The evaluation of growth performance, blood health, oxidative status and immune-related gene expression in Nile tilapia (Oreochromis niloticus) fed dietary nanoselenium spheres produced by lactic acid bacteria

The present study was conducted to investigate the effects of lactic acid bacteria-produced nanoselenium spheres (LAB-Se) on the growth performance, blood health, oxidative status and immune-related gene expression in Nile tilapia (initial weight, 14.03 +/- 0.04 g). LAB-Se was incorporated into the basal diet at 0.5, 1, 1.5 and 2 mg/kg of diet and fed to the fish for 8 weeks. The results revealed significantly improved final body weights, weight gain, specific growth rates and feed efficiency ratios in fish fed varying levels of LAB-Se (quadratic, P = 0.002, P = 0.002, P = 0.002, and P = 0.04, respectively). The blood haematology and biochemistry parameters of the fish fed varying levels of LAB-Se showed normal values with nonsignificant (P > 0.05) differences, indicating the non-toxic effect of LAB-Se. Additionally, dietary LAB-Se had significant influences on blood total protein and lysozyme and phagocytic activities in tilapia in a dose-dependent manner (quadratic, P = 0.04, P = 0.02, and P = 0.001, respectively). Dietary LAB-Se significantly increased SOD and CAT enzyme activities and decreased MDA levels (quadratic, P = 0.001, P = 0.03, and P = 0.007, respectively); GPX was not significantly affected by LAB-Se inclusion the diets (P > 0.05). Liver and spleen TNF-alpha expression was significantly upregulated in the fish fed LAB-Se (quadratic, P = 0.007 and P = 0.009, respectively). The expression of liver IL-1 beta was also upregulated significantly in the fish fed LAB-Se (quadratic, P = 0.005), while spleen IL-1 beta was not significantly affected by LAB-Se (P > 0.05). Thus, LAB-Se at 1 to 2 mg/kg can be effectively supplemented in tilapia diets to improve growth, oxidative status and immune-related gene expression.