The reproductive biology of the two-banded sea bream (Diplodus vulgaris) from the southwest coast of Portugal

The study of the reproduction of Diplodus vulgaris (Geoff.) as part of a ba se-line study of the fishery resources of the southwest coast of Portugal, was based on the analysis of the spawning season, gonad maturation, size at maturity, fecundity and hermaphroditism. The spawning season is relatively long, from December to March, with peaks in January and February. No signi ficant differences were found either in the sex ratio (M:F = 1.01) over the year or by size. The size at first maturity (L-50) for all sexes and undet ermined individuals combined was 18.33 cm total length (TL), with no signif icant differences between males and females. The estimated L-50 is consider ably greater than the minimum legal size in Portugal of 15.0 cm. Mean absol ute fecundity (F-a) was 131 127 oocytes, ranging from 31 523 to 250 608. Th e relationship between absolute fecundity and total length (TL) (F-a = 25 3 98 TL-484 426) and somatic weight (SW) (F-a = 878.8SW-71 416) was of the li near type. The mean number of oocytes per gram of somatic weight was 526, r anging from 194 to 887. The reproductive strategy of this species is charac terized by a rudimentary hermaphroditism with possible protandry, as eviden ced by the existence of individuals in sexual transition.