Photoperiodic manipulations of the reproductive cycle of sea bass (Dicentrarchus labrax) and their effects on gonadal development, and plasma 17ß-estradiol and vitellogenin levels

The annual profile of plasma vitellogenin (VTG) and 17ß-estradiol (E2) levels, as well as gonadal development and spawning characteristics were investigated in captive female sea bass (Dicentrarchus labrax). Endocrine and gonadal changes were studied in fish reared under natural conditions or exposed to manipulated photothermal cycles. In natural conditions of photoperiod and temperature, sea bass spawned from February through March (East coast of Spain, 40°N 0°E). One or two months of constant long-days (15L/9D) in a constant short-day photoperiod regime (9L/15D) all-year-round, given early in the year (March and March–April), advanced spawning by 3 months. The same treatment applied later in the year (September–October) delayed spawning by 1 month, compared to controls.