Inclusion of Fermented Soybean Meal in Rainbow Trout Diets

The inclusion of fermented soybean Glycine max meal (FSBM) was evaluated in five experiments with Rainbow Trout Oncorhynchus mykiss. In the first experiment where FSBM directly replaced fish meal, growth was significantly decreased in fish fed diets containing 40% or more FSBM. In the second experiment, decreased weight gain and increased feed conversion ratios occurred with diets containing 40% or 50% FSBM which were supplemented with either methionine, or methionine and additional amino acids. However, all feed conversion ratios were still below 1.00. The supplementation of amino acids in addition to methionine had no noticeable effect. In the third experiment, after 205 days, diets containing 35% FSBM produced similar results as the fish mealbased control, but were significantly different from diets containing 50% FSBM. Significant differences were observed in distal intestine morphology among the diets at day 94, but none were observed at the end of the trial on day 205. Immunological metrics were not significantly different among the dietary treatments. In the fourth experiment, no significant differences were observed between two strains of Rainbow Trout, Shasta and McConaughy, fed diets containing FSBM. However, feeding 50% FSMB diets to both strains led to reduced growth compared to diets containing either 0 or 35% FSBM. Changes in distal intestine morphology were only observed in the Shasta strain fed 50% prior to, and during, a random mortality event. There were no significant differences in qualitative health assessments, distal intestine morphology, or immunological metrics in fish fed either diet. Based on these results, FSBM can constitute at least 35% of Rainbow Trout diets, or safely replace at least 62% of the fish meal component, without any decrease in rearing performance or without any increase in disease susceptibility and mortality compared to a reference blend containing fish meal