Nofima study finds salmon must respond within 48 hours to repel sea lice.
New findings from Nofima indicate that salmon must mount an immune response within 48 hours of sea lice attachment in order to effectively resist infestation — a discovery that may inform future breeding and treatment strategies in aquaculture.
The research, led by Lene Sveen at the Norwegian Institute of Food, Fisheries and Aquaculture Research (Nofima), focused on the localised immune response at the site of sea lice attachment. Rather than analysing the entire immune system, researchers concentrated on the initial point of contact between the parasite and the fish’s skin.
“This is precisely where the battle begins,” said project leader Nick Robinson. “If the salmon can respond quickly enough, it can prevent the louse from gaining a foothold.”
The study, published under the CrispResist project, demonstrated that coho salmon — a Pacific species long known for its sea lice resilience — initiates a strong inflammatory response within two days, leading to the detachment of lice. In contrast, Atlantic salmon displayed a markedly weaker reaction at the site of attachment.
The findings also highlighted physical characteristics contributing to resistance. Coho, pink, and chum salmon were found to have a high density of mucous cells in the skin, creating a surface that appears inherently hostile to the parasite. In some cases, lice could only attach after the fish were anaesthetised.
“This suggests that several mechanisms are at play in preventing lice establishment,” said Sveen. “We have never been closer to understanding how species like coho defeat sea lice.”
The research is part of the four-year CrispResist project, which aims to identify the biological basis of species-level resistance to sea lice and apply those insights to improve Atlantic salmon. Partners in the project include academic and industry institutions such as the University of Edinburgh, Benchmark Genetics, Mowi, and SalMar. Funding is provided by FHF – The Norwegian Seafood Research Fund.
The full study is titled Local inflammation at the salmon louse (Lepeophtheirus salmonis) attachment site contributes to copepodid rejection in coho salmon (Oncorhynchus kisutch).