Deepest Fish Caught on Camera
The short answer
A snailfish. In August 2022, a baited camera filmed a snailfish 8,336 m (27,349 ft) down in the Izu Ogasawara Trench, south of Japan. That's almost as deep as Mount Everest is tall. It is still the deepest fish on record.
The deepest fish ever actually caught came from shallower water: two snailfish trapped at 8,022 m in the Japan Trench, also in 2022. That is why the film always says "caught on camera".
Why the pressure doesn't crush it
Lots of fish carry a swim bladder, a pocket of gas that helps them float. Gas squashes easily, so deep sea pressure has something to crush. Snailfish have no swim bladder. The deep living ones are soft and jelly like, mostly water, with thin, soft bones.
Water barely squishes. With no gas space inside, the water in a snailfish's body pushes out just as hard as the ocean pushes in, so it keeps its shape. In the Mariana snailfish, another trench species, even the skull isn't fully closed. Scientists think that helps keep the pressure equal inside and out.
Why no fish goes deeper
Pressure also bends proteins, the tiny machines inside a fish's cells. Deep fish protect them with a molecule called TMAO, and the deeper a fish lives, the more TMAO it holds. After a fish dies, bacteria turn TMAO into trimethylamine, the source of the fishy smell.
Yancey and colleagues predicted that at about 8,200 m a fish would be as salty inside as the seawater around it, and couldn't hold any more. Researchers put the likely limit between 8,200 and 8,400 m. No fish has ever been seen below about 8,400 m (27,560 ft). The record fish, at 8,336 m, was just above that line.
What goes deeper than any fish
The deepest known spot in the ocean, the Challenger Deep in the Mariana Trench, is about 10,935 m down. That leaves about 2.5 km of water below the 8,400 m line where no fish has been seen. A single use plastic bag has been recorded at 10,898 m in the Mariana Trench. It is the deepest known piece of plastic.
Key numbers
| What | Number | Source |
|---|---|---|
| Deepest fish ever filmed, a snailfish in the Izu Ogasawara Trench (2022) | 8,336 m (27,349 ft) | University of Western Australia, 2023 |
| Deepest fish ever caught, two snailfish trapped in the Japan Trench (2022) | 8,022 m | University of Western Australia, 2023 |
| Depth where a fish was predicted to be as salty inside as seawater | about 8,200 m | Yancey et al. 2014, PNAS |
| Likely depth limit for any fish | about 8,200 to 8,400 m | NOAA Ocean Exploration |
| No fish has ever been seen below | about 8,400 m (27,560 ft) | Yancey et al. 2014, PNAS |
| Deepest known point, the Challenger Deep | about 10,935 m, give or take 6 m | Greenaway et al. 2021, Deep Sea Research I (NOAA repository) |
| Water below the 8,400 m line in the Challenger Deep with no fish ever seen | about 2.5 km | Our arithmetic from Greenaway et al. 2021, Deep Sea Research I (NOAA repository) |
| Deepest plastic bag on record, Mariana Trench | 10,898 m | Chiba et al. 2018, via National Geographic Education |
What the film simplifies
- The film's snailfish is the season's character. The record fish was an unidentified snailfish of the genus Pseudoliparis in the Izu Ogasawara Trench, and the soft bones and open skull come from studies of another species, the Mariana snailfish.
- "Air" stands in for the gas inside a swim bladder.
- "I'm... full." turns a prediction into a hard wall. The limit near 8,200 to 8,400 m is scientists' best estimate. The fact the film states is the observation: no fish has been seen below about 8,400 m.
- The film draws the record fish, the 8,400 m line and the bag in one trench, and the bag lands on a floor tagged 10,898 m. The record was set in the Izu Ogasawara Trench. The bag was found in the Mariana Trench, where the deepest point is about 10,935 m.
- Pressure with fists, the gear machines in her cells, the TMAO helpers and the doorman at the velvet rope are cartoon. She is only drawn above the 8,400 m line, and nothing alive is shown crushed.
For teachers
Runtime 1 minute 6 seconds · Topics: Deep sea life, Water pressure, Fish biology, Ocean trenches · Captions on YouTube · Full script below
Ask your class
Deep sea pressure crushes things that have air inside. Why doesn't it crush a snailfish?
Answer
A snailfish has no gas filled swim bladder. Its body is mostly water, which barely squishes, so the water inside pushes out as hard as the ocean pushes in.
No fish has been seen below about 8,400 m, and the Challenger Deep is about 10,935 m deep. How much water at the Challenger Deep lies below that line?
Answer
About 2.5 km: 10,935 m minus 8,400 m is 2,535 m.
Deep fish hold more TMAO the deeper they live. Why could that set a depth limit for fish?
Answer
TMAO protects a fish's proteins from pressure, so deeper fish need more of it. Scientists predicted that around 8,200 m a fish would be as salty inside as seawater and couldn't hold any more. That fits with no fish ever being seen below about 8,400 m.
The script
Pressure: Nobody gets to the bottom!
Snailfish: Ooh. A little to the left?
Host: That's the deepest fish ever caught on camera, almost as deep as Everest is tall!
Host: Down here, Pressure crushes almost everything.
Pressure: EVERYTHING!
Pressure: Anything with air inside, I win!
Pressure: So where's your air?
Snailfish: Air? I didn't bring any.
Host: Lots of fish float on a bubble of air. She's soft jelly, full of water.
Host: And water barely squishes, so it pushes back just as hard.
Pressure: That's CHEATING!
Pressure: ...You didn't break.
Snailfish: Why would I? You're just the water.
Snailfish: Ooh! Now I can go to the bottom!
Pressure: Fine. Round two.
Host: Deeper down, Pressure bends the tiny machines inside her cells.
Host: So she packs in TMAO, the stuff that turns into that fishy smell.
Pressure: Ew!
Host: The deeper she goes, the more she needs.
Snailfish: I'm... full.
Host: No fish has ever been seen below about 8,400 meters.
Pressure: Below here? Mine.
Snailfish: Hey! How come a BAG gets to go?
Sources
- A snailfish filmed at 8,336 m in 2022 set the depth record.University of Western Australia, 2023
- That 8,336 m snailfish is still the deepest fish on record.NOAA Ocean Exploration
- The Mariana snailfish has soft bones and a skull not fully closed.Wang et al. 2019, Nature Ecology & Evolution
- Deep fish build up TMAO to protect their proteins from pressure. No fish has been seen below about 8,400 m.Yancey et al. 2014, PNAS
- A plastic bag was found 10,898 m down in the Mariana Trench.Chiba et al. 2018, via National Geographic Education
- The Challenger Deep is about 10,935 m deep.Greenaway et al. 2021, Deep Sea Research I (NOAA repository)