Requirement of Yamame Oncorhynchus masou for Essential Fatty Acids

Abstract

Two experiments were conducted to determine the effect of the oleate basal diet supplemented with linoleate (18: 2n-6), linolenate (18: 3n-3), arachidonate (20: 4n-6) and a n-3 highly unsaturated fatty acid (n-3 HUFA) mixture in the total amount of 5% respectively, on growth and fatty acid composition of liver lipids. The lowest growth and feed efficiency together with high mortality were observed in the fish receiving the diet containing 5% oleate as a sole lipid source, and were effectively improved by the supplementation with n-3 fatty acids, but not with n-6 fatty acids. The highest growth and feed efficiency were obtained in fish fed the diet containing 1% 18: 3n-3. However, an EFA value of n-3 HUFA seemed to be slightly inferior to that of 18: 3n-3 in growth rate. No additive effect of 18: 2n-6 to 18: 3n-3 was observed. The hepatosomatic index, the liver lipid content and the ratio of 20: 3n-9 to 22: 6n-3 in the polar lipid fractions of liver were found to be the highest with fish fed the 5% oleate diet. These values were reduced by supple-mentation with n-6 or n-3 fatty acids. The ratio of 20: 3n-9 to 22: 6n-3 became less than 0.4 by supplementation with 1-2% 18: 3n-3 or 1% n-3 HUFA. The results obtained in this experiment indicate that n-3 fatty acids, especially 18: 3n-3 are essential for Yamame and the requirement of 18: 3n-3 is approximately 1% in diet.