Effects of light color, photoperiod, and growth-related gene interference or overexpression on the survival, growth, or physiological and biochemical indices of red claw crayfish juveniles

To determine the optimal light color and photoperiod conditions for red claw crayfish juveniles, we studied the effects of these factors on their survival, growth, monoamine content, antioxidant capacity, nonspecific immune index, and the expression of EcR and α-AMY genes. Experiments involving five light color groups (red, green, blue, yellow, and white light), five photoperiod groups (0 L:24D, 6 L:18D, 12 L:12D, 18 L:6D, and 24 L:0D), besides, we also studied the effects of interference and overexpression of these genes on growth, survival, and their expression. (1) The red light group showed the highest survival rate, while the blue light group showed the fastest growth rate. Further, the red light group showed significantly higher superoxide dismutase [SOD], acid phosphatase [ACP], and alkaline phosphatase [AKP] activities, but significantly lower malondialdehyde [MDA], serotonin [5-HT], noradrenaline [NE], and dopamine [DA] concentrations. The yellow light group presented significantly higher SOD activity, and lower DA concentration. The blue light group showed the highest α-AMY expression level, while the EcR expression levels corresponding to the yellow and red light groups were significantly higher. (2) The 0 L:24D and 6 L:18D photoperiod groups showed significantly higher survival rates than the 24 L:0D group. Additionally, the SOD and ACP activities corresponding to the 6 L:18D and 0 L:24D group were significantly higher, while its MDA and DA concentrations were significantly lower. (3) The 6 L:18D, 12 L:12D, and 0 L:24D groups showed significantly higher α-AMY expression levels, while EcR expression was significantly higher in the 6 L:18D and 0 L:24D groups. (4) EcR or α-AMY gene interference or overexpression had no significant effect on juvenile crayfish survival. However, interfering with ECR expression reduced juvenile growth rate, while ECR or α-AMY gene overexpression enhanced their growth rate. Overall, red claw crayfish juveniles showed higher survival rates, greater antioxidant and immune activities, and lower monoamine contents under red light, 6 L:18D or 0 L:24D conditions. Thus, these conditions possibly improved digestion and absorption and also promoted molting in the juveniles. Additionally, ECR and α-AMY expression could reflect the growth rate of the juveniles, but not their survival.