Live transport of Atlantic salmon in open and closed systems: Water quality, stress and recovery

The goal of the study was to compare open and closed transports of adult Atlantic salmon in terms of water quality and stress (blood chemistry and white muscle biochemistry). The study comprised of two phases: (i) live transport from a commercial farm by vessel (open system) and vehicle (closed system) to flow-through laboratory tanks and (ii) after post-transport recovery, simulated live transports in open and closed systems. The stress reaction the salmon experienced during transfer from fish farm to laboratory tanks was severe. Some delayed mortalities were observed possibly related to extreme acidosis. The fish were left to recover for 65 h before the simulated open and closed transports were carried out. By then, they had not yet fully recovered to baseline levels. The simulated transports did not cause excessive stress reactions relative to the partially recovered fish. However, deteriorating water quality during closed transport eventually affected fish behaviour where fish welfare could be questioned. The main finding was that crowding and transport due to commercial transport overshadowed stress-related results obtained during the laboratory study. The results may also be viewed as effects of repeated fish handling operations, a typical feature of salmon farming.