Variation in content of Ω3 fatty acids in farmed Atlantic salmon, with special emphasis on effects of non-dietary factors

Abstract

The main aim of the present study was to examine the impact of some biological and environmental factors on the lipid and fatty acid compositions of farmed Atlantic salmon (Salmo salar), with special emphasis on Ω3 fatty acids. Two year groups of salmon at nine fish farms distributed along the Norwegian coast were fed the same diet and were sampled every second month. The data are believed to give a representative characterization of lipid and fatty acid content of salmon farmed in Norway.

Multiple regression analysis revealed that variation in lipid content and body weight explained 80% of the variation found in Ω3 fatty acids in farmed salmon, and 22:6 Ω3 showed greater variation than other Ω3 fatty acids. Further analysis of lipid-corrected values revealed only minor effects of latitude on the per cent content of highly unsaturated Ω3 fatty acids, and hardly any effect of seawater temperature, with the exception of 22:6 Ω3, which decreased slightly with increasing temperature.

The per cent 22:6 Ω3 in the fillet became gradually reduced with increasing fish age and body weight, whereas the content of 20:5 Ω3 and other Ω3 fatty acids remained relatively constant. The per cent content of 22:6 Ω3 of young salmon was higher than in the feed, but approached the feed value gradually as body weight increased. The lipid content of the salmon increased with fish age, and the absolute quantitative contents of both 22:6 Ω3 and 20:5 Ω3 increased meanwhile, even though the per cent content of 22:6 Ω3 decreased quite pronouncedly.

The per cent 22:6 Ω3 and other Ω3 fatty acids was higher in wild than in farmed salmon, but the absolute quantitative content was higher throughout in farmed salmon, which had higher lipid contents. The Ω3/Ω6 ratio, which is important in human health evaluation, was lower in farmed than in wild salmon. The large flexibility of Ω3 fatty acids and lipid content of farmed salmon leave us with the option of producing a wide variety of salmon qualities requested by the market. Both per cent and absolute quantitative Ω3 contents, as well as the Ω3/Ω6 ratio, may readily be manipulated.