INDUCTION OF SEX INVERSION IN JUVENILE GROUPER, EPINEPHELUS-SUILLUS, (VALENCIENNES) BY INJECTIONS OF 17-ALPHA-METHYLTESTOSTERONE

Four groups of two-year old juvenile groupers (Epinephelus suillus), e ach with 8-9 individuals of mean body weight (BW) 1.2 kg, were treated with 17alpha-methyltestosterone (MT). MT was injected intramuscularly within the range of 0.5-5.0 mg kg-1 BW every 15 days. Gonadal biopsy and stripping of the abdomen was done every 15 days, the fish being sa crificed after six or twelve injections. Initial controls had immature ovaries containing primary oocytes in lamellae that extended into the central lumen. After six injections, proliferation of stromal and gon ial cells were observed in all fish sampled. Regardless of treatment, gonad sections of fish with a minimum BW of 1.2 kg showed degeneration of primary oocytes and the presence of spermatogenic cells. Milt was also present in larger-sized fish (BW: 1.5 kg) given 0, 0.5 and 1.0 mg MT kg-1 BW, after such fish had received an accumulated dose of 5 or 12 mg MT kg 1 BW. However, gonad sections of smaller-sized fish follow ing these treatments contained only primary oocytes and gonial cells a fter six (BW: 0.7-1.0 kg) or twelve (BW: 0.6-1.3 kg) injections. In co ntrast, all fish treated with 5 mg MT kg-1 BW had testes in active spe rmatogenesis after six (BW: 1.2-1.6 kg) or twelve (BW: 0.8 kg) injecti ons. Gonad weight and gonadosomatic index values decreased during cons ecutive sampling. Induction of female-to-male sex inversion in juvenil e E. suillus by MT was probably synergistic with age and size.