Hypophthalmus fimbriatus

Oliveira, Edinbergh Caldas De, Bialetzki, Andréa & Assakawa, Luciana Fugimoto, 2008, Morphological development of Hypophthalmus fimbriatus and H. marginatus post-yolk-sac larvae (Siluriformes: Pimelodidae), Zootaxa 1707, pp. 37-48 : 39-41

Hypophthalmus fimbriatus ( Fig. 2 a–f)

Description of the larvae. Sixty-one larvae (18 preflexion, 22 flexion and 21 postflexion), with standard lengths between 12.7 and 13.1 mm, were analyzed. The larvae of this species exhibit a long body (12.4 to 19.8% SL) while head lengths vary from small to moderate (16.1 to 25% SL) ( Table 1 ). There is no trace of yolk. In preflexion, the mouth is open and terminal during its entire development. The nostrils are single and become double at approximately 10.2 mm SL (postflexion). Barbles were formed: 2 mental pairs and 1 maxillary pair. They are shorter and thicker compared to those of H. marginatus . The embryonic membrane (median fin fold) is hyaline and surrounds the body from the middle region of the dorsum to the abdominal portion, become totally absorbed by the end of the postflexion stage (13 mm SL). The eyes are rounded and pigmented, with a diameter varying from 7.8 to 15.7% HL, classifying it as small throughout development ( Table 1 ). The operculum is formed at about 10.1 mm SL. The intestine is short, and the position of the anal opening does not reach the middle portion of the body. The myomeres are evident until the postflexion stage, and the total number varies from 54 to 58 (13 to 16 pre- and 40 to 44 postanal). Proportions of head depth (65.3 to 100% HL), head width (53.3 to 92% HL), and pre-ventral-fin length (34.8 to 36.6% SL) decreased during development, while snout length (25 to 50% HL), interorbital distance (26.3 to 50.3% HL), pre-pectoral-fin length (17.2 to 23.3% SL), pre-dorsal-fin length (36.6 to 41.9% SL) and pre-anal-fin length (37.7 to 43% SL) increased ( Table 1 ).

Pigmentation. The larvae of H. fimbriatus are poorly pigmented. The pigments are evident starting at 10.9 mm SL (postflexion) and are restricted to the upper region of the head.

Fin development. The notochord, visible due to transparency, is flexed at 5.1 mm SL, giving support to the rays of the caudal fin that start to appear at 6.4 mm SL (flexion) and are formed at 7.6 mm SL (flexion). At the beginning of the flexion stage, it is possible to see the pectoral fin bud, in addition to the outline of the anal and dorsal fins that until the this stage (about 9.6 mm SL) showed the rays entirely formed. Between the flexion and postflexion stages (11 mm SL), the pelvic fin bud also appears; the first rays appear at approximately 11.9 mm SL. The formation of the unpaired fins is completed during the postflexion stage, including the segmentation of the rays. The numbers of fin rays in H. fimbriatus are pectoral: i, 8–10, dorsal: i, 8–9, and anal: 58–60.

Figures

FIGURE 2. Larval development of Hypophthalmus fimbriatus. Developmental stages are: a) preflexion (4.20 mm SL); b) early-flexion (7.25 mm SL); c) mid-flexion (9.30 mm SL); d) late-flexion (9.40 mm SL); e) early-postflexion (10.87 mm SL); and f) mid-postflexion (13.28 mm SL). Scale = 1 mm.