Effects of an Enzyme Complex-Treated Rice Protein Concentrate on Growth Performance and Feed Utilization of Rainbow Trout Oncorhynchus mykiss Juveniles

This study investigated the effect of the inclusion of an enzyme complex-treated rice protein concentrate (RPC) in an extruded diet of juvenile rainbow trout (Oncorhynchus mykiss). A mixture of RPC, corn gluten and soybean meal was pretreated with an enzyme complex before extrusion processing of the diets. An enzyme complex-pretreated RPC (5, 10 and 15%) was formulated with 20% fish meal. A diet without RPC was used as a control. A total of 240 rainbow trouts with an average body weight of 6.04 g were placed in 12 rectangular glass aquaria and fed one of the experimental diets at apparent satiation for 12 weeks. There were no significant differences in growth, feed intake and survival among the groups. Slightly inferior weight gain and specific growth rate were observed in the RPC15E group compared to those in the other groups. The protein and ash contents of the whole body of the final fish were not significantly different among all groups, but the lipid content was significantly lower than that of the control when the dietary RPC level was >10%. Protein digestibility was negatively affected by increased RPC levels in diet. Significantly lower phosphorus digestibility was observed in fish fed the diet containing 5% enzyme-treated RPC than the control. Although there was no significant difference in lipid digestibility in all groups, significantly lower lipid retention was observed in fish fed a diet formulated with more than 10% RPC. These results suggest that the inclusion of RPC in the diet affects lipid retention and the content of rainbow trout. It also decreased protein digestibility. In conclusion, rainbow trout can be fed an extruded diet formulated with 20% fishmeal and 10% enzyme-treated RPC without negative effects on fish growth.