The reproductive biology of blackspot sea bream Pagellus bogaraveo in captivity. I. gonadal development, maturation and hermaphroditism

Gonadal development, maturation, spawning and hermaphroditism were investigated in captive blackspot sea bream, Pagellus bogaraveo Brünnich, 1768, during the second, third and fourth years of life. The gonads of 224 fish were examined macroscopically and histologically. Undifferentiated gonads were found in fish smaller than 22.0 cm. Adult fish showed four gonadal differentiations: ovotestes with functional testis and quiescent ovary (Mf), ovotestes with functional ovary and regressed testis (mF), ovotestes with both ovary and testis at a resting stage (mf), and ovaries with no male tissue (F). The overall incidence of gonochoric females F was 41%. Functional males Mf were more frequent in age classes 1+ and 2+, whereas functional females mF predominated in the 3+ age class, above 25.0 cm TL. Histological examination revealed testicular degeneration and atrophy in functional females mF. On the basis of both histological data as well as size and age frequency distribution, it is suggested that the reproductive strategy of P. bogaraveo in captivity is characterized by protandrous hermaphroditism, with a high incidence of female gonochorism. Spawning occurred in March–April, at a size of 28.0 cm and age 3 in males and at 29.5 cm and age 4 in females. The gonosomatic index (GSI) remained constantly low (≤ 0.05) throughout the second and third years of life. A significant increase in GSI was noted in both males and females at the accomplishment of the fourth year of life, coinciding with the spawning season. The results are compared with information available on wild P. bogaraveo and discussed with a view to a possible exploitation of this species in aquaculture, through a reliable control of reproduction.