VACCINATING SALMON AGAINST WINTER WOUNDS

Vaccinating salmon against winter wounds. Last winter, many farmed salmon died from winter wounds. Researchers now have new knowledge about the skin of salmon and vaccines, which can be useful when fish farmers face a new winter.

The result is that it can be better vaccinated against ulcers.

“We have documented what everyone thought,” says senior researcher Christian René Karlsen. He talks about salmon that get wounds on their bodies because of bacteria.

Fish health scientists at Nofima have been concerned with the skin of salmon for a long time.

“It’s the body that gets the first impressions from the environment. The skin will feel all the environmental changes that affect the fish,” Karlsen explains.

In winter-cold seawater, salmon can get wounds. Behind the winter wounds is a bacterium called Moritella viscosa.

It is possible to vaccinate against the winter ulcer bacteria. The problem is that the bacterium comes in very many varieties. When you vaccinate salmon, the vaccine works much better if you make it using just the right variant of the bacteria.

Vaccine gets better

Even the vaccine does not keep all the fish healthy, namely. Christian René Karlsen talks about high wound development also in fish that have been vaccinated. In a recent experiment where fish with wounds were mixed with healthy fish, 15 per cent of the fish suffered deep wounds and 25 per cent suffered superficial wounds.

“The vaccine is not complete. That’s why we’ve moved on,” he says.

In addition to looking at what the different Moritella viscosa variants have to say, the researchers have learned how the wound bacterium begins to harm the fish.

“It gets stuck on the surface of the shells. There it expands and creates a colony,” Karlsen explains.

Major wounds

The shells are not the outermost part of the salmon.

“At the far end is a slime layer. The bacterium manages to settle between this outermost layer and the shells. Then they create wounds that can become so large that they go down to the muscle,” he says.

When the fish is given a vaccine shot, it has the first bacteria on its shells. In the unvaccinated fish, the bacteria go deeper in the skin earlier. Now there are several vaccines against different Moritella viscosa bacteria on the market.

The research has been done in collaboration with the vaccine company Pharmaq, and funded by the Research Council of Norway.

Image: Moritella viscosa is one of the types of bacteria that causes wounds in salmon. Here, Christian Karlsen grows two varieties of the bacterium in the lab. Jon-Are Berg-Jacobsen © Nofima.

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