Growth, fish welfare and the quality of salmon muscle are all improved with high levels of the omega-3 fatty acids EPA and DHA in the feed rather than low levels. This is the main conclusion of a comprehensive trial in which salmon nutrition and health are seen in context.
In the autumn of 2019, senior scientist Bente Ruyter presented parts of the results from the research, which were submitted for publication in a scientific journal.
Limited access to fish oil for use in salmon feed is one of the biggest challenges for further growth in the salmon industry. At the turn of the millennium, feed consisted of 31 percent marine oils, while the proportion in recent years has been reduced to approximately 10 percent according to the recent Nofima report ‘Resource utilisation of Norwegian salmon farming in 2016’.
When the level of marine oils in fish feed is reduced and replaced with plant oils, the fatty acid composition in the salmon’s tissues and organs changes. Fat levels and specific fatty acids play key roles in many biological functions, and changes in fat composition in the feed can therefore affect growth, muscle quality and the health and robustness of the fish.
This is the background for the new research, where scientists have tested whether the level of the essential fatty acids EPA and DHA in the feed has effects on salmon survival rates and welfare, growth and fillet quality.
The research methodology
In the research, groups of salmon received four different feeds. All feeds contained low levels of marine protein (basic feed). The feeds differed from each other in that they contained four different levels of fish oil as a source of EPA and DHA. The levels were 1, 1.3, 1.6 and 3.5 percent EPA and DHA in the feed. This corresponds to 4-10 percent EPA+DHA of the total fatty acids in the feed, and the levels in the four feeds are above and below the current commercial level (which is approximately 2.2 percent of the feed). Based on the result, this means that it is not possible to say for sure how the group that was fed with the highest level of EPA and DHA will compare to salmon fed with a commercial level of EPA and DHA.
The trial ran from October 2017 to January 2019 and started when the salmon weighed 400 grams and continued until they reached a slaughter weight of five kilograms.
The results showed a clear pattern
An example of high-quality salmon fillet from a salmon that has been fed a 3.5% diet. Photo: Thomas Larsson/Nofima.
The results of the latest research are clear; Salmon fed with an increasing proportion of omega-3 fatty acids in the feed result in:
- Better fish health and more robust fish
- Faster growth and better quality
- Fewer melanin spots
- Salmon fillets that have a more intense red colour
- A higher proportion of EPA and DHA (omega-3) in the finished product
New marine sources
The purpose of the research is to obtain new knowledge about the levels of fats and fatty acids required to ensure the production of robust Atlantic salmon. In the years to come, various sources of the omega-3 fatty acids EPA and DHA must be used in salmon feed in addition to utilising existing marine sources as efficiently as possible. Microalgae, being primary producers of EPA and DHA, are a source that has been used commercially to some extent. Fish oil obtained from lower trophic species such as krill, as well as oil from species of deep-sea fish, are also possible sources that can be used in the future.
In another project, Nofima has conducted research on oil extracted from genetically modified rapeseed plants. This oil is rich in the omega-3 fatty acid DHA, and trials show that salmon utilise the omega-3 fatty acids in this oil in the same way as they do from fish oil. Unlike other countries, this type of oil is currently prohibited from use in Norway.“While the fish oil content has previously been reduced as far as possible, we now have ways of increasing the EPA and DHA levels again, and feed manufacturers are already starting to do this. Our research reveals that high EPA and DHA levels are beneficial regarding fish health, and I am happy to be able to provide documentation which helps the industry to make better decisions for the fish”, says Ruyter.
About the OptiHealth project
- Duration: 1 February 2017 – 1 February 2020
- Funded by: The Research Council of Norway (NFR) and the Norwegian Seafood Research Fund (FHF)
- Partners: The Norwegian Institute of Marine Research, NIVA, the University of Oslo, BioMar, Skretting (Norway) and the University of Stirling (UK). Nofima was responsible for the project management.
- The trial took place in sea-based net-pens at Gifas’ research station in Nordland County.