OBSERVATIONS ON OOCYTE MATURATION AND HYDRATION IN-VITRO IN THE BLACK-SEA BASS, CENTROPRISTIS-STRIATA (SERRANIDAE)

A protocol for the incubation of Centroprostis striata ovarian follicl es in vitro from females that spawn repeatedly under laboratory condit ions was developed. Isolated follicles underwent maturation after 15-2 4 h of incubation of 25 degrees C in 75% Leibovitz L-15 medium, contai ning relatively low doses of human chorionic gonadotrophin (hCG) or ho molgous pituitary extract (50% response with approximately 2 IU/ml and 0.02 pituitary equivalents/ml, respectively). During maturation in vi tro, follicles underwent a remarkable volume increase (about 340%) tha t was correlated with proteolysis of primarily the largest yolk protei n in the oocyte. The maturation response of follicles to hCG was size- dependent within a range from 400 to 600 m in diameter, with a maximum response displayed by 530-600 m follicles. The response of these foll icles to hCG was not inhibited within a range of incubation temperatur es from 15 to 28 degrees C, but the length of time required for the fo llicles to achieve 50% maturation was negatively correlated with incre asing temperatures (r(2) = 0.97; p less than or equal to 0.01). Howeve r, the largest follicles (530-600 mu m) did not undergo maturation in response to high doses (1 mu g/ml) of the major maturation-inducing st eroids (MISs) known in teleosts, 17,20-dihydroxy-4-pregnen-3-one (17,2 0 beta) and 17,20 beta,21-trihydroxy-4-pregnen-3-one (20 beta S), even after a previous incubation period of follicles with 10 IU/ml hCG for 1, 3 or 6 h. These observations indicate that C. striata follicles ar e very sensitive to increasing doses of gonadotropin, and that their r esponsiveness to this hormone is highly size-dependent within a very n arrow range. The preliminary results also suggest that 17,20 beta and 20 beta S are not the MIS in this species.