Stocking density in salmon farms significantly affects fish welfare through water quality, injury risk, and chronic stress. Evidence-based density standards are essential.
Stocking density is one of the most important and modifiable determinants of welfare in farmed salmon. At high densities, fish compete for optimal water positions, experience increased aggression, suffer more fin and scale injuries, and have limited ability to perform natural behaviours. Water quality deteriorates as fish load increases, reducing dissolved oxygen and increasing carbon dioxide and metabolic waste concentrations. Chronic crowding stress activates the hypothalamic-pituitary-interrenal axis, suppressing immune function and increasing disease susceptibility. Welfare-conscious aquaculture operations maintain lower densities than legal maximums and monitor welfare indicators including mortality rates, fin damage, and swimming behaviour.