Crowding stress in farmed Atlantic salmon is one of the most significant welfare challenges in aquaculture, affecting behavior, physiology, and long-term health outcomes.
Crowding welfare in salmon aquaculture is both a direct welfare concern - fish experience behavioral restriction and social stress - and an indirect one, as crowding exacerbates disease transmission, reduces individual access to oxygenated water, and increases competition for resources. Reducing stocking densities to welfare-appropriate levels has production cost implications that industry has been slow to accept. Certification schemes that set stocking density ceilings based on welfare evidence rather than production optimization provide a framework for improvement. The growing scientific evidence that salmon experience aversive states at high density - demonstrated through choice behavior and stress physiology - strengthens the welfare case for density reduction.