Effects of light color and photoperiod on hatching percentage, survival rate and larval growth indices in rainbow trout (Oncorhynchus mykiss)

Light is one of the most important factors affecting the growth and survival of larvae in fish. In a 55-day experiment, the effects of light color and photoperiod on hatching percentage, survival rate and larval growth indices in rainbow trout (Oncorhynchus mykiss</em>) were evaluated. Three light colors red, white and yellow  and four light periods (20 D / 4 L, 16 D / 8 L, 10 D / 14 L, 4 D / 20 L and 0 D / 24 L)  and natural situation as control group were tested in three replications.The results of this study showed that the highest percentage of hatching (94.86%) was observed in red light with darkness of 20 hours and the lowest (77.13% and 77.33%) in yellow and red light in 24 hours of brightness (P <0.05). Twenty days after hatching, the highest survival percentage and mean weight of larvae were observed in treatment with shorter photoperiod and red light, which had a significant difference with other treatments (p <0.05); however, different photo period and light colors did not significantly affect the mean larval length at the end of the twentieth day After 55 days of feeding, a significant increase in weight, the best feed conversion ratio and the highest specific growth rate were observed in larvae that were exposed to longer photoperiod and yellow light (p <0.05). In general, in the pre-hatch period, red light with longer darkness, and after-hatch yellow and white light with longer brightness can be effective in increasing hatching and growth.