Improving Growth, Digestive and Antioxidant Enzymes and Immune Response of Juvenile Grass Carp (Ctenopharyngodon idella) by Using Dietary Spirulina platensis

The present study was designed to investigate the effect of Spirulina platensis (SP) supplemented diets on the growth performance, digestive enzymes, hepatic antioxidants and innate immunity biomarkers in juvenile grass carp (Ctenopharyngodon idella). Two hundred and forty grass carp juveniles (average weight 4.81 +/- 0.13 g) were divided into four treatment groups in triplicates (20 fish/replicate) and fed with diets containing 0, 1, 5, and 10% Spirulina for 90 days. A significant increase in growth (p < 0.05) was observed in fish fed with diets having 1 and 5% Spirulina. Intestinal protease and lipase activities increased significantly (p < 0.01) in fish fed with a diet having 5% Spirulina while intestinal amylase activity increased significantly (p < 0.01) in fish fed with diets having 1, 5, and 10% Spirulina. Hepatic lipid peroxidation decreased significantly (p < 0.05) in fish fed with a 1 and 5% Spirulina supplemented diet. The activity of catalase, glutathione-S-transferase, and glutathione levels increased significantly (p < 0.05) in the livers of fish fed with 1% Spirulina supplemented diets while no significant difference (p > 0.05) was observed for hepatic superoxide dismutase levels when compared to the control. Significant increases in the skin mucus protease (p < 0.05), antiprotease (p < 0.01), lysozyme (p < 0.001), and peroxidase (p < 0.05) activities were observed in fish fed with 5% Spirulina-supplemented diets. Gene expression analysis of head kidney showed that fish fed with a 1% Spirulina diet had significantly (p < 0.01) higher expression of tnf-alpha, il-8, and inf-gamma. In conclusion, the present study suggested that the inclusion of 5% Spirulina platensis in the diet of grass carp has positive effects on growth, digestive enzymes, antioxidants, and innate immunity.