Sea lice infestations are a major welfare and production challenge in salmon farming. Treatment methods vary widely in their welfare implications, creating an urgent need for better alternatives.
Sea lice treatment represents a welfare dilemma in salmon aquaculture: untreated infestations cause chronic pain and welfare harm from lesions and osmotic disruption, while many treatments cause acute welfare harm through handling, temperature shock, or chemical exposure. Mortality during treatment operations is a measurable welfare indicator, with some mechanical treatments showing significant fish losses. Preventive strategies — deeper farm positioning, enclosed containment, selective breeding for lice resistance, and strategic fallowing — reduce treatment frequency and associated welfare harm. The welfare of cleaner fish used as biological control is also significant — wrasse and lumpfish die in large numbers on salmon farms and deserve inclusion in welfare assessments.