Sea lice delousing treatments impose acute welfare costs on farmed salmon, and improving treatment methods is a major welfare priority for the salmon industry.
Delousing treatments represent the acute welfare crisis within sea lice management, concentrated into intensive handling events that stress already compromised fish. Thermal delousing causes scalding injuries and mortality when temperature calibration is imprecise. Mechanical methods cause physical trauma and osmotic stress. The cumulative welfare impact of multiple delousing events per year on the same cohort of fish is significant and poorly measured at industry level. The development of lice vaccines and genetic resistance represents the most welfare-positive long-term solution. In the interim, improving treatment protocols to reduce fish handling stress, post-treatment mortality, and injury rates is the primary welfare improvement pathway available.