Stocking density is one of the most significant determinants of farmed fish welfare, with overcrowding causing chronic stress, aggression, injury, and suppressed immune function across aquaculture species.
Crowding imposes multiple simultaneous welfare costs on farmed fish: physical injury from conspecific aggression and contact with tank walls, physiological stress from chronic cortisol elevation, reduced access to food and preferred water conditions, and behavioural restriction from inability to perform normal spacing and swimming patterns. These harms compound over time — a fish subjected to high density throughout its grow-out period experiences cumulative welfare damage. The welfare case for lower stocking densities is strong and supported by evidence from cortisol studies, injury assessments, and behavioural research. Market incentives currently push toward higher densities to maximise production per volume of water, making regulatory or certification-based density limits essential.