Optimum dietary levels of phytase from Bacillus megaterium on the utilization of phosphorus in the diets of Nile tilapia, Oreochromis niloticus

A feeding trial was conducted to determine the effects of dietary B. megaterium phytase at 250, 500, 1,000 and 1,500 Phytase Units (FTU) kg-1 diet and diets containing Pi 1.5% mono-sodium phosphate and 1.0% calcium carbonate (positive control). Fish fed diets containing 250 FTU kg-1 phytase and above exhibited comparable results on weight gain and specific growth rate (SGR) with those of fish fed the diets containing P. Fish fed the Pi diet exhibited lower feed conversion efficiency (FCE), protein efficiency ratio (PER) and protein retention than did fish fed diets supplemented with 500 FTU and 1,000 FTU kg-1 phytase. No significant differences in body crude protein, ash, P, Ca and Mg among fish fed the dietary treatments. Fish fed the diet supplemented with 1,000 FTU kg-1 phytase exhibited significantly the highest body crude lipid. Phosphorus concentration in scales, bone and vertebrae of fish fed the Pi diets displayed lower concentration than did fish fed 500 FTU kg-1 and 1,000 FTU kg-1, respectively. Fecal P was significantly lower in fish fed diets containing various levels of phytase than in those fed the inorganic phosphorus Pi diet. Findings of the present study revealed that addition of 500-1,000 FTUkg-1 of B. megaterium kg-1 to tilapia diet improved bioavailability of phytate in Nile tilapia diets thereby it could potentially lessen the P content in pond effluent from 27% to 39%.