Aspects of reproductive biology of the Mediterranean amberjack (Seriola dumerilii Risso) during the spawning period

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 size-frequency distribution has shown a group synchronous ovarian development type. The testes have a typical lobular-type structure. Depending on lobules and sperm duct development and on the abundance of germ cells, testis maturity was classified in four stages. Maturity rate according to age and size was also determined. 100% of 1-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.