Induced sex change of dusky grouper Epinephelus marginatus

Epinephelus marginatus is a monandric protogynous hermaphrodite in which sex change mainly occurs in individuals 14-17 years old or 80-90 cm long. This sexual pattern arises several problems for broodstock management and artificial propagation. Our study aimed at identifying precocious sex inversion techniques for aquaculture practices. Sex inversion was induced in wild juveniles (mean body weight 1.6 Kg, BW) both by oral and intramuscular administration of 17-methyltestosterone (MT). Eighteen fish, kept in PVC tanks isolated or grouped, received MT at 1-mg/Kg BW using different feeding methods. Eight fish were treated by MT injection at 2-mg/Kg BW dosage, every 7-10 days. Four fish were used as controls. Milt was evaluated for volume, sperm density, vitality and motility. Histological analyses of gonads were carried out at the beginning and at the end of the trials both in successful and unsuccessful sex-inverted fish. Sex inversion from immature females to spermiating males was observed in 3 of 8 MT injected fish (mean accumulated dose of 30.6mg/Kg BW) after 16 weeks. MT oral administration was successful in 13 of 18 treated fish after 14-18 weeks (mean MT accumulated dose of 66.4 mg/Kg BW, range 36.8-92.1 mg/Kg BW). Spermiating fish produced 10-100 l of milt. Sperm density ranged between 14 x106 and 7.7x109 cell/ml. Milt from sex inverted fish was effective in egg fertilisation (62%). Histologically, after sex change ovary was completely replaced by male tissue with cysts of germ cells at different stages. Free spermatozoa filled the spermatic ducts. RIAs of 17ß-estradiol (17ß-E), testosterone (T), 11-ketotestosterone (11-KT) and 11ß-hydroxyandrostenedione (11ß-OHA) are in progress to identify key-sex steroids involved in sex change.