Astyanax abramis Jenyns 1842

Astyanax abramis (Jenyns, 1842)

(Fig.10 A; Table 2)

Tetragonopterus abramis Jenyns, 1842: 123 (Type locality: “Paraná River, as high up as Rozario”, Argentina). Bertoniolus paraguayensis Fowler, 1918: 141 (Type locality: Puerto Bertoni, Paraguay).[Syn. nov.]

Diagnosis. Astyanaxabramis is distinguished from other species of the genus Astyanax by presenting a horizontally oval black humeral spot and two vertical brown bars situated in the humeral region, characteristics that include it in the Astyanax bimaculatus group. It is distinguished from A.argyromarginatus, A.clavitaeniatus, A. goyacensis, A. incaicus, A. novae, A. rupununi, A. saltor, A. siapae, A. unitaeniatus, and A. utiariti by the absence of a conspicuous midlateral black stripe, extending above the lateral line from the humeral spot or just behind it (from the second vertical bar) tothe caudal peduncle, continuing along the median rays of the caudal fin; the midlateral stripe continually narrows forward (vs. midlateral black stripe present). It is also distinguished by the presence of one black spot on the caudal peduncle (vs.spot absent). From the other species of the same group, A. abramis is distinguished by an elevated number of scales on the lateral line, 42–48 vs. 30–39 (rarely 40 or 41 in A. lacustris). Furthermore, it differs from A. validus by the absence of horizontal lines forming a zigzag (vs. presence). It differs from A. bimaculatus due to the presence of horizontal stripes that begin from spots at center of the scales (vs. horizontal stripes absent), and because of a markedly concave external surface of the second tooth of the internal series of the pre-maxilla with misaligned cusps (vs. tooth with slightly concave surface and cusps aligned in one single plane). See “Note on other species of the Astyanax bimaculatus subgroup caudal peduncle spot” for A. maculisquamis, A. borealis, and A. vittatus, and “Remarks” on Astyanax lacustris for A.orbignyanus.

Description. Morphometric data summarized in Table 2. Body compressed and high, with greatest body depth in around origin of pelvic fins. Dorsal profile of head straight or slightly concave from region above eye to supraoccipital spine. Dorsal body profile convex from tip of supraoccipital spine to dorsal-fin origin; straight from that point to adipose fin origin. Ventral profile of body convex from mandibular symphysis to anal fin origin and posterodorsally slanted along anal-fin base. Caudal peduncle deep, nearly straight on dorsal and ventral margins. Snout rounded from margin of upper lip to vertical through anterior nostrils. Head somewhat pointed anteriorly in lateral profile. Mouth terminal, jaw isognathous. Maxilla extending posteriorly to vertical through anterior margin of orbit. Maxilla widened anteroposteriorly.

Two tooth rows in premaxilla; outer row with 4(44) or 5(2)tricuspid teeth, central cusp longer; inner row with five teeth, gradually decreasing in length from first to fifth; usually with five or six cusps on first tooth, six or seven cusps on second to fourth teeth and four or five cusps on fifth tooth; central cusp twice as long and broad as other cusps. Maxilla without teeth, rarely one tricuspidate present (MCP 11592, 2 specimens) Four anteriormost dentary large teeth four, five and sixcuspid; remaining six teeth smaller (1 c&s), uni- to tritracuspid (Fig. 9 B).

Dorsal-fin rays iii (1 c&s) (first very small),9(46); second unbranched ray approximately half length of thirth ray. Distal margin of dorsal fin nearly straight to slightly convex. Dorsal fin origin slightly behind middle of SL. Origin of adipose fin at vertical through sixth, seventh or eighth last anal-fin rays. Anal-fin rays iv(1 c&s), 26(2), 27 (5), 28(11), 29(16), 30(8) or 31(3). Anal fin profile smoothly concave. Anal fin origin posterior to vertical through base of last dorsal-fin ray. Pectoral-fin rays i,11(7), 12(29) or 13(20). Pectoral-fin tip reaching or slightly surpassing pelvic-fin insertion. Pelvic-fin rays i,7. Pelvic fin originslightly anterior to vertical through dorsal-fin origin. Pelvic-fin tip does not reach or barely reaches anal-fin origin. Caudal fin forked, lobes similar in size, i+17+i principal rays, no scales in the lobes. Procurrent rays, dorsal 11 and ventral 9 (1 c&s).

