Comparative performance of two rainbow trout strains fed fermented soybean meal

The comparative response of the Shasta and McConaughy strains of rainbow trout (Oncorhynchus mykiss) to diets containing fermented soybean meal was evaluated during a 94-d feeding trial. Three isonitrogenous and isocaloric diets contained 0, 35, or 50 % fermented soybean meal and 40, 15, or 0 % fish meal, respectively. In each of the diets, rearing performance was significantly better in the Shasta strain, with an approximate 30 % improvement in percent gain and 20 % improvement in feed conversion ratio compared with the McConaughy strain. The relative response of both strains to the different diets was similar. The 50 % fermented soybean meal diet produced a weight gain of 172 % in the McConaughy strain, which was significantly less than the 219 and 250 % gain exhibited by the control and 35 % fermented soybean meal diets. Similarly, weight gain in the Shasta strain was 220 % in the 50 % fermented soybean meal diet compared to 330 and 375 % in the control and 35 % fermented soybean meal diets, respectively. Feed conversion ratio was also significantly higher in both strains in the 50 % fermented soybean meal diet. Distal intestine morphology was only significantly different in the Shasta strain rainbow trout fed the 50 % fermented soybean meal diet. The hepatosomatic index was significantly greater in the McConaughy strain, but was not influenced by diet, while the viscerosomatic index was not significantly affected by either strain or diet. Based on these results, diets containing up to 35 % fermented soybean meal are acceptable for either strain.