Sea lice are the most significant parasite in salmon farming, and the treatments used to control them raise serious welfare concerns for both farmed and wild salmon.
Sea lice treatment represents a genuine welfare dilemma: untreated lice cause chronic welfare harm; all current treatments cause acute welfare harm. Thermal treatments expose fish to temperatures that cause stress, fin damage, and mortality. Mechanical treatments cause physical injury from pressure. Chemical treatments cause acute toxicity stress. The welfare-best approach combines prevention (closed containment systems, location management) with the least harmful treatments when necessary. Lumpfish used as cleaners have their own welfare needs that are often poorly addressed. The ecological spillover to wild salmon compounds the welfare impact. Industry investment in sea lice vaccines and in-land recirculating systems would be the highest-impact long-term welfare and conservation improvement.