Sea lice infestation is the most significant welfare and economic challenge in Atlantic salmon farming, with treatments that themselves carry welfare costs for the fish.
Sea lice management in salmon farming creates a layered welfare problem: the lice themselves cause ongoing physical damage and stress, and the treatments used to remove them cause additional acute stress events. A salmon experiencing heavy lice burden has eroded skin, impaired osmoregulation, and behavioral indicators of chronic distress. Treatment with chemical baths or mechanical removal temporarily reduces lice counts but causes its own acute stress — elevated cortisol, handling injury, and physiological shock in some cases. The cleaner fish approach deploys wrasse whose welfare is poorly understood and inadequately managed. Truly welfare-positive sea lice management requires minimizing infestation through site selection, fallowing, and barriers before it reaches levels requiring stressful treatment — prevention rather than repeated acute intervention. Snorkel barriers, deep lights, and optimal stocking density are preventive strategies that reduce both lice burden and treatment frequency.