Sea lice cause more welfare harm to farmed salmonids than any other single factor. This comprehensive review covers the biology, welfare impact, and management of this key welfare challenge.
Sea lice infestation represents the most significant welfare challenge in Atlantic salmon aquaculture globally. The ectoparasites attach to host salmon, feeding on mucus, skin, and underlying tissue. Tissue damage from feeding creates open wounds that affect both osmoregulation and provide entry points for secondary bacterial infections. Heavy infestations cause profound welfare harm — fish show avoidance behaviors, reduced feeding, and physiological stress markers.
The welfare impact of treatments is a secondary but important consideration. Chemical treatments (hydrogen peroxide, azamethiphos) cause acute physiological stress. Mechanical delousing methods (hydrolicer, thermolicer, laser) cause physical injury and handling stress that can result in significant mortality. Biological control using cleaner fish (wrasse, lumpfish) requires maintaining those fish appropriately in their own right — a welfare consideration often overlooked in sea lice management discussions.
Integrated pest management that prevents lice populations reaching welfare-impacting thresholds — through farm site selection, stocking timing, deep light and feed management, and skirt systems — reduces both lice burden and treatment welfare harm. Real-time lice monitoring using automated camera systems enables earlier, lighter interventions. The welfare goal is zero treatment rather than frequent treatment of high infestations.