Hepatic Fatty Acid and Transcriptome Profiles during the Transition from Vegetable- to Fish Oil-Based Diets in Rainbow Trout (Oncorhynchus mykiss).

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 the outcomes of a fish oil finishing diet upon the hepatic fatty acid and transcriptome 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 8 weeks, or (3) VO/fd/FO: the VO diet between weeks 1-12, 2 weeks of feed deprivation, then the FO diet for 6 weeks. Hepatic fatty acid and transcriptome profiles were analyzed at week 12, 14, and 20. Hepatic 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 VO-induced 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 at week 14 with enrichment of genes associated with extracellular matrix assembly, supporting liver remodeling during the early finishing diet period. Only 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, even after the hepatic fatty acid equilibration following a finishing diet.