Sea lice infestations cause pain and disease in farmed salmon. Chemical and mechanical treatments used to control lice also cause significant welfare harms, creating a difficult welfare dilemma.
Sea lice management in salmon aquaculture creates a welfare dilemma: untreated lice infestations cause pain, tissue damage, and death, but many treatments themselves cause acute suffering. Chemical bath treatments stress fish through handling and exposure to toxic compounds. Mechanical treatments cause physical trauma — thermolicer-related salmon mortality events have been documented at significant scales. Cleaner fish used as biological controls often receive poor welfare consideration: wrasse collected from the wild are frequently kept in inadequate conditions and die in large numbers. Breeding for lice resistance and improving pen hygiene through fallowing offer welfare improvements that reduce both the problem and treatment harms. Closed containment aquaculture eliminates lice exposure entirely but requires major infrastructure investment.