Effect of alpha-ketoglutarate supplementation on growth, antioxidant capacity, gene expression and amino acid profile in Nile tilapia (Oreochromis niloticus) under varying protein diets

Protein is the most expensive component in aquafeed and emphasis is given to reduce dietary protein levels without compromising growth. Alpha ketoglutarate (AKG) promotes protein synthesis in fish and improves growth. The present experiment was conducted to investigate the effect of AKG with different dietary protein levels on growth, nutrient utilisation, antioxidant status and immunity in Nile tilapia (Oreochromis niloticus). Five diets were prepared with different levels of protein such as 20 (P20A), 25 (P25A), 30 (P30A) and 35 % (P35A) with 1 % AKG and 35 % protein without AKG (P35C). Nile tilapia fingerlings (300) were randomly stocked in fifteen 150 L capacity FRP tanks with 20 fingerlings (9.91 +/- 0.06 g) in each. The fish were then fed with experimental diets twice daily for 60 days. The fish fed with P30A had significantly (P < 0.05) higher growth performance and nutrient utilisation. However, there was no significant (P > 0.05) difference in final body weight and weight gain of tilapia fed with P35C and P25Adiets. The feed conversion ratio (FCR) was significantly higher (P < 0.05) in P20A group and other groups showed alike (P > 0.05) FCR value. The whole body protein and lipid contents of final fish were significantly (P < 0.05) higher in P30A and P25A, respectively. The P25A, P30A and P35A showed increased (P < 0.05) activities of superoxide dismutase (SOD) and catalase (CAT). The activity of metabolic enzymes were also higher in higher protein levels with AKG (P30A and P35A). The expression level of growth gene insulin like growth factor 1 (IGF-1) was significantly up-regulated (P < 0.05) in the P30A. In addition, the relative expression levels of the pro-inflammatory factors tumour necrosis factor (TNF-alpha) were significantly (P < 0.05) lower in P30A, P25A, and P20A. Total amino acid profile of fish was higher in P35C group. In summary, the optimal choice for enhancing growth and health in Nile tilapia appears to be a diet comprising 30 % protein and 1 % AKG. However, diet of 25 % CP with AKG showed equivalent result in terms growth that of 35 % CP level without AKG. Hence, 25 % protein with 1 % AKG can effectively fulfil protein requirement in tilapia.