As of December 2014, the deepest-living fish known to man is the deep-sea snailfish, which was discovered at 26,000 feet below the ocean's surface. This snailfish, which was discovered at a nearly 5-mile depth in the Pacific Ocean's Mariana Trench, is likely a previously unknown species.
This new deep-sea snailfish species has unique physical characteristics among the snailfish, including a partially transparent body and a bulbous head that is said to be shaped like a dog's head. This six inch long, transparent body is said to be very delicate, and the fish moves in a way that looks similar to tissue paper gliding through water. Scientists believe that below 26,900 feet, fish would be unable to withstand the pressure and it's cells would likely be crushed.