The species - a type of snailfish of the genus Pseudoliparis - was filmed swimming at 8,336m (27,349ft).
It was filmed by an autonomous "lander" dropped into the Izu-Ogasawara Trench, south of Japan.
The lead scientist said the snailfish could be at, or very close to, the maximum depth any fish can survive.
BBC reports the previous deepest fish observation was made at 8,178m, further south in the Pacific in the Mariana Trench. This discovery therefore beats the depth record by 158m.