Recirculating aquaculture systems recycle water to allow fish farming with minimal environmental discharge. Their welfare implications differ importantly from open-net pen farming and require specific attention.
RAS welfare profiles differ from open-net pen systems in important ways. The elimination of sea lice reduces one significant welfare challenge. However, the extremely high stocking densities possible in RAS can create chronic crowding stress. Engineering failures - pump failures, filtration problems, power outages - can cause rapid water quality deterioration causing mass distress events. The absence of tides, currents and natural environmental variation creates a sensory-impoverished environment. Behavioral indicators of stress including reduced feeding, increased aggression and stereotypic swimming are observable in RAS salmon. The welfare of RAS salmon compared to sea cage salmon depends heavily on specific management practices rather than the technology type alone - RAS is neither inherently better nor worse from a welfare perspective.