Sea lice are the most serious health challenge in Atlantic salmon farming. Treatment methods vary widely in their welfare impact on the fish being treated.
Sea lice treatment welfare impacts are among the most significant acute welfare events in salmon farming. Hydrogen peroxide bath treatments expose fish to rapid temperature change and oxidative chemical stress, causing behavioral distress and physiological responses lasting hours. Mechanical delousing causes scale loss and abrasion injury. The welfare calculus involves comparing treatment welfare costs against the ongoing welfare burden of untreated sea lice infestation — both cause harm. Biological control through cleaner fish represents a better welfare balance when cleaner fish are themselves kept under appropriate welfare conditions. The development of sea lice vaccines would represent the most welfare-positive advance available.