The shortage of omega-3 is one of the biggest long-term obstacles when it comes to industrial growth of the aquaculture industry.
“The marine omega-3 content in salmon fillets has declined in recent years, but farmed salmon still contains enough to be an important source of marine omega-3 in human diets,” according to scientist and project manager Nini Sissener of the National Institute of Nutrition and Seafood Research in Norway (NIFES).
However, for the fish itself, little omega-3 can be a health risk. Salmon have a need for the long omega-3 fatty acids EPA and DHA in order to maintain good health. These are known to have a role in the development of vision and for good growth and they are also essential for the immune system. Nevertheless, since omega-3 is scarce in the market, it is preferable not to use more in feed than is necessary. This is a topic that is the subject of much research.
The food research institute Nofima and NIFES have studied all available data concerning what should be a safe low marine omega-3 content in feed for farmed salmon, and what is, at the same time, adequate to ensure that the fish is healthy. The results of this study are now presented in a new report titled “Effects of changes in fatty acid composition of salmon feed related to health, welfare and robustness.”
“There is a lot that has to be in place before we can say for certain how little omega-3 is safe for commercial production of farmed salmon,” says Bente Ruyter, senior scientist at Nofima.
What scientists do know is that there must be more than 1 per cent marine omega-3 in feed under ideal farming conditions. In land-based tanks with seawater, long-term experiments show that it is safe for the salmon to have over 1 per cent marine omega-3 in the feed, while the situation is less clear when it comes to salmon in cages at sea.
So far, long-term tests in cages at sea show that 1.6 per cent omega-3 or more does not result in any growth reduction or survival.
“In the sea, there are varying environmental conditions that allow several factors that have an impact on the salmon’s need for marine omega-3. That means that even if one level can be sufficient for the fish under good farming conditions, the fish may need more omega-3 under demanding environmental conditions,” says Ruyter.
The content in today’s commercial feeds varies, but all have well over 1 per cent.
Nofima and NIFES have completed a number of tests on salmon at sea where they have tested various levels and studied the consequences of too little omega-3.
It would appear that the consequences of a lack of omega-3 are that the salmon are less robust and more prone to developing viral diseases. The scientists also know that the composition of the fat in the diet affects how the fat is distributed in the salmon’s body, and that it can affect the course of the disease during viral infections. The ultimate consequence of these effects is that the salmon’s overall health deteriorates and fewer fish survive life in farming.
Scientists know a great deal about the risk relating to giving salmon too little omega-3. But how the salmon absorbs, converts and stores omega-3 depends on the biology and the environment in which it lives. This varies, and it is therefore difficult to set a universal need.
The study, funded by the Research Council of Norway and the Norwegian Fishery and Aquaculture Industry Research Fund, was conducted by the National Institute of Nutrition and Seafood Research (NIFES) and the food research institute Nofima.
