Efficacy of phytase on phosphorus utilization in practical diets fed to striped bass Morone saxatilis

Abstract

Several experiments were conducted to determine the effects of phytase on dietary phosphorus (P) utilization by striped bass Morone saxatilis fed high phytate diets. The experiments were designed to determine the effectiveness of various dietary levels of a dry or liquid phytase concentrate incorporated in diets to improve the P utilization of striped bass. Fish were fed various basal diets containing over 700 g kg−1 plant feed ingredients and 4.9–7.1 g kg−1 P and 1.5–1.7 g kg−1 non-phytin P. A diet supplemented with potassium monophosphate (PMP) and containing 9 g kg−1 total P and 6 g kg−1 non-phytin P with no added phytase was the positive control. The dietary treatments were assigned to duplicate tanks and diets were fed to juvenile striped bass for up to 14 weeks. The effectiveness of the phytase treatments was determined by measuring weight gain, feed conversion, serum, scale and vertebral calcium and P, as well as P absorption. Apparent P absorption was determined using 5 g kg−1 chromic oxide as an indigestible marker in the diet. In experiment one, significant improvements (P < 0.05) were found in scale and vertebral phosphorus concentrations with 2400 Phytase Units (PU) kg−1 (PU is the quantity of enzyme which liberates one micromole of inorganic P per minute from 0.015 tool L−1 sodium phytate at 37°C and pH 5.5) added to the diet. In experiment two, significant differences were observed between serum phosphorus in the phytase and no-phytase groups, while there were no differences between the positive control (PMP supplemented) and the phytase-treated fish. It was concluded that 2400 PU kg−1 of enzyme resulted in bone mineralization and serum phosphorus concentrations equal to that observed with 13 g kg−1 dietary PMP addition (9 g kg−1 total P).