Hepatic fatty acid and transcriptome profiles during the transition from vegetable- to fish oil-based diets in rainbow trout (Oncorhynchus mykiss)

Authors: Cleveland, Beth; Gao, Guangtu; Radler, Lisa; Picklo, Matthew

Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2020
Publication Date: 10/13/2020
Publication URL: https://handle.nal.usda.gov/10113/7175943
Citation: Cleveland, B.M., Gao, G., Radler, L.M., Picklo, M.J. 2020. Hepatic fatty acid and transcriptome profiles during the transition from vegetable- to fish oil-based diets in rainbow trout (Oncorhynchus mykiss). Lipids. https://doi.org/10.1002/lipd.12287.
DOI: https://doi.org/10.1002/lipd.12287

Interpretive Summary: Traditional aquafeeds contain high amount of fish oil that increase heart-healthy omega-3 fats in the rainbow trout fillet. Transition to more sustainable plant oils reduces fillet omega-3 content, but this can be combated by feeding a fish oil-rich finishing diet in the weeks prior to harvest. By analyzing the fat and gene expression profiles, this study determined that the liver exhibits a unique metabolic response that differs depending on the type of dietary oil that is being consumed. Transitioning to a finishing diet also appears to force the remodeling of liver tissue which may compromise its metabolic capacity. These findings suggest that a gradual transition to the finishing diet may be an optimal approach for improving aquaculture sustainability while maintaining high levels of omega-3 fatty acids in rainbow trout fillets.

Technical Abstract: A finishing diet strategy is effective at increasing fillet long chain n-3 fatty acid content in fish consuming sustainable plant oil-based diets. This study investigates how a fish oil finishing diet affects the hepatic fatty acid and transcriptomic profile in rainbow trout (Oncorhynchus mykiss). Fish were placed on one of three feeding treatments: 1) FO: a fish oil (FO) diet for 20 weeks, 2) VO/FO: a vegetable oil (VO) diet during weeks 1-12 then the FO diet for eight weeks, or 3) VO/fd/FO: the VO diet between weeks 1-12, two weeks of feed deprivation, then the FO diet for six weeks. Hepatic fatty acid and transcriptome profiles were analyzed at week 12, 14, and 20. Fatty acid profiles at week 12 were similar to dietary profiles; transcriptomic analyses indicated 131 differentially regulated genes (DEG) between VO- and FO-fed fish, characterized by up-regulation of cholesterol and long-chain fatty acyl-CoA synthesis and oxidation-reduction processes. At week 14 the hepatic fatty acid profile was similar between VO/FO and FO, although concentrations of 18:3n-3 remained higher in the VO/FO group. Thirty-three DEG were detected with enrichment of genes associated with extracellular matrix assembly, supporting increases in liver remodeling during the early finishing diet period. Five DEG were detected at week 20 between VO/FO and FO. Collectively, these findings suggest that it takes several weeks for liver to reach a homeostatic state after switching to a finishing diet, and a gradual transition may be beneficial for liver health and metabolic capacity.