Phytase top-coated onto extruded all-vegetable diets reduces the need for dicalcium phosphate and decreases phosphorus loss in fast-growing juvenile Nile tilapia

This study evaluated the effects of reducing dietary dicalcium phosphate (DP) levels by supplementing liquid-form phytase (PHY) at 1000 PHY units (FTU)/kg diet on growth performance, vertebral mineralization, plasma parameters, and phosphorus (P) loss of juvenile Nile tilapia, Oreochromis niloticus. Fish (n = 240; 12.1 ± 0.4 g) were distributed into 20–70 L each aquarium in a completely randomized design with 5 treatments and 4 replicates of 12 fish each. Dietary treatments comprised a nutritionally adequate positive control diet containing 300.5 g/kg crude protein, 18.9 MJ/kg digestible energy and 8.6 g/kg available P (PC); a P-deficient negative control diet without DP or PHY (NC); and three additional diets based on the NC diet: one without DP (NC1) plus PHY, one with 10 g/kg DP (NC2) plus PHY, and one with 20 g/kg DP (NC3) plus PHY. Fish were hand-fed 6 times daily until apparent satiety for 8 weeks. Fish fed PC and NC2 diets displayed similar body weight gain (BWG), feed conversion ratio (FCR), whole-body ash, calcium (Ca) and P, vertebrae Ca, P and manganese (Mn), and plasmatic P levels, which were higher than those fed NC diet. Feed efficiency ratio (FER), vertebrae zinc (Zn), plasmatic Ca, and cholesterol responses were not affected by dietary treatments. Compared to PC diet, fish fed NC2 diet showed markedly reduced lower P loss by −0.4 g/kg of BWG. This study identified PHY enabling a 20 g/kg reduction in dietary DP without negatively impacting the growth performance and health of juvenile Nile tilapia.