The effects of 4 different scotophase, the dark phase of photoperiods, LD8:16 (8 h light: 16 h dark), LD12:12 (12 h light: 12 h dark), LD16:8 (16 h light:8 h dark) and LD24:0 (24 h light:0 h dark) on growth, feed conversion and survival rate of rainbow trout, Oncorhynchus mykiss fry with 2 g initial weight were investigated. The fry exhibited better growth and feed utilization in longer light periods but differences appeared only after 60 days of exposure time. The highest growth rate and lowest feed conversion ratio were recorded in LD16:8 groups. In addition, growth and feed conversion ratio in the fry exposed to LD12:12, LD16:8 and LD24:0 photoperiods were statistically better than that of LD8:16 photoperiod (p<0.05). There was no significant photoperiod effects on the survival rate (p>0.05). Consequently, it can be supposed that growth and feed utilization of rainbow trout fry were improved when cultured in longer light periods.