Optimal dietary supplementation of phytase for red drum (Sciaenops ocellatus) based on growth and mineral utilization

Abstract

A 9-week feeding trial was conducted with juvenile red drum to evaluate the potential benefits of supplementing dietary phytase on growth performance and utilization of phosphorus (P) and various trace minerals. The negative control diet (0.9% of total P and 0.57% of available P) was formulated to have inadequate available P based on the established P requirement of red drum. The positive control diet contained extra monocalcium phosphate (MCP) to provide 0.73% available phosphorus to meet the red drum's minimum P requirement. Another four phytase-supplemented diets were made via adding Quantum Blue phytase (AB Vista, Plantation, Florida) at either 1000, 2000, 4000, or 8000 phytase units (FTU)/kg to the negative control diet. Each diet was fed to quadruplicate groups of 20 juvenile red drum (initial weight of 4.99 ± 0.09 g) in 110-L aquaria operated as a brackish water (7 ppt) recirculating aquaculture system for 9 weeks. The results showed that compared to red drum fed the negative control diet, fish fed the phytase-supplemented diets had significantly (P < 0.05) increased weight gain, feed efficiency, and protein retention. In addition, significantly increased apparent availability of P was observed in red drum fed the diets containing phytase compared to those fed the negative control diet. Red drum given the phytase-supplemented diets also had significantly enhanced utilization of various minerals, except for whole-body retention of Mn and bone deposition of Fe, compared to fish fed the negative control diet. According to the results based on the orthogonal polynomial contrasts, the optimal dietary phytase dosage was found to be 5520 FTU/kg of dry diet. Consequently, the supplementation of dietary phytase significantly improved growth performance of red drum and partly substituted for dietary MCP in diets containing 40% soybean meal and insufficient available P. In addition, dietary phytase supplementation significantly enhanced the utilization of dietary protein and various minerals by red drum.