Possible application of mibolerone for induced sex inversion of grouper Epinephelus coioides

Thirty immature juvenile grouper Epinephelus coioides (19-168 g bodyweight, BW) were randomly stocked in four units 6t tanks to determine if miboleron e can be used to induce sex inversion in groupers. After acclimatization an d weaning to artificial feed, the feed given daily (4% BW/day) was suppleme nted with 0, 50, 100, and 200 mug mibolerone/kg feed for about 18 weeks. Th ereafter, the hormone treatment was withdrawn and the experiment was termin ated at Week 24. Ten fish were killed for gonad histology at stocking to se rve as an initial control while about three to five fish were killed every 8 weeks. In general, ovaries of initial controls showed the presence of mod erate stromal cells and gonia and few primary oocytes. At Weeks 8 and 16, o varies of the control fish (0 mug/kg) were similar to that of the initial c ontrol except that primary oocytes increased at Week 24. Gonads of fish fed diets containing 100 and 200 mug/kg had none to moderate spermatocytes and few spermatids at Week 8 and 16, although spermatozoa were not observed, i ndicating that the fish were undergoing spermatogenesis. Spermatogenesis at 50 mug/kg was not as advanced since only few spermatocytes occurred at Wee ks 8 followed by moderate gonia and no spermatocytes and spermatids at Week 16. However, the presence of few primary oocytes was observed when miboler one was withdrawn suggesting that sex-inversed fish reverted back to a fema le condition. These results show that sex inversion in juvenile grouper can be induced by oral administration of mibolerone and may have possible appl ication on mature females to produce functional males.