Two feeding trails were conducted with Nile tilapiaOreochromis niloticus fingerlings to determine the effect of dietary phytase level with partial or complete replacement of fish meal (FM) by soybean meal (SBM) on growth, feed utilization, nutrients digestibility as well as dietary phosphorus discharge. A total of 960 Nile tilapia fingerlings with an average body weight of 18.8±0.3 g were divided in the twenty-experimental treatments (duplicate for each treatment). The experiment was conducted for 13 week. Five basal diets were formulated to be isonitrogenous 30% crude protein and isocaloric 19.5 MJ kg-1 diet gross energy. The control diet (diet 1) was prepared with FM as the main protein source. Diets 2-5 each SBM were substituted, for an isonitrogenous amount of FM control diet, to provide 25% (diet 2), 50% (diet 3), 75% (diet 4) or 100% (diet 5) of the FM crude protein. Another three groups of similar previous five basal diets were formulated and supplemented with 1000, 1500, 2000 FTU kg-1 diet, respectively of phytase enzyme. The present results suggest that a 25% substitution of dietary FM with SBM in Nile tilapia fingerlings diets has enhance growth performance and feed efficiency. With increasing dietary SBM levels; comparably lower growth indices were obtained compared to 100%-FM control diet. Irrespective of dietary SBM levels, supplementation of microbial phytase at 1000 FTU kg-1 level has demonstrated to be efficient for increasing dietary phosphorus supply for Nile tilapia fingerlings, thereby reducing the phosphorus effluent from aquaculture facilities. This may have to be taken into consideration for ongoing feeding strategies for the control of waste discharge.
Ashraf M.A.S. Goda , 2007. Effect of Dietary Soybean Meal and Phytase Levels on Growth, Feed Utilization and Phosphorus Discharge for Nile tilapia Oreochromis niloticus (L.). Journal of Fisheries and Aquatic Science, 2: 248-263.