High stocking densities in salmon aquaculture cages cause chronic stress and impair welfare through competition, injury, and physiological activation of stress pathways.
Chronic crowding stress in salmon aquaculture is a pervasive welfare problem that affects millions of fish across the industry. The physiological stress response triggered by overcrowding is not merely an inconvenience but a sustained impairment of normal biological function. Chronically stressed fish show reduced immune competence making them more susceptible to disease outbreaks that in turn cause further suffering. Reducing stocking densities below current regulatory maxima, even by modest amounts, demonstrably improves welfare indicators. Industry welfare certification schemes increasingly require density monitoring and limits.