Swimming performance at different temperatures and fatty acid composition of Arctic charr (Salvelinus alpinus) fed palm and rapeseed oils

Alternative ingredients in fish feeds such as vegetable oils need to be evaluated from several aspects in order to justify their use. This study investigated the effects of feeding a coldwater species, Arctic charr (Salvelinus alpinus L.), diets where 75% of the fish oil (FO) was replaced with either rapeseed oil (RO) or equal ratios of rapeseed oil and palm oil (ROPO) on swimming performance at three different temperatures (4, 10, 17 °C). Fish fed ROPO had a significantly lower critical swimming speed (Ucrit) at 4 °C compared to fish fed FO and RO diets. Similar patterns of impeded performance of the vegetable oil fed fish compared to the FO fed fish, albeit non-significant, was observed at 10 °C and 17 °C. The dietary compositions had no effect on growth but the total lipid content in white muscle was significantly higher in ROPO fed fish (2.7%) compared to fish fed FO and RO (2.0% and 2.1%, respectively). Considerable changes in the fatty acid composition were found with a decrease in the highly unsaturated fatty acids (HUFA) 20:5n-3, 22:6n-3 and an increase in 18:2n-6 and 18:1n-9 in the vegetable oil fed fish. The ratio of n-3 HUFA and saturated fatty acids is suggested to be partly responsible for the alternations in swimming performance at different temperatures because they both are involved in temperature-influenced metabolic mechanisms in fish.