Preparation and nutrient analysis of lactic acid bacterial ensiled salmon viscera

The objective of this study was to define a procedure for converting salmon viscera into a co-dried product that could eventually be the major protein ingredient in dry salmonid feeds. A lactic acid bacteria fermented silage, and for comparative purposes, a sulfuric acid silage were prepared from salmon viscera (Oncorhynchus nerka and Oncorhynchus gorbuscha). Both ensiled products were separately co-dried with poultry by-product meal in a final ratio of 1:1 (w/w) on a dry weight basis. Nitrogen levels of the co-dried products were 9 to 11%, sufficiently high to be the main protein source in dry feeds for salmonids. Methionine was the limiting amino acid in the co-dried products. Protein fractionation by size exclusion chromatography of samples obtained on the first and fourteenth day of ensilage showed that proteins were hydrolyzed to low molecular weight of proteins, peptides, and amino acids. The co-dried products had low numbers of aerobic bacteria and low water activity, which would enhance storage stability. Formation of high levels of thiobarbituric acid reactive substances in freeze-dried silage was inhibited by the addition of 0.025% (w/w) ethoxyquin to the silage prior to drying.