ABSTRACT
All aerobic animal species living in terrestrial or marine habitats are concerned about reactive oxygen species (ROS). Indeed, reactive nitrogen species (RNS) such as ROS are produced as normal by-products of cellular metabolism. This chapter deals with the relationships between ROS/RNS and pressure not only in mammals through the hyperbaric oxygenation and anoxia-reoxygenation in diving species but also in fish since some of them are confronted with high hydrostatic pressure. Two to three million years ago, oxygen began to appear at high concentrations in the biosphere when photosynthetic organisms were able to photolyze water. Then, oxygen progressively became a major environmental element for mitochondrial energy production via the oxidative phosphorylation in all aerobic organisms. The term ROS refers not only to oxygen free radicals, but also to non-radical active species such as hydrogen peroxide (H2O2), which is also susceptible to generate free radicals through chemical reaction.
