Hypophthalmus marginatus
Creators: name: Oliveira, Edinbergh Caldas De
name: Bialetzki, Andréa
name: Assakawa, Luciana Fugimoto
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Siluriformes
Pimelodidae
Hypophthalmus
Hypophthalmus marginatus

description: Hypophthalmus marginatus (Fig. 3 a–f)
Description of the larvae. A total of 66 larvae (14 preflexion, 49 flexion and 3 postflexion) with standard lengths between 3.0 and 13.1 mm were analyzed. The larvae of this species exhibit a relatively long body (12.4 to 16.7% SL) and a head length varying from small to moderate (14.6 to 25% SL) (Table 1). There is no trace of yolk. During the preflexion stage the mouth is open and terminal. The nostrils are single and become double at approximately 12.2 mm SL (postflexion). The barbles are formed: 2 mental pairs and 1 maxillary pair. They are longer and thinner compared to those of H. fimbriatus. The embryonic membrane (median fin fold) is hyaline and surrounds the body from the middle region of the dorsum to the abdominal portion and is totally absorbed at the end of the postflexion stage (13.1 mm SL). The eyes are rounded and pigmented with a diameter varying from 5.6 to 9.4% HL, classifying it as small during it’s entire development (Table 1). The operculum is formed at about 12.2 mm SL. The intestine is short, and the position of the anal opening does not reach the middle portion of the body. Myomeres are evident until the flexion stage with a total number varying from 54 to 57 (13 to 15 pre- and 40 to 42 post-anal). Proportions of head depth (62.5 to 100% HL), head width (54.8 to 100%) and interorbital distance (33.5 to 54% HL) decrease during development while snout length (25 to 54% HL), pre-pectoral-fin length (17.9 to 26.% SL), pre-dorsal-fin length (39.9 to 44.7% SL), and preanal-fin length (39.8 to 43.2% SL) increase (Table 1).
Pigmentation. As with the larvae of H. fimbriatus those of H. marginatus are also poorly pigmented. Some pigments can be observed dispersed along the body starting at 9 mm SL (postflexion). At about 10.8 mm SL they can also be barely visible on the upper region of the head.
Fin development. The transparent notochord is visible and flexed at 4.3 mm SL giving support to the caudal-fin rays that appear at 4.5 mm SL (flexion) and are fully formed at 7.1 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. By the end of this stage (about 10.8 mm SL), all of the aforementioned rays are formed except the pectoral. Between the flexion and postflexion stages (about 12.5 mm SL), the pelvic fin bud appears, and the first rays are formed at about 13.1 mm SL. In the postflexion stage, the formation of the unpaired fins is completed including the segmentation of the rays. The numbers of fin rays in H. marginatus are pectoral: i+9, dorsal: i, 6–8, and anal: 61–62.
Proportions of body. ANCOVA showed a significant relationship between head depth, snout length, interorbital distance, eye diameter and head width (all as a proportion of HL) (Fig. 4 a–e), and between head length, body depth and pre-pectoral-fin length. Pre-dorsal-fin length and pre-anal-fin length (all as a proportion of SL) (Fig. 5 a–e) also showed significant relationships. The variable pre-ventral-fin length was not analyzed due to the lack of data on H. marginatus.
Only a few of the analyzed variables showed differences between the two species. Eye diameter is initially similar between the two species. It increases gradually but more so in H. fimbriatus (Fig. 4 d). Head width also differed between the two species, being slightly greater in H. marginatus (Fig. 4 e).
The analysis showed significant differences between the two species for both body depth and pre-pectoral-fin length. Both were initially greater in H. marginatus, but became greater in H. fimbriatus at about 5.5 mm SL for body depth and 9.5 mm SL for pre-pectoral-fin length (Fig. 5 b–c).
description: Published as part of Oliveira, Edinbergh Caldas De, Bialetzki, Andréa & Assakawa, Luciana Fugimoto, 2008, Morphological development of Hypophthalmus fimbriatus and H. marginatus post-yolk-sac larvae (Siluriformes: Pimelodidae), pp. 37-48 in Zootaxa 1707 on pages 41-44, DOI: 10.5281/zenodo.180930