Sea lice are the most significant disease challenge in Atlantic salmon aquaculture. Control methods range from chemical treatments to biological and physical alternatives, each with distinct welfare implications.
Sea lice control presents a welfare dilemma: uncontrolled sea lice cause significant fish suffering through tissue damage and immune stress, but control treatments themselves cause welfare compromise through chemical toxicity, handling stress, and physical trauma. Chemical treatments require crowding fish in tarps or well-boat tanks, then exposing them to bath treatments — a stressful procedure. Warm water delicing (Thermolicer) uses rapid temperature elevation to knock lice off fish — effective but causes some mortality and thermal stress if not carefully managed. Laser systems (Stingray) kill lice with targeted light pulses without chemical or physical handling stress — a significant welfare improvement. Breeding for lice resistance represents the most durable long-term solution. Biological control (wrasse, lumpfish) has welfare costs of its own for the cleaner fish deployed.