Atlantic salmon in aquaculture are held at densities far exceeding natural conditions, causing chronic physiological stress that impairs immune function, increases aggression, and reduces welfare throughout the production cycle.
The welfare evidence against high-stocking-density salmon farming is substantial and consistent. Chronic crowding stress is not a transient acute stressor — it is a persistent condition that reshapes physiology, behaviour, and health outcomes over weeks and months. Chronically stressed salmon show immunosuppression, making them more susceptible to sea lice infestations, bacterial infections, and gill disease — all of which cause further suffering. Behavioural indicators of crowding stress include increased aggression, reduced feeding, and abnormal swimming patterns. The fish cannot escape or seek relief. Lower-density farming (below 20 kg/m3) demonstrably improves welfare outcomes but reduces profitability per unit of water volume. Welfare-forward certification schemes now set density limits as a key criterion. Consumer demand for certified lower-density salmon products is one of the most direct levers available to improve conditions for millions of farmed fish.