Recirculating aquaculture systems (RAS) offer potential welfare and environmental advantages over sea cage salmon farming, but require careful management to avoid specific welfare risks from intensive indoor conditions.
Recirculating aquaculture systems represent a genuine potential advance for salmon welfare by eliminating sea lice and providing environmental control, but their welfare promise is only realized when properly managed. High stocking densities in poorly designed or managed RAS produce crowding stress comparable to or exceeding sea cage systems. CO2 accumulation, which can develop rapidly in sealed recirculating systems, causes acute respiratory distress. Stereotypic circular swimming patterns in RAS salmon are a documented welfare concern linked to the monotonous circular tank environment that provides no environmental heterogeneity. Well-designed RAS that incorporate lower stocking densities, environmental enrichment, and rigorous water quality monitoring represent the most welfare-positive current production option for Atlantic salmon.