Astyanax guianensis Eigenmann 1909

Figs. 1–2, Table 1

Astyanax guianensis Eigenmann 1909: 16 [type locality: Warraputa (= rio Essequibo at Warraputa cataract, Guyana)].— Eigenmann 1910: 434 [citation].— Eigenmann, 1911: 177 [closely allied to Astyanax guaporensis].— Eigenmann 1912: 350 [identification key; literature compilation].— Eigenmann 1921: 274, plate 53, Fig. 4 [identification key; literature compilation].— Eigenmann 1927: 328 [literature compilation].— Henn 1928: 60 [type catalog].— Böhlke 1953: 22 [type catalog].— Géry 1977: 426 [identification key].— Nijssen et al. 1982: 14 [type catalog].— Böhlke 1984: 47 [type catalog].— Ibarra & Stewart 1987: 12 [type catalog].— Vari & Howe 1991: 6 [type catalog].— Nijssen et al. 1993: 216 [type catalog].— Garutti & Venere 2009 [literature compilation].— Lima 2009: 29 [Guiana Shield at Amazonas and Bolivar States, Venezuela].— Lima et al. 2003: 109 [questionably Venezuela].— Marinho & Birindelli 2013: 46 [similar to Astyanax multidens and A. guaporensis].—Marinho & Ohara 2013: 476 [tentative identification of material from rio Beni].

Moenkhausia sp. “ collettii alta”.— Lima et al. 2013: 322 [rio Madeira basin, brief description].

Diagnosis. Astyanax guianensis can be distinguished from all congeners, except A. angustifrons (Regan), A. aurocaudatus Eigenmann, A. gisleni Dahl, A. goyanensis (Miranda Ribeiro), A. guaporensis, A. henseli Melo & Buckup, A. leopoldi Géry, Planquette & Le Bail, A. multidens, A. nasutus Meek, A. nicaraguensis Eigenmann, A. superbus Myers, and A. totae Haluch & Abilhoa by having five to 10 maxillary teeth (vs. none to four). Astyanax guianensis is distinguished from the aforementioned species, except A. angustifrons, A. goyanensis, A. guaporensis, A. leopoldi, A. multidens, A. nicaraguensis, and A. totae, by having 31 to 35 pored lateral-line scales (vs. more than 35). It can be distinguished from A. angustifrons, A. goyanensis, A. leopoldi, A. multidens, and A. nicaraguensis by having the middle caudal-fin rays hyaline (vs. middle caudal-fin rays dark), from A. guaporensis by having five, rarely six (4 out of 59 examined specimens) horizontal scale row above lateral line (vs. six to seven) and the absence of a midlateral series of dark anteriorly-directed chevrons (vs. presence), and from A. totae by presenting 21 to 25 branched anal-fin rays (vs. 15 to 18).

Description. Morphometric data for Astyanax guianensis presented in Table 1. Small sized species (largest examined specimen 53.3 mm SL). Body compressed laterally, moderately elongate. Greatest body depth at dorsalfin origin. Dorsal profile of head convex from tip of snout to vertical through anterior border of anterior nostril and straight from that point to tip of supraoccipital spine. Dorsal profile of body straight to slightly convex at predorsal region, straight at dorsal-fin base, straight from end of dorsal-fin base to adipose-fin origin, and concave along caudal peduncle. Ventral profile of head and body slightly convex from anterior tip of lower lip to anal-fin origin, straight along anal-fin base, and slightly concave along caudal peduncle.

Jaws aligned vertically, mouth terminal. Premaxillary teeth in two rows. Outer row with 2(4), 3(32), 4(30) or 5*(3) tricuspid teeth. Inner row with 5*(66) or 6(3) teeth, 4 of which pentacuspid, and lateralmost one tricuspid. Maxilla with 5(17), 6*(22), 7(22), 8(5), 9(3) or 10(1) uni- to tetracuspid teeth. Dentary with 4(26) large pentacuspid teeth, followed by one or two smaller tricuspid and one series of 5 to 12 small uni- to tricuspid teeth. Central median cusp in all teeth longer than lateral cusps (Fig. 2). Branchiostegal rays 4. First gill arch with 2(3) or 3(3) rakers on hypobranchial, none (3) or 1(3) raker on intermediate cartilage, 10(2) or 11(4) rakers on ceratobranchial, 1(6) raker on intermediate cartilage, and 7(3) or 8(3) rakers on epibranchial. Each gill raker bearing small denticles.

Supraneurals 3(3) or 4*(4), upper portion with bony lamellae. Dorsal-fin rays ii,9*(65), first unbranched ray about one-half length of second unbranched ray. First dorsal-fin pterygiophore inserted posterior to neural spine of 7th(1) or 8th*(6) vertebrae. Dorsal-fin origin slightly posterior to vertical through pelvic-fin origin. Adipose-fin origin at vertical through base of 18th or 19th branched anal-fin rays. Pectoral-fin rays i(64), 12(22), 13(37) or 14(4). Tip of adpressed pectoral fin extending beyond pelvic-fin origin. Pelvic-fin rays i*(65), 6(1) or 7*(64). Tip of adpressed pelvic fin extending beyond anal-fin origin. Anal-fin rays iv*(7), 21(8), 22(6), 23*(18), 24(27) or 25(5). First anal-fin pterygiophore inserted posterior of haemal spine of 15th*(7) vertebra. Anal-fin origin located at vertical through base of 5th or 6th branched dorsal-fin ray. Principal caudal-fin rays i,9*(57) at upper and i,8*(57) at lower lobe. Dorsal procurrent caudal-fin rays 11(1), 12(4) or 13(1) and ventral procurrent caudal-fin rays 9(2), 10(2) or 11(2). Caudal fin forked, lobes pointed.

