The Mariana snailfish, Pseudoliparis swirei, is the deepest dwelling fish that’s been collected from the ocean floor. Mackenzie Gerringer, of the University of Washington’s Friday Harbor Laboratories, says: “They don’t look very robust or strong for living in such an extreme environment, but they are extremely successful.”
Snailfish are found at many different depths in marine waters around the world, including off the coast of San Juan Island, where Gerringer is continuing research on the family of fish. In deep water, they cluster together in groups and feed on tiny crustaceans and shrimp using suction from their mouths to gulp prey. Little is known about how these fish can live under intense water pressure, which at that sort of depth would be similar to an elephant standing on your thumb.
Source : practicalfishkeeping.co.uk