Astyanax erythropterus ( Holmberg, 1891 )

Soneira, Paula, Casciotta, Jorge, Almirón, Adriana, Ciotek, Liliana & Giorgis, Pablo, 2010, Redescription of Astyanax erythropterus (Holmberg, 1891) (Teleostei: Characiformes: Characidae) from La Plata basin in Argentina, Neotropical Ichthyology 8 (4), pp. 771-785 : 771-785

Astyanax erythropterus ( Holmberg, 1891) Figs. 1-4

Diagnosis. Astyanax erythropterus is distinguished from all species of the genus, except A. pelegrini , by the presence of a long anal fin bearing 38 to 42 branched rays (vs. 34), a large number of perforated scales on the lateral series (49-54 vs. 48), and the juveniles (18.0- 29.9 mm SL; Fig. 1 ) with the dorsal, anal and caudal fins vermilion red. Astyanax erythropterus differs from A. pelegrini by the number of transverse scales below the lateral line (8-10 vs. 7-8). Astyanax erythropterus can be distinguished from the six sympatric species by the great number of branched anal-fin rays 38-42 (vs. 30-34 in A. abramis , 30-32 in A. asuncionensis , 29-33 in A. correntinus ; 22-24 in A. eigenmanniorum ; 23-26 in A. rutilus ; and 25-30 in A. stenohalinus ).

Description. Body deep, with maximum body depth located at dorsal-fin origin ( Figs. 1-4 ). Dorsal profile of head slightly convex from snout tip to vertical through anterior margin of eyes, concave from this last point to supraoccipital spine in adults, slightly convex in juveniles. Dorsal profile of body markedly convex from tip of supraoccipital spine to base of first dorsal-fin ray in adults, slightly convex in juveniles. Dorsal profile slanting ventrally from dorsal-fin origin to caudal peduncle; slightly concave on caudal peduncle. Ventral profile of body convex from tip of lower jaw to anal-fin origin, posterodorsally slanted along analfin base, slightly concave on caudal peduncle. Dorsal-fin origin almost equidistant from snout tip and caudal-fin base. Pelvic-fin origin anterior to vertical through dorsal fin-origin. Anal-fin origin slightly posterior to vertical through base of last dorsal-fin ray. Origin of adipose fin at vertical through base of 25-27 branched anal-fin rays. Tip of longest pectoral-fin rays always extending slightly beyond pelvic-fin origin. Tip of longest pelvic-fin rays not reaching anal-fin origin in adult specimens, reaching or extending slightly beyond this point in specimens less than 60 mm SL. Head short, mouth terminal; snout relatively short and blunt. Lower and upper jaws isognathous. Premaxilla ascending process triangular-shaped; alveolar process long, bearing two series of teeth. Outer row with 4 or 5 tricuspid or pentacuspid teeth, not expanded distally, with central cusp larger, and lateral ones well-developed. Third tooth slightly displaced in relation to remaining outer row teeth. Inner row teeth 5, each with 4 to 7 cusps ( Fig. 5a ). Anterodorsal process of maxilla long, lateral process laminar, long and slender. Maxilla with one tooth with 5 or 7 cusps ( Fig. 5a ). Dentary with four anterior large teeth with 5 or 7 cusps, followed by one medium size tooth with 4 to 5 cusps, and four smaller ones with 1 to 3 cusps ( Fig. 5b ). Eye larger than snout, interorbital distance wide. Third infraorbital not contacting latero-sensory canal of preopercle either ventrally or posteriorly. Dorsal fin ii-iii,8 (2), 9(25); when 3 unbranched rays present, first very short; last unbranched dorsal-fin ray longest. Anal fin iii-iv,38 (3), 39 (8), 40(11), 41(6), 42(2), 43(1), 45(1) rays. Principal caudal fin-rays i,17,i. Lower caudal-fin lobe slightly longer than upper one. Pectoral-fin rays i,12 (2), 13 (21), 14 (5); distal margin of fin slightly curved. Pelvic-fin rays i,7; pelvic-fin distal margin slightly curved. Scales cycloid. Lateral line series with 47 (1), 49 (10), 50 (7), 51(6), 52(3), mm SL, Argentina, Provincia de Entre Ríos, Parque Nacional

P. Soneira, J. Casciotta, A. Almirón, L. Ciotek & P. Giorgis 781

53(2), 54(1) perforated scales. Eleven to thirteen longitudinal scale rows between dorsal-fin origin and lateral line; 8 to 10 between lateral line and pelvic-fin origin. Scales around caudal peduncle 18-20. Thirty-five to thirtynine scales along anal-fin base, covering bases of all unbranched and branched anal-fin rays. Twenty percent of caudal fin base covered by scales. First branchial arch with 24 gill-rakers (15 on ceratobranchial, 1 on cartilage, and 8 on epibranchial) (2). Total vertebrae: 33 (2).

Morphometrics characters of 28 specimens are presented in Tables 1-2 and Fig. 6 . Absolute and log-transformed data were used to test differences in means of morphometric attributes between juveniles and adults. Test results shown that mean value of each attibutes were significantly different between both groups (t -Test; p<0.05; Table 1 ). Lineal equation provided a very good fit to the relationships between both standard and head length and morphometric attributes ( R 2 = 0.84- 0.99; p<0.05; Table 2 ). Most of regressions shown higher slopes in juveniles than in adults, specially in pectoral and pelvic-fin length and predorsal length ( Fig. 6 ). The differences of the slopes betwen groups were not-significant in all cases (t -Test; p <0.05). Therefore, we conclude that morphometrics changes during the ontogeny would be not very deep .

