Stocking density in salmon sea cages is one of the most important determinants of welfare. High crowding creates physiological stress, increases aggression, and elevates disease susceptibility in ways that harm both fish welfare and farm productivity.
Crowding stress in farmed salmon operates across multiple timescales. Chronic sub-acute crowding at high but legally permissible densities creates background physiological stress that elevates cortisol, suppresses immune function, and creates conditions for disease outbreaks. The welfare cost of this chronic stress is difficult to quantify precisely but is well-supported by experimental evidence. Acute crowding during management operations — vaccination, lice treatments, harvest — adds intensive short-term stress on top of chronic background levels. Welfare-conscious aquaculture management treats crowding as a primary welfare parameter, using biomass monitoring systems to predict and prevent threshold exceedances, and adopting voluntary density targets below regulatory maxima. The alignment between welfare-positive stocking and economic outcomes — lower disease rates, better growth efficiency, reduced mortality — creates commercial incentives that strengthen the welfare case for lower density production.