Sea lice are the most economically significant parasite in Atlantic salmon farming — treatments designed to control them can themselves cause significant welfare harms to fish.
Sea lice treatment presents a welfare dilemma: the lice themselves cause welfare harm, but the treatments used to control them also cause harm. Thermal delicing injuries — cataracts from overheated water, scale loss, and crowding stress during the process — are documented and significant. Chemical bath treatments cause acute physiological stress. Mechanical laser systems, while targeted, still involve significant crowding and handling stress. The welfare ideal is preventive management through site selection, fallowing, and cleaner fish that reduces lice burdens without requiring reactive treatments — but this requires industry-wide coordination and investment that market pressures often prevent.