42).
A. aeneus, from Arroyo Las Flores, México, shares with A aramburui the presence of breeding tubercles and bony hooks on all fins of mature males, but differs from the latter species by the greater preanal distance (62.1-64.8 vs. 54.5-61.8) and smaller eye diameter (38.8-40.5 vs. 41.1-45.8).