Stocking density in fish aquaculture directly affects welfare outcomes, with overcrowded fish showing elevated stress hormones, increased aggression, injury, and disease susceptibility that compound over the production cycle.
Stocking density is the single most manipulable welfare variable in fish aquaculture. Above threshold densities, welfare indicators — cortisol, aggression, fin damage, disease susceptibility — deteriorate measurably and progressively. The economic argument for high density is challenged by evidence that lower densities can produce equivalent total yield with better individual fish condition. Welfare-certified aquaculture that sets species-appropriate density limits demonstrates that welfare and productivity are not fundamentally opposed.