STUDIES ON THE LARVAL DEVELOPMENT OF LEIOCASSIS LONGIROSTRIS GüNTHER

The present paper deals with the larval development of Leiocassis longirostris Günther. The larval development of L.longirostris can be divided into prolarval,larval and juvenile sta- ge,on the basis of the external morphology,internal morphogenesis and biological characters. At water temperatures of 21-27℃,the newly hatched larval bears around yolk sac,with the digestive tube formed.The total length is 5.33℃6.62 mm.Nine hours after hatching, pigments deposit on the eyes and the otic capsule.The gill archs appear 15 hours after hat- ching.The lower jaw of larval is formed 24 hours after hatching.The second mentomeckelion barbel appears 48 hours after hatching.Sixty-eight hours and 20 minutes after hatching,the caudal fin rays are differentiated,and the stomach and air bladder appear.Seven-eight gill buds grow on each gill arch,forming later a series of gitl filaments with feather-like gill lamallae.The lamallae increase rapidly in number.The liver and kidney appear 4 days after hatching.About 5-6 days after hatching,the yolk sac is almost absorbed,and the larva can swim freely and starts feeding.There are 5 gill takers on each gillarch.Seventh days after hatching,the jaw teeth appear.The external naris and pelvic fin buds are differentiated 8-9 days after hatching.Eleventh to twelfth days after hatching,the yolk is completely ab- sorbed.Thirteenth days after hatching,the larvae enter the juvenile stage.The dorsal,pecto- ral,anal and caudal fins are fully developed:D.2,6-7;P.1,9;A.14-17;C.20-23. There are three white bands around the body.The first and second band are anterior and posterior of the dorsal fin respectively,and the third is behind the adipose fin.Sixteenth days after hatching,1 fin ray appears in the pelvic fin.The pelvic fin and laternal line are for- med 18-20 days after hatching.The fry is fully developed in external morphology,with a total length of 18.0-19.0 mm. The internal organs and systems are formed 10 days after hatching.