Nile tilapia Oreochromis niloticus as a species with high growth rate and high tolerate to environmental conditions and stocking density, have been culturing in the world more and more. Because of feed expenses necessity and better growth rate and feed conversion efficiency in brackish water, despite of existing many studies on protein requirements, lipid utilization and protein sparing effect of Nile tilapia, they were studied on all males in brackish water, again. A 4 × 3 factorial design with three replicates was planned based on the proximate and amino acids analysis of protein sources to contain four crude protein (15, 22, 29 and 36 %) and three crude lipid (5, 9 and 13%) levels. Growth indices including weight gain and specific growth rate improved by protein accretion and reduced by lipid increasing. The best growth performance was obtained in 5% crude lipid. Feed conversion ratio reduced by protein increasing, and the best one observed in the diet containing 36% crude protein. Protein efficiency ratio and Protein conversion efficiency increased by protein accretion up to 29% crude protein. Protein efficiency, except 15% crude protein, increased up to 9% crude lipid and then reduced but not significantly; so, protein-sparing effect appeared, unclearly. In this study, at 25.6% crude protein with 265 mg protein per gram body weight, fish can keep their carcass protein percentage. In economic point of view, based on growth, feed and protein performances, the levels of 29% crude protein and 5% crude lipid are sufficient for convincing growth rate. The results show that isotonic environment cannot Change protein and lipid requirements compared to the other studies in the fresh water.
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