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 °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 °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 (W0), water temperature was progressively decreased in all tanks from 22 to 6 °C over a 6-week period and kept at 6 °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 °C in another tank (HIaD), or maintained at 16L : 8D (HIc) in the last tank. From W0 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 β-estradiol (E2, 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 E2 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 pre-inductive period can highly disturb the planning of reproductive cycle.