Effects of different photoperiod conditions on juvenile tench ( Tinca tinca L.) under intensive rearing

Summary Two 120‐day experiments with 5‐month‐old juvenile tench ( Tinca tinca L.) were conducted to evaluate different photoperiod conditions. In the first experiment, juveniles were exposed to natural winter photoperiod (ca. 11 h light: 13 h dark), continuous light or continuous darkness. In the second experiment, two photoperiods were tested: natural winter or an extended photoperiod (16 h light: 8 h dark). In all cases, survival was high (95.8–100%). In the first experiment, tench under the natural winter photoperiod had the highest growth (52.3 mm TL , 1.84 g W, 1.28% d −1 SGR ). In the second experiment, the extended photoperiod enabled a significantly higher growth (56.8 mm TL , 2.51 W g, 1.75% d −1 SGR ) than in the natural winter photoperiod. Percentages of deformed fish ranged from 1 to 31.2%.