Sea lice are the most significant welfare and economic problem in salmon farming. Treatment methods each carry their own welfare costs, requiring careful balancing.
Sea lice management creates a welfare dilemma: lice cause ongoing suffering if untreated, but most treatments also cause acute stress or injury. Chemical treatments require crowding fish under tarps, causing crowding stress and sometimes mortality. Mechanical removal using jets or lasers causes physical trauma. Cleaner fish — lumpfish and wrasse deployed to eat lice — face their own welfare problems in the salmon farming environment, including injuries from salmon and poor survival rates. The welfare-optimal approach involves preventing lice rather than treating established infestations — through strategic siting, fallowing, and research into biological and genetic resistance. But prevention requires industry-wide coordination that market competition often prevents.