Developmental Hypoxia Has Negligible Effects on Long-Term Hypoxia Tolerance and Aerobic Metabolism of Atlantic Salmon (Salmo salar)

Exposure to developmental hypoxia can have long-term impacts on the physiological performance of fish because of irreversible plasticity. Wild and captive-reared Atlantic salmon (Salmo salar) can be exposed to hypoxic conditions during development and continue to experience fluctuating oxygen levels as juveniles and adults. Here, we examine whether developmental hypoxia impacts subsequent hypoxia tolerance and aerobic performance of Atlantic salmon. Individuals at 8 degrees C were exposed to 50% (hypoxia) or 100%(normoxia) dissolved oxygen(DO) saturation(as percent of air saturation) from fertilization for similar to 100 d (800 degree days) andthenraisedinnormoxic conditions for a further 15 mo. At 18 mo after fertilization, aerobic scope was calculated in normoxia (100% DO) and acute (18 h) hypoxia (50% DO) from the difference between the minimum and maximum oxygen consumption rates ((M) over dotO(2min) and (M) over dotO(2max), respectively) at 10 degrees C. Hypoxia tolerance was determined as the DO at which loss of equilibrium (LOE) occurred in a constantly decreasing DO environment. There was no difference in (M) over dotO(2min), (M) over dotO(2max), or aerobic scope between fish raised in hypoxia or normoxia. There was some evidence that hypoxia tolerance was lower (higher DO at LOE) in hypoxiaraised fish compared with those raised in normoxia, but the magnitude of the effect was small (12.52% DO vs. 11.73% DO at LOE). Acute hypoxia significantly reduced aerobic scope by reducing (M) over dotO(2max), while (M) over dotO(2min) remained unchanged. Interestingly, acute hypoxia uncovered individual-level relationships between DO at LOE and (M) over dotO(2min), (M) over dotO(2max), and aerobic scope. We discuss our findings in the context of developmental trajectories and the role of aerobic performance in hypoxia tolerance.