Induced sex reversal of dusky grouper, Epinephelus marginatus (Lowe)

The present paper describes sex reversal in dusky grouper, Epinephelus marginatus (Lowe). Over a 4-month feeding period, 5 mg kg(-1) of the male hormone 17-alpha methyltestosterone was combined with frozen fish as feed. After 2.5 months of treatment, the gonads of all six fish treated in the experiment presented tissues with oocytes and spermatogonia, and after 3 months, there were only a few remnants of oogonial tissue left in the gonads. All fish in the experiment gave sperm of varying quality after 4 months of the trial. The quantity of the hormone administered to the fish over these 4 months was 89-113 mg kg(-1). Spermatozoid motility varied from 95% to 40%, and lasted for about one hour in sea water. Using the combined sperm of three males, fertilization ranged from 50% to 95%. Fertilized eggs and hatched larvae continued to develop normally.