Stocking density in farmed Atlantic salmon sea cages is a primary determinant of welfare outcomes, affecting aggression, disease susceptibility, and behavioral welfare across the grow-out period.
Salmon crowding creates a cascade of welfare problems. At high densities, the three-dimensional space available per fish falls below their behavioral needs, causing frustration and aggression. Fin damage from aggressive interactions is a direct welfare indicator visible at slaughter, and studies have shown that fin damage rates increase with stocking density. Immune suppression from chronic stress increases disease susceptibility, leading to welfare harms from disease and chemical treatment cycles. Reduced access to feed in crowded conditions increases competition and subordinate fish welfare. The welfare improvement from reducing stocking density is well-supported by evidence, but economic pressures resist adoption. Premium welfare-certified producers operating at lower densities demonstrate commercial viability of welfare-improved systems.