Investigating the effects of photoperiod on growth performance and sextual maturation of Caspian trout (Salmo trutta caspius)

Photoperiod is one of the very important environmental factors that extremely affect growth performance, feeding and reproduction of various fish species. Thus In this research effects of different photoperiod regimes on Caspian Salmon during the premature stage (18 months old at the beginning of experiment) were investigated. One thousand liter tank with 20 premature fishs were allocated for each treatment. Applied photoperiod regimes during 6 months experimental period were: (1) continues light (24L/0D), (2) 18L/6D during first three months and 6L/18D during second three months, (3) 6L/18D during first three months and 18L/6D during second three months and (4) continues dark (0L/24D). Results indicated that growth performance, feeding and reproduction were influenced by the photoperiod regimes. The highest values of SGR (0.44 % d^-) and the lowest values of FCR (4/3) were observed in treatment 4 that showed significant differences as compared with treatment 1 (0.35 % d^- and 4.4) treatment 2 (0.33 % d^- and 4.7) and treatment 3 (0.34 % d^- and 4.5). Maturation of females was not influenced by experimental photoperiod regimes but maturation of males was significantly influenced. As all males of treatment 2 reached sexual maturity at the end of experiment. In contrast, treatments 3 and 4 postponed gonad development and maturation of males. Therefore, to increase the growth of Caspian salmon, the 24-hour dark photoperiod and to stimulate its sexual maturation, the 18 and 6-hour light photpperiod is recomonded in the first and second trimesters of the six-month photpperiod regime, respectively.