Differing nutritional responses to dietary soybean meal in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar)

This study was carried out to compare the responses of rainbow trout and At lantic salmon to being fed defatted soybean meal. Two extruded experimental diets containing either low-temperature (LT)-fish meal as the sole protein ingredient or 32% fish meal and 30% soybean meal, were each fed to triplic ate groups of 0.1 kg trout or 0.2 kg salmon maintained in 7 degrees C fresh water. The experiment lasted 84 days, divided into three periods. Weight ga in of the trout was similar with both diets, whereas the salmon gained 44% more weight with the fish meal diet than with the soybean meal diet. The ap parent digestibilities were 6% higher for nitrogen, 8% higher for fat, and 11% higher for energy in the trout than in the salmon. The feed conversion ratio (FCR) was 24% lower, the nitrogen retention 34% higher, and the energ y-retention 28% higher in the salmon than in the trout. Within each species , the digestibility of nitrogen was similar for both diets. In trout, the d igestibilities of fat and energy were 4% higher, the nitrogen retention 8% higher, and the energy retention 9% higher with the fish meal than with the soybean meal diet. Similarly, but more severe within the salmon, the respe ctive digestibilities of fat and energy were 16% and 9% higher, the nitroge n retention 19% higher, and the energy retention 23% higher with the fish m eal than with the soybean meal diet. Both species developed enteritis in th e distal intestine when fed the soybean meal diet. (C) 2000 Elsevier Scienc e B.V. All rights reserved.