Digestion of the 1-O-alkyl diacylglycerol ethers of Atlantic dogfish liver oils by Atlantic salmon Salmo salar

Abstract

Dogfish (Squalus acanthias) liver poses a waste disposal problem in Canada because it is not utilized for any commercial purpose. The liver of Atlantic dogfish, which is often up to 20% of the weight of the fish, contains 40-70% oil. The oil contains about 30-40% 1-O-alkyl diacylglycerol ethers (DAGE) which render it unacceptable for human use, and it has also not been considered satisfactory for animal feed use. Polyunsaturated fatty acids (20:5n-3 and 22:6n-3) are present in dogfish liver oils at levels comparable to those in herring oil. Dogfish liver oil could be a source of essential fatty acids for Atlantic salmon (Salmo salar), but their ability to hydrolyze DAGE from dogfish oil has not been examined. Experiments were designed to measure the digestibility of fatty acids of DAGE in salmon. The fatty acid moieties were liberated by the digestive enzymes of the fish and made readily available as a source of energy. The 1-O-alkylglycerol ether moiety was absorbed to a small extent but should not constitute a health problem in either the fish or the human fish consumer. The long-chain polyunsaturated fatty acids were particularly well absorbed, with an apparent digestibility in salmon of 87-95% when feeding on dogfish liver oil. The total fatty acids and other lipids were in fact both absorbed to the extent of approximately 85%.