The protogynous hermaphrodite groupers Epinephelus suillus were given bi-weekly injections of 17 alpha-methyltestosterone (MT) intramuscularly for three to six months. Spermatogenesis occurred after three months of MT treatment while spermiation was observed after five to six months of MT treatment in larger fish. Neither cannulated tissue nor milt was obtained when the remaining fish were sampled four months after withdrawal of exogenous MT. However, vitellogenic eggs (size range = 0.34 to 0.56 mm) were cannulated eight months after termination of MT treatment. Presence of eggs in fish which previously had expressible or cannulated milt indicates that the sex-inversed male E. suillus reverted back to the female condition upon withdrawal of exogenous MT. This information is useful in the line production of functional males which is the limiting factor in induced breeding of groupers