Lateral line complete with 42(9), 43(14), 44(12), 45(6), 46(3) or48(1) scales. Scale rows between dorsal-fin origin and lateral line 8(16),9(30) or 10(1); scale rows between lateral line and pelvic-fin origin 6(6), 7(37) or 8(6); scale rows between lateral line and anal-fin origin 7(5), 8(23) or 9(21). Scale rows around caudal peduncle 15(1), 16(14), 17(13), 18(3) or 19(2).

Precaudal vertebrae 14; caudal vertebrae 21; total vertebrae 35. Supraneurals 5 (1 c&s). Gill-rakers upper branch 9(18), 10(27) or 11(4); lower branch 13(2), 14(14), 15(23), 16(9) or 17(1); total number 22(1), 23(8), 24(13), 25(16), 26(8) or 27(1).

Color in alcohol. Dorsal and dorsolateral portions of head and body dark brown. A dark humeral spot, horizontally oval, followed by two vertical bars tenuously dark; one exceeds the oval spot and the other is two or three scales from it. Dark spot on the caudal peduncle, conspicuous, extending on the median rays of the dorsal fin; in front it can reach the vertical that passes by the origin of the adipose fin. Lateral side of body with dark spots in the posterior region of scales, forming from 2 to 5 horizontal stripes above the lateral line and 2 to 5 below. Intensity of spots can vary; in some specimens a silver coloration dominates the middle-bottom portion of the body and stripes are reduced to few chromatophores.

Sexual dimorphism. Males with hooks on pelvic and anal fins. Hooks are distributed in one pair per segment and occur from the last non-ramified ray (absent in two specimens) until the second, sixth, or ninth ramified rays. On the pelvic fin, hooks are present on the fourth, fifth, or sixth ramified rays. Of the three male specimens examined, only one presented hooks on the pelvic fin. Gill fusion glands were not found macroscopically on the first gill arch. Téran et al. (2014) did not find any glandular cells in the gill filaments of mature males or females.

Distribution. Middle and lower rio Paraná drainage, rio Paraguai drainage, and lower rio Uruguai drainage (Fig. 7 B).

Remarks.Examination of the holotype of Bertoniolus paraguayensis showed that this name belongs to a species of the Astyanax bimaculatus subgroup with a spot on the caudal peduncle, and has meristic and morphometric characters similar to A. abramis (data from Jenyns, 1842; type not found). Of greater relevance, however, is the fact that both have an elevated number of perforated scales on the lateral line (46 in the holotype of B. paraguayensis), which does not occur in any other species of the subgroup. In the absence of diagnostic characters between Bertoniolus paraguayensis and A. abramis, the former name is considered junior synonym of the second (ICNZ, 1999: art. 23).

