EFFECTS OF PHYTASE ON GROWTH, DIGESTION AND NUTRIENT UTILIZATION OF JUVENILE CHINESE MITTEN CRABS (ERIOCHEIR SINENSIS)

To investigate the effects of phytase on the growth, digestibility and nutrient utilization of juvenile Chinese mitten crab Eriocheir sinensis, six diets were designed that included the control group with no phytic acid (C) and phytase and five experimental groups with 10 g/kg of phytic acid and 0, 500, 1000, 1500 or 2000 U/kg phytase that were named as P0, P500, P1000, P1500 and P2000, respectively. Juvenile crabs with an initial body weight of (4.33±0.05) g were fed with these diets for 56 days. The results showed that the weight gain rate, specific growth rate and protein efficiency of the juvenile crabs in P0 group were lower than those of the C group, and the feed coefficient was higher than that of the C group (P<0.05). The weight gain rate, specific growth rate and protein efficiency of juvenile crab increased with the increased phytase with the highest one in P2000 that had the lowest feed coefficient (P<0.05). Phosphorus content of whole crabs of P1500 and P2000 was significantly higher than that of P0 (P<0.05). P2000 had the highest trypsin activity, amylase activity in the hepatopancreas and trypsin activity in the intestine of juvenile crabs (P<0.05). The protein digestibility and phosphorus dialysis rate of Eriocheir sinensis increased gradually with the increased phytase. P2000 had the highest nitrogen and phosphorus retention rates (P<0.05). These results indicated that 2000 U/kg phytase in the diet can significantly increase the growth, protein utilization rate and trypsin activity, and reduce the feed coefficient of juvenile crabs fed the diets containing phytic acid, and promote nitrogen/phosphorus deposition rate of juvenile crabs.