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Assessment of species differences in infection susceptibility for Atlantic salmon, sea trout and Artic char in Altafjord

Differences in salmon lice infection in Atlantic salmon, sea trout, and Arctic char were studied in the Altafjord system. Fjord migrating Atlantic salmon smolts were only captured during June/July and probably left the fjord after this. Most smolts were uninfected with salmon lice, except a few fish in outer fjord areas, which carried low numbers of lice. Pelagic feeding sea trout and Arctic char had surprisingly high infection levels in June/July, suggesting that their pelagic feeding pattern expose them for high risks of infection.

In contrast, littoral feeding brown trout and Arctic char had very low infection during June, slightly increasing in July, and peaking in August.

These observations indicate that Atlantic salmon may have a mismatch between time of lice infection and their fjord migration in northern fjords. In contrast, brown trout and Arctic char feed within the fjords throughout the summer and consequentially have higher risk of harmful infections. These results are highly relevant for lice management in Norway, as measures taken have focused on reducing infection pressure on wild Atlantic salmon smolts. The results have recently been submitted for publication, and will aid authorities in an ongoing process evaluating the Norwegian Action Plan Against Lice on Salmonids.

Reported by

Norwegian Institute Fisheries and Aquaculture Research
University Campus Breivika
N-9291 Tromsø
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