The use of closed containment (CCS) or semi‐closed containment systems (S‐CCS) for Atlantic salmon Salmo salar aquaculture is under evaluation in Norway. One such system is the Preline S‐CCS, a floating raceway system that pumps water from 35 m depth creating a constant current through the system. Exposing fish to moderate water currents is considered aerobic exercise and it is often perceived as positive for fish welfare, gro...