EFFECTS OF ACCELERATED PHOTOPERIOD REGIMES ON THE REPRODUCTIVE-CYCLE OF THE FEMALE RAINBOW-TROUT .1. SEASONAL-VARIATIONS OF PLASMA-LIPIDS CORRELATED WITH VITELLOGENESIS

Female rainbow trout were exposed to a simulated natural photoperiod ( control group N) and to two accelerated photoperiod regimes (S9 and S6 groups). Early spawning was achieved in both the S9 and S6 groups, co upled, however, with a reduction of mean egg size. To investigate this reduction of egg size, some morphometric parameters, as well as some plasma parameters such as lipids and vitellogenin levels, were regular ly measured. Regardless of the photoperiod regime, a preferential util ization of lipids for energy purposes was observed during previtelloge nesis and Type I-vitellogenesis, whereas during Type II-vitellogenesis , mobilized lipids were preferentially used for lipoproteins and notab ly for vitellogenin synthesis. Different patterns of the viscerosomati c index, triacylglycerols, and non-esterified fatty acids were observe d during previtellogenesis and Type I vitellogenesis, whereas-similar patterns of all paremeters were observed during Type II-vitellogenesis . From these results it may be concluded that previtellogenesis and Ty pe T-vitellogenesis are photosensitive periods, whereas Type II-vitell ogenesis is probably under the control of an endogenous biological rhy thm synchronized by the photoperiod. Our findings also demonstrate tha t the reduction of egg size could be explained neither by lower plasma TG levels nor by lower vitellogenin (Vtg) levels, since both were muc h higher during Type II-vitellogenesis. (C) 1997 Elsevier Science Inc.