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

Summary

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.