Sea lice are the most significant health and welfare problem in Atlantic salmon farming. Treatment methods vary widely in their welfare impact, and prevention offers a more humane path forward.
Sea lice management in salmon farming creates a welfare dilemma: the parasites themselves cause significant suffering through skin damage and immune compromise, while many treatment methods cause additional acute welfare harms. Chemical bath treatments cause disorientation, gill irritation, and stress; mechanical treatments physically dislodge lice through water pressure or thermal shock, causing significant injury and mortality in treated fish. Biological control using cleaner fish raises separate welfare concerns for the wrasse and lumpfish used — these are typically wild-caught and may suffer high mortality in salmon cages. The most welfare-positive path is prevention through closed containment or land-based systems that eliminate sea lice exposure entirely. For existing open-net farms, genetic selection for lice resistance and refined treatment protocols that minimize injury offer partial welfare improvement.