Dietary available phosphorus requirement of adult GIFT strain ofOreochromis niloticusreared in freshwater

Abstract

The present study was conducted to estimate the optimum requirement of dietary available phosphorus for adult GIFT strain of Nile tilapia Oreochromis niloticus reared in freshw ater. Six semi-purified diets w ere formulated to contain graded levels( 0. 15%,control diet,0. 40%,0. 66%,0. 91%,1. 17% and1. 43% t) of available phosphorus( KH2PO4w as the source of phosphorus). Each diet w as fed to triplicate groups of 20 fish w ith initial average w eight( 184. 46 ± 8. 13) g for 9 w eeks. The results show ed that fish fed the tw o diets w ith available phosphorus levels of 0. 66% and 0. 91% had significantly higher w eight gain rate( WGR) and specific grow th rate( SGR) than those fed the other diets( P 0. 05),and the feed efficiency( FE) was significantly higher than that of control diet( P 0. 05). The whole body viscerosomatic index( VSI),hepatosomatic index( HIS) and condition factor( CF) decreased significantly with the increases of the dietary available phosphorus levels( P 0. 05),w hile the survival rate( SR) of fish had no significant differences among various dietary treatments( P 0. 05). Crude protein,ash,and phosphorus concentration in w hole body increased significantly w ith the increases of the dietary available phosphorus levels,as w ell as vertebrae and scale ash and phosphorus concentration( P 0. 05). Crude lipid concentration in w hole body decreased significantly w ith the increases of the dietary available phosphorus levels( P 0. 05). Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining maximal grow th of tilapia w as 0. 85%.