Research at Nofima indicates that removal of the adipose fin in farmed salmon can be the easiest and cheapest method.
A project managed by the food research institute Nofima tested different methods for external marking of farmed salmon, which is necessary for secure identification of escaped farmed salmon.
The project assessed the following methods: complete and partial removal of the adipose fin, freeze branding and visible implant elastomer (VIE).
A happy salmon without adipose fin
The marking is performed on anaesthetised fish at a weight of 20 - 50 g. There is nothing to indicate that the fish have a negative reaction to the adipose fin removal.
“There is reason to believe that this is no different to the tagging of animals, which has been common for a long time,” says Senior Scientist Atle Mortensen.
None of the marking methods that were tested had any impact on growth or survival in comparison with the unmarked control fish, and all the marks were clearly visible four months after the date of marking.
However, after a period of 10 months the freeze branding had completely disappeared and the VIE marking was difficult to read. It is common that damaged or removed tissue is regenerated or, in other words, grows again.
“With partial removal of the adipose fin, we observed partial regeneration in half of the marked fish, but with complete removal of the adipose fin regeneration was not a problem and the marking was clearly visible for the duration of the trial,” says Mortensen.
Meets requirements of Animal Welfare Act
Around 200 million salmon smolts are transferred to sea cages in Norway on an annual basis. It would be a formidable job to mark all of these, and the marking must be performed in accordance with current regulations and the Animal Welfare Act.
All salmon transferred to sea cages from hatcheries in Canada and USA have had their adipose fin removed. The adipose fin removal may be performed manually or mechanically.
The Norwegian Food Safety Authority recommends that such marking should occur in conjunction with vaccination to avoid unnecessary strain – on both fish and people.
“Automatic adipose fin removal is possible, but this cannot currently be combined with vaccination,” says Mortensen. “The best option therefore would be fitting vaccination machines with equipment for automatic marking. Even though there is major uncertainty surrounding the costs, everything indicates that adipose fin removal is the cheapest and most efficient tagging method.”
Who do the markets say?
From a market perspective, the removal of adipose fins can be a potential problem if the fish are sold whole, but the focus on this varies from market to market. This is the conclusion of a survey among the Norwegian Seafood Council’s international representatives.
“An overall assessment shows that the durability/readability, effect on growth and survival, technology and any market reactions indicate that complete removal of the adipose fin is the only one of the tested methods that can be recommended,” concludes Senior Scientist Atle Mortensen.
