Sea lice infestations cause significant welfare harm to farmed salmon. Understanding control approaches and their own welfare implications helps assess progress in sustainable aquaculture.
Sea lice represent both a welfare problem and a welfare dilemma. Heavy lice burdens cause real suffering in affected salmon: lesions, reduced feeding, behavioral changes indicating pain, and secondary infections. But some control methods cause their own welfare problems. Thermolicer treatment (brief immersion in hot water) causes acute thermal stress. Chemical treatments have welfare implications for non-target organisms. Cleaner fish, widely used as a biological control measure, have poorly understood welfare needs and often die at high rates in salmon farms. Addressing sea lice welfare requires integrated approaches that minimize suffering from lice themselves while also minimizing welfare costs of control interventions.