Plant based feed ingredients pose a risk for developing intestinal inflammatory lesions in fish. The salmon is particularly sensitive to solvent extracted soybean meal. Recent studies have shown that dietary inclusion of a bacterial meal (BM) grown on natural gas containing mainly Methylococcus capsulatus can prevent SBM-induced inflammation. This Norwegian study was conducted to identify BM fractions and/or products responsible for this beneficial effect.

A fish meal based control diet was compared to a diet with 200 g/kg soybean meal, and six diets with 200 g/kg soybean meal in combination with several BM products/fractions. The diets were fed for four weeks to triplicate tanks of juvenile Atlantic salmon (Salmo salar) reared in salt water. No significant (P < 0.05) differences were found for feed intake and growth among fish fed the experimental diets. Measurements of intestinal tissues revealed that most BM products provided significant protection against SBM-induced enteritis. The effective component in the BM products was present in the retentate that mainly consisted of large molecules and water insoluble components. Nucleic acids and small water soluble molecules did not seem to provide any protective effect. (Note: The results of this study may expand soybean meal’s use in some fish species. Additional research can be easily justified).