Omega-3 plays an important role in feed for farmed fish. But if the level of omega-3 in feed is too high and the fat is poorly protected against rancidity, the health and quality of the fish may suffer. A new doctoral dissertation at Nofima shows that too much plant oil in feed is not good either. Moderation is the key.
In her doctoral research, Marte Avrandan Kjær studied how feed containing various levels of plant oil and omega-3 affects fat transport and oxidative stress in fish.
The fat in feed for farmed salmon is becoming more and more plant-based, and plant oils contain totally different fatty acids than traditional fish oils. Today, 20-70 percent of the fat in commercial salmon feed is plant-based.
Moderation is healthy
It is known that omega-3 reduces the level of fat in the bloodstream, which helps to prevent lifestyle diseases. If a large percentage of fat in feed is based on plant oils, Kjær's studies show that we don't see a positive effect of omega-3 because the secretion of fat from the liver increases. This may lead to higher levels of fat in the bloodstream.
Kjær's studies also show that fish which had eaten feed containing large amounts of omega-3 also had damaged mitochondria. Mitochondria are organelles in the cells that metabolize fat. When the mitochondria membranes suffer oxidation damage, less fat is metabolized into energy.
Need good antioxidants
Higher levels of omega-3 may negatively affect the health of fish if the fatty acids are not protected against oxidation (rancidity). As mentioned, rancidity may cause damage to the mitochondria, reduce the utilization of fat for energy production, affect fat storage in the body and decrease liver functioning. Studies of salmon muscle showed that the membranes of the fish muscle are rich in polyunsaturated fatty acids, which makes them especially vulnerable to oxidation damage and in turn may affect muscle quality. Kjær's studies indicate that if the proportion of omega-3 in feed is high, the use of antioxidants must be carefully considered.
Continuing her work with cod
Marte Avranden Kjær is 30 years old and began her PhD work at the Norwegian University of Life Sciences (UMB) and Nofima in 2005. Her supervisor has been Professor Bente Ruyter of Nofima. The title of her dissertation is "Lipids in fish diets - Special emphasis on lipid transport and oxidative stress". Kjær will continue her work at Nofima with a study of how the quality of fish oil affects fat liver in cod.