Revealed: The deepest fish in the ocean

Thursday, November 30, 2017, 12:55 PM - If you're the kind of person who doesn't like swimming anywhere you can't see the bottom, try not to think too hard about the Marianas Trench.

That Pacific Ocean abyss is almost 11 km at its deepest, so deep the pressure would crush you instantly. You'd surely be forgiven for thinking it must be home to Leviathan or some other terror from the deep.

In reality, such life as there is in the lower parts of the trench is small, and this week we now have a better look at what researchers are calling the deepest fish in the ocean: The Mariana snailfish, or Pseudoliparis swirei.

"They don’t look very robust or strong for living in such an extreme environment, but they are extremely successful," post-doctoral researcher Mackenzie Gerringer at the University of Washington said in a release from the university.

Pseudoliparis swirei. Credit: Mackenzie Gerringer/University of Washington

The research team's description of the species was published this month in the journal Zootaxa, based on their examination of 37 specimens of the creature collected from 2014 to 2017, at depths ranging from 6,900 m to 8,000 m. However, earlier this year an expedition of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) released video footage of a cluster of snailfish at a depth of 8,178 m, the deepest any fish had ever been observed.

It looks pudgy and soft, but don't let that fool you. It's adapted to living in depths where the pressure is "like an elephant standing on your thumb," the researchers say. It's a apex predator as well, sucking in prey like crustaceans into its mouth (the image below, provided by the university, includes a CT scan of one in its belly. Note the outline of the snailfish's teeth).

Credit: Adam Summers/University of Washington

The researchers brought specimens to the surface by sinking waited cages, then pinging them with an acoustic signal to drop their weights and rise to the surface.

Even though the depths at which the specimens were collected was not even near the deepest parts of the trench, it still took the cages about four hours to reach their target depth, the researchers say. 

The deepest part of the Marianas Trench, known as Challenger Deep, is named after HMS Challenger, which made the first attempts at sounding out its depths in the late 1800s. The first manned exploration of the trench took place in 1960, using the deep-sea diving bathyscaphe Trieste.

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SOURCES: University of Washington | Zootaxa | JAMSTEC