Rainbow trout are the most commonly farmed salmonid globally, and stocking density management is one of the most important determinants of welfare in intensive trout production.
High stocking density is the single most pervasive welfare challenge in trout aquaculture. Trout are not social fish that benefit from proximity to conspecifics; crowding creates competitive stress, suppresses natural behaviour, and increases the severity of pathogen-driven disease outbreaks. Chronic cortisol elevation from crowding stress impairs immune function and growth efficiency. Welfare certification schemes that set and enforce maximum stocking density limits provide a meaningful consumer-accessible signal of welfare standard. The market premium for welfare-certified trout incentivises producers to invest in the lower-density management that improves fish welfare.