In the dark abyss of the Pacific Ocean’s Mariana Trench, about 27,000 feet down, lives the deepest fish ever discovered. The Mariana snailfish is a tadpole-like 2- to 4-inch creature that’s much more successful than it looks; this small, translucent fish appears to be the top predator of her underworld.
Human divers cannot go where Mariana snailfish swim, but an international research team did sink cameras and traps deep into this difficult-to-reach and rarely-studied area over three years. The traps took four hours to fall from the ocean’s surface to where this snailfish swims. When raised, they held healthy, well-fed snailfish, and the camera footage had captured their deep sea activities.
[qz.com]
It's just amazing that anything can live at that pressure and darkness.