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HAVBRUK2-Stort program for havbruksforskning

EPA immune - Can dietary EPA affect viral response in Atlantic salmon?

Alternative title: EPA-immun - kan EPA i dietten påvirke laksens virusrespons?

Awarded: NOK 11.5 mill.

Project Manager:

Project Number:

327013

Project Period:

2021 - 2025

Location:

Partner countries:

The production of aquacultured Atlantic salmon is dependant on feed ingredients of high quality. The fish have a requirement for the fatty acids typical in marine food webs, like EPA and DHA. These are the two main marine fatty acids mentioned when discussing requirements of marine fatty acids in both humans and fish. Less research has been done on how they affect the health individually. DHA has long been prioritized in research and has been seen as the marine fatty acid most closely linked to positive health effects. In Atlantic salmon, as in mammals, DHA is selectively stored in tissues in case of a low supply of EPA and DHA, while EPA is to a higher degree converted into DHA in the tissues and also used more for energy purposes than DHA. Recent research is, however, indicating that EPA has a specific and unique health-promoting role, different from its "big brother", DHA. Trials done with Atlantic salmon have shown indications that EPA might be essential for an optimal immune response in the case of a viral infection. The ratio between EPA and DHA in most fish oils is approximately 1:1. Fish oil has been the predominant source of the essential EPA and DHA in diets for farmed aquatic animals, including Atlantic salmon. Large growth in the global aquaculture production combined with a stable fish oil production, has led to a search for alternative sources of EPA and DHA. Algae oils and oils from genetically modified plants and yeast are viable options for obtaining these fatty acids today. These sources do, however, not always contain an EPA:DHA ratio of 1:1. They can actually contain exclusively either EPA or DHA, thus possible leading to a large imbalance in the dietary supply of the two marine fatty acids. In this project we are going to study the specific roles of EPA, with emphasis on its role in the immune system and viral response in Atlantic salmon.

The main hypothesis of the project is that dietary ratio between EPA/DHA or a supplementation of EPA can affect Atlantic salmon viral response and inflammatory status. An increased use of novel non-fisheries sources of EPA and DHA can cause an imbalance between the two fatty acids, thus creating a fatty acid deficiency. This is hypothesized to cause a disproportionate inflammatory response in cases of long-term inflammation caused by viruses. For a more flexible dietary composition for Atlantic salmon and inclusion of novel sources of omega-3 without loss of robustness, the project aims to learn more about the specific roles of EPA in inflammation and immune response in Atlantic salmon. With a combination of different fish- and cell trials we are aiming to increase knowledge on this area. Work Package 1: The effect of EPA/DHA ratio and EPA supplementation on Atlantic salmon post-smolt performance and inflammatory status will be assessed in fish grown from 200-800 g in an experimental facility. The fish will be monitored for health and inflammatory status and the digestion and metabolism of fatty acids will be measured. Work Package 2: The fish from WP1 will be used in a trial where the fish will be challenged with piscine rheovirus (PRV), the virus that causes Heart and Skeletal Muscle Inflammation (HSMI). During this challenge the fish will be monitored for fish health markers by histopathology and inflammatory status will be evaluated. Work Package 3: A newly developed small fry model for disease studies will be used to study HSMI as well as PD. PD will be studied by using a novel SAV clone which causes a reduced disease response, but which will still activate the immune system. Work Package 4: Cells isolated from WP1 will be immune-stimulated with a viral mimic or SAV clone to study details on interactions between diet and viral response in the cells. The role of the autophagic system and effects on diets on this will also be studied.

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning