Reproduction in the dusky grouper from the southern Mediterranean

Demographic data and gonad histology confirmed that the: dusky grouper Epin ephelus marginatus is a protogynous hermaphrodite that follows a monandric pathway to sexual development. Females reached first sexual maturity at 36. 7 cm L-S and estimated mean length at first maturity (L-50) was 43.8 cm L-S for females and 81.3 cm L-S for males. Adult se ratios during the reproduc tive period were c. 3.5:1 females to males. Females exhibited group-synchro nous ovarian development and multiple ovulation occurred over the spawning period. Gonads were ripe from early May and spawning occurred From June unt il early September. The size of ripe testes (0.6% W) indicated strong oligo spermy and suggested a mating system with no sperm competition. Sexual tran sition was protogynous involving regression of ovarian tissue and prolifera tion 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 (L-S) long and the size distributions of males and females overlapped over 27% of the L-S range. Special zones w ere recognized as gathering areas for sexually mature dusky groupers during the reproductive period. (C) 2001 The fisheries Society of the British Isl es.