Atlantic salmon in net pen aquaculture are typically held at high stocking densities that cause chronic stress, suppress immune function, and compromise their welfare throughout the production cycle.
The welfare implications of crowding in salmon farms are cumulative and chronic. Individual fish at the bottom of dominance hierarchies experience persistent aggression, reduced access to food, and disproportionate disease burden. Chronic stress suppresses immune function, increasing vulnerability to sea lice and bacterial infections that themselves cause further welfare harm. The interaction between stocking density, water quality, feed distribution and social dynamics is complex - maximum density limits alone are insufficient without attention to distribution and habitat complexity within pens.