There appears to be competition between two fish species for the record ocean depth for fish. The first is a species of cuskeel (family Ophidiidae) called Abyssobrotula galatheae. This 20 cm long fish was collected from the Puerto Rico Trench at a depth of 8,370 metres (27,455 feet). This deep sea dwelling fish species is listed by the Australian Museum online.
Recently, in fact today, The Times dated April 3, 2023, reports that the gelatinous snailfish (scientific name: Liparidae) has been filmed 8 km beneath the surface of the Pacific Ocean which the author claims is a record depth for any fish. Either they are correct or the Australian Museum is!
Australian researchers led by Prof Alan Jamieson recorded the snailfish at 8,336 metres which is about 5 miles below the surface. It was filmed in the Izu-Ogasawara oceanic trench of Japan.
Jamieson said that until his recording no one had ever filmed a fish at such depths. The pressure down there is 100 times that of the surface. Fish can live at this depth because they equalise the pressure inside their bodies with the pressure outside their bodies. This is in comparison to a submersible which has to protect against enormous pressure because there isn’t an equality of pressure within and outside the vehicle.
Jamieson believes that the snailfish is that a maximum depth at which any fish can survive. He said:
I think there’s probably no more significant increase in deaths to be had. I think from now on it will just be incremental; maybe five, maybe 10 m.
They trapped fish at 8,022 m. The adults snailfish is about 10 inches long (25 cm). Remarkably they can live in water which is a few metres deep as well as the deepest waters in the world.
The gelatinous nature of the fish means that it uses less energy to enhance survivability in a low food environment. They don’t have scales and skin which also mean using less energy and maintenance.
They have basically chipped away everything that a fish has that is kind of unnecessary. They use a gel rather than skin. Their bone density is very low, so they don’t need a lot of buoyancy. It’s like fish 2.0. It has refinements in every department. They sort of don’t fit the stereotype when you say to someone what are the deepest fish in the world. You see this ridiculous little pink thing.
In order to film the fish, they used a device equipped with sensors, cameras and bait together with a 220 pounds weight to ensure that it sinks to the bottom. They can reach depths of 11,000 m and they are controlled by acoustic signals rather than being tethered to a ship because it’s too deep.