Swimming at Increasing Speeds in Steady and Unsteady Flows of Atlantic Salmon Salmo salar : Oxygen Consumption, Locomotory Behaviour and Overall Dynamic Body Acceleration.

Simple Summary: Temperature rises, competition for coastal resources, and stricter regulations are forcing finfish farms to move from sheltered shore locations to more exposed open ocean areas. But knowledge is lacking on how the flow conditions in sea pens in these open areas will affect their physiological performance. To evaluate the swimming performance under steady and unsteady flows at increasing flow speeds, post-smolt Atlantic salmon were induced to swim in a swim tunnel under laboratory conditions. Oxygen consumption and locomotory behaviour were monitored, and overall dynamic body acceleration (ODBA) was recorded by implanted acoustic sensor tags. ODBA correlated strongly with oxygen consumption, allowing the application of such sensor tags to predict energy use. Swimming in unsteady flow is energetically more costly for post-smolt Atlantic salmon than when swimming in steady flow. The swimming performance of cultured finfish species is typically studied under steady flow conditions. However, flow conditions are mostly unsteady, for instance, as experienced in sea pens in exposed sea areas. Using a Loligo swim tunnel, we investigated the effects of swimming in steady and unsteady flows at increasing swimming speeds on post-smolt Atlantic salmon. Oxygen consumption (MO2), locomotory behaviour, and overall dynamic body acceleration (ODBA), as determined with implanted acoustic sensor tags, were compared between both flow conditions. Results were obtained for mean swimming speeds of 0.2 to 0.8 m.s−1 under both flow conditions. Sensor tags that were implanted in the abdominal cavity had no significant effects on MO2 and locomotory parameters. The MO2 of fish swimming in unsteady flows was significantly higher (15–53%) than when swimming in steady flows (p < 0.05). Significant interaction effects of ODBA with flow conditions and swimming speed were found. ODBA was strongly and positively correlated with swimming speed and MO2 in unsteady flow (R2 = 0.94 and R2 = 0.93, respectively) and in steady flow (R2 = 0.91 and R2 = 0.82, respectively). ODBA predicts MO2 well over the investigated range of swimming speeds in both flow conditions. In an unsteady flow condition, ODBA increased twice as fast with MO2 compared with steady flow conditions (p < 0.05). From these results, we can conclude that (1) swimming in unsteady flow is energetically more costly for post-smolt Atlantic salmon than swimming in steady flow, as indicated by higher MO2, and (2) ODBA can be used to estimate the oxygen consumption of post-smolt Atlantic salmon in unsteady flow in swim tunnels. [ABSTRACT FROM AUTHOR]