INDUCTION OF SEX-CHANGE IN FEMALE EPINEPHELUS COIOIDES BY SOCIAL-CONTROL

Mature female groupers (Epinephelus coioides) of different sizes were stocked in three floating net cages (2 fishes each) and in tanks (2-4 fishes) to induce sex change in the bigger female grouper after isolat ion from the original group. All the bigger fish (initial body weight 5.0-6.1 kg) in the floating net cages changed into males by the end of the experiment, while the smaller ones (initial body weight 4.5-5.2 k g) remained female. The fastest sex change was in cage 1 where the big ger fish had atretic oocytes one month after stocking and was milting after four months. In the other cages, milt production in the bigger f ish was observed 6-10 months after stocking. In the tank-reared groupe rs, the biggest fish (initial body weight 6.4 kg) in the tank with fou r fishes was found to be milting about two months after stocking while the smaller fishes (initial body weight 3.4-4.0 kg) were still female s. The fishes started to spawn two months later. In another tank that was stocked with two females, no sex change was observed in the bigger fish even 16 months after stocking. These results indicate that femal e groupers can be sexually changed into male by social control at the shortest period of four months in floating net cages and two months in tanks. However, there may be cases wherein sex change will not occur.