Sea lice infestations in farmed Atlantic salmon require treatment interventions that carry their own significant welfare costs, creating a difficult trade-off in welfare management.
Sea lice management creates a genuine welfare dilemma: untreated lice cause chronic suffering and potentially fatal damage, while most available treatments impose their own acute welfare costs. Mechanical delousing subjects fish to capture, crowding, handling, and physical forces that cause scale loss, fin damage, and physiological shock — mortality rates of 1-2% per treatment are common, representing hundreds of thousands of fish deaths annually in Norway alone. Chemical bath treatments risk hypoxia and chemical irritation. The salmon welfare perspective strongly favors prevention over treatment: optimized stocking densities, improved farm siting, coordinated area management, and selective breeding for lice resistance all reduce treatment burden. Cleaner fish welfare requires dedicated attention, as wrasse and lumpfish used for biological control have their own significant welfare needs that are often inadequately addressed.