Sea lice (Lepeophtheirus salmonis) cause significant welfare harm to farmed salmon. Treatments including medications, thermal methods, and cleaner fish each carry their own welfare implications that must be managed.
Sea lice management sits at the intersection of fish welfare and sustainability concerns in salmon farming. Untreated infestations cause severe pain and immune compromise. However, many treatments carry their own welfare costs: pharmaceutical bath treatments cause acute chemical stress; thermal treatments can cause thermal burns and scale loss if water temperature is not precisely controlled; mechanical treatments cause physical injury and handling stress. Balancing these competing welfare harms requires careful evidence-based decision-making about when and how to treat. Preventive approaches including deeper cages, cleaner fish deployment, and selective breeding for lice resistance offer the most welfare-positive long-term trajectory. Consumer demand for certified sustainable, welfare-positive salmon creates market pressure for these investments.