Recently a type of snailfish was found in the Mariana Trench at a depth of 8.143 km – which makes it the deepest living fish ever seen. In honour of this sighting, I’m going to write about snailfish, a group of fairly ugly and strange fish.

Snailfish live in a number of different habitats, from shallow waters to the ridiculous depths described above. They can be found in waters ranging from the Arctic to Antarctic Oceans, with different species preferring a variety of different living conditions. Some snailfish live inside scallops, while others like kelp forest. Still other species like to hang out in muddy ocean bottoms. There are 361 known species of snailfish, in 30 genera.

Snailfish are pretty ugly.  Image source: Wikipedia
Snailfish are pretty ugly. Image by Public Domain,

Why they are called snailfish I do not know – if anything they should be called ‘slugfish’ because they look a whole lot more like slugs. They range in size from 5 cm to over 70 cm and 11 kg. Snailfish have small eyes (which are sometimes non-existent in deep sea species), and don’t have any scales, further making them look like slugs. The deep sea species navigate the darkness of their world by using vibration receptors on their nose. The dorsal and anal fins merge with the fish’s tail, giving the snailfish a tadpole-like appearance. The pectoral fins, on the other hand, are large and are snailfish’s main way of moving.

Reproduction in snailfish varies from species to species. One type of snailfish is a mouth-brooding species, where the males hold the eggs in their mouths until they hatch. Another species lays its eggs in the gill cavities of king crabs, of all places. I’m not sure how the crab feels about this, but it seems to work well for the snailfish.

Unfortunately the deep sea varieties of snailfish are very poorly studied – it’s pretty hard to find fish in the open ocean where there’s actual light, so finding one in the dark depths must be nearly impossible. Still, hopefully we will find a way to study the deep snailfish, because deep sea animals are some of the most interesting out there. They have to find a way to survive the crazy pressures that exist in the deepest waters in world. I’m not sure how the snailfish does it, but somehow they’ve managed to be the deepest fish ever found.

Cover image by ゆうき315, CC BY-SA 4.0, via Wikimedia Commons