Atlantic salmon stocking density in aquaculture is a primary driver of welfare outcomes, with high densities linked to increased aggression, injury, disease and stress.
High stocking densities in salmon cages prevent individual fish from escaping aggression, establish feeding hierarchies that cause chronic subordinate stress, and reduce water oxygenation. Physiological stress markers including cortisol and gill chloride cell density are elevated in densely stocked fish. Density reduction is one of the highest-impact interventions available for improving farmed salmon welfare.