Effect of wet-incubation of dietary plant feedstuffs with phytases on growth and mineral digestibility by common carp (Cyprinus carpio L)

Common carp (Cyprinus carpio) has no stomach, and with intestinal pH above 6, the fish cannot effectively digest phytate in plant based diets. Effect of wet-incubation of dietary plant feedstuffs (PF) with two different phytases Pt1 or Pt2 before pelleting on growth, mineral digestibility and mineral deposition in the fish was evaluated. Treatments (T1-T7) used for the study consisted of diets with un-incubated PF (UPF), incubated PF (IPF), UPF supplemented with 3.0 g phosphorus (P) kg− 1 (UPFP), UPF plus 4000 U Pt1 kg− 1 (UPFPt1), PF incubated with 4000 U Pt1 kg− 1 (IPFPt1), UPF plus 4000 U Pt2 kg− 1 (UPFPt2) and PF incubated with 4000 U Pt2 kg− 1 (IPFPt2). The diets were fed to common carp at 2.5% of their body weight daily for 12 weeks. Fish grew from 30.9 ± 0.9 g to 101.3, 133.6, 153.5, 101.0, 179.4, 105.0 and 156.8 g in T1-T7. Fish fed diet containing PF incubated with Pt1 had higher (P < 0.05) weight gain, SGR, feed intake and better FCR than the fish fed diet with only incubated PF (diet 2) or diet supplemented with Pt1 without incubation. Fish fed diet containing PF incubated with Pt2 showed similar trend over the fish fed diet 2 or diet supplemented with Pt2 without incubation. The weight gain, SGR, feed intake and FCR of the fish in T2 were superior (P < 0.05) to the values of fish from T1, T4 or T6. Fish in T3 had higher (P < 0.05) weight gain, SGR, feed intake and better FCR than those in T1, T4 or T6. Apparent digestibility coefficient (ADC) of P and Mg were the same in fish from T5 or T7. Fish in T4 or T6 also had the same ADC of P and Mg. P and Mg concentrations in the bones of fish in T5 or T7 were the same (P > 0.05), but higher (P < 0.05) than that in other fish. Fish in every treatment besides T2 had higher (P < 0.05) bone Zn concentration than fish in T3. P (g kg− 1 DM) discharged by fish in T6 (9.10) or T7 (9.33) was the same (P > 0.05) but less (P < 0.05) than that discharged by other fish. Results indicated that common carp digested the dietary minerals better when the PF were incubated with the phytases.