INVOLVEMENT OF GONADAL-STEROIDS IN FINAL OOCYTE MATURATION OF WHITE PERCH (MORONE AMERICANA) AND WHITE BASS (MORONE-CHRYSOPS) - IN-VIVO ANDIN-VITRO STUDIES

Plasma estradiol-17 beta (E(2)), testosterone (T), 17 alpha,20 beta-di hydroxy-4-pregnen-3-one (DHP) and 17 alpha,20 beta,21-trihydroxy-4-pre gnen-3-one (20 beta-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that we re induced to undergo final oocyte maturation (FOM) with human chorion ic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) an d germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 2 0 beta-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E(2) and T levels wer e greatest during GVM and GVBD in both species and decreased to low le vels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, pro duced both DHP and 20 beta-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E(2) and T and their oocytes did not complete G VBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide block ed in vitro production of DHP and 20 beta-S and oocyte GVBD by white p erch follices. DHP and 20 beta-S were equipotent inducers of FOM in th e GVBD bioassay. None of several other structurally-related steroids t ested were effective within a physiological range of concentrations. T hese results indicate a role for DHP and 20 beta-S in the control of F OM in white perch and white bass.