Effect of dietary substitution of fish oil with flaxseed or sunflower oil on muscle fatty acid composition in juvenile steelhead trout (Oncorhynchus mykiss) reared at varying temperatures

The effect of changing temperature on muscle fatty acid composition was examined in juvenile steelhead trout (similar to 120 g) with complete substitution of fish oil (herring oil; HE) with either flax seed oil (FLX; also known as linseed oil) or sunflower oil (SF). The temperature was increased from similar to 10.0 degrees C to 18.0 degrees C following seasonal temperature changes in similar to 2 degrees C incremental steps with plateaus. Dietary lipid analysis showed the HE diet was rich in marine lipids, docosahexaenoic acid (DHA, 22:6 omega 3), eicosapentaenoic acid (EPA, 20:5 omega 3) and docosapentaenoic acid (DPA, 22:5 omega 3). In contrast FLX was rich in linolenic add (ALA, 18:3 omega 3) and SF in linoleic acid (LA, 18:2 omega 6). Both diet and temperature had no significant effect on growth but significant effects were observed on muscle fatty acid composition. Proportions of marine fatty acids in HE fed fish were significantly higher than in both SF and FIX fish at the end (41,31 and 31% respectively), with significantly lower levels of terrestrial plant fatty acids compared to the beginning of the experiment. Substitution of SF and FIX had a direct influence on muscle EPA:AA and omega 6:omega 3 ratios which could be detrimental to the health of the fish, as well as to the quality of the end product for human consumption. (C) 2014 Elsevier B.V. All rights reserved.