Effect of supplemental phytase on growth, phosphorus digestibility and bone mineralization of common carp (Cyprinus carpio L)

The effect of dietary phytase on phosphorus (P) digestibility, growth, bone mineralization and plasma P of common carp (Cyprinus carpio) was investigated. Five diets, D0, DP, PHYT1, PHYT2 and PHYT4, were used. D0 contained no supplement. DP was supplemented with 2.6 g P (Na₂HPO₄× 2H₂O) kg⁻¹. PHYT1, PHYT2 and PHYT4 comprised 1000, 2000 and 4000 U phytase [Ronozyme P (CT)] kg⁻¹. D0, PHYT1, PHYT2, PHYT4 had average of 7.95 g P kg⁻¹; DP contained 10.3 g P kg⁻¹. After 126 days of feeding, fish grew from 115 to 347 g (D0), 583.7 g (DP), 352.6 g (PHYT1), 393.3 g (PHYT2) and 406.4 g (PHYT4). Addition of phytase significantly increased daily feed intake, but only led to a marginal improvement in the weight gain, SGR and FCR of fish fed PHYT2 and PHYT4 compared with fish fed D0. Fish fed DP showed the best (P<0.05) growth performances. Fish fed DP and PHYT4 significantly digested dietary P more than the fish fed D0. Fish fed D0, PHYT1, PHYT2 and PHYT4 retained higher (P<0.05) Zn in their bones than fish fed DP. However, there was no further effect on bone mineralization. Plasma P scarcely improved by between 14% and 26% in fish fed PHYT2 and PHYT4 relative to fish fed D0. P concentration of the faeces was reduced by about 9–22% in fish fed PHYT1 and PHYT4 compared with fish fed D0.