Sea lice are parasitic crustaceans that attach to salmon and cause painful lesions. The spread of sea lice from fish farms to wild salmon populations is a major welfare and conservation concern.
Sea lice infestations cause tangible physical suffering in salmon, including skin erosion, open lesions, osmotic stress, and compromised immune function. Fish welfare science increasingly recognizes that fish experience pain and stress in ways that matter morally. The scale of the problem — affecting millions of wild salmon along major migration routes — makes it one of the largest animal welfare issues in aquatic systems. Reducing the footprint of open-net fish farming and supporting closed containment alternatives are among the highest-impact actions available to address this issue.