Norwegian salmon production 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 roughly 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 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.
In her PhD thesis at Nofima, Marta Bou Mira researched what the minimum level of marine omega 3 fatty acids is needed 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 – which are currently largely derived from fish oil. 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.
Her research involved feeding salmon diets 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 1 percent marine omega 3 fatty acids in the feed leads to 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 also 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.