EFFECTS OF DIETARY LIPID LEVELS ON GROWTH PERFORMANCE,NUTRIENT DIGESTIBILITY AND BLOOD BIOCHEMICAL INDICES OF GIFT TILAPIA(OREOCHROMIS NILOTICUS)

In order to determine the optimal levels of the lipid of GIFT strain Nile tilapia(Oreochromis niloticus),630 GIFT with average weight of(2.63±0.16) g were divided into six groups(1.73% lipid,3.71% lipid,5.69% lipid,7.67% lipid,9.64% lipid and 16.55% lipid) randomly.One with triplication was the control group fed with basal diet(1.73% lipid),the others were the treated groups fed with basal diet(1.73% lipid) supplemented with 2%,4%,6%,8% and 15% fish oil,respectively.After rearing 90d,the growth,feed conversion ratio,nutrient apparent digestibility and blood bio-chemical parameter were determined.Results showed that,along with dietary lipid level raising,weight gain rate and specific growth rate had a trend of going up first then falling down(P0.05),protein efficiency ratio improved(P0.01) and feed conversion ratio reduced(P0.01).Second-order regression of weight gain rate on concentrations of dietary lipid indicated that the optimal dietary lipid for maximal growth of GIFT tilapia was about 9.34%.Crude protein and dry-matter digestibility had no significant effected by dietary lipid levels(P0.05).Crude lipid and phosphorus digesti-bility raised significantly with dietary lipid level increasing(P0.05).Albumin and albumin/globulin ratio in 1.73% group(this group did not added fish oil) was significantly higher than other group(P0.05).Along with dietary lipid level raising,cholesterol and alkaline phosphatase of fish serum raised significantly(P0.01).Dietary lipid level had significantly influence on blood glucose(P0.05),and there was no significantly influence on the content of triglyceride and the activities of glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase(P0.05).It indicated that the level of lipid in the dietary could improve the growth,the apparent digestibilities of crude lipid and phosphorus to some degree,but excessive amount of lipid content in the dietary may be negative effects of fish growth and immune ability in GIFT.So 7.67%-9.34% lipid of the dietary are the optimal levels of GIFT Seedlings in aquaculture.