Sea lice - selection study

Sea lice - selection study

A new project to investigate resistance development in sea lice to azamethiphos and pyrethroid treatment has been initiated.

The project was initiated by VESO in collaboration with Fish Vet Group, Marine Harvest Norway and Lerøy and is co-funded by Fiskeri- og Havbruksnæringens Forskningsfond (FHF).

Selection of resistance of sea lice (Lepeophtheirus salmonis) to organophosphate and pyrethroid by combined treatment methods.

Combined treatments with pyrethroids (AlphaMax/ deltamethrin, Betamax/ cypermethrin) and organophosphate (Salmosan/ azamethiphos) have been used in Norway since 2009 and a variety of these methods are used today. There are indications of increasing resistance, especially to azamethiphos, and cross-resistance seems to develop in geographic areas where combination treatments are used.

The project partners share a common concern regarding resistance development when treatment agents are combined in rapid succession. Questions have been raised if the combined treatment methods generate faster loss of sensitivity and with different resistance mechanisms, i.e. cross-resistance, compared to single treatments. Optimal use of azamethiphos and pyrethroid, both as single and combined treatments could keep resistance development under control.

The objective of the project is to observe and investigate resistance development to azamethiphos and pyrethroid by exposing four generations of sea lice to sub-lethal doses of azamethiphos (single treatment), pyrethroid (single treatment) and combined treatment methods. The treatments will be carried out at VESO Vikan Research Facility. The degree of resistance and the resistance mechanisms will be compared across treatment regimes. The resistance mechanisms will be investigated by determining the frequency of genetic markers for pyrethroid and azamethiphos resistance. This work will be carried out by the Sea lice Research Centre, University of Bergen and the Department of Pharmacology and Toxicology, Norwegian School of Veterinary Science. Recommendations for optimal use of both methods will be shared with the salmon farming industry.

For further information, please contact Project Manager Sigmund Sevatdal ( 47 90 60 37 85).

Photo: Stian Mørch Aaen

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