Stocking density in rainbow trout farming is one of the primary determinants of welfare outcomes, affecting fin damage, aggression, disease susceptibility, and overall wellbeing in farmed salmonids.
Stocking density creates a welfare gradient in trout farming that is directly measurable through observable indicators. Fin damage - worn down, ragged fins caused by repeated collisions with tank walls and conspecifics in crowded conditions - serves as a visible welfare indicator at the population level. The more crowded the fish, the more fin damage. Elevated cortisol from chronic crowding stress translates into suppressed immune function, increased disease incidence, and compromised growth - welfare and production consequences aligned in the same direction. The economic case for welfare-appropriate stocking densities is stronger in trout than in some other farmed species because the welfare harms of overcrowding directly reduce the economic value of production through disease and mortality losses.