Effects of light intensity on growth, immune response, plasma cortisol and fatty acid composition of juvenile Epinephelus coioides reared in artificial seawater

Because light is one of the major environmental factors and regulates the physiological and biochemical processes of fish, the effects of light intensity on growth, immune response, and plasma cortisol and fatty acid composition of juvenile Epinephelus coioides (orange-spotted grouper, also known as estuary cod) reared in a recirculating artificial seawater system were researched and evaluated in this study. A completely randomized design with five light treatments (0, 10-50, 320-550, 600-1150 and 3000-3500 lx) and three replicates was used. The experiment lasted for 56 days. The weight gain rate (WG, %), specific growth rate (SGRd) and survival rate were significantly higher (p ≤ 0.05) in the 320-1150-lx treatments compared with the other treatments. Activities of acid phosphatase (ACP) and total superoxide dismutase (T-SOD) and content of nitric oxide (NO) were significantly higher at 600-1150 lx, whereas the highest activity of alkaline phosphatase (AKP) was at 320-550 lx (p ≤ 0.05). Plasma cortisol concentration was significantly lower at 320-1150 lx and significantly higher at 0 lx and 3000-3500 lx (p ≤ 0.05). The content of total polyunsaturated fatty acids (∑ PUFA) was significantly higher at 320-550 lx than in the other treatments. However, total saturated fatty acids (∑ SFA) were significantly higher at 10-50 lx than at 320-1150 lx (p ≤ 0.05). The results showed that light intensity could significantly affect growth, immune response, plasma cortisol and fatty acid composition of juvenile E. coioides, with optimal light intensity being 320-1150 lx.