Rainbow trout are the most widely farmed salmonid in Europe and North America. Welfare challenges center on stocking density, disease, and harvest methods.
Trout welfare in aquaculture is shaped primarily by stocking density and water quality management. At commercially common densities, trout show elevated stress indicators, increased fin damage from conspecific aggression, and suppressed immune function that increases disease susceptibility. The welfare and production efficiency arguments align in favor of lower stocking densities, as overcrowded trout grow less efficiently than those maintained at welfare-optimized levels. Slaughter welfare varies significantly — percussion stunning followed by gill cutting is more humane than CO2 exposure, which causes distress before insensibility. Welfare certification schemes for trout are developing, with some requiring minimum water quality parameters and stocking density limits.