Abstract: The direct addition of arginine into diets causes malabsorption of other amino acids in farmed fish. To study the biological effects of arginine in Nile tilapia, we replaced arginine with N-Carbamylglutamate (NCG), an essential cofactor glutamate in the endogenous arginine synthesis pathway. We examined the effects of NCG (actual content of 80%) in different doses (0.025%, 0.05%, 0.1 %, 0.2 %, 0.4 % and 0.5%) on the concentration of amino acids in the blood, the growth, and the fat deposition in Nile tilapia. The results showed that there was no significant difference between the control group and the NCG-containing groups in the levels of lysine, threonine, leucine, valine and isoleucine in the blood. The blood arginine level increased significantly in the fish fed with 0.4% NCG, which was four times as the control group, but there was no difference in the fish fed with 0.5% NGG compared to the control (P0.05). In terms of the final weight gain rate, the specific growth rate, the feed coefficient rate, the viscera-somatic index and the condition factor, there were no differences between the NCG groups and the control group (P0.05). The weight gain and the protein efficiency ratio were significantly elevated in the fish fed with 0.2% NCG (P0.05). The whole fish protein content of all NCG groups, except for the group of 0.1% NCG addition, was significantly higher than that of the control group (P0.05). The hepatosomatic index of all NCG groups was significantly lower than that of the control group (P0.05), and the whole fish fat content of the NCG groups was higher than that of the control group, except for the group of 0.1% NCG addition, which implied the transfer of fats from the liver to the muscles. The diet containing 0.4% NCG effectively improved the arginine level in the blood but did not affect the absorption of other amino acids. The diet with 0.025%0.5% NCG reduced the liver fat deposition and increased the muscle fat deposition. Our results should provide important information for future studies on the effects of arginine on fish fat deposition.