Stocking density in fish aquaculture is one of the most significant welfare variables, affecting aggression, oxygen availability, disease transmission, and stress physiology simultaneously.
Stocking density is the master welfare variable in fish aquaculture, affecting virtually every other welfare parameter simultaneously. High density compromises water quality, increases disease pressure, amplifies aggression, and elevates stress physiology - a compound welfare harm. Regulatory density limits set evidence-based upper bounds, but the welfare-optimal density is typically lower than regulatory maximums. Consumer support for certification schemes specifying density limits creates market incentives for welfare-conscious stocking.