The diversity of fish is larger than for any other vertebrate group. There are more fish species (over 25,000) 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 (Nielsen, 1977), thus spanning an extremely wide range of hydrostatic pressures. This means that members of this taxonomic group experience a range of pressure from less than 0.1 MPa up to more than 82 MPa (1 atm = 1 bar = 14.7 psi = 0.10 MPa).