At a depth of more than eight kilometres underwater, a new record for the deepest fish ever filmed and the deepest fish ever caught has been set by scientists from The University of Western Australia and Japan.

“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.”

UWA Professor Alan Jamieson

In August 2022, the research ship DSSV Pressure Drop undertook a two-month expedition to the deep trenches around Japan in the north Pacific Ocean. 

The mission was to explore the Japan, Izu-Ogasawara and Ryukyu trenches at 8,000m, 9,300m and 7,300m deep respectively as part of a 10-year study into the deepest fish populations in the world.

UWA Professor Alan Jamieson, founder of the Minderoo-UWA Deep Sea Research Centre and chief scientist of the expedition, worked with a team from the Tokyo University of Marine Science and Technology to deploy baited cameras in the deepest parts of the trenches.

In the Izu-Ogasawara Trench, south of Japan, the team managed to film the deepest record of a fish, the unknown snailfish species of the genus Pseudoliparis, at a depth of 8,336m. 

A few days later, in the Japan Trench the team collected two fish in traps from 8,022m deep. These snailfish, Pseudoliparis belyaevi, were the first fish to be collected from depths greater than 8,000m and have only ever been seen at a depth of 7,703m in 2008.

“The Japanese trenches were incredible places to explore; they are so rich in life, even all the way at the bottom,” Professor Jamieson said. 

Image: Images of the snailfish alive from 7500-8200m in the Izu-Ogasawara Trench.

“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.”

“In other trenches such as the Mariana Trench, 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.”

Despite the large and somewhat lively population of fish living at these depths, the solitary individual that claims the accolade of the deepest ever found, was an extremely small juvenile. Snailfish tend to be the opposite of other deep-sea fish where the juveniles live at the deeper end of their depth range.

“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,” Professor Jamieson said.

The expedition was supported by Victor Vescovo at Caladan Oceanic and Inkfish.