High stocking densities in fish farms cause physiological stress, increased aggression, and disease vulnerability across virtually all farmed species — from salmon to tilapia.
Chronically elevated cortisol in densely stocked fish suppresses immune function, impairs reproduction, and reduces growth efficiency. Fish under crowding stress show fin-biting, reduced feeding, and abnormal shoaling behaviour. The paradox is that reducing stocking density improves both animal welfare and production efficiency — yet adoption is slow because of higher facility costs per kilogram produced.