Embryonic and larval development of threatened bronze featherback, Notopterus notopterus (Pallas)

Abstract

Fertilized eggs (egg capsule 3.5±0.5 mm and yolk sphere 2.5±0.5 mm) of N. notopterus were spherical, adhesive and lacked oil globule in the yolk sphere. On day 4, embryonic rudiment becomes distinct with 7-8 somites, the anterior protuberance formed head and the posterior part elongated in tail. Hatching took place on day 5-6 of fertilization at 26±10C water temperature. At this stage, embryo showed twitching movements, lashed out its tail, ruptured the egg capsule towards head region and emerged. During day 1-3, the head and body of larvae (4 mm) were bent around yolk sac, attached to the substratum by thread-like red coloured capillaries that disappeared on day 3. In 5-6 days old larvae larvae (8±0.5 mm; eye diameter 0.25 mm), head rudiment appeared, mouth opened, upper and lower jaws were clearly visible. In 7-8 days old larvae (size 9±0.5 mm, yolk sac 2.64 mm, head length 1.8 mm, eye diameter 0.35 mm), head and mouth were prominent, eyes clearly seen, notochord initially developed and alimentary canal thicker and convoluted. In 9-10 days old larvae (11±0.5 mm, head length 2.0, eye diameter 0.5 mm oval yolk sac 2.42 mm), head well-developed, notochord increased in length and anal fin slightly visible. On day 12-14, the larvae (light brown) measured 14±0.5 mm, completed yolk absorption, notochord clearly visible, dorsal, pectoral and anal fins were prominent except the ventral fin. Terminal mouth with nearly straight large cleft reaching midventral orbit, eyes were shining, abdominal portion highly pigmented, granular structure appeared near the intestine, four gill arches in opercular cavity and air-bladder developed. Adult characters developed after day 28 of hatching, the pectoral, pelvic, dorsal and anal fins depicted 6-7, 3-4, 5-7 and 25-45 rays, transverse bars along the dorsal ridges relatively prominent, dark spots also developed on the whole body.