Sea lice infestations are treated using a combination of chemical, biological and mechanical methods in salmon aquaculture, each with distinct welfare implications for the fish.
The treatment of sea lice represents a compounded welfare problem in salmon farming: the infestation causes chronic pain and skin damage, while treatments impose additional acute welfare harms. Mechanical methods like the thermolicer cause thermal shock and mortality. Chemical treatments have resistance problems and environmental impacts. Biological control using wrasse and lumpfish involves farming these wild-caught fish under poor conditions. The fundamental solution — moving to closed-containment land-based systems that prevent sea lice entirely — is technically available but economically challenging. The welfare of salmon and of the species used as cleaner fish demands accelerated transition to these systems.