Germinal vesicle break down (GVBD) was examined in ovarian follicles of sterlet A. ruthenus L. after in vitro incubation with progesterone (P4), 11-deoxycortisol (S), and 11-deoxycortisone (P21) at different concentrations (600, 800, 1000 1200 nM). After short-term exposure (1, 5 min), and incubation of ovarian follicles in steroid-free media, it was demonstrated that all tested steroids were potent in inducing GVBD, but P4 was significantly more effective than S and P21.