| Abstract: | Swimming performance was measured in Atlantic salmon (Salmo salar, L.) fed one of four isonitrogenous and isoenergetic experimental diets, in which the supplemental lipid (25% of diet) originated either solely from menhaden oil (rich in highly unsaturated fatty acids of the n-3 series; n-3 HUFA), or from different proportions of this oil and canola oil (rich in 18-carbon unsaturated fatty acids).The results indicate that dietary fatty acid composition influenced swimming performance in Atlantic salmon through changes in maximum swimming speed (Ucrit). Salmon fed a diet in which menhaden oil furnished all of the supplemental lipid had a significantly lower Ucrit than those fed a diet in which the supplemental lipid was an equal blend of menhaden and canola oil. Furthermore, there was a highly significant linear relationship between dietary and/or muscle levels of particular fatty acids or groups of fatty acids and Ucrit.There was a negative relationship between dietary n-3 HUFA content and Ucrit, but there was no relationship between Ucrit and muscle n-3 HUFA content nor between Ucrit and the levels of the eicosanoids thromboxane A2 and prostacyclin, or of their ratio, in the heart and gills of fatigued salmon. These results indicate that the differences in exercise performance were not a result of differences in n-3 HUFA metabolism amongst the dietary groups.Indeed, although there was a highly significant positive relationship between Ucrit and total n-6/n-3 fatty acid ratio of muscle lipids, this was largely due to the associated positive relationship between Ucrit and content of the most common n-6 fatty acid in muscle lipids, linoleic acid. There was also a significant positive relationship between content in muscle lipids of the most prominent fatty acid in canola oil, oleic acid, and Ucrit. It is suggested that metabolism of these 18-carbon unsaturated fatty acids accounts for the effects of the diets on exercise performance. |
