Reproduction in the dusky grouper (Epinephelus marginatus, Lowe 1834) from South Mediterranean.

Demographic data and gonad histology confirmed that the dusky grouper Epinephelus marginatus is a protogynous hermaphrodite that follows a monandric pathway to sexual development. Females reached first sexual maturity at 36•7 cm LS and estimated mean length at first maturity (L50) was 43•8 cm LS for females and 81•3 cm LS for males. Adult sex ratios during the reproductive period were c. 3•5 : 1 females to males. Females exhibited group synchronous ovarian development and multiple ovulation occurred over the spawning period. Gonads were ripe from early May and spawning occurred from June until early September. The size of ripe testes (0•6% W) indicated strong oligospermy and suggested a mating system with no sperm competition. Sexual transition was protogynous involving regression of ovarian tissue and proliferation of testicular tissue in the gonads. Transitional individuals occurred from May through November and accounted for 9% of sampled adult population. Sex change occurred in fish 69–93 cm (LS) long and the size distributions of males and females overlapped over 27% of the LS range. Special zones were recognized as gathering areas for sexually mature dusky groupers during the reproductive period.