Salmon lice - resistance to chemotherapeutants

The Norwegian Veterinary Institute has a surveillance program on resistance in salmon lice towards medicines used for salmon lice treatments.

The aim of the program is to describe resistance towards and give advice on the use of these medicines.    


The number of medicinal treatments applied against salmon lice was reduced in 2018. This continued a yearly trend that started in 2015. Despite this, the level of resistance seen in salmon lice remained high in 2018. However, the tendency towards a reduction in the level of resistance that started in 2017, continued in 2018. Resistance towards deltamethrin, azamethiphos and emamectin benzoate were generally widespread along the Norwegian coast. Less resistance was found towards hydrogen peroxide than towards the other medicines, but loss of sensitivity was indicated in several areas. 484 prescriptions for medicines against salmon lice were prescribed in 2018, which was a 38 percent reduction compared to 2017. The number of non-medicinal treatments increased with 21 percent, to 2023 reported treatments, in the same period. Non-medicinal methods for treatment and prevention were thereby the dominating
methods for salmon lice control. Thermic delousing accounted for 68 percent of the non-medicinal treatments in 2018.

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