FATTY-ACID COMPOSITIONS OF 10 FRESH-WATER INVERTEBRATES WHICH ARE NATURAL FOOD ORGANISMS OF ATLANTIC SALMON PARR (SALMO-SALAR) - A COMPARISON WITH COMMERCIAL DIETS

Ten species of freshwater invertebrates that are natural food organisms available to Atlantic salmon pan were collected and their lipid composition determined: stonefly nymphs (Plecoptera), beetle larvae (Coleoptera), Chironomidae (Diptera), water boatmen (Corixidae and Notonecta; Heteroptera), mayfly nymphs (Ecdyonurus venosus, Caenis, Ephemerella; Ephemeroptera), gammerids (crustaceans), Oligochaeta (anelids). Neutral lipids represented 40-70% and polar lipids 26-55% of total lipids. Triacylglycerol was always more than 35% of total lipids. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were the major components of phospholipids. Monoenoic fatty acids and polyunsaturated acids (PUFA) were the most abundant fatty acids in total lipids. Saturated fatty acids comprised only 20-30% of the total fatty acids. PUFAs were principally present as the n-3 series, especially 18:3n-3 and 20:5n-3. 22:6n-3 was present only in small amounts. Fatty acids of the n-6 series were mostly represented by 18:2n-6 and 20:4n-6. The invertebrate organisms analysed contained higher levels of 18:2n-6, 18:3n-3, 20:4n-6 and 20:5n-3 but considerably less 22:6n-3 than commercial diets used in smelt production. These results suggest that a dietary fatty acid composition more closely resembling the freshwater invertebrates might be beneficial for growth, development and the prevention of pathologies in salmon parr.