THE EFFECT OF DIFFERENT PROCESSING TREATMENTS ON SOYBEAN-MEAL UTILIZATION BY RAINBOW-TROUT, ONCORHYNCHUS-MYKISS

A 12-week feeding trial was conducted with 38 g rainbow trout to evalu ate the effect of 20% dietary protein replacement of brown fish meal i n a control diet (diet C) by commercially full-fat soybean meal (diet S1 ), full-fat extruded soybean meal (diet S2), solvent-extracted soyb ean meal (diet S3), and solvent-extracted soybean meal, treated by inf rared radiation (diet S4). In a separate trial the apparent digestibil ity of the diets was measured in triplicate groups of rainbow trout, u sing an automatic faeces collector. Growth rate, feed conversion ratio and nitrogen retention (%Nl) of fish fed diets S1, S3 and S4 were bet ter than in fish fed S2 and the diet based on brown fish meal. The poo rest results were observed in trout fed the diet S2. Energy retention (%El) was not significantly different among the dietary treatments. At the end of the trial there were no significant differences in body co mposition, hepatosomatic and visceral indexes among experimental group s. Apparent protein digestibility coefficients of the experimental die ts were significantly (P<0.05) higher than that of the control diet. T here were no differences among experimental groups in apparent dry mat ter and energy digestibilities, except in trout fed diet S2 which had an apparent energy digestibility significantly lower than in trout fed the fish meal based diet. It is concluded that at the 20% dietary rep lacement level of brown fish meal by soybean meal improves the growth performance of rainbow trout. However, the commercially extruded full- fat soybean meal did not seem to improve the nutritional value of this plant protein source for rainbow trout.