When I picture what an alien might look like, qualities like a translucent head and large green eyes are among the first to come to mind. It’s interesting to note that these same qualities can be found right here on Earth in the deep sea. 

Barreleye fish are decidedly mysterious fish with strange eyes. These fish can be found in the northern Pacific Ocean, although it’s not exactly easy to spot one. For years, scientists had never seen a barreleye fish alive and in its natural habitat—that is, until a ROV (remotely operated vehicle) operated by MBARI (Monterey Bay Aquarium Research Institute) successfully recorded this rare fish. (For the record, they’ve recorded many other weird and wild deep-sea animals, including vampire squid and dragonfish).

Clearly there are many fascinating deep-sea creatures to explore, but, for now, stick around as we dive into the elusive barreleye fish.

Appearance

The barreleye fish is typically dark gray or black and relatively small, ranging in size up to about six inches. This strange-looking fish is well known for its amazing eyes: two large green tubes or barrels that naturally rest looking upwards (although they can also rotate to face forward which can help them better see their next meal). This fish also features a translucent dome-like forehead that acts as a fluid-filled barrier for its sensitive eyes. The two dark circles that look like they should be eyes are in fact nares, the equivalent to the barreleye’s nose, where their olfactory organs are located.

Habitat

This fascinating fish lives in the ocean’s twilight zone at a depth of 2,000-2,600 feet, although I could also see it featured in Rod Serling’s The Twilight Zone. (It’s got that creepy factor.) Within this ocean twilight zone, sunlight is almost non-existent. Like many deep-sea creatures, such as the amazing glass octopus, barreleye fish are equipped with special features that help them live in darkness. These features include the barreleyes glowing green eyes that help them see in the dark, or the bioluminescent substance vampire squid release to deter potential predators. 

Reproduction

The barreleye fish is a solitary species, and there is little known about their reproduction. Scientists believe they release eggs and sperm in pelagic spawning, which means the fertilized eggs are dispersed in open water.

Feeding

A typical day for a barreleye fish consists mainly of sitting relatively still in the deep sea, looking up for their next meal. Barreleyes have large fins that allow them to smoothly hover along, barely moving the water surrounding them. These fins are used to stabilize them while scanning the water above for food, mostly zooplankton. However, scientists also believe that these stealthy fish tend to steal their prey from siphonophores, which are long jelly-like stinging creatures. Luckily, barreleyes have their translucent domes to shield their eyes from these creatures’ powerful stinging cells.

More to explore

It’s official: Having a translucent head sounds kind of awesome. Still, despite all we already know about the fascinating barreleye fish, it’s clear that we’ve only just begun to learn about them and many other deep-sea creatures. It’s imperative that we continue to explore the unknown, if only so we can know just how to protect these creatures from human impacts. Ready to advocate for our ocean wildlife including some wonderfully rare deep-sea creatures? Visit Ocean Conservancy’s Action Center and check out our Wildlife Library for more translucent alien-like friends.