Histological observation on gonadal sex differentiation in Cynoglossus semilaevis Günther

Gonadal development and differentiation of .Cynoglossus semilaevis. Gunther were observed by using histological techniques.The differentiation stage could be divided into three phrases,i.e.,the primary,the early differentiation stage and the complete differentiation stage.Gonad remained undifferentiated 50 days after hatching.When fry gained 40.5mm in total length,the presumptive ovary proliferated more rapidly,and contained clusters of primary germ cells,some of which came into mitosis.The presumptive testis was small and narrow,which contained less primary germ cells without any mitotic phase.At 120 days after hatching,when the fry gained 60mm in total length,the presumptive ovary began to form an ovarian cavity and possessed the primary oocyte.In presumptive testis,the formation of efferent duct and seminiferous tubules fist occurred in fish of approximately 100 days and 150 days after hatching respectively,The cytological differentiation of the testis was about 40 days later than that of the ovary.