Effect of Extrusion Processing on the Utilization of Soybean Meal Diets for Rainbow Trout

Abstract

The effect of extrusion processing by a twin screw extruder on the nutrient utilization, and the availability of defatted soybean meal (SBM) as partial protein source were studied with rainbow trout of about 4–5 g. In Expt. I, fish were fed the control and 30% SBM diets with and without extrusion processing for 6 weeks. In Expt. II, fish were fed ordinary steamed dry pellets (DP) containing 30% SBM or 30% extruded SBM (ExSBM) as a partial substitute for fish meal, and extruded soft-dry pellets (SDP) with 30% SBM for 8 weeks. Expt. I: There was no marked difference in growth or feed efficiency between the control and 30% SBM diets. Their dietary values and growth rate were not significantly improved by the extrusion, although the digestibility of starch was markedly elevated. The digestibility of dietary protein was not influenced by extrusion processing, ranging between 88 to 91%. Expt. II: Of the 30% SBM diets, SDP with a higher energy content produced higher growth, PER, protein, and energy retention than DP. Feed consumption was slightly lower in SDP with the higher energy level, leading to improved feed efficiency. Replacement of 30% SBM with the same level of ExSBM did not result in any nutritional improvement of DP. © 1993, The Japanese Society of Fisheries Science. All rights reserved.