Recirculating aquaculture systems (RAS) offer potential welfare improvements for farmed salmon over traditional net pens, but they introduce new challenges around water quality management and stress from artificial environments.
RAS salmon farming presents a mixed welfare picture. The elimination of sea lice — which cause painful lesions and immune suppression in net-pen fish — is a significant welfare gain. The controlled environment removes weather-related stressors and predator-induced panics. However, RAS introduces its own challenges. CO2 accumulation (hypercapnia) in poorly managed systems causes chronic physiological stress and behavioral changes. High stocking densities can still cause aggression and fin damage. The artificial, stimulus-poor environment may cause chronic boredom or frustration compared to the more complex sensory environments of net pens or rivers. Water quality failures can rapidly become catastrophic, with potential for mass mortality events. Best-practice RAS operations with rigorous monitoring represent a welfare improvement over conventional net pens, but only if CO2 control and density management are prioritized.