Effects of long-term exposure to hydrostatic pressure per se (101 ATA) on eel metabolism

Oxygen consumption, MO2, has been measured in yellow freshwater eels (Anguilla anguilla L.) exposed in normoxic conditions for 31 days at a hydrostatic pressure of 101 ATA (atmosphere absolute; 1 ATA = 0.1 MPa) using a high pressure water circulation system. The results (series I) show that from a maximal value observed at the end of compression, MO2 decreases exponentially with time (tau congruent to 1.4 days) then reaches a steady state (MO2 = 0.67 +/- 0.05 mmol.h-1.kg-1) at a lower level than observed at 1 ATA before compression (MO2 = 1.04 +/- 0.03 mmol.h-1.kg-1). These observations are in agreement with the hypothesis that shallow water fish are able to adapt to pressure; the possible mechanisms of this adaptation are discussed. Results from a second experimental series show that fish previously submitted to pressure for 1 month (then decompressed to 1 ATA) adjust faster to a new pressure exposure (4 days later) than fish that have never experienced pressure exposure. This observation suggests that the mechanisms triggered by long-term pressure exposure could persist, at least in part, for several days after decompression to atmospheric pressure.