Control of final gonadal maturation in the hybrid sturgeon, bester.

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Testicular development in the adult male F1 sturgeon hybrid, the bester (Huso huso L.female x Acipenser ruthenus L.male) was examined monthly in relation to serum sex steroid levels. Spermatogenesis lasted for 1 year, with meiosis generally starting September and spermatogenesis in November, although there was considerable variation in testiculal developmental stages between fish sampled monthly. Testicular development continued, slowly, during the winter months until April. Fish did not exhibit spontaneous spermiation, and phagocytotic cavity of Sertoli cells became prominent from May onwards. Androgen levels increased during spermatogenesis and remained high throughout the pre-spermiation period. In the degeneration stage, 11-ketotestosterone concentrations declined to low levels, b while testosterone (T) levels remained high. The serum concentration of 17alpha, 20beta-dihydroxy-4-pregnen-3-one (DHP) was low throughout the reproductive cycle. Based on these resultss, it is suggested … More that the time appropriate for induction of final maturation would be from November-December to April when the testes are in the late stage of development.Changes in serum levels of estradiol-17beta (E_2)T,DHP and vitellogenin (VTG), in cultured adult female were examined in relation to ovarian development during a 1-year sampling period. Considerable variationsin oocyte development were found among fish. Oocytes at previtellogeenic ssatge generally started to develop conconitantly with the degeneration of the first batch ofoocyte. In vitellogenic individuals, ovaries were comprised of more advanced oocytes with diameter ranging from 0.6 to 2.6 mm and in the post-vitellogenic class, oocytes attained their largest size while the geminal vesicle was migrating towards the animal pole. Oocytes with a migrating nucleus were maintained during the winter period and massive degeneration started in April-May without germinal vesicle breakdown (GVBD) or ovulation occurring. Seasonal changes in E2, T and VTG levels were well correlated with the advancement of oogenesis. Their levels increased during vitellogenesis, whereas in the posstvitellogenic (migratory nucleus) stage the levels of E2 declined from 2-4 ng/ml to 1-2 ng/ml and VTG from 4-10 ng/ml to 0.2-0.5 ng/ml while T levels remained high. In contrast, serum levels of DHP were constantly low throughout the reproductive cycle. These results indicate that the time appropriate for induction of artificial reproduction would be from October-November to April-May when the oocytes are in the late stages of the development. Less