Salmon in aquaculture are often held at stocking densities that cause chronic stress. Understanding density effects on welfare informs better regulation and purchasing decisions.
Stocking density is the most tractable and impactful welfare variable in salmon aquaculture. At high densities, salmon cannot avoid contact with other fish, resulting in increased aggression and fin damage. Chronic crowding elevates cortisol levels, suppresses immune function, and increases susceptibility to disease. Lower density stocking improves individual welfare outcomes across multiple indicators simultaneously. The commercial pressure toward high density is driven by cage space costs, but the welfare improvement from density reduction is measurable and significant. Certification schemes that specify maximum density limits and require behavioral welfare monitoring provide consumers with confidence that welfare is genuinely considered in production.