Cataracts affect a significant proportion of farmed Atlantic salmon, impairing vision and likely causing ongoing discomfort. This welfare problem is linked to dietary deficiencies and has proven difficult to eliminate.
Salmon cataract welfare is a significant and underappreciated problem affecting potentially hundreds of millions of fish annually across global aquaculture. Vision is important for salmonids in feeding, predator avoidance, and social navigation. Cataract-affected fish show impaired feeding behavior, reduced growth, and likely experience visual disturbance or pain from lens opacity. The relationship between histidine deficiency in plant-based feeds and cataract development represents a welfare cost of the environmental improvements from fishmeal replacement — demonstrating that sustainability transitions require careful welfare monitoring. Feed formulation improvements maintaining adequate histidine levels have reduced but not eliminated the problem. Genetic selection for cataract resistance offers a complementary approach through breeding. The welfare significance of cataracts in fish is difficult to assess given our limited understanding of fish subjective visual experience, but the precautionary approach warrants treating it as a significant welfare concern.