No abstract

No abstract

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 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 sex ratios during the reproductive period were c. 3·5 : 1 females to males. Females exhibited groupsynchronous 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 (L S ) long and the size distributions of males and females overlapped over 27% of the L S range. Special zones were recognized as gathering areas for sexually mature dusky groupers during the reproductive period. 2001 The Fisheries Society of the British Isles

No abstract

Wild Seriola dumerilii were collected in the South Mediterranean Sea during the 1990, 1991 and 1992 spawning seasons. Macroscopic and cytological characteristics of ovary and testis were analysed. Depending on the presence and the number of oocytes at different stages, a five point maturity scale was proposed for ovarian maturity. Nine maturity stages of the oocytes are described. Oocyte sizefrequency distribution has shown a group synchronous ovarian develo ment type. The testes have a ty ical lobular-type structure. Depending on lobules and sperm duct deveyopment and on the abundance .?germ cells, testis maturity was classified in four stages. Maturity rate according to age and size was also determined. 100 % of I-year-old fish show immature gonads. The proportion of females with mature ovaries was 0, 12.5,84.6 and 100 % at the age of 2,3,4 and 5 years respectively. The proportion of males with mature testes was 14.3, 40, 80 and 100 at the same age. The median standard length at which 50 % of the fish attained maturity is 109 and 113 cm SL in males and females respectively.