Deposition and mobilization of lipids varies across the rainbow trout fillet during feed deprivation and transition from plant to fish oil-based diets

Authors: Cleveland, Beth; Raatz, Susan; Picklo, Matthew

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2018
Publication Date: 3/9/2018
Citation: Cleveland, B.M., Raatz, S.K., Picklo, M.J. 2018. Deposition and mobilization of lipids varies across the rainbow trout fillet during feed deprivation and transition from plant to fish oil-based diets. Aquaculture. 491:39-49. https://doi.org.10.1016/j.aquaculture.2018.03.012.
DOI: https://doi.org/10.1016/j.aquaculture.2018.03.012

Interpretive Summary: Traditional aquafeeds contain high amount of fish oil which 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. While a short period of feed deprivation prior to the finishing diet has been proposed as an approach to improve omega-3 enrichment, our study indicated that this approach was largely not effective when considering the fillet on the whole. However, when examining the different fillet regions, it was apparent that a period of feed deprivation prior to the finishing diet had variable effectiveness. The central region lost fats during feed deprivation but rapidly regaining them during the finishing phase, while fats in the dorsal region were more resistant to changes in feed intake. Region-specific gene expression responses also support variable capacities to synthesize omega-3 fats across different fillet regions. These findings indicate that while the fat profile of the whole fillet is important from a consumer standpoint, this merely represents the mean of spatially distinct regions, each of which pose a unique physiological and metabolic response to feeding strategies.

Technical Abstract: Identifying aquaculture feeding strategies that reduce the consumption of fish oil without sacrificing the cardioprotective lipid profile of the salmonid fillet will improve aquafeed economics and sustainability. Transitioning fish from a plant oil-based diet to a finishing diet rich in fish oil and long chain n-3 fatty acids (LCn3) for several weeks prior to harvest is effective at boosting the fatty acid profile of the whole salmonid fillet. This study determined whether the response to short-term feed deprivation and a finishing diet varies across different regions of the triploid rainbow trout fillet. Fish were placed on one of three feeding treatments: 1) FO: a fish oil (FO) diet for the entirety of the 20-week study, 2) VO/FO: a vegetable oil (VO) diet between weeks 1-12 then the FO diet for the final eight weeks, or 3) VO/fd/FO: the VO diet between weeks 1-12 followed by a two week period of feed deprivation before transitioning to the FO diet for the final six weeks. Fillets were divided horizontally into three sections (ventral, central, and dorsal) and the fatty acid profile of each was determined. There were unique responses to feed deprivation across fillet regions; the central region exhibited a loss of fatty acids, the dorsal region gained fatty acids, but there was no net gain or loss of fatty acids in the ventral region. The ventral and dorsal regions responded similarly to a high-FO finishing diet, increasing concentrations of fatty acids and LCn3, although not to levels observed in the FO treatment group. In contrast, the fatty acid profile in the central region remained largely unaffected by the finishing diet, with the exception of LCn3 in the VO/FO group that increased to levels comparable to the FO-treatment group. Expression of genes related to muscle atrophy (fbxo32) and LCn3 metabolism (fads5) also varied across different fillet regions and in response to dietary treatments. This study provides evidence that regulation of muscle growth and lipid metabolism varies significantly across the fillet, a concept that should be considered when evaluating a representative subsample or the entire fillet as a single unit.