Liquid phytase as a complete substitute for supplemental inorganic phosphorus in plant-based diets for commercially farmed Nile tilapia (Oreochromis niloticus)

Abstract This research project addressed the effect of commercial, liquid phytase (Ronozyme ® HiPhos- 20,000 FYT g − 1 ) (dsm-firmenich, Switzerland), produced by Aspergillus niger , on growth performance, economic return, enzymatic activities, and immune defense in Nile tilapia ( Oreochromis niloticus ) raised in a commercial tilapia farm. Adult, all-male fish, weighing 75.28 ± 0.66 g on average, were housed in triplicate in 2-m 3 hapas, placed in an earthen fishpond, at a density of 40 fish hapa − 1 . The fish were offered a basal commercial, extruded (floating) tilapia diet (3 mm diameter, 30% CP and 18.6 MJ kg − 1 ), supplemented with 10 g monocalcium phosphate (MCP) kg − 1 (control), 2000 FYT phytase kg − 1 or 50% of both MCP and phytase (5 g MCP + 1000 FYT kg − 1 ) for 80 days. performance, muscle composition, and the activities of digestive and liver enzymes were not affected ( P > 0.05) in all treatments. Phosphorus (P) content in fish flesh and bones significantly increased in individuals fed phytase-based diets compared to the MCP-based feed. Phytase-based diets at 2000 FYT kg − 1 (with no MCP supplementation) and 1000 FYT kg − 1 plus 5 g MCP kg − 1 were more profitable than the reference diet. Exogenous phytase significantly increased ( p < 0.05) blood erythrocytes (RBCs), hemoglobin (Hb), and leukocytes (WBCs), while mean corpuscular hemoglobin (MCH), packed cell volume (PCV), and mean corpuscular volume (MCV) remained unchanged. Immune and antioxidant parameters were also enhanced in fish fed the phytase-based feed, as evidenced by significant increases in alternative complement activity (ACH50), lysozyme activity, superoxide dismutase, and catalase, alongside reduced malondialdehyde concentrations ( P < 0.05). Overall, these findings suggest that supplemental phosphorus (P) can be completely excluded from commercial tilapia feeds when the phytase enzyme (Ronozyme ® HiPhos) is added at approximately 2000 FYT kg − 1 . Phytase could also enhance the immune response and reduce the environmental impacts that would otherwise result from P release into the environment.