تاثير دوره هاي نوري كوتاه و بلند مدت بر تكامل تخمك و ميزان رشد بدن در ماهي ماده قزل آلاي رنگين كمان(Oncorhynchus mykiss)

Effects of long and short-term photoperiods on oocyte development and body growth rate in female rainbow trout0Oncorhyrtchus mykiss)

Effects of different artificial photoperiods were investigated on gonadal development and somatic growth in female rainbow trout (Oncorhyrtchus mykiss). Two years old females (279.94 ± 2.25 gr BW [mean ± SE]) were subjected to three different artificial photoperiods for 5 months, starting from August 2008. Constant light photoperiod (LD 24:0), long-day photoperiod (LD 18:6) and short-day photoperiod (LD 6:18) were considered as artificial regimes and ambient photoperiod was considered as the control group. At the end of the experiment, significant differences were found in gonadosomatic indice (GSI) and oocyte diameter between both control and LD 6:18 groups with LD 18:6 and LD 24:0 groups (P < 0.05). The highest body weight (635.45 ± 16.19 g) and specific growth rate (SGR) (1.03 ± 0.04 gr/day) were recorded in LD 24:0 compared with the other groups (P < 0.05). The specimens subjected to LD 24:0 and LD 18:6 photoperiods, had the highest condition factor, which were 1.44 ± 0.01 and 1.44 ± 0.02, respectively; while this value for the control and those subjected to LD 6:18 were 1.27 ± 0.01 and 1.34 ± 0.02, respectively. We conclude that long light photoperiod during gonadal development is one of the effective methods for retarding gonadal development and inducing somatic growth in rainbow trout.