INDUCED GONADAL DEVELOPMENT AND SPAWNING OF IMMATURE RED-SEA BREAM PAGRUS-MAJOR WITH LHRH-A ADMINISTRATION IN DIFFERENT WAYS DURING WINTER SEASON

The response of sexually regressed red sea bream Pagrus major to LHRH- a (des Gly(10)-[D-Ala(6)] LHRH ethylamide) was investigated during the non-spawning season, from November to December. Fifty-five fish were divided into five groups and the following treatments were accomplishe d: initial and final controls (not treated), LHRH-a 200 mu g cholester ol pellet (group CP200), LHRH-a 1 mu g/day osmotic pump (group OP1), a nd LHRH-a 5 mu g/day osmotic pump (group OP5). In all females in the t hree experimental groups, gonadal maturation and spawning were induced 12 to 14 days after implantation. The cumulative amounts of LHRH-a re leased from each mold during the period from pellet or pump implantati on were about 11 mu g (CP200), 14 mu g (OP1), and 60 mu g (OP5), respe ctively. These results suggest that all treatments of LHRH-a were foun d to be equipotent in inducing red sea bream females to mature and spa wn. It seems that the amounts of sustaining release of LHRH-a from LHR H-a 200 mu g cholesterol pellet are enough to induce ovarian maturatio n, and a higher dosage of LHRH-a is not necessary. On the contrary, ev ery treatment of LHRH-a showed insufficient effects on testicular matu ration, and the possible cause was discussed. The results of the prese nt study may be used as a basis for producing eggs and fingerlings all year round.