A fish found off the coast of Japan could be the deepest ever recorded.

Japanese and Australian researchers filmed a Pseudoliparis snailfish at 8,336 metres depth, as part of an expedition to some of the world's deepest ocean trenches. This is 158m deeper than a previous recording made by the team in 2017, and close to the depth limit for all fish.

The fish were found during a two-month expedition of deep trenches around Japan in the north Pacific Ocean. The mission explored trenches at 8,000m, 9,300m and 7,300m depth, as part of a 10-year study into the deepest fish populations in the world.

University of Western Australia professor Alan Jamieson, chief scientist of the expedition, worked with a team from Tokyo University of Marine Science & Technology to deploy baited cameras in the deepest parts of the trenches.

“The Japanese trenches were incredible places to explore, they are so rich in life, even all the way at the bottom," he says. “We have spent over 15 years researching these deep snailfish; there is so much more to them than simply the depth, but the maximum depth they can survive is truly astonishing.

"We were finding them at increasingly deeper depths, just creeping over that 8,000m mark, in fewer and fewer numbers, but around Japan they are really quite abundant."

Snailfishes are a family of fish that has been successful in exploiting inhospitable habitats, such as cold and deep water, allowing them to rapidly evolve into a multitude of species. There are over 400 species of snailfishes, with the deepest living found to be the Pseudoliparis, which have adapted to life in a place where the pressure is 1,000 times greater than at sea level.

Today, much of the exploration of the deep sea is carried out with remotely operated vehicles and landers. This allows the depth of any observed fish to be more accurately reported, and captured on camera. In recent years, this has led to reliable records of fish from over 8,000 metres.

Jamieson said, “The real take-home message for me is not necessarily that they are living at 8,336m, but rather we have enough information on this environment to have predicted that these trenches would be where the deepest fish would be. In fact, until this expedition, no one had ever seen nor collected a single fish from this entire trench.”