Browsing by Author "Nagai, Akimasa"
ArticleGF Quinitio, JD Tan-Fermin & A Nagai -
Fisheries Science, 2001 - Japanese Society of Fisheries ScienceThirty immature juvenile grouper Epinephelus coioides (19-168 g bodyweight, BW) were randomly stocked in four units 6 t tanks to determine if mibolerone can be used to induce sex inversion in groupers. After acclimatization and weaning to artificial feed, the feed given daily (4% BW/day) was supplemented with 0, 50, 100, and 200 μg mibolerone/kg feed for about 18 weeks. Thereafter, the hormone treatment was withdrawn and the experiment was terminated at Week 24. Ten fish were killed for gonad histology at stocking to serve 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 moderate stromal cells and gonia and few primary oocytes. At Weeks 8 and 16, ovaries of the control fish (0 μg/kg) were similar to that of the initial control except that primary oocytes increased at Week 24. Gonads of fish fed diets containing 100 and 200 μg/kg had none to moderate spermatocytes and few spermatids at Week 8 and 16, although spermatozoa were not observed, indicating that the fish were undergoing spermatogenesis. Spermatogenesis at 50 μg/kg was not as advanced since only few spermatocytes occurred at Weeks 8 followed by moderate gonia and no spermatocytes and spermatids at Week 16. However, the presence of few primary oocytes was observed when mibolerone was withdrawn suggesting that sex-inversed fish reverted back to a female condition. These results show that sex inversion in juvenile grouper can be induced by oral administration of mibolerone and may have possible application on mature females to produce functional males.
Successive spawning of grouper, Epinephelus suillus (Valenciennes), in a tank and a floating net cage Wild Epinephelus suillus (Valenciennes) were collected in 1989 to early 1990. To monitor natural spawning in captivity, 6 mature females (3.5–5.0 kg) and 4 mature males (7–12 kg) were transferred to a 4.6×4.6×2 m concrete tank, and one mature female (5.3 kg) was paired with two spermiating males (6.0–6.5 kg) in a 4×4×3 m floating net cage. Spontaneous spawning occurred successively 5–17 times a month from July 1990 to June 1991 (except in May) in the tank and 5–10 times a month from July to October 1990 in the floating net cage. The number of eggs collected, mean fertilization rate and mean hatching rate in the tank and the floating net cage each month ranged from 0.5–15.8 million and 2.3–3.9 million, 67–88% and 72–89%, and 2–81% and 29–68%, respectively. The onset of the monthly spawning cycle in both holding systems was observed over a period of 3 days either before or after the last quarter moon. The results indicate that a minimum number of E. suillus broodstock are required for a year-round supply of fertilized eggs.