日本鳗鲡产卵后生存及其繁育

为证明日本鳗鲡(Anguilla japonica)生活史最后一步一产后鳗的命运,本研究模拟产后的日本鳗鲡继续在海水中养殖,观察其存活率及繁育情况.结果表明,产后鳗在海水中停食约18 d后,体能得到恢复,部分亲鱼开始出现摄食,1个月左右全部恢复摄食,经244 d养殖,雌、雄鳗体质量增加,存活率达94.6%.随后,给产后鳗注射外源性促性腺激素(鲤鱼脑垂体匀浆CPE和人绒毛膜促性腺激素HCG)后激发其退化的性腺(卵巢和精巢)重新发育(与当年银鳗作对照).通过性腺组织切片观察产后鳗和对照鳗性腺发育成熟的全过程及其差异,发现产后鳗起初性腺发育比当年银鳗差,但经多次注射激素后,产后鳗性腺成熟与当年银鳗同步,证明产后鳗生殖细胞对激素的敏感件高.应用17α,20β-双羟孕酮和促性腺激素释放激素类似物(GnRH-A3)使催熟的产后鳗和对照鳗均产卵和排精,并孵化出仔鱼,从而有力地证明,鳗鲡产后虽体质弱,但待体能恢复后能够继续生存和繁殖.本研究旨在探讨利用产后鳗作为今后鳗鲡人工繁殖亲鳗的可行性.

Survival and reproduction in post-spawning Japanese eel, Anguilla japonica

To testify the fate of post-spawning Japanese eel at the last stage of its life history, the post-spawning Japanese eels were simulated to be cultivated in sea water, and the survival rate and reproduction of these eels were observed. The results showed that some post-spawning eels resumed their body energy and started to eat after halt-eating for about 18 days in sea water. All eel resumed eating after about one month. The body weight of male and female eel increased and the survival rate was 94.6% after cultivation for 244 days. Then, the gonads (ovary and testis) of these post-spawning Japanese eel developed and ripened by treatment of exogenous gonadotropin (carp pituitary extract and human chorionic gonadotrophin, CPE and HCG) injection, with silver eel of the year as control. The sections of gonads provided the difference in the process of gonad development and maturation between post-spawning eel and control eel, and revealed that although at first the gonad development of post-spawning was not as good as that of silver eel of the year, after several times injection of hormone, the post-spawning matured with silver eel synchronism which suggested a high sensitivity of germ cells to hormone in post-spawning eel. The oviposition and spermiation in these hormone-ripened post-spawning eel could be induced by 17, 20-dihydroxy-4-pregene-3-one and gonadotropin-releasing hormone analogue (GnRH-A), and larvae could be hatched. The above results effectively proved conclusive evidence that although post-spawning eels were weak they could continue to live and propagate after resumed their body energy.