Effect of Growth Temperature on Muscle Lipid Class and Fatty Acid Composition in Adult Steelhead Trout (Oncorhynchus mykiss) Fed Commercial Diets with Different andomega;6 to andomega;3 Fatty Acid Ratios

The effect of fluctuating temperature on muscle lipid composition was examined in 1.8 Kg steelhead trout fed 3 commercial diets with varying proportions (16.5 - 31% total) of Σω3 fatty acids and large differences (5×) in ω6:ω3 fatty acid ratios. Temperature was increased from 13.5°C to 18.0°C and then dropped back down to 13.5°C over a period of 12 weeks. Diet had no significant effect on growth or on total polyunsaturated fatty acid (PUFA) proportions in muscle tissue, but significant changes were observed in individual fatty acids. There was a greater response to changes in diet in the fatty acids than there was to changes in temperature. Muscle C20–C22 ω3PUFA and C18 unsaturated fatty acids reflected dietary inputs leading to very different (up to 40%) ω6:ω3 fatty acid ratios. Independent of diet, increasing temperature significantly increased total lipids and saturated fatty acids, especially 16:0, and decreased monounsaturated ones, especially 18:1ω9, as well as the PUFA 18:2ω6. The ω6:ω3 fatty acid ratio was also lowest at 18.0°C. Increasing total lipids, sterols and saturated fatty acids with increasing temperature, has important implications for both cultured and wild fish in terms of their nutrition, food quality for humans, and resource availability for aquafeeds.