Laemolyta orinocensis ( Steindachner, 1879 )

Mautari, Kelly Cristina & Menezes, Naércio Aquino, 2006, Revision of the South American freshwater fish genus Laemolyta Cope, 1872 (Ostariophysi: Characiformes: Anostomidae), Neotropical Ichthyology 4 (1), pp. 27-44 : 36-38

Laemolyta orinocensis ( Steindachner, 1879) Fig. 16

Anostomus orinocensis Steindachner, 1879: 154 , plate II, fig. 7 and 7a. [original description, type-locality: río Orinoco]; Garman, 1890: 20, 21 [correction of meristic data]; Eigenmann, 1910: 425 [listed]; Eschmeyer, 1998: 1250 [catalog].

Laemolyta orinocensis: Eigenmann & Eigenmann, 1891: 50 [listed]; Myers, 1950: 197 [diagnosis, type-locality]; Géry, 1964: 466 [identification key]; Géry, 1974: 159 [identification key]; Taphorn et al., 1997:55–100 [catalog]; Garavello & Britski, 2003: 73 [catalog]; Lasso et al., 2004:105–195 [list of species and distribution].

Anostomus (Schizodontopsis) orinocensis: Borodin, 1931: 48 [listed].

Anostomus (Laemolyta) orinocensis: Géry, 1977: 182 [identification key, distribution].

Laemolyta proxima non ( Garman, 1890): Lasso, 1992: 15, fig. 4, 22 [in part, only lot MHNLS 5512, specimen 90.3 mm SL].

Material examined. Nine specimens (76.7–166.7 mm SL). Venezuela. Ciudad Bolivar, Orinoco, NMW 62820, 1 lectotype (by present designation), 166.7 mm SL; Ciudad Bolivar, Orinoco, NMW 62595, 1 paralectotype, 149.1 mm SL. Anzoategui, Independencia, laguna Terecaya, to the side of río Orinoco , near

Ciudad Bolivar, MZUSP 62443, 2, 130.7– 134.5 mm SL. Apure, laguna 2 km SE of caño la Pica, MHNLS 4231, 1 of 7, 133.5 mm SL. Río Suapure, Rabo de Cochino, Pijiguaos, MHNLS 5512, 1 of 3, 90.3 mm SL. Anzoategui, paso de río Mamo, 2 km from Juajullal, via Mamo, Soledad, MHNLS 8250, 2 of 3, 89.5–94.7 mm SL. Delta Amacuro, caños Macareo y Mariusa, delta río Orinoco, caño el Tambor (tributary of caño Macareo), MHNLS 14019, 1 of 2, 76.7 mm SL.

Diagnosis. Laemolyta orinocensis can be distinguished from L. garmani , L. taeniata and L. proxima in having more scales along the lateral line (47–52, usually 49 vs. 40–47), from L. garmani and L. taeniata in having more longitudinal rows of scales from the lateral line to the dorsal-fin origin (7–8 vs. 4–5) and from the lateral line to the anal-fin origin (6 vs. 4–5) and also by lacking longitudinal light stripes above the lateral line (vs. having such stripes). Laemolyta orinocensis differs from L. fernandezi by the conspicuous midlateral longitudinal dark stripe and the very inconspicuous transverse dark bars on the body vs. an inconspicuous median longitudinal dark stripe and four transversal dark bars or blotches on the body in L. fernandezi . It can also be further distinguished from L. fernandezi in having a shallower body (21.3–25.1 % vs. 22.9–31.6 %, Fig. 17 ).

Description. Meristic and morphometric data presented in Table 4. Body moderately large (SL = 76.7–166.7 mm). Dorsal profile of body straight or slightly concave from tip of snout to end of supraoccipital spine, slightly convex from that point to dorsal-fin origin, straight and posteroventrally-inclined or slightly convex from base of posterior-most dorsal-fin ray and straight and posteroventrally-inclined or slightly convex from that point to caudal peduncle. Ventral profile of body slightly convex from tip of lower jaw to near isthmus, slightly convex from that point to anal-fin origin and slightly concave at insertion of pelvic fins.

