The Effects of Different Levels of Dietary Protein and L-Carnitine on Blood Sugar and Lipids of the New GIFT Strain of Juvenile Nile Tilapia (Oreochromis niloticus)

The new GIFT (Genetically Improved Farmed Tilapia) strain of Nile tilapia is a popular cultivated fish in Asia, but intensive aquaculture using nutritionally imbalanced feed has led to disorder of lipid metabolisms. An 8-week feeding experiment was conducted in order to assess the effects of different levels of L-carnitine (0, 200, 400, 600, and 800 mg/kg) and dietary protein (22, 25, and 28%) on blood sugar and blood lipid contents of the new juvenile GIFT strain of Nile tilapia. Results showed that dietary protein and L-carnitine had significant influences on glucose (GLU), high-density lipoprotein–cholesterol (HDL-C), total cholesterol (TC), triglyceride (TG), and low-density lipoprotein–cholesterol (LDL-C) in the blood serum. The contents of GLU and HDL-C increased with the increases in dietary protein and L-carnitine levels, while the contents of TC, LDL-C, and TG decreased with the increases in dietary protein and L-carnitine levels. The interactive effect of both dietary protein and L-carnitine was most significant on GLU (p = 0.0001), followed by TG (p = 0.001), TC (p = 0.005), HDL-C (p = 0.056), and LDL-C (p = 0.109). These results suggested that high levels of dietary protein and L-carnitine supplementation reduce blood lipids and the burden of the fish liver.