Effect of Phytase on Growth and Phosphorus Utilization in Japanese Flounder (Paralichthys olivaceus)

An experiment was conducted to investigate the effect of phytase supplementation on weight gain, phosphorus and protein digestibility and retention in Japanese flounder (Paralichthys olivaceus) fed a soybean meal (SBM)-containing diet. Six levels of phytase-supplemented diets containing 0, 150, 300, 450, 900 and 1500 FTU (phytase unit)/100g diet were assigned to triplicate tanks and fed to Japanese flounder (20 fish/tank, initial average weight 151.4 g) for 40 days. The increase of soluble phosphorus and decrease of phytic acid remained relatively constant for all levels receiving the 300 FTU diet and greater. Significantly (P<0.05) greater weight gain and higher feed conversion ratios (FCR) were observed in fish fed diets supplemented at 300 FTU or greater compared to the control (0 FTU) diet. Significantly (P<0.05) improved apparent protein and phosphorus digestibility, as well as serum calcium concentration were found in fish fed the 300 FTU diet. All diets supplemented at 300 FTU or greater also showed a significantly (P<0.05) improved concentration of bone calcium and zinc. The 150 FTU inclusion level showed only better protein and phosphorus retention, bone phosphorus and magnesium than the control (0 FTU) diet. Therefore, this study indicated that supplementation of phytase is effective and that the 300 FTU/100g SBM-containing diet resulted in the maximum release of soluble phosphorus, and as a consequence improved weight gain, FCR, bone minerals, phosphorus and protein digestibility and retention in Japanese flounder.