Diacylglycerol oil reduces fat accumulation and increases protein content by inducing lipid catabolism and protein metabolism in Nile tilapia (Oreochromis niloticus)

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The increase of dietary lipid utilization leads a supply of more energy to reduce protein breakdown and promote protein deposition in fish. Therefore, a search for feed additives to stimulate lipid metabolism interests fish nutritionists. Diacylglycerol oil (DGO), as a safe food additive in human, can increase lipid metabolism and prevent obesity in mammals, but it has not been studied in fish feed. The present study evaluated the role of DGO on lipid utilization and protein deposition in Nile tilapia (Oreochromis niloticus) by feeding fish with the diets containing three levels of dietary DGO (0%, 0.5% or 2.5%) for 8 weeks. The 0.5% dietary DGO increased weight gain and significantly decreased the hepatosomatic and mesenteric fat mass. The total lipid and triacylglycerol (TG) contents of the whole fish, liver and muscle tissues, as well as the serum free fatty acid content were significantly lower in the fish fed with both doses of the DGO diet compare to the control (0%). The fish fed DGO diets also exhibited lower lipid droplets in liver tissues than in the control. Moreover, dietary DGO increased the protein content in the whole fish and muscle tissues. The fish fed with the 0.5% DG diet showed an increasing trend on the gene expression of lipid catabolism and protein metabolism in the liver and muscle tissues. However, the 2.5% dietary DGO tended to downregulate metabolism gene expression and upregulate inflammation and stress genes expressions in liver. This study indicates that proper dose of dietary DGO can improve lipid utilization and help to promote protein deposition, and could be a potential additive in aquaculture feeds.