HISTOLOGICAL STUDIES ON THE GONADAL DEVELOPMENT OF AN ENDEMIC TIBET FISH GYMNOCYPRIS NAMENSIS

The histology of the gonadal development of namucuo naked carp, Gymnocypris namensis which is endemic to the Namucuo Lake, Northern Tibet, was studied. The volume of the ovary increased markedly in August and attained at maximum in December, egg-laying was from April to August. At the end of the spawing, a larger number of oocytes which remained in ovary became astrophied and were re absorbed subsequently. The oogenesis is composed of six phase. In the phase 2 of the development of the oocytes, the yolk nucleus, which was possibly related to the formation of yolk, broke up and formed a ring in the outer cortex. From the later phase 2 to the middle phase 3, the nucleoli of the oocytes contained substance, which was probably related to the formation of protean yolk granules, and entered into cytopalsm by the part rupture of the nuclear membrane. In the phase 4, vitelline membrane was composed of 2 layers: zona radiata or the primary membrane which is mostly formed by oocyte and the second membrane which is possibly formed by granulosa. The micropyle canal was blocked by more than 10 micropylar cells whichs formed a vesicle. In a reproductive season, the ovary of namucuo naked carp matured only once in a year and the mature fish could spawn surely more than one time.