The binding of soybean agglutinin (SBA) to the intestinal epithelium of Atlantic salmon, Salmo salar and Rainbow trout, Oncorhynchus mykiss, fed high levels of soybean meal

A lectin present in soya, soybean agglutinin (SBA), was identified in electrophoretic profiles and immunoblots of dehulled solvent-extracted soybean meal (DSSM), full-fat soybean meal (FFSM) and of aqueous extracts of feeds incorporating them in their formulation. A quantitative estimation was made of the proportion of SBA comprising the total protein in FFSM and a trial diet was prepared containing an amount of pure SBA similar to that in diets incorporating high levels of the whole soya product. Fish fed with this diet exhibited similar pathological disruption of the intestinal tract to that observed in fish given a diet with a high level of DSSM (60% of the diet). Furthermore, immuno-histochemistry revealed the binding of the SBA to the enterocytes lining the intestinal villi both of fish fed a diet incorporating pure SBA and those fed a diet containing a high-level of soya (60%). Our results suggest that SBA binds in vivo to the intestinal epithelium of fish and has a contributory role in pathological changes associated with fish feeds containing high levels of soybean proteins.