A Study On The Ontogenesis, Differentiation And Developmental Annual Change Of Gonad In Kareius Bicoloratus

Stone flounder (Kareius bicoloratus) is a high-value flatfish prized by commercial fishers. The ontogenesis, differentiation and developmental annual change of gonad in K. bicoloratus were studied by histological and cytological methods in this research. The results will provide basic biological data for reproductive biology of K. bicoloratus. This information is useful for commercial stone flounder culture.The morphological characteristic and development speed of embryos and larvae in K. bicoloratus have been studied by photographed alive. Fertilized eggs hatch out at about 77 h post fertilization (HPF) at (12?.5) . Mouth opens at 2.5 d, and metamorphosis Is compIetecTaTabbut 27 d after Hatching (DAH)A systemic study on the gonadal ontogenesis and differentiation in K. bicoloratus raised in an aquaculture plant has been made through histological methods. The results show that there are about 2 primordial germ cells (PGCs) present in the newly hatched larva, and are located between the gut and the mesonephric duct. After the mitotic proliferation the number of PGCs increases to about 8. Then PGCs migrate to the genital ridge. In larva 9 days after hatching (DAH) PGCs reach the germinal ridge and begin to form the gonadal rudiment together. Gonadal rudiment begins to form in a larva 10 DAH, which is 7.2mm total length (TL), and completes at about 18 DAH (larva is 8.5mm TL). The primordial gonad starts to be form in a 15mm TL larva 40 DAH. And the presence of an ovarian cavity, an early sign of female sex differentiation, is first seen in stone flounder 32.5mm TL 66DAH. In presumptive testis the differentiation is late, and is found in a 91mm TL fish. The form of ovarian cavity is begun with an aggregation of somatic cells in one side of the primordial gonad, then extends to the other side of it and eventually fuse together to form anarrow ovarian cavity. The testicular differentiation character is the formation of the tubules leading to the sperm duct.The annual change of gonad development and the ontogenesis of germ cells in Kareius bicoloratus have been studied by using histological methods and electronic microscope. The samples were bought from the market monthly. The gonadal development can be divided into six stages. Stage I of both male and female stone flounder appears only once in all its life, and the germ cells are comprised by spermatogonia or oogonia. The gonad from Mar to Aug keeps at stage II. The gonad index (GI) of testis at this stage is 0.037%, and the amount of spermatogonia is increased quickly. There is some linear germ plasm in the cytoplasm of spermatogina. In ovary at this stage it is mostly composed by oocyte of phase 2 which the character is the appearance of yolk nucleus, and no zona radiate in membrane. The mean GI of ovary is 1.95%. From Sep to Oct gonad is at stage III which testis is composed by lots of spermatogina and few spermatocytes, and the mean GI of testis at this stage is 0.086%. In ovary the ooctyes at phase 3 are in dominate position, the yolk nucleus disappear. And the GI of this stage is 3.35%. Both testis and ovary are at stage IV in Nov. hi testis the germ cells are in spermiogenesis, and the mean GI is 0.93%. hi ovary the oocytes are mostly at phase 4, which are filled in the cytoplasm with vitellin granule, and the zona radiate in membrane begins to formation. Nucleus moves to one side of the oocyte gradually. The mean GI of ovary at this stage is 9.37%. The reproductive season of stone flounder is between Dec and Feb, and during this period the GI is the highest in a year, 1.97% in testis and 26.78% in ovary respectively, and the gonad stage was at stage V. The testis is filled with spermatozoa, and the ovary is composed by oocytes at phase 5. The oocytes are dissociated in the ovary cavity, and the nucleus membranes begin to dissolve.