A scientific expedition near Japan caught footage that marks a new record for the deepest-dwelling fish ever found.
The Pseudoliparis, or snailfish, was trolling the ocean floor at a record 8,336 meters — 158m deeper than a previous record for the same species in 2017.
The find occurred in the Izu-Ogasawara Trench, southeast of Japan. An autonomous deep ocean vessel captured the footage last August. The craft was operating in conjunction with the DSSV Pressure Drop, crewed by a team from the Minderoo-UWA (University of Western Australia) Deep-Sea Research Centre and the Tokyo University of Marine Science and Technology.
The snailfish was able to survive immense pressure. At eight kiometers deep, water pressure reaches 80 megapascals — 800 times the amount at the ocean’s surface. (For another comparison, that’s nearly as deep as Mount Everest is high.)
In fact, the species was more or less thriving in those extreme waters. The team also baited the submersible farther up, at 8,022m, and captured a few snailfish — the first ever fish recovered from deeper than 8,000m, it said.
Snailfish captured from deeper than 8,000 m. Photo: screenshot
How the fish survives those pressures
The species can live at such depths partly because it has no swim bladder. The specialized organs house gas in most fish, to regulate buoyancy. But they’re not found in the gelatinous bodies of snailfish, which helps them withstand the crushing pressure of the deep.
“They’re speciated into every corner of the globe,” expedition leader Alan Jamieson said in a Reuters interview. “These [snailfish] you see in the video are 1,000m deeper than what you would normally think of as being a ‘deep-sea fish.’”
Far from the varyingly nightmarish creatures that usually inhabit the ocean’s deepest nooks and crannies, snailfish bear more resemblance to tadpoles. In fact, the fishes’ ancestors used to thrive in shallow waters like river estuaries.
The lone, record-setting fish that appeared on camera was a juvenile, and Jamieson told The Guardian there’s a reason for that. Diving farther than many deep-sea predators comes with its advantages.
“Because there’s nothing else beyond them, the shallow end of the range overlaps with a bunch of other deep-sea fish, so putting juveniles at that end probably means they’ll get eaten,” Jamieson said. But when you get down to the mega-depths, 8,000-plus metres, he adds, there are few if any predators.
Rock bottom?
The discovery could also signal the limit of any fish’s deep-sea survivability. As early as 2014, Jamieson’s team hypothesized fish could not live deeper than 8,200-8,400m below the surface. Fish all need osmolyte, a chemical found in their cells, to counteract pressure — and according to The Guardian, the Minderoo-UWA researchers are finding the limit at which any fish can produce it.
“When you get to about 8,200 to 8,400m — the variation is probably temperature-dependent…it reaches what’s called isosmosis, which means you can’t increase the concentration of that fluid in the cells anymore,” Jamieson told the outlet. “After all these years of hammering away at this [theory], it seems to be pretty solid.”
Perhaps astonishingly, 25% of the ocean actually lies below 8,400m. Challenger Deep is rock bottom at around 11,000 m. What’s down there? We don’t really know.
Fewer people have visited the ocean’s bottom than the surface of the moon.
