Effects of hydrostatic pressure on energy metabolism and osmoregulation in crab and fish

This review will focus on the effects of hydrostatic pressure on the oxidative metabolism and on the energy production of the eel Anguilla anguilla, in comparison with the results of investigations conducted on the other powerful euryhaline species, the chinese crab Eriocheir sinensis. Anguilla and Eriocheir were chosen as being both aquatic ectotherms with comparable life modes, the eel being however ''preadapted'' to high pressure while the crab normally never encounters high levels of pressure during its life cycle. Comparison between both species should lead to better knowledge of the biological effects of hydrostatic pressure per se. Experimental evidence suggests that the oxygen consumption MO(2) decrease observed in both animal species during exposure to 101 ATA hydrostatic pressure and which follows a transient increase, likely results from a decrease in O-2 use at the cell level. That idea of an alteration of aerobic metabolism during the first hours under pressure is substantiated by a set of experiments on the eel. However, results indicate that, after some days under pressure, the shallow water fish is quite able to acclimate perfectly to high pressure. The hypothesis that pressure induces a state resembling histotoxic hypoxia during the first hours of exposure is put forward and discussed. The second part of the review focuses on some results showing that osmoregulation is also concerned with hydrostatic pressure. Results obtained on the freshwater eel clearly establish the occurrence of a Nai balance impairment at the tissue level induced by a long-term (30 days) exposure to pressure. It is interesting to point out that this impairment occurs at the same time when a new state of energetic metabolism results from adjustments of intertissue coupling of anaerobic and aerobic metabolisms induced by pressure. It is shown that the physiological processes involved in the control of the hydromineral balance in the chinese crab (which never experiences high pressure exposure in the course of its life cycle) are outstandingly resistant to pressure by comparison with other crustaceans like the crayfish and the shore crab. Disturbances in hydromineral balance and energetic metabolism in the chinese crab are rapidly resorbed and adjusted to a new state of activity. Copyright (C) 1997 Elsevier Science Inc.