Aquaculture for all

Seeking the Optimal Diet for Salmon

Salmonids Nutrition Health +6 more

NORWAY - There are great expectations for growth in aquaculture, but there is already a shortage of more of the raw materials used in fish feed. Most acute is the lack of marine fatty acids. Researchers from Nofima and NIFES seeking the answer to how much fish oil is needed for salmon and trout need to stay fit and healthy.

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The companies have compiled what they know and identified the knowledge needed to answer what is the fish's minimum requirements for the long-chain omega-3 fatty acids EPA and DHA. More than 200 scientific publications were reviewed.

The research team comprised of scientists with expertise in nutrition, fish health, welfare and fish metabolism. They have considered fish in the following criteria:

- Resistance to viruses, bacteria and parasites
- Eye Disorders cataract (cataract)
- bone development and bone health
- cardiovascular health
- Stress
- Intestinal Health
- Fat Storage and inflammation

There is evidence that the fatty acid composition in feed influences infection and immune response in Atlantic salmon, but the knowledge of what is optimal fatty acid composition is lacking.

"We need more knowledge about the fatty acid compositions which provide good protection against virus infections and the fish's ability to deal with bacterial infections or lice and how fatty acid composition influences stress. In addition, it is important to have more knowledge about the long-term effects of low EPA and DHA levels in the diet," says Senior Bente Ruyter Nofima.

Different needs at different life stages

Salmon and trout are more vulnerable at different stages in life, such as the early development of eggs and early juvenile stages, smoltification and sexual maturation, and there is a need for more knowledge about the nutritional needs of these phases.

Freshwater fish require a minimum of one per cent EPA and DHA. In seawater most studies suggest that salmon tolerate high interference levels of various vegetable oils or vegetable oil mixes (75-100 per cent vegetable oil mix). But the majority of the experiments carried out are often limited to short periods of fish life, and thus, the knowledge about long-term effects deficient. More knowledge is needed

There are clear indications that nutrition is an important factor in epigenetic regulation, meaning that there are changes in DNA that is expressed in later life stages and transferred to the next generation.

"Knowledge of epigenetic regulation may be important in efforts such as selecting the fish families as excellent net producers of EPA and DHA. A future goal for salmon and trout should be that the fish are net producers of the long-chain omega-3 fatty acids," says Bente Ruyter.

To achieve this, it is necessary that studies look at resource utilisation throughout the production cycle, taking into account both seasonal variations and different stages in the life cycle.

Fish are what they eat

When the feed is changed, so does the nutritional content of the pieces of fish we eat. So when the fatty acid composition of the feed changes, it affects the amount of EPA, DHA, omega-6 and monounsaturated fats in fish flesh.

Farmed fish should continue to be a good source of long-chain omega-3 fatty acids and optimised feed strategies can ensure that farmed salmon is a net producer and a major source of EPA and DHA.

In this context, more knowledge is needed about what is the upper tolerable amount of omega-6 in the feed, and what is the optimal ratio of omega-3 and omega-6.

"We now know that when the amount of monounsaturated fats and omega- 6 fats in the diet increases, the amount equivalent in fillets also increases," says Bente Ruyter.

The report was financed by the Fishery and Aquaculture Industry Research Fund (FHF).

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