Lipid utilization, protein sparing effects and protein requirement of all male Nile tilapia (Oreochromis niloticus Linnaeus, ۱۷۵۸) in underground brackish water

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 ۴ × ۳ factorial design with three replicates was planned based on the proximate and amino acids analysis of protein sources to contain four crude protein (۱۵, ۲۲, ۲۹ and ۳۶ %) and three crude lipid (۵, ۹ and ۱۳%) 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 ۵% crude lipid. Feed conversion ratio reduced by protein increasing, and the best one observed in the diet containing ۳۶% crude protein. Protein efficiency ratio and Protein conversion efficiency increased by protein accretion up to ۲۹% crude protein. Protein efficiency, except ۱۵% crude protein, increased up to ۹% crude lipid and then reduced but not significantly; so, protein-sparing effect appeared, unclearly. In this study, at ۲۵.۶% crude protein with ۲۶۵ 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 ۲۹% crude protein and ۵% 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.

Keywords:

Protein , Lipid , Tilapia , Brackish water