Lateral line straight to slightly curved ventrally, with 31(3), 32(7), 33(17), 34(17) or 35*(16) perforated scales from supracleithrum to caudal-fin base. Longitudinal scale rows between dorsal-fin origin and lateral line 5*(55) or 6(4). Longitudinal scale rows between lateral line and pelvic-fin origin 4*(44) or 5(10). Predorsal scales 8(14) or 9(51) in one aligned series. Single row of 4–8 scales overlying base of anteriormost anal-fin rays. Scale rows around caudal peduncle 14*(50). Scales usually at base of caudal fin, not extending over lobes; some specimens with scales along basal one-sixth of lower lobe. Abdominal vertebrae 14*(5) or 15(2), caudal vertebrae 18(3) or 19*(4). Total vertebrae 32(1) or 33*(6).

Color in alcohol. General body color pale yellow (Figs. 1 a–c). Upper and lower lips, anterior portion of maxilla, snout, top of head, dorsal portion of opercle and pectoral girdle with scattered small dark chromatophores. Some specimens with dark chromatophores scattered on third infraorbital. Middorsal horizontal scale rows bordered by dark pigmentation, forming slightly reticulated pattern. More pigmented specimens with faint dark chromatophores bordering all scales, except on ventral portion of body. Scattered dark chromatophores above analfin base. More pigmented specimens with dark chromatophores concentrated along margins of myosepta of posterior half of lower portion of body, between lateral line and anal-fin base. Humeral blotch vertically oriented, extending over one scale row ventral to, and three scale rows dorsal to lateral line, and over three scales horizontally. Portion of humeral blotch located dorsal to lateral line often interrupted by clear horizontal stripe. Humeral blotch followed posteriorly by clear area and then by pigmented area progressively fading posteriorly as a longitudinal stripe, from vertical through 7th or 8th lateral-line scale to caudal peduncle. Some specimens retaining guanine over longitudinal stripe. Dark pigmentation along horizontal septum extending approximately from vertical through dorsal-fin origin to caudal peduncle, falling short of caudal-fin base. Faint pigmented area at caudal peduncle. First unbranched dorsal-fin ray with dark chromatophores, remaining dorsal-fin rays hyaline. Distal half of interadial membranes of all dorsal-fin rays with scattered dark chromatophores. Pectoral, pelvic, caudal and adipose fins with few scattered dark chromatophores. Distal portion of interadial membranes of branched anal-fin rays with concentration of dark chromatophores; proximal portion with few scattered dark chromatophores.

Color in life. General body coloration silver to pale (Fig. 1 d). Dorsal portions of head and eye, middle portions of dorsal and anal fins (especially anteriorly), adipose fin, and base of upper and lower caudal-fin lobes yellow to orange. Humeral blotch and longitudinal stripe conspicuous in life. Tip of the three longest pelvic-fin rays white. Tip of first six dorsal- and anal-fin rays milky white.

Sexual dimorphism. No sexually dimorphic characters observed.

Geographic distribution. Astyanax guianensis is widespread throughout the Guiana Shield drainages and also in the Amazon and Orinoco river basins (Fig. 3).

Habitat and ecological notes. Astyanax guianensis was collected in clear water streams, running over sand and silt bottoms, at altitudes ranging from 204 to 240 m above sea level, in habitats characterized by slow to moderate water current, less than one meter deep. The riparian vegetation was mainly composed by grass, shrubs, and trees. The analysis of stomach contents of five specimens of A. guianensis (MZUSP 97149 and MZUSP 109674) revealed the presence of organic debris, aquatic insects (caddisflies larvae, chironomids pupae, and Odonota nymph), and fragments of other unidentified arthropods.

Remarks. Most features described by Eigenmann (1909) in the original description of Astyanax guianensis matches those observed by us. There are only two exceptions. Eigenmann (1909) mentioned four to seven maxillary teeth. In 70 examined specimens, five to 10 tiny teeth were counted in the maxilla, none had four. Eigenmann (1909) also mentioned the presence of 34 to 35 (rarely 36) scales on the lateral series. In 60 examined specimens, 31 to 35 scales were counted on the lateral series, none had 36.

In the label corresponding to lot CAS 68733 (ex IU 12078), the word cotype, is written in reference to one specimen of Astyanax guianensis collected by Eigenmann at Rupununi, near Rockstone. A second label was found inside the jar, stating that this specimen was not cited in the original description of A. guianensis and should not be considered as cotype. We agree with this remark and thus will not consider this specimen as paratype.

Pearson (1924) mentioned 12 specimens of Astyanax guaporensis from lagoons near Reyes [= pampa town 24 mi NE of Rurrenabaque], rio Beni, Bolivia, identified as Astyanax cf. guianensis by Marinho & Ohara (2013). Examination of this material (CAS 68730 [ex IU 17322]) confirmed the identification of the specimens as Astyanax guianensis .

Lowe-McConnell (1991) cited Astyanax guianensis from rio das Mortes, rio Araguaia basin. These specimens could not be analyzed herein. However, extensive material from that drainage was examined and did not yield any specimen of A. guianensis .