青鱼性腺发育的研究

湖南地区生长于池塘环境的青鱼,性成熟年龄是5—6年,雄性比雌性普遍地早熟一年。卵母细胞和滤泡细胞是同源的,都来自于卵原细胞。池养青鱼的卵母细胞只能发育到初级卵母细胞阶段(Ⅳ时相),必须通过人工催情,才能进行染色体的减数分裂,使卵母细胞由第Ⅳ时相发育到第Ⅴ时相。精细胞的发生,能够完成由精原细胞到精子的全部发育过程。青鱼在第一次性周期内,雄性精巢在第5个冬季进入第Ⅳ期,雌性卵巢在第6个冬季进入第Ⅲ期,从此以后,每年冬季,雄性精巢回复到第Ⅳ期,雌性卵巢回复到第Ⅲ期,这种性腺季节周期变化的规律,为生产上选留亲鱼提供了理论依据。青鱼雌性卵母细胞由第Ⅲ时相到第Ⅳ时相是同步性的;经人工催情产卵或自然退化后,卵巢的组织学结构又回复到第Ⅱ期,证明青鱼是一次产卵类型。已经达到性成熟年龄的雌性青鱼,卵母细胞的卵黄形成有两种不同的类型。第一种类型是泡内卵黄,第二种类型是泡外卵黄。如果饲养管理工作如投饵、水质调节不适宜,卵母细胞不能正常形成卵黄,就会出现卵子的败育现象,这是生产上一个重要问题,必须进一步研究。  

STUDIES ON THE GONADAL DEVELOPMENT OF THE SNAIL CARP,MYLOPHARYNGODON PICEUS

In Hunan,the age of sex maturity of Mylopharyngodon piceus which grows inthe environment of a pond is 5—6 years;the male spawners ripen one year earlierthan the female ones generally.Oocytes and follicular cells are of the same origin,both derived from the oogonia.The oocytes of the pond-cultured Mylopharyngodon piceus can only develop to the period of primary oocytes (phase Ⅳ),hence it isvery necessary to induce maturation division artificially so that meiosis can takeplace and the oocytes can develop from phase Ⅳ to phase Ⅴ.The entire course ofspermatogenesis,from spermatogonium to spermatozoon,can be completed endo-genously in the pond environment.The testes develop to stage Ⅳ in the fifth winterof the first sex cycle;the ovaries develop to stage Ⅲ in the sixth winter of thefirst sex cycle.After this,the testes remain in stage Ⅳ and the ovaries remain instage Ⅲ throughout the winter of every year.The law governing such seasonal chan-ges in the gonads provides a theoretical basis for the selection of the spawners infish-culture.The oocytes develop from phase Ⅲ to phase Ⅳ synchronously.Thehistological structure of the ovaries returns to stage Ⅱ after induced spawning orafter natural degeneration,which testifies that female Mylopharyngodon piceus isthe type of fish that spawns only once a year.According to our research,two different types of yolk are formed in the oocytesof this fish at the age of sex maturity.One type of yolk is intravesicular,whileanother type is extravesicular.If pond management,such as feeding and water-qua-lity regulation,is not appropriate and yolk formation becomes aberrant,then thephenomenon of abortive eggs is bound to occur.This is an important problem infish-culture,the solution of which depends on further researches.