Sea lice are the most significant health and welfare problem in Atlantic salmon farming. Treatments to control infestations — medicinal baths, mechanical removal, cleaner fish — each carry their own welfare implications for salmon and other species.
Sea lice management exemplifies the difficulty of welfare trade-off decisions in aquaculture. Untreated infestations cause progressive suffering, secondary infections, and mortality. But treatments also impose welfare costs: mechanical delousing causes scale loss, bruising, and physiological stress that can persist for days. Chemical baths expose fish to stressful handling and the pharmacological effects of the treatment. Cleaner fish — biologically elegant solution — raise their own welfare concerns: wrasse are complex reef fish with significant environmental and social needs that are poorly met in salmon pen environments. The welfare priority is to minimise total treatment frequency through biosecurity and early intervention, to use the least welfare-impacting treatment appropriate to infestation severity, and to develop cleaner fish welfare standards that are currently largely absent from the industry.