OBSERVATION ON THE GONADAL DEVELOPMENT AND EMBRYONIC DEVELOPMENT OF XENOCYPRIS ARGENTEA GUNTHER

In Hunan, the age at first sex maturity of Xenocypris argentca Gunther which grows in the environment of Xiangjiang river, pond and reservoir is 2 years; the male spawners ripen 1 year earlier than the female generally. During the breeding season. Xenocypris argentca of the Xiangjiang river begin their sexual activities-di.splaying of estrus, such as ovulation and discharging milt. In the environment of a pond, it, is impossible for the pond-cultured Xenocypris argentca to propagate naturally because of the shortage of certain ecological conditions. The oocytes of the pond-cultured Xenoeypris argentca can only develop to the period of primary oocytes (phase Ⅳ), hence it is very necessary to induce maturation division artificially so that meiosis can take place and the oocytes can develop from phase Ⅳ to phase Ⅴ. The entire course of spermatogenesis,from spermatogonium to spermatozoon, can be completed endogenously in the pond environment.Duing the winter, the testes of those fish which reach sex maturity develop to stage Ⅳ; the ovaries develop to stage Ⅲ. Induced spawing has been successfully carried out from mid-April until early-May, with the water,temperature from 20℃ to 22℃.The matured egg of Xenocypris argcntea is spherical in shape, and semi-pelagic.The embryonic development of Xenocypris argentca is as follows: When the water temperature is 21—23℃, the duration of incubation from fertilized egg to the larva breaking off from the membrane lasts about 26 hours. It takes 112 hours for the fertilized egg to grow into a larva. The embryonic development of Xenocypris argentea can be divided into 5 stages: fertilized egg stage, cleavage-blastula stage, gastrula stage, organogenesis stage and hatching.