| Summary: | Two indoor feeding trials were conducted to investigate the effects of dietary superdosing of Quantum Blue® phytase on the growth performance, as well as mineral and amino acid utilization of juvenile channel catfish (initial weight of 8.02 ± 0.18 g) and red drum (initial weight of 4.99 ± 0.09 g) over 8 and 9 weeks, respectively. Both feeding trials had a negative control diet formulated to contain adequate nutrients but deficient in available phosphorus based on the established requirement of each species. Another four diets were produced from the negative control formulation with Quantum Blue® phytase supplemented at either 1000, 2000, 4000, or 8000 FTU/kg dry diet. A positive control diet also was prepared with supplemental monocalcium phosphate (MCP) to meet the available phosphorus requirement of each species. Both channel catfish and red drum fed the phytase-supplemented diets had significantly (P < 0.05) improved weight gain and feed efficiency compared to fish fed the negative control diet. In addition, dietary phytase supplementation significantly enhanced bone concentrations and whole-body retention of various minerals, although slightly differences were found between the two species. Furthermore, dietary phytase supplementation significantly increased apparent availability of phosphorus from the posterior intestinal region, and reduced excretion of nitrogen and various minerals. Additionally, apparent digestibility coefficients (ADCs) for most indispensable and dispensable amino acids were promoted by dietary phytase. Based on regression analysis of weight gain data from channel catfish and red drum feeding trials, the optimal dietary phytase dosage was estimated to be 5,492⁵⁰⁵⁰∕₅₇₇₃ and 5,520⁵¹⁵⁰∕₆₁₇₅ FTU phytase /kg of dry diet, respectively. In addition, a pond feeding trial was carried out with channel catfish (initial weight of 39.8 ± 3.46 g) reared in cages to evaluate the effect of dietary phytase supplementation of a commercial diet and the interaction between dietary MCP and phytase ...
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