The methods used to treat sea lice infestations in farmed salmon cause varying degrees of welfare harm, and choosing the least invasive effective treatment is a key welfare decision for producers.
Every sea lice treatment method currently in widespread use causes some degree of welfare harm to salmon. The key welfare decision is choosing the least harmful effective method for the current lice burden and fish condition. Thermal treatments are fast but temperature-sensitive, with narrow safety margins that can cause cataracts or mortality if fish are stressed or the water too warm. Mechanical treatments cause physical trauma. Chemical treatments cause respiratory stress. The welfare-optimal approach integrates multiple methods — prioritizing biological control with cleaner fish, using chemical treatment as a second line, and reserving mechanical methods for severe infestations. Treatment protocols should include post-treatment welfare assessment.