Evaluating the inclusion of phytase sources to phosphorus-free diets for GIFT tilapia (Oreochromis niloticus): Growth performance, intestinal morphometry, immune-antioxidant responses, and phosphorus utilization

Abstract

The current study aimed at evaluating the growth performance, phosphorus (P) retention, and welfare status of GIFT strain of Nile tilapia (Oreochromis niloticus) fed on P-free diets containing fungal phytase (FPhyt) and/or a novel hybrid bacterial phytase (HB-Phyt). The control reference diet (T1) was supplemented with dicalcium phosphate (DCP; 8.7 g total P/kg). Other five low-P (with no DCP; 5.9 g total P/kg feed) diets were supplemented with 500, 1000 FTU/g of FPhyt (T2-T3) or 500, 1000 FTU/g of HB-Phyt (T4 – T5), while T6 contained 1000 and 1000 FTU/g of both phytase sources. Each diet was allocated randomly to three 100-L tanks stocked with GIFT tilapia (n = 15 fish per tank, initial mean weight, 2.38 ± 0.22 g). Fish were fed on experimental diets up to satiation thrice a day for 60 days. Fish in T1, T3, T5, and T6 recorded highest growth performance; meanwhile, highest values of villi length/width and absorption area were observed in T3, T5, and T6 fish groups as compared with other groups. Highest values of hematological indices (red blood cell, hemoglobin, packed cell volume, white blood cell, and lymphocytes %) and immune-antioxidant biomarkers (superoxide dismutase, catalase, lysozyme, and respiratory burst activity) were highest in the case of fish in T3, T5, and T6 with no significant difference among them. Meanwhile, feeding fish on diets with 500 FPhytase (T2) or 500HB-Phyt (T4) showed lowest values of immune-antioxidant indices accompanied with highest value of malondialdehyde as compared with other treatments. Compared with other treatments, highest values of bone-P were observed in T3, T5, and T6, while highest whole-body P values were detected in T5 and T6 only, with no significant difference among them. The present study revealed much lower feed input per unit production accompanied with higher return on investment in GIFT fed on diets supplemented with 500 FTU/g of HB-Phyt than 1000 FTU/g of either FPhyt or HB-Phyt. Hence, the present study showed that the dietary inorganic P could be compensated by adding 1000 FTU/g of either FPhyt or HB-Phyt to fish diets. The growth and immune-antioxidant indices in fish fed with HB-Phyt were superior to FPhyt treatments. No synergetic effects of using both of FPhyt and HB-Phyt were detected in this study.