Effect of soybean protein on serological response, non-specific defense mechanisms, growth, and protein utilization in rainbow trout.

Rainbow trout (Oncorhynchus mykiss) were fed chemically and immunologically defined diets containing either a low-temperature fish meal or soybean preparations containing high (SBM) or low levels of the globular antigenic proteins glycinin (G) and beta-conglycinin (BC) for 26 weeks. While trout fed both soybean preparations exhibited poorer growth than those fed fish meal, those fed the soya diet with high levels of G and BC showed the most significant growth diminution, elevated feed conversion and impaired utilization of dietary protein. Changes in intestinal morphology were also observed in fish fed the SBM diet, coinciding with the inferior nutritional performance. Several serologic and non-specific immune defense mechanisms were monitored. Cell counts showed increased leukocyte cell numbers as well as increased concentrations of plasma protein and immunoglobulin in the soya-fed fish. Increased neutrophil, monocyte and macrophage activity, as assessed by several oxidative radical production and phagocytic index assays, were higher in the soya-fed fish, possibly indicating an inflammatory or hypersensitivity response. The results of this study suggest that antigenic soya protein affects non-specific defense mechanisms, growth performance, and protein utilization in rainbow trout. Furthermore, it would appear that dietary sensitivity can be overcome by process removal of this immunologically characterized antigen in soybean protein. Serological and immunological assessments appear to be very useful criteria for evaluating various protein sources for fishes.