Fish silage as a dietary ingredient for salmon. I. Nutritional and storage characteristics

Fish silage was produced from freshly caught sprats by the addition of 3% acid. The effects of temperature and the presence or absence of a lipid antioxidant (ethoxyquin) on various parameters were examined. The essential amino acids appeared to be stable under the various conditions, except tryptophan which proved to be labile, with the maximum loss (60%) occurring after 24 weeks at the highest temperature regime. The lipid fractions of the silages without ethoxyquin, rapidly developed hydroperoxides and secondary breakdown products as measured by the anisidine value. The peroxide value was highest (190 mequiv./kg) in the silage stored at 10°C, while the anisidine value was highest (86.9) in the silage stored at 20°C. No detectable loss in the level of polyunsaturated fatty acids was noted after 8 weeks despite high peroxide and anisidine values, but by 24 weeks there was evidence of considerable fatty acid oxidation. Ethoxyquin proved to be a very effective antioxidant with both the peroxide values and the anisidine values remaining low even after 24 weeks storage. The results are discussed in relation to incorporating the silages into moist salmon diets.