Atlantic salmon in sea cage aquaculture are held at stocking densities that cause significant chronic stress. Understanding the physiological and behavioural consequences of crowding is essential for improving salmon welfare.
Crowding in salmon aquaculture is a fundamental and largely preventable welfare problem. The economic incentive to maximise production per cubic metre of water conflicts directly with what salmon need for good welfare. Evidence consistently shows that salmon prefer and thrive at lower densities, and that commercial densities cause chronic physiological stress. The welfare consequences include not just measurable stress hormones but reduced immune function making fish more susceptible to sea lice infestation and disease - creating a cycle where poor welfare increases disease burden, which then requires treatments that impose further welfare costs. Reducing stocking density would improve welfare, reduce disease, and likely improve product quality - but requires industry willingness to accept lower volume per production unit.