Sea lice are the major parasite challenge in Atlantic salmon aquaculture. Treatments to control infestations carry their own welfare costs — understanding these trade-offs guides more humane practice.
Sea lice treatment creates a welfare paradox: leaving lice untreated causes progressive tissue damage and immune stress; treating them involves procedures that are themselves acutely stressful and sometimes harmful. Thermolicer treatment at carefully controlled temperatures is effective and reasonably welfare-compatible if equipment is properly calibrated. At incorrect temperatures or with excessive fish density during treatment, it causes serious injury and mortality. Cleaner fish — wrasse and lumpfish introduced to eat lice from salmon — face their own welfare challenges: they have high mortality rates in sea cages, exposure to lice treatments toxic to them, and inadequate refuge from salmon. Investing in breeding programs for disease-resistant salmon genetics and developing sea lice vaccines represent the long-term welfare solutions that can break the treatment cycle.