Reduced growth and feed consumption of Atlantic salmon (Salmo salar L.) fed fish meal made from stale fish is not due to increased content of biogenic amines

Atlantic salmon (Salmo salar L.) smolts were fed for 11 weeks a diet based on fish meal made from fresh herring (Diet 1) or a diet based on fish meal made from herring stored until stale (Diet 2) in addition to three diets made by adding to Diet 1 combinations of biogenic amines to a level comparable to that found in Diet 2: cadaverine, histamine, putrescine plus tyrosine (Diet 5) and cadaverine plus histamine (Diet 6). Salmon fed diets based on fish meal made from stale herring had reduced growth and feed consumption and impaired efficiency of feed utilisation compared with those fed fish meal made from fresh herring. Furthermore, salmon fed fish meal made from stale herring showed gross and histological changes in the liver and intestines that were either not found or found to a lesser extent in fish fed fish meal from fresh herring. Addition of biogenic amines to the diet based on fish meal made from fresh herring neither affected production performance nor led to pathological changes in the gastrointestinal tract. Reduced production performance resulting from fish meal produced from stale herring most probably has a multiple background. Reduced palatability due to compounds formed in stale fish or during processing of stale fish reduces feed intake and thereby growth and feed utilisation. Bacterial action in the fish raw material during unfavourable storage conditions reduces the content of essential amino acids and leads to diminished protein supply with reduced growth and impaired efficiency of feed utilisation as a consequence. Finally and probably most significant, toxic compounds formed in stale fish or in processing of stale fish cause pathological changes in vital organs that results in reduced growth. These compounds are not the biogenic amines histamine, cadaverine, putrescine and tyramine. However, the content of biogenic amines may be indicator for freshness of the fish raw material and thereby serve as a quality criterion for fish meal.