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United States Department of Agriculture

Agricultural Research Service

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Research Project: Disease Risk Reduction and Lcn3 Rich Rainbow Trout

Location: Cool and Cold Water Aquaculture Research

Project Number: 8082-31000-010-01
Project Type: Interagency Reimbursable Agreement

Start Date: Feb 15, 2014
End Date: Feb 14, 2019

Objective:
Consumption of the long chain n-3 fatty acids (LCn3) eicosapentaenoic acid (20:5 n3) and docosahexaenoic acid (22:6 n3) is associated with prevention of inflammation and reduction of cardiovascular disease (CVD) risk. Inflammatory diseases and CVD are major negative outcomes of obesity and cost > $100 billion annually in the United States alone. While marine fish such as farmed Atlantic salmon (Salmo salar) are recognized as excellent sources of LCn3, there is a need to develop alternative food sources of LCn3. Farmed, fresh water rainbow trout (Oncorhynchus mykiss) has the potential to become an attractive, alternative source of LCn3 and its land-based production is viewed as environmentally sustainable. Rainbow trout contain significant amounts of LCn3 so there is a need to identify the production practices that increase LCn3 content in these fish. The US trout industry raises primarily diploid (2N) trout; however, there is a demand for triploids (3N) for their larger fillets. Our initial data indicate that female 3N rainbow trout have levels of LCn3 comparable to that of farmed Atlantic salmon. While we have shown that consumption of farmed Atlantic salmon significantly elevates LCn3 status in humans, the consumption of 3N rainbow trout may represent a new choice for American consumers to achieve optimal LCn3 levels and reduce the risk of disease. Furthermore, as the amount of LCn3-rich fish oil is reduced in rainbow trout feed in favor of the more sustainable but LCn3-deficient vegetable oils, the negative effects of this transition on fillet LCn3 content is a concern. Therefore, to improve the sustainability of the rainbow trout industry without sacrificing the health benefits of its products, there is a need to determine how vegetable oil-based feeding strategies affect the LCn3 content in large rainbow trout fillets. Therefore, the specific aims of this proposal are to 1) evaluate the relative LCn3 content in diploid and triploid fillets at various stages of development, 2) determine whether consumption of rainbow trout improves indices of inflammation and cardiac health in obese adults, and 3) evaluate the effect of vegetable and fish oil feeding strategies on the LCn3 content of rainbow trout fillets.

Approach:
Specific aim 1. Identifying production practices that affect the accumulation of LCn3 content in the fillet is critical for establishing rainbow trout as a dietary source of LCn3. In the United States, the rainbow trout industry raises primarily diploid (2N) and triploid (3N) fish. Diploid trout are harvested young while triploid rainbow trout fill the demand for larger fillets because the female triploids are unable to sexually mature, thereby avoiding the negative effects of sexual maturation on fillet quality. Understanding whether diploids or triploids, and at which stage of development, yield the greatest fillet LCn3 content will indicate production practices that maximize benefits on consumer health. Specific aim 2. Consumption of fish enriched with the long chain n-3 fatty acids (LCn3) is associated with prevention of inflammation and reduction of cardiovascular disease (CVD) risk. Prevention of CVD is a public health goal and comprises several avenues of action, of which inclusion of LCn3-rich fish in the diet is one of the most effective. A previous study indicated that consumption of Atlantic salmon improves LCn3 status in humans, which is an index of inflammation and cardiac health. To establish the health benefits of rainbow trout consumption, obese human volunteers will receive twice weekly meals containing either diploid or triploid rainbow trout fillets. Measures of inflammation and cardiac disease risk, specifically those related to LCn3 function, will be monitored to assess positive effects on health. Specific aim 2. As growth of the aquaculture industry increases, so does the demand for fish oil and fishmeal, ingredients which are collected from marine capture and forage fisheries. Vegetable oils like soy, canola, and flax can be produced in sufficient quantities and are generally less expensive than fish oil. However, many of the vegetable oils are rich in medium-chain omega-3 fatty acids (MCn3), not LCn3, therefore their incorporation in aquafeeds reduces the concentration of LCn3s in the diet and also in the fish itself, thereby minimizing one of the most attractive health benefits of rainbow trout. A strategy that partially reestablishes fillet LCn3 is to feed a fish oil finishing diet after consumption of a vegetable oil grower diet. However, it remains unknown if increased consumption of LCn3 fatty acids occurring during the transition from a low-LCn3 vegetable oil grower diet to a high-LCn3 fish oil finishing diet varies by fillet location. Determining how the fatty acid profile varies by fillet subsection and lipid storage location will indicate how dietary LCn3 content affects aspects of fillet quality, and contribute to the establishment of sustainable feeding strategies that aim to maximize aspects of fillet health and quality. Further analysis of the physiological basis for variations in fillet LCn3 content can be achieved by transcriptome analysis using RNAseq. Applying this technique in rainbow trout will determine how the liver transcriptome is affected by sustainable feeding strategies and indicate the nutrient-gene interactions regulating the fatty acid profile of the fillet.

Last Modified: 10/20/2014
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