DIETARY FATTY-ACID COMPOSITION INFLUENCES SWIMMING PERFORMANCE IN ATLANTIC SALMON (SALMO-SALAR) IN SEAWATER

Swimming performance was measured in Atlantic salmon (Salmo salar, L.) fed one of four isonitrogenous and isoenergetic experimental diets, i n which the supplemental lipid (25% of diet) originated either solely from menhaden oil (rich in highly unsaturated fatty acids of the n-3 s eries; 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 i n Atlantic salmon through changes in maximum swimming speed (U-crit). Salmon fed a diet in which menhaden oil furnished all of the supplemen tal lipid had a significantly lower U-crit than those fed a diet in wh ich the supplemental lipid was an equal blend of menhaden and canola o il. Furthermore, there was a highly significant linear relationship be tween dietary and/or muscle levels of particular fatty acids or groups of fatty acids and U-crit. There was a negative relationship between dietary n-3 HUFA content and U-crit, but there was no relationship bet ween U-crit and muscle n-3 HUFA content nor between U-crit and the lev els of the eicosanoids thromboxane A(2) and prostacyclin, or of their ratio, in the heart and gills of fatigued salmon. These results indica te that the differences in exercise performance were not a result of d ifferences in n-3 HUFA metabolism amongst the dietary groups. Indeed, although there was a highly significant positive relationship between U-crit and total n-6/n-3 fatty acid ratio of muscle lipids, this was l argely due to the associated positive relationship between U-crit and content of the most common n-6 fatty acid in muscle lipids, linoleic a cid. There was also a significant positive relationship between conten t in muscle lipids of the most prominent fatty acid in canola oil, ole ic acid, and U-crit. It is suggested that metabolism of these 18-carbo n unsaturated fatty acids accounts for the effects of the diets on exe rcise performance.