Dietary available phosphorus requirement of adult GIFT strain of Oreochromis niloticus reared in freshwater

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 freshwater.Six semi-purified diets were formulated to contain graded levels(0.15%,control diet,0.40%,0.66%,0.91%,1.17% and 1.43%t)of available phosphorus(KH₂PO₄ was the source of phosphorus).Each diet was fed to triplicate groups of 20 fish with initial average weight(184.46±8.13)g for 9 weeks.The results showed that fish fed the two diets with available phosphorus levels of 0.66% and 0.91% had significantly higher weight gain rate(WGR)and specific growth 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),while the survival rate(SR)of fish had no significant differences among various dietary treatments(P＞0.05).Crude protein,ash,and phosphorus concentration in whole body increased significantly with the increases of the dietary available phosphorus levels,as well as vertebrae and scale ash and phosphorus concentration(P<0.05).Crude lipid concentration in whole body decreased significantly with 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 growth of tilapia was 0.85%.