Sea lice infestations are the primary health challenge in Atlantic salmon farming, and the treatments used to control them have significant welfare implications for both infested fish and treatment targets.
Sea lice represent a welfare problem embedded in the biology of intensive salmon farming - dense concentrations of fish in sea cages create ideal transmission conditions for parasites that rarely reach damaging levels in wild fish. The suffering caused by severe lice infestations is significant: lesions expose tissue to secondary infection, osmoregulation is impaired, and heavily infested fish become lethargic and immunosuppressed. Treatment creates additional welfare events - mechanical removal methods are physically traumatic, while chemical bath treatments stress fish through handling and hypoxia. Cleaner fish deployed to control lice have their own welfare needs that are frequently neglected - wrasse and lumpfish suffer high mortality in sea cages due to inadequate nutrition and predation.