Identification of a photolabile period for reducing sexual maturation in juvenile male sea bass ( Dicentrarchus labrax ) by means of a continuous light regime

The objective of this study was to identify a photolabile period suitable for reducing precocious gonadal maturation in juvenile male sea bass ( Dicentrarchus labrax ) through the exploration of discrete windows of continuous light (LL), 1–2 months in duration, in late summer-early autumn. Somatic growth, 11-ketotestosterone plasma levels, and the rates of testicular maturation and spermiation were analyzed to evaluate the effect of the applied photoperiodic regimes. Three LL treatments, with duration of 2 months each, were previously screened between the months of August and November. Administration of LL during the October–November period failed to show any differential effects in reducing early maturation, as compared to the simulated natural photoperiod. However, the August–September period was considered to be a likely candidate for photolability. To define this photolabile period, four LL treatments with duration of 1 month were then screened within the same late summer period. Our results demonstrate that the time interval including the month of September is the most sensitive photolabile period in order to reduce precocious gametogenesis in sea bass.