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In order to determine the most effective hormones on the in vitro oocyte maturation (germinal vesicle breakdown - GVBD) in a hybrid sturgeon bester, ovarian follicles were incubated at the migratory nucleus stage in the presence of several steroids, gonadotropin preparations and forskolin. Occurrence of GVBD and 17,20β-dihydroxy-4-pregnen-3 -one (DHP) production were followed during an experimental period of one year of germinal vesicle (GV) migration. From all the steroids tested, three progesterone derivatives-17α- hydroxyprogesterone (17αOHP), 17, 20β, 21-trihydroxy-4-pregnen-3-one (17, 20 β, 21- triol), and DHP-were the most potent steroid inducers of GVBD, followed closely by deoxycorticosterone (DOC). No GVBD responses were found in ovarian follicles in July when the GV was still central. The responsiveness increased gradually from then and reached its peak in November when the GV had migrated fully towards the oocyte periphery. Their potencys gradually declined later from December and the oocytes lost their ability to mature the next July when degeneration set in. DHP production by ovarian follicle during successive months of nucleus migration demonstrated a relatively similar pattern of GVBD frequencies. These results indicated again a relevant role for DHP on oocyte maturation in the bester and also suggested that GV localization along with in vitro oocyte maturation assay can be used as practical tools for selecting the appropriate individuals in exogenous induced spawning in bester.