Effect of dietary phytase on phosphorus use efficiency and dynamics in aquaponics

Phytase is a phosphatase enzyme used as dietary supplement when significant portions of plant-based ingredients are used in fish feed formulations. This work thus assessed the effects of a phytase-supplemented diet on the P dynamics, P availability, P budget, fish and plant growth parameters, and carcass composition of Nile tilapia and phosphorus content of lettuce plants in aquaponic systems. The diet supplemented with phytase at the concentration of 1000 FTU kg⁻¹ showed a significant increase in released phosphorus compared to the control in an in vitro assay. Phytase supplementation increased accumulation of phosphorus in fish carcass compared to the control, but did not affect growth performance. The addition of phytase to fish diets improved phosphorus utilization by fish, reducing phosphorus excretion. The lower amount of phosphorus excreted in the water caused by phytase did not impair the growth or phosphorus content of lettuce grown using the aquaponic nutrient solution. It is recommended that, even though the use of phytase in fish feeds increased the overall utilization of phosphorus in the present study, a small portion of inorganic phosphorus must be supplemented to meet minimum fish requirements.