Color in alcohol. Background light yellow, dorsal region of body and head darker ( Figs. 3-4 ). Dark narrow stripe extending along dorsal midline from supraoccipital spine tip to base of dorsalmost caudal-fin ray. Dark lateral band wide beginning at upper opercular posterior margin, ending with a triangular spot on caudal peduncle. Adults usually with faint dark vertically elongated humeral spot situated between 4 th to 7 th scales of longitudinal series above lateral line, upper half of humeral spot wider than lower half. Humeral spot always present in juveniles, absent in some adults. Scales of upper half of body with scattered dark chromatophores. Small chromatophores present on premaxilla and lower jaw regions. Gray chromatophores aligned on dorsal margin of lower jaw region. Dorsal and adipose fins pale gray; dorsal fin with scattered black chromatophores on its surface, adipose fin with black cromatophores more concentrated on its margin. Caudal fin pale gray with small black chromatophores on distal margin. Anal fin pale yellow. Pectoral fin pale gray with scattered chromatophores on first five rays. Pelvic fins pale yellow.

Color in life. Adults ( Fig. 2 ): background silvery, dorsal region of body and head with green glints. Wide silvery lateral band from posterior opercular margin and ending as a triangular

782 Redescription of Astyanax erythropterus from La Plata basin in Argentina

mm SL, Argentina, Provincia de Entre Ríos, Parque Nacional spot on caudal peduncle. Dark humeral spot on flank very faint, some specimens with a second very faint lateral spot 4 or 5 scales behind the humeral spot. Dorsal and adipose fins hyaline; dorsal fin with scattered black chromatophores. Caudal fin hyaline with dark area on base and scattered chromatophores on rays. Anal and pectoral fins hyaline. Pectoral fins with scarce chromatophores on first ray. Pelvic fins hyaline.

Juveniles ( Fig. 1 ): Background of midventral body silvery, dorsal region of body and head darker with black chromatophores. Body areas closer to anal-fin base, caudal and dorsal fin with scattered red chromatophores. Small dark chromatophores on premaxilla and lower jaw regions. Gray chromatophores aligned on dorsal margin of lower jaw region. Dark humeral spot on flank. Dorsal, anal and caudal fins vermilion red, with distal third hyaline and bearing scattered dark cromathophores. Adipose, pectoral and pelvic fins hyaline with scattered dark chromatophores.

Sexual dimorphism. Secondary sexual dimorphism was found on anal and pelvic-fin rays of males and body depth. Males have hooks on last unbranched and following 22 to 30 branched anal-fin rays. Anal-fin hooks on posterior branches of rays, one pair on each segment curved dorsally. Pelvic fin of males with 8 to 18 small hooks on first to sixth branched rays, one or two on each segment. Body of males less deep than in females (42.8-47.5 vs. 46.0-48.6 % of SL, respectively).

P. Soneira, J. Casciotta, A. Almirón, L. Ciotek & P. Giorgis 783

Distribution. Astyanax erythopterus was found in the middle and lower río Paraná and Río de la Plata basin ( Fig. 7 ).

Material examined. Astyanax erythropterus : Argentina: Provincia de Chaco: MACN-ict 8568, 4, 36.9-56.5 mm SL, Chaco without other data. Provincia de Corrientes: MACN-ict 9448, 14, 78.4-96.9 mm SL, ciudad de Yahapé, río Paraná. AI 265, 1 c&s, 84.7 mm SL, ciudad de Yahapé, río Paraná. MACN-ict 9449, 2, 79.2-88.4 mm SL, ciudad de Ituzaingó, río Paraná. Provincia de Buenos Aires, Punta Lara, Río de la Plata basin:MACN-ict 9450, 2, 49.3-55.5 mm SL, Arroyo Capitán.AI 266, 1 c&s, 48.3 mm SL, Arroyo Capitán. MACN-ict 9451, 3, 36.8- 40.9 mm SL, Arroyo Baldovinos. Provincia de Entre Ríos, Parque Nacional Pre-Delta, río Paraná basin:MACN-ict 9452, 1, 25.7 mm SL, Arroyo La Ensenada , Camping Municipal. MACN-ict 9453, 1, 29.9 mm SL, cuneta en camino de acceso. MACN-ict 9454, 1, 18.0 mm SL, Arroyo La Ensenada , Camping Municipal. MACN-ict 9455, 1, 89.3 mm SL, Rowing Club, desembocadura delArroyo La Ensenada .

Figures

Fig. 1. Astyanax erythropterus (juvenile), MACN-ict 9453, 29.9 Pre-Delta, río Paraná basin. Photographed in life.

Fig. 2. Astyanax erythropterus (adult), MACN-ict 9455, 89.3 mm SL, Argentina, Provincia de Entre Ríos, Parque Nacional Pre- Delta, río Paraná basin Rowing Club, mouth of the Arroyo La Ensenada. Photographed in life.

Fig. 3. Astyanax erythropterus (juvenile), MACN-ict 9453, 29.9 Pre-Delta, río Paraná basin.

Fig.4. Astyanaxerythropterus (adult),MACN-ict 9448,88.4 mmSL,Argentina,Provincia de Corrientes,ciudad deYahapé, ríoParaná.

Fig. 5. Astyanax erythropterus, AI 265, 84.7 mm SL: left premaxilla, maxilla, and lower jaw, internal view. Scale bar = 1 mm.

Fig. 6. Scatter plot and regresión line of pelvic-fin length, pectoral-fin length, and predorsal length on standard length in A. erythropterus. Triangles = juveniles; circles = adults.

Fig. 7. Distribution of examined material of Astyanax erythropterus. 1) Yahape and Ituzaingó cities. 2) Chaco. 3) Parque Nacional Pre-Delta. 4) Río de la Plata basin.