Successive spawning of grouper, Epinephelus suillus (Valenciennes), in a tank and a floating net cage

Abstract

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.