Effects of dietary n-3 polyunsaturated fatty acids on lipid and fatty acid composition and haematology of juvenile Arctic charr Salvelinus alpinus (L.).

The effect of dietary n-3 and n-6 polyunsaturated fatty acids (PUFAs) on juvenile Arctic charr Salvelinus alpinus (L.) were investigated with respect to essential fatty acid (EFA) deficiency and lipid metabolism using one commercial and 12 casein-based test diets. Arctic charr with mean weight of 1.6g were fed test diets for 12 weeks at 10°C. At the end of the feeding, blood, liver, muscle and whole fish were sampled to determine haematocrit, haemoglobin, water content, lipid and fatty acid composition. Charr fed diets containing 0-1.0% n-3 PUFAs showed typical EFA deficiency signs: fatty liver or elevated water content in whole body or substantial accumulation of 20:3n-9 in liver polar lipids. These signs were less apparent or disappeared when charr were fed diets containing ≥ 2.0% 18:3n-3. No correlation was found between dietary PUFAs and haematocrit or haemoglobin values. Significant changes in fatty acid composition of liver polar lipids in charr fed dietary PUFAs indicate that charr can convert 18:3n-3, 18:2n-6 and 20:5n-3 into long-chain PUFAs. While charr had a direct incorporation of dietary 22:6n-3 into liver and muscle there appears to be preferential utilization of n-3 PUFAs for elongation and desaturation. The conversion of 18:4n-3 was less in muscle than in livers. These findings, combined with data on growth and feed efficiency reported previously by Yang and Dick (1993), indicate that charr require 1-2% dietary 18:3n-3 (dry weight). Small amounts of dietary 18:2n-6 (up to 0.7%) did not have detrimental effects on charr.