The ocean is home to a myriad of creatures. Giant squids, monstrous sharks, and graceful whales all make their homes in the ocean. There are weirder animals too, like anglerfish, the red-lipped batfish or the dumbo octopus. And don’t forget about dear old Cthulhu. Still, I think today’s group of animals make it right up there as some of the ocean’s most bizarre creatures.

There are eight genera of barreleye fish (also known as spook fish), grouped together in the family Opisthoproctidae. They are found in the Pacific, Atlantic, and Indian Oceans, in tropical and temperate waters. Barreleye fish are found in deep waters, probably because they don’t want anyone to see how ugly they are.

A lovely drawing of a species of barreleye. You can clearly see this fish’s bizarre eyes. Image by Brauer, A., Public domain, via Wikimedia Commons

Barreleye fish come in three body types: short and stout, long and thin, and somewhere in the middle. Most species are dark coloured, with pretty silver scales adorning their bodies. They are relatively small fish, with most being under 20 cm in length, and the largest reaching an average of 50 cm.

By far the most unusual (and creepy) part of barreleye fish are their eyes. Their eyes are enclosed in tubular ‘barrels’ (hence the name), and usually point directly upward. Barreleye fish hang out just where light from above fades into darkness, and stare upwards looking for silhouettes of prey above them. Their eyes have large lenses and retinas, to collect as much light as possible in their dark environments. One species even uses mirrors in its eyes to help focus images, the only vertebrate known to do so.

Obviously these eyes are very important to barreleye fish, otherwise they wouldn’t be named after them (that’s how taxonomy works, right?). To protect their precious eyes, barreleye fish have a transparent dome making up the top half of their heads. Barreleyes are thought to steal food from siphonophores, which are equipped with nasty stinging cells. The domed heads of barreleyes protects them from these stingers, as well as letting in more light so the fish can see as much as possible.

Some species of barreleye have nice partnerships with bacteria to create bioluminescence. The lights are placed on the fish’s bellies, providing them with camouflage from predators in the depths. The light shining down from the barreleye blends into the light coming form above, disguising the fish and making them hard to catch. Pretty clever, right?

I don’t think I’d ever want to go into the deep ocean. I like watching documentaries on what’s down there, but all the creatures that live in the depths are so weird I don’t think I could handle it. At least they give me good material for blog posts!

Cover image by Emma Kissling, Public domain, via Wikimedia Commons