ABSTRACT
The diversity of fish is larger than for any other vertebrate group. There are more fish species than of all the other vertebrates together. Fish also inhabit more diverse habitats than any other group of vertebrates, from Himalayan or Andean brooks at 4,000 meters to abyssal depths of at least 8,370 m, thus spanning an extremely wide range of hydrostatic pressures. In studying the effects of hydrostatic pressure on biological systems it is fundamental to experimentally dissociate those effects from those of other factors, though these interactions could be of obvious interest. Particularly difficult, at all levels of biological organization, is the distinction between hydrostatic pressure effects per se and increased gas partial pressures effects. As P. Sebert and A. G. Macdonald pointed out, it is a curious fact that few marine biologists in general, and fish biologists in particular, have responded to the extraordinary range of interesting hyperbaric phenomena which fish present.
