Potential physiological mechanisms behind variation in rainbow trout (Oncorhynchus mykiss) to biosynthesize EPA and DHA when reared on plant oil replacement feeds

Authors: Overturf, Kenneth; Abernathy, Jason; KUELTZ, DIETMAR - University Of California, Davis; BLEDSOE, JACOB - University Of Idaho; NARUM, SHAWN - Columbia River Intertribal Fish Commission; Welker, Thomas

Submitted to: Aquaculture Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2025
Publication Date: 1/25/2025
Citation: Overturf, K.E., Abernathy, J.W., Kueltz, D., Bledsoe, J., Narum, S., Welker, T.L. 2025. Potential physiological mechanisms behind variation in rainbow trout (Oncorhynchus mykiss) to biosynthesize EPA and DHA when reared on plant oil replacement feeds. Aquaculture Reports. 41:102655. https://doi.org/10.1016/j.aqrep.2025.102655.
DOI: https://doi.org/10.1016/j.aqrep.2025.102655

Interpretive Summary: Aquaculture is the fastest growing sector of animal production. However, current impediments to continued aquaculture expansion include the limited availability of fishmeal and fish oil, the primary energy components of aquaculture feeds for the last several decades. Aquaculture uses over 60% of the fish meal and more than 80% of the available fish oil produced globally. Due to this, fish oil has been reduced greater than 70% in feeds for certain aquaculture species. Fish oil contains relatively high levels of specific human healthy omega-3 fatty acids. Since the level of fatty acids in the muscle of fish tends to mimic the composition of the diet, aquaculture products are reduced for some of the healthy dietary components passed to consumers. The ARS has selectively bred a strain of rainbow trout for the ability to consume certain plant oils and covert those oils to healthy omega-3 fatty acids and store them in the muscle. The research presented in this manuscript describes possible physiological mechanisms that are responsible for the improvement of this trait in selected fish. Specifically, the liver, the major site of processing for lipids, and the muscle were studied. The findings from this study determined that physiological changes relevant to muscle omega-3 fatty levels in the muscle were due mainly to regulation of transport of the lipids and not pathway enzymatic modification.

Technical Abstract: Lipids provide essential fatty acids necessary for proper fish growth and maintaince 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.