Life under 1,100 atmospheres
The Mariana snailfish (Pseudoliparis swirei) lives in the hadal zone of the Mariana Trench, a region deeper than Mount Everest is tall. At depths of 6,198 to 8,178 meters, the hydrostatic pressure is immense—more than 1,100 times greater than at the surface, equivalent to an elephant standing on your thumb. To survive, the fish has a suite of remarkable adaptations. Its body is small and pinkish-translucent, with no scales. The skin is so clear that its liver is visible.
Important to its survival is a molecule called trimethylamine N-oxide (TMAO). This organic compound permeates the fish's cells and counteracts the effects of extreme pressure on proteins, preventing them from being distorted and rendered non-functional. The concentration of TMAO in marine animals increases with depth, and the Mariana snailfish has the highest levels ever recorded in a fish. This chemical stabilization is so effective that scientists believe the 8,200-meter mark may represent a biochemical limit for fish, beyond which they cannot accumulate enough TMAO to survive. Other adaptations include a skeleton that is not fully ossified, meaning its bones are more cartilaginous and flexible. The skull bones are not completely fused, which helps to equalize the immense pressure. Unlike many fish, it has no swim bladder, a gas-filled sac that would be crushed at these depths.