EFFECTS OF CONSTANT PHOTOPERIOD ON SPAWNING AND PLASMA 17-BETA-ESTRADIOL LEVELS OF SEA BASS (DICENTRARCHUS-LABRAX)

This work examines the effects of constant long and short days on the hormonal profile of plasma 17 beta-oestradiol (E2) levels and the ovar ian vitellogenic events, as well as on the fecundity, time of spawning and egg quality of sea bass. Constant short days first administered i n April advanced spawning (by 45 days on average) whereas exposure to constant long days from the same date induced a delay (averaging 38 da ys) compared to controls reared on an ambient light regime (Lat. 40 de grees N). These light regimes produced shifts in the profiles of plasm a 17 beta-oestradiol and in the percentage of the vitellogenic oocytes according to the spawning time of the respective groups. Relative fec undity of the short day group was similar to controls (257,000 versus 230,000 eggs/kg spawned female, respectively). However, in the long da y group, relative fecundity was reduced to one half that of control fi sh (124,000). Plasma oestradiol showed a bimodal pattern under long da ys and vitellogenetic and atretic oocytes were present for a longer pe riod (6-7 months compared to 4-5 months in controls). In summary, in t his paper we describe, for the first time in the sea bass, the effect of constant photoperiod regimes on the 17 beta-oestradiol plasma profi les, the timing of spawning and the quality of the eggs.