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

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