Potential Physiological Mechanisms Behind Variation in Rainbow Trout (oncorhynchus Mykiss) to Biosynthesize EPA and DHA when Reared on Plant Oil Replacement Feeds

Lipids provide essential fatty acids necessary for proper fish growth and maintenance of crucial functions. The fatty acid profile of the dietary lipids effects the smell, taste, and fatty acid profile of the final product which is of high consumer concern. The omega-3 fatty acids, docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3), are of primary concern as they provide significant health benefits such as reducing inflammation and improving heart and health function. However, the DHA; 22:6n-3 and EPA; 20:5n-3 available for aquaculture feeds is primarily provided by fish oil which is already limited in availability and expensive, and dietary lipids are consistently being replaced with oil sourced from plants. To identify the physiological mechanisms responsible for the conversion of dietary plant lipids and deposition of the omega-3 fatty acids DHA; 22:6n-3 and EPA; 20:5n-3 in rainbow trout, families obtained from three generations of trait selection were evaluated. After screening 450 fish from 30 families for relative EPA +DHA levels, thirty-six fish were selected based on individual and family performance and separated into low, average, and high-performance groups (12 fish per group). The high performing group averaged 8.86 % for EPA+DHA muscle fatty acid ratios, the average group was 6.33 %, and the low performing group was 4.84 %. Transcriptomic and proteomic analysis of liver and muscle tissue was used to evaluate differences between these groups to identify potential mechanisms responsible for the trait. No genes or proteins were identified in the muscle that were linked to lipid synthesis or deposition. However, while in the liver a few genes with notable association to lipid synthesis were detected across individual group comparisons, there were no potential proteins linked to lipid processing that were found to be significantly upregulated in fish across all comparisons that presented with increased EPA and DHA muscle values. However, protein fatty acid binding protein levels were found to change significantly and in a corresponding manner between all treatment groups and could be used as a selective marker for genetic improvement of lipid bioconversion and storage.