Studies On Sex Differentiation And Early Gonadal Development Of Chinese Black Sleeper Bostrichthys Sinensis

In this paper,the fertilized eggs of Chinese Black Sleeper(Bostrichthys sinensis) were incubated and larvae were cultivated at three different water temperatures (24±0.5℃,28±0.5℃,31±0.5℃).The growth of the larvae was investigated.The migration of primordial germ cells(PGCs),the gonad sex differentiation and sex ratio were investigated using histological methods.The effects of temperature on sex differentiation and growth were studied,in order to provide the scientific data for the influence of temperature on sex differentiation.The results were as follows:Under the cultivated temperature(28±0.5℃),on day 1,the PGC was at the peritoneal epithelium.On day 5,PGCs migrated towards the pronephric ducts.The genital ridge and primordial gonads were formed on day 20.On day 25,PGC was found in the genital ridge.The anatomical sign of ovarian differentiation was the formation of ovarian cavity,which appeared 50 days after hatching.The mitosis of oogonia happened on day 55.The anatomical sign of spermatic differentiation was the formation of seminiferous lobular and vas efferens,which appeared 95 days after hatching.The mitosis of spermatogonia appeared 2 months after hatching.The seminal vesicle was found 4 months after hatching.Under the lower temperature (24±0.5℃),the the formation of ovarian cavity happened on day 60.The mitosis of oogonia happened on day 80.Under the higher temperature(31±0.5℃),the formation of ovarian cavity and the mitosis of oogonia happened on day 50.The phase of early gonad sex differentiation was related to the body length.The histological characteristics of PGCs,oocyte cell,spermic cell and seminal vesicle were observed.The spermatogonium and spermatocyte were found in the seminal cysts.The structure of the testes was lobular type,but the arrangement of the seminiferous lobulus is irregular.The seminal vesicle was divided into many locule lumina by the connective tissue partition.The locule iumina were full of secretion.The tissue outgrowths on gonad elongated and then fused to form the ovarian cavity.Lower temperature and higher temperature could increase the female sex ratio slightly compared with cultivated temperature(28±0.5℃).