Prolonged photoperiod inhibits growth and reproductive functions of rohu Labeo rohita

Among the environmental factors, photoperiod plays an important role in growth and reproduction of fish. This study was conducted to assess the effects of photoperiod on growth of juveniles and reproductive functions of matured female rohu (Labeo rohita), a commonly cultured freshwater fish species. Two experiments were conducted each with three different photoperiod treatments, such as 6 h of light and 18 h of dark (06L:18D), 12 h of light and 12 h of dark (12L:12D), and 18 h of light and 6 h of dark (18L:06D), each treatment with three replications. In the first experiment, fingerlings (2.39 +/- 0.35 g BW, 6.67 +/- 1.23 cm TL) were exposed in the three photoperiod conditions for 30 days and sampled fishes were sacrificed on 7, 15 and 30 days of exposure to measure growth parameters (weight gain (g); percent weight gain; specific growth rate, SGR and feed conversion ratio, FCR) and major hemato-biochemical parameters (Hemoglobin, Hb; Red blood cell, RBC; White blood cell, WBC and blood glucose). Final weight gain (g), percent weight gain and SGR were highest in 12L:12D and the lowest in 18L:06D conditions. FCR was lowest in 12L:12D conditions. In prolonged photoperiod (18L:06D), the Hb and RBC decreased significantly, while WBC and blood glucose level increased significantly during initial days of exposure. In the second experiment, sexually matured females were exposed in the three photoperiod conditions for 30 days and the sampled fishes were sacrificed on 0, 15 and 30 days of exposure to know gonadosomatic index (GSI) and gonadal histology. The mean GSI values, oocyte diameter and proportions of vitellogenic oocyte were maximum in the fishes of 06L:18D treatment indicating stimulation of vitellogenesis. On the other hand, the same parameters were minimum in the fishes of 18L:06D, revealing the inhibition of vitellogenesis. This study indicates that prolonged photoperiod negatively affect growth and reproductive performances of rohu.