A new doctorate shows that marine omega 3 fatty acids are necessary in feed to protect the good health of farmed salmon.

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Reidun Lilleholt Kraugerud  

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In her PhD thesis at Nofima, Marta Bou Mira studied what minimum level of marine omega 3 fatty acids is required in feed to ensure that farmed salmon maintain health and grow well through various life phases under differing environmental conditions. The particular fatty acids she has studied are EPA and DHA, and fish oil is the more important source of these fatty acids. There is an ongoing shortage of fish oil in the market. It is therefore undesirable to use more omega 3 fatty acids than necessary in fish feed.

In the PhD thesis, salmon are fed feed containing 0 to 2 percent EPA and DHA from the beginning of feeding until they reach a slaughter weight of 4 kilograms. Bou Mira’s work shows that it is most efficient with up to 1 percent marine omega 3 fatty acids in the feed, which gives the highest self-production of marine omega 3 in the salmon. The research team has previously shown that salmon have the ability to transform plant omega 3 to marine omega 3 to compensate when the level of marine omega 3 in the feed is low.

The experiments showed, however, that 1 percent EPA and DHA in the feed, a level that has previously been viewed as the required level, is too low for salmon to maintain good health in a demanding environment in pens at sea.

The lowest level of omega 3 fatty acids in feed led to structural changes in the intestine and spine, as well as to higher mortalities after sea lice treatment in high seawater temperatures. The amount of marine omega 3 in commercial Norwegian salmon feed is well over the level resulting in negative effects in the study.

The experiments showed that the long marine omega 3 fatty acids EPA and DHA are necessary in salmon’s feed to protect their good health and robustness.

Bou Mira will defend her thesis on 4 May at the Norwegian University of Life Sciences, NMBU, in Ås, Norway.

Continuing with studies of salmon’s lipid metabolism

Marta Bou Mira is 33 years old and from Alicante in Spain. She has a master’s in fish nutrition from the University of Barcelona and began her PhD at NMBU and Nofima in 2013. Her thesis supervisor has been Bente Ruyter, a senior researcher at Nofima and professor at NMBU. Bou Mira will continue to work with Nofima in a post-doc position finances by Norway’s Research Council. Marta Bou Mira will continue her studies of salmon’s lipid metabolism.

Omega 3 in salmon feed

The production of Norwegian farmed fish has more than doubled in recent decades, which has resulted in an increased demand for raw ingredients for feed. Since access to fish meal and fish oil is limited, today’s salmon feed is comprised of ca. 70% plant proteins and plant oils. This has led to a reduction in the level of the healthy marine omega 3 fatty acids EPA and DHA in salmon’s tissues and organs. The proportion of plant-based ingredients in fish feed is expected to grow further in future, a development that requires new knowledge on salmon’s needs for the essential omega 3 fatty acids.

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