Perforated scales on lateral line 47–52 (47*, usually 49, Table 2). Longitudinal scale rows from lateral line to dorsalfin origin 7–8 (7*, usually 7); scales rows from lateral line to anal-fin origin 6 (6*). Predorsal scales irregularly arranged. Scales rows around caudal peduncle 16–20 (19*, usually 19).

Dorsal-fin rays ii,11; distal margin of fin slightly rounded. Anal fin short, slightly falcate, with ii,8 rays. Pectoral-fin rays i,11–14 (14*, usually 14). Pelvic-fin rays i,8; distal margin of fin truncate. Vertebrae 41–43 (43*, usually 42, N=7).

Color in alcohol. Large adult specimens with dorsal part of body usually dark, extending ventrally to 1 or 2 longitudinal scale rows above lateral line. Conspicuous dark midlateral longitudinal stripe covering 1.5 to 2 longitudinal scale rows extending from tip of snout to rear of caudal peduncle. Ventral part of body lighter from lower limit of longitudinal dark stripe to midventral line. Some specimens with very inconspicuous dark blotch present posterior to opercular margin and another one under dorsal-fin base.

Dorsal, pectoral, and pelvic fins hyaline. Scattered dark chromatophores on anal and caudal fins and along dorsal and ventral edges and median rays of caudal fin.

Young specimens ( Fig. 18 ) with dark, midlateral, longitudinal stripe more conspicuous and narrower at opercle and caudal peduncle. Some specimens with narrow, transverse, dark bars on dorsal part of body and with anal fin dark.

Distribution. Rio Orinoco basin ( Fig. 13 ).

Remarks. Laemolyta orinocensis was considered by Steindachner (1879) to be very similar to L. taeniata (Kner) , but to differ from it in scales counts. In the original description of L. orinocensis, Steindachner (1879) referred to the presence of 3.5 scales between the lateral line and the ventral margin of the body, but Garman (1890) observed that this count is probably incorrect since six scales can be easily counted below the lateral line in the figure of the species in Steindachner’s paper. Laemolyta orinocensis and L. taeniata are very similar in having the dark, longitudinal midlateral stripe on body more evident in young specimens; however, in L. orinocensis the dorsal and ventral margins of the stripe are not absolutely straight. In the syntype specimens (NMW 62820:1 and 62595:1) the longitudinal dark stripe is no longer apparent. In these specimens, however, a vestigial longitudinal dark stripe is still visible, but most of the stripe is silvery due to the presence of guanine on the scales. The silvery color on the centers of the scales above the lateral line form a reticulate pattern. In the original description, Steindachner (1879) designated two syntypes (NMW 62820:1 and 62595:1). The one specimen in NMW 62820:1 is herein designated as the lectotype.

Notwithstanding the similarity of color patterns between young specimens of L. orinocensis and L. fernandezi , the dark longitudinal stripe on the midlateral portion of the body is more conspicuous in L. orinocensis . Laemolyta orinocensis furthermore lacks the dark peduncular spot present in L. fernandezi

Figures

Fig. 16. Laemolyta orinocensis, NMW 62820: 1, lectotype, 166.7 mm SL; Venezuela, Ciudad Bolivar, río Orinoco.

Fig. 17. Regression lines of body depth on standard length for specimens of Laemolyta orinocensis and L. fernandezi.

Fig. 18. Young of Laemolytaorinocensis, MHNLS 4231, 133.5 mm SL; Venezuela,Apure, Laguna, 2 km southeast of caño la Pica.

Fig. 13. Geographic distribution of Laemolyta proxima (black dots; open circle = type-locality), Laemolyta garmani (black squares; open squares = type-locality), and Laemolyta orinocensis (black triangles; open triangle = type-locality). Some symbols might correspond to more than one locality.