EXPERIMENTAL CONDITIONS FOR OOCYTE MATURATION IN THE ZEBRAFISH, BRACHYDANIO-RERIO

An in vitro protocol was established for studying oocyte maturation in the zebrafish, Brachydanio rerio. When appropriate size follicles (0. 575-0.625 mm diameter) were incubated at 26 degrees C for 8-24 h in 60 % Leibovitz L-15 medium containing 1 mu g/ml of 17 alpha,20 beta-dihyd roxy-4-pregnen-3-one (DHP), their oocytes underwent maturation. Under these conditions, but in the absence of exogenous steroid, control fol licles remained arrested in prophase I. Germinal vesicle breakdown was used to indicate that maturation had occurred, and this event was rea dily visible in living follicles viewed through a dissecting microscop e. Furthermore, as maturation takes place, the rather opaque prematura tional follicles became translucent. In the process of establishing a reliable in vitro bioassay for oocyte maturation in the zebrafish, we compared the effects of gonadotropin (human chorionic gonadotropin) an d a steroid hormone (DHP) on the in vitro stimulation of maturation, o ver a range of doses and incubation times. Finally, the relative effec tiveness of several steroids and their metabolites in eliciting oocyte maturation in vitro was determined, and DHP appeared to be most effec tive. (C) 1994 Wiley-Liss, Inc.