Tetragonopterus orbignyanus Valenciennes in Cuvier & Valenciennes, 1850 was described based on specimens collected by Alcide d´Orbigny and M. Baillon in rio de La Plata, environs of Buenos Aires, Argentina. Lots MNHN A-9816(2 specs.), MNHN A-9817 (1spec.), MNHN 9818 (1spec.), and MNHN 0000-4530(1spec.) are part of a syntypic series, all in poor condition. Eigenmann (1921: 248) stated that “one of the types of Tetragonopterus orbignianus (sic) Cuv. & Val. belongs to this variety”, referring to Astyanax (Poecilurichthys) abramis (= A. abramis). This decision was probably a consequence of the different number of scales on the lateral line between the syntypes (see below). Eigenmann then considered that the species of Valenciennes was in part a synonym of A. abramis and in part a synonym of Astyanax (Poecilurichthys) bimaculatus (= A. bimaculatus). Eigenmann probably examined the types of T. orbygnianus during his visit to Europe between 1906 and 1907 when he visited the Musée National d´Histoire Naturelle, Paris, among others (Stejneger, 1937). Examination of photographs of the syntypes showed that all belong to the Astyanax bimaculatus subgroup with caudal peduncle spot, the exception of which was specimen MNHN 9818. This specimen has a comparatively lower body,does not have an apparent humeral spot or vestiges of one (the humeral region is rather damaged), and has 21 or 22 branched anal-fin rays, a number that is not in the range of A. abramis and rarely present in the range of A. lacustris. Despite the poor state of the syntypes, it was possible after examining photographs to estimate the number of perforated scales on the lateral line of each specimen, the only known character that securely distinguishes A. abramis from other species in the Astyanax bimaculatus subgroup with caudal peduncle spot: MNHN 9816-A (about 110.0 mm SL) ca. 40 scales, MNHN 9816-B (about 120.0 mm SL) ca. 43 (Fig. 28), MHNH 9817 (about 100.0 mm SL) ca. 36 scales, MNHN 9818 (about 90.1 mm SL) ca. 38, and MNHN about 4530 (100.5 mm SL) ca. 39 scales. For the material examined in this study of A. abramis, the variation of this count was from 42 to 48 (vs. 32 to 40 in A. lacustris). Garutti &Britski (2000: table 3), upon examining 1,978 specimens of A. altiparanae (= A. lacustris), encountered 3 specimens with 40 scales and one with 41.Specimen MNHN 9816-B exhibited better conditions for an approximate count of scales on the lateral line and, therefore, it is tentatively identified as A. abramis (Fig. 10 C lower),while the others are probably A. lacustris, as defined in this work.Although making T.orbignyanus a senior or junior synonym of A. lacustris remains among the current possibilities, depending on the specimen chosen as lectotype, we prefer a more conservative decision in view of the differences already noted for specimen MNHN 9818 when compared to the other specimens of the syntypic series. This specimen must be examined in greater detail to verify its identity, but for now we prefer not to associate it with any species of the Astyanax bimaculatus group.In addition to the possibility of specimen MNHN 9818 even representing a valid species, we prefer to consider T. orbignyanus as species inquirenda, keeping the name available until a more thorough study, including a greater number of specimens from the region, is undertaken. Our decision is mainly concerned with preserving nomenclatural stability.

Specimens of four lots from the drainages of rio Pari and rio Cuiabá (rio Paraguay drainage) showed differences in body height when compared to the others (33.0–38.6% SL, m=36.4% vs. 39.5–50.8% SL, m=44.3%). Analysis of other morphometric and meristic characters, as well as coloration pattern, did not show additional differences.Until a greater number of specimens can be analyzed, these lots are identified as Astyanax cf. abramis (see comparative material examined).

Material examined. Type. Paraguay: Bertoniolus paraguayensis, Puerto Bertoni, holotype, ANSP 47686, 71.8 mm pict.

Non-types. Brasil: Mato Grosso state:Rio Paraguai drainage: CPUFMT 2733 (2, 79.8 mm) rio Itiquira. MCP 47858 (7, 49.1–67.1 mm), ribeirão Figueira. MCP 15631 (14, 58.6–75.4 mm) stream on the road Barra dos Bugres – Cáceres. MCP 37706, 2, 82.1–89.0 mm SL, rio Pari. MCP 39750,3 (1, 57.0 mm c&s) rio Sangradouro. MCP 47857, 7, 48.3–72.6 mm, ribeirão Figueira. MCP 44429, 2, 67.2–72.6 mm, stream ca 1km from Diamantino. MCP 47856, 2, 58.4–64.7 mm SL, arroio on the road BR-070. MCP 15600 (2, 48.3–53.0 mm SL), rio Bugres. MCP 48462, 74.0 mm SL, stream tributary of rio Caeté, drainage of rio Jauru. Mato Grosso do Sul state: MCP 45960, 3, 66.3–77.0 mm, tributary of rio Miranda. MCP 45960 (3, 67.1–77.7 mm SL), stream tributary of rio Miranda. Argentina:Lower Rio Paraná drainage: MCP 11592 (3, 76.1–86.9 mm, 1) Arroyo dona Flora. Rio Uruguai drainage: MCP 48431(1, 63.9 mm) arroio Chimiray.