EMBRYONIC AND LARVAL-JUVENILE DEVELOPMENTAL CHARACTERISTICS OF PSEUDASPIUS LEPTOCEPHALUS

In order to verify the embryonic and larval-juvenile development characteristics of Pseudaspius leptocephalus, we continuously observed and analyzed the developmental process of the fertilized eggs obtained through artificial propagation of the parent fish. The results indicated that the mature eggs of Pseudaspius leptocephalus were yellow, and the mean diameters of the eggs were about (1.77±0.20) mm; moreover, the eggs were slightly sticky in the presence of water. At 23℃, the embryonic development of Pseudaspius leptocephalus lasted for 47h55min, and experienced ygophase, cleavage stage, blastula stage, gastrula stage, neurula stage, organogenesis stage and hatching stage were subdivided into 26 periods. At (23±1)℃, the newly-hatched larvae experienced the yolk-sac larvae (0—7d), the (8—26d), and post-larval stage (27—31d), and then entered the juvenile stage. The larvae had lower swimming capability at yolk-sac larvae stage; with the decrease of yolk-sac, the pigment spots on the body surface, the pectoral fin, tail fin and digestive tube were fully developed gradually, and the swim bladder inflation were also accomplished. Late stage larvae had better swim and feed abilities and the yolk-sac vanished; in addition, the ventral fin formation of late stage larvae completed and the skin were still transparent at this stage. Until the end of post-larval stage, there is no difference between the individuals and the adult fish in scale formation. The relationship between the total length of Pseudaspius leptocephalus with days post hatch were in accord with equation TL=0.0125x²+0.3579x+6.2058 (R²=0.9953), indicating that the larvae grow slowly within 15 days post hatch with only (0.38±0.02) mm per day, and larvae grow very fast and reached (1.24±0.09) mm per day after 15 days. In this study, we illuminated the embryonic and larval-juvenile development characteristic, and provided theoretical basis to large-scale propagation and breeding of Pseudaspius leptocephalus.