Short-term exposures to continuous light during pregametogenesis reduce early sexual maturation in juvenile sea bass (Dicentrarchus labrax)

Abstract

The effect of short-term exposure to continuous light (LL) to reduce early male sexual maturation was investigated in the sea bass. Four LL light regimes (1 or 2-month duration) were established during the pregametogenesis, whereas a simulated natural photoperiod (SNP) and a long-term exposure group (12-month duration) to LL were kept as controls according to previous tria) in this species. Somatic growth, gonadal development, plasma testosterone (T), 11-ketotestosterone ( 11-KT) and 17􀀁-estradiol (E2) were analysed as indicators of maturation. Growth in ali treatments was overall similar in ali photoperiod treatments. In contrast, ali the LL treatments were effective to alter the reproductive wave in comparison to the SNP group, affecting the progression of germ cells to more advanced stages of testicular development. Furthermore, the hepatosomatic index fluctuated seasonally without showing clear differences among the experimental groups, whereas the viscero-somatic index significantly increased in the SNP group (> 5%) in comparison to that in all LL treatments before the onset of gametogenesis. These results evidenced that fish needs to attain a critica] energetic status to enable maturation to begin. Exposure to different LL treatments induced a differential response on the sex-steroid levels. Particularly, significant differences in the levels of 11-KT were observed in February between the SNP group and the LL groups. These results suggested the role of this androgen as a putative threshold determining early puberty in the sea bass as previously reported. Thus, the identification of a short­term exposure to LL approach can be of interest for sea bass aquaculture, since it could reduce the presence of early sexual maturing males under farming conditions.