Sea lice infestation is one of the most significant welfare problems in Atlantic salmon farming, with treatment methods that themselves raise welfare concerns.
Sea lice management in salmon farming illustrates how addressing one welfare problem can create others. The welfare harm from sea lice infestations is real and significant — chronic ectoparasite load causes measurable physiological stress and physical damage. But many current treatment methods themselves cause significant welfare harm, particularly thermal delousing. The welfare-optimal approach requires viewing the entire management cycle: preventing lice loads from reaching welfare-concerning levels, using treatment methods with the least welfare impact (in-feed medications have lower immediate stress but resistance concerns; biological control has welfare implications for cleaner fish), and developing longer-term solutions including genetic resistance. Welfare certification for farmed salmon is increasingly examining lice management protocols as a key welfare indicator — farms that maintain consistently low lice loads with welfare-considered treatment methods meet higher standards than those allowing lice to accumulate and treating with high-stress methods.