Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

To improve the understanding of energy changes in fasting steelhead trout Oncorhynchus mykiss Walbaum, the profiles of specific fatty acids in white muscle and liver tissues of Snake/Columbia River steelhead trout were evaluated at three intervals during their prespawning migration and at kelt emigration. A total of 28 discrete fatty acids were identified in tissues across sampling intervals. Changes in the proportion of saturated, monounsaturated, and polyunsaturated fatty acids, and the specific fatty acid composition of paired samples of white muscle and liver tissues from each fish were compared to explore correlations. To evaluate changes in total fatty acid content over time, the lipid fraction from proximate analyses of tissues was used to normalize the quantity of fatty acids to an equivalent mass of wet tissue. Saturated fatty acids and monounsaturated fatty acids were depleted between late summer migration and kelt emigration, while polyunsaturated fatty acids were conserved. Liver tissues were depleted of fatty acids more rapidly than muscle tissues. By the time of kelt emigration, the equivalent weights of fatty acids were all highly depleted. Three fatty acids remained in samples throughout sampling: C16:0, C18:1, and C22:6n3, and likely these were structurally important. The depletion of structurally important fatty acids likely degrades the physiological performance of steelhead kelts and reduces survival.