What is the deepest known fish habitat, where the Mariana snailfish has been observed?

The Mariana snailfish has been observed in the hadal zone, the deepest region of the ocean. Hadal habitats occur mainly in ocean trenches at depths greater than 6,000 metres, where pressure is immense and sunlight never reaches.

Mariana snailfish have been recorded at depths of about 8,000 metres in the Mariana Trench. Their soft, gelatinous bodies and specialised physiology help them function under pressures hundreds of times greater than those at the surface. They feed on small crustaceans and other prey on the trench floor.

The abyssal zone is another deep-ocean region, but it generally covers the seafloor from about 3,000 to 6,000 metres. The hadal zone is specifically associated with the deepest trenches. “Hadal” comes from Hades, the ancient Greek underworld, reflecting the darkness and extreme conditions of these environments.