Tone-kari Knutsdatter Ostbye at the Nofima research institute in Norway has been investigating whether it is possible to retain the ability of juvenile farmed salmon to convert omega-3 fatty acids by delaying smoltification and keeping the fish in freshwater longer.
Salmon have a natural ability to convert omega-3 fatty acids from plants into the marine omega-3 fatty acids EPA and DHA, but this ability is greatest in the fish before smoltification
With this in mind scientists at the Nofima research institute in Norway have been investigating whether it is possible to retain the ability of farmed salmon to convert omega-3 fatty acids by delaying smoltification and keeping the fish in freshwater longer.
Two groups of fish
Since the timing of smoltification is controlled by light, this fact was used to create one group of salmon destined to smoltify early (at weight 85 gram) and another group destined to smoltify late (at weight 400 gram). After the salmon that weighed 85 gram had been transferred to seawater, all of the fish were given feed in which only 10% of the fat came from fish oil, with the remaining 90% from rapeseed oil.
Larger smolts – richer in omega-3
The results showed that salmon that had remained in freshwater until they weighed 400 gram had a higher fraction of marine omega-3 fatty acids than salmon that had remained in freshwater until they weighed 85 gram before transfer to seawater.
The fractions of the total fatty acids for marine omega-3 in the two groups were 9.2% and 7.5%, respectively.
“This is an important result, since the levels of healthy marine omega-3 fatty acids in farmed salmon are central to the health of the salmon themselves, and for the health-promoting qualities of the salmon products that we eat,” says scientist Tone-Kari Knutsdatter Østbye at Nofima.
The project was commissioned by the Norwegian Seafood Research Fund whose director of aquaculture, Kjell Maroni, believes that the production of larger smolts can be a way forward for more producers in the aquaculture industry.
“Many companies in the aquaculture industry use a strategy in which parts of the smolt production are kept in freshwater until they are larger than the size at which smoltification has normally taken place,” he says. “It can only be positive if this strategy contributes also to an increased use and increased natural production of omega-3 in the salmon.”