Influence of pre-inductive photoperiod variations on Eurasian perch Perca fluviatilis broodstock response to an inductive photothermal program

The objective of this study was to determine the effect of pre-inductive photoperiod variations on the reproductive response of Eurasian perch Perca fluviatilis to an inductive photo-thermal program. Broodstock was reared at constant temperature and photoperiod (T=22-24 degrees C, 13L:11D). Then five batches (25 fish per tank, 150-200 g) were transferred into 5 tanks for a 2-week acclimatization phase. During this phase, water temperature was maintained between 22-24 degrees C and 3 different photoperiod regimes were applied (8L:16D, 12L:12D and 16L:8D), corresponding to a high photoperiod decrease (HD), a slight photoperiod decrease (SD) and a high photoperiod increase (HI, 3 batches), respectively. At the end of the acclimatization phase (WO), water temperature was progressively decreased in all tanks from 22 to 6 degrees C over a 6-week period and kept at 6 degrees C over a 3-week period. For the HI regime, photoperiod was progressively reduced to 8L: 16D in one tank over a 6-week period (HIpD), abruptly reduced to 8L:16D when temperature was close to 11 degrees C in another tank (HIaD), or maintained at 16L:8D (HIc) in the last tank. From WO and over a 9-week period, five fish were sampled per tank every third week for calculation of gonadosomatic index (GSI) and assessment of plasma testosterone (T), 17 beta-estradiol (E-2, females only) and 11-keto-testosterone (11-KT, males only) levels. No gametogenesis was observed in males nor females when photoperiod was increased during the acclimatization phase (HI), mean GSI remaining below 1%. A significant GSI increase (to a final value of 5%) was observed in treatments SD and HD in males and females. In these treatments, plasma T and 11-KT in males, and plasma T and E-2 in females were significantly higher. Our results demonstrate that a photoperiod increase during the acclimatization phase before the application of a photo-thermal programme (pre-inductive period) inhibits the onset of the gametogenesis in Eurasian perch. Photoperiodic manipulations during the preinductive period can highly disturb the planning of reproductive cycle. (c) 2006 Elsevier B.V. All rights reserved.