Sea lice infestations are the most costly welfare and production problem in salmon farming. Treatment methods vary enormously in the suffering they cause, with thermal and mechanical treatments raising serious concerns.
Sea lice treatment is a welfare crisis embedded within a welfare crisis. The lice infestation itself causes skin lesions, head wounds, and chronic stress — significant welfare harms. But treatment methods frequently cause additional acute suffering: thermal treatment burns fish, causing scale loss and tissue damage; mechanical treatment physically traumatizes animals; crowding for treatment causes acute stress and oxygen depletion. Fish welfare during treatment depends heavily on water temperature, oxygen supplementation, and handling duration — parameters that are frequently inadequately controlled in commercial operations. Preventive approaches — cleaner fish, closed containment, selective breeding for lice resistance — offer better welfare outcomes by reducing both infestation burden and treatment frequency.