Stocking density is one of the most fundamental welfare parameters in fish farming, with crowding causing physiological stress, injury, and disease susceptibility across all farmed species.
Stocking density is a proxy welfare parameter that interacts with water quality, feeding management, and social dynamics. High density amplifies the welfare impact of other stressors - poor water quality at high density is more damaging than at low density, and aggressive interactions are more frequent when fish cannot establish stable spatial positions. The welfare cost of crowding operates chronically: elevated cortisol over weeks and months suppresses immune function, reduces growth efficiency, and predisposes to secondary disease. The welfare optimum varies by species - some fish are more tolerant of conspecifics than others - but reductions in stocking density consistently improve measurable welfare indicators across all farmed species studied.