Immunological, physiological and pathological responses of rainbow trout (Oncorhynchus mykiss) to increasing dietary concentrations of soybean proteins

High concentrations of dietary soya were shown to suppress salmonid growth rates and nonspecific immune capacity. The immunosuppression became evident at dietary inclusion rates of 60-70% and was coincident with a reduction i n weight gains and the appearance of demonstrable pathological changes in t he distal intestine. Further increases in soya concentrations to 80-89% cau sed a progressive decline in specific growth rates and exacerbation of the intestinal pathology. There was no evidence of circulating antibody respons es to dietary soybean proteins at any of the rates of inclusion. These obse rvations confirm the findings of other authors that, at concentrations of u p to 20-30% inclusion in diets, soybean proteins can provide a partial repl acement for fish meal, but at higher concentrations detrimental effects bec ome apparent, not only through reduced weight gains, but also through other physiological and immunological changes. (C) 1999 Elsevier Science B.V. Al l rights reserved.