Effects of light intensities on the growth and physiology of Megalobrama pellegrini larvae and juveniles

Light intensity significantly influences multiple aspects of fish growth and physiology. To investigate the effects of light intensity on early-stage growth and physiology of Megalobrama pellegrini and determine the optimal light intensity for their early development in a recirculating aquaculture system (RAS), we conducted a rearing experiment exposing M. pellegrini larvae to four light intensities: 0 Lx, 100 Lx, 500 Lx, and 2500 Lx. The results demonstrated that the growth performance was maximized at 2500 Lx and was significantly higher than other groups ( P < 0.05). Quadratic regression analysis indicated that the optimal light intensity range for growth performance was between 1911.9 and 2139.6 Lx. The expression of growth-related genes under different light intensities mirrored changes in body weight and total length. Specifically, GH , GHRa , and IGF-2 mRNA expression levels increased at 2500 Lx. High light intensity (2500 Lx) promoted the digestion of starch and protein by increasing the activities of α-amylase (AMS) and trypsin (TPS) while enhancing phosphatase metabolism, which was conducive to growth. Conversely, low light intensity impaired fat digestion, reduced phosphatase metabolism, and concurrently elevated antioxidant enzyme activity, leading to increased oxidative stress and adversely affecting growth. In conclusion, a light intensity range of 1911.9–2139.6 Lx is recommended as the optimal light environment for rearing M. pellegrini larvae and juveniles in RAS. The findings contribute to optimizing light conditions for the breeding of black bream seedlings and provide a theoretical foundation for enhancing early-stage rearing practices of M. pellegrini in RAS. • The optimal light intensity range for the seedling cultivation stage of M. Pellegrini was 1911.9–2139.6 Lx. • High light intensity enhanced starch and protein digestion alongside phosphatase metabolism supporting optimal growth. • Low light intensity impaired fat digestion and phosphatase metabolism, elevating oxidative stress and stunting growth. • The expression of growth-related genes under different light intensities mirrored changes in body weight and total length.