Growth performance, antioxidative status, and immune response of Nile tilapia (Oreochromis niloticus) fed dietary fermented Spirulina platensis

Fermented Spirulina platensis (FS) has recently attained attraction in human food due to its high functionality and rich content of bioactive compounds. Therefore, the current study investigated the potential roles of dietary FS on the growth performance, digestion capacity, antioxidative status, and immune response of Nile tilapia. Dietary FS at 0, 0.5, 1, 2, 4, and 8 g/kg were fed to Nile tilapia for 60 days. All formulated diets were isonitrogenous and isocaloric with 30.48 % crude protein and 6.63 % total lipids, respectively. The results indicated that the final weight (FW, P=0.004), weight gain (P=0.023), and specific growth rate (SGR, P=0.021) were influenced by dietary FS in a significant quadratic manner. Accordingly, the regression analysis revealed that the suggested doses of FS supplementation in Nile tilapia diets to show the highest FW and SGR are 4.26 and 3.98 g/kg, respectively. Furthermore, dietary FS enhanced the amylase (P=0.035) and lipase (P=0.004) activities in a quadratic manner. The elevated doses of dietary FS instigated prominent improvement of the villous height and goblet cell and increased branching of intestinal villi in the middle segments, particularly in fish fed 4 and 8 g/kg. The red blood cells (P=0.009), hemoglobulin (P=0.004), hematocrit (P=0.034), and white blood cells (P=0.014) were increased significantly with dietary FS in a quadratic manner. No marked effects were seen on the alanine transaminase, aspartate aminotransferase, urea, creatinine, total cholesterol, and triglycerides. Meanwhile, the total protein (P=0.039), albumin (P=0.021), and globulin (P=0.002) were increased significantly by dietary FS in a quadratic manner. The superoxide dismutase (P=0.005) and catalase (P=0.022) were increased, while malondialdehyde level (P=0.028) was decreased significantly with dietary FS in a quadratic manner. The lysozyme activity was higher in fish-fed FS at 0.5, 1, 2, 4, and 8 g/kg than in fish-fed FS at 0 g/kg. The phagocytic activity was higher in fish-fed FS at 2 and 4 g/kg than in fish-fed FS at 0, 0.5, and 8 g/kg without significant differences with fish-fed FS at 1 g/kg (P˃0.05). The regression analysis revealed that the suggested doses of FS supplementation in Nile tilapia diets to show the highest lysozyme activity and catalase activity are 3.52 and 3.79 g/kg, respectively. In conclusion, dietary FS enhanced growth performance, feed utilization, digestive enzyme activity, blood health, immunity, and antioxidative response. Overall, dietary FS can be added at 3.52–4.26 g/kg to enhance the productivity and well-being of Nile tilapia.