Stocking density is one of the most significant determinants of welfare in fish aquaculture. High-density crowding causes chronic stress, increased aggression, impaired immune function, and elevated mortality across multiple species.
Stocking density represents a core commercial-welfare tension in aquaculture: higher density means more fish per volume of water but at significant welfare cost. Research consistently shows that welfare outcomes deteriorate as density increases beyond species-specific thresholds — more injuries, higher disease pressure, reduced feeding motivation, and greater suppression of subordinate individuals. Welfare-positive farms set maximum density limits based on welfare evidence rather than production economics alone, and proactively reduce density when behavioural or physiological indicators of stress emerge. Regulatory frameworks in countries like Norway and the UK set maximum density limits for salmon, but these are often contested as too high by welfare advocates.