Effects of pressure and pressure acclimation on activity and oxygen consumption in the bathypelagic mysid Gnathophausia ingens

Oxygen consumption and activity of the bathypelagic mysid Gnathophausia ingens acclimated at 1 and 75 atm were measured at 5 pressures (1, 75, 150, 225, and 300 atm). Pressure changes (both compression and decompression) caused transient increases in activity. Activity then declined and became relatively constant after approximately 2 h. Activity levels were higher at 75 than 1 atm. Higher pressures led to reductions in activity. Activity rates of 75-atm acclimated animals were lower at all pressures than those of 1-atm acclimated animals. The relationship between activity and oxygen consumption was not significantly different at all pressures for both acclimation groups. The importance of separating acute and chronic responses to pressure and the necessity for controlling activity in studies of pressure effects on oxygen consumption are discussed.