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Today on Animal Fact Files, we’re discussing barreleyes. Dive deep with us each week by subscribing to keep up with new animal episodes. Barreleye is an apt name for these deepsea fish because have some seriously strange eyballs. Heck, eyeballs isn’t even the best way to describe them, they’re more like eye tubes. A barreleye’s eyes are excellent at finding animals swimming above them in the water column where nearly imperceptible traces of light create a silhouette shadow of potential prey items for these freaky fish. As they sit almost motionless in the water, an act aided by their large, flat fins, their eyes face upwards. In this way, the barreleye’s eyes act like binoculars giving it a good idea of what’s swimming over them, but a relatively small field of view. It’s kind of like if you held binoculars to your own eyes, or even two used up toilet paper rolls. You can clearly see where the rolls are directed, but everywhere else is blocked out. It was once believed that barreleye eyes were fixed in this upturned position, but it has seen been observed that barreleyes can rotate their eyes within the transparent, fluid filled dome covering their heads. Once they do find a morsel in the form of free floating jellyfish and plankton, or even a crustacean already caught in another animal’s tentacles, a barreleye adjusts its eyes forward and rushes in to meet its meal.

Just to be clear, there are actually multiple species of fish commonly known as barreleyes swimming in the Pacific, Indian, and Atlantic Oceans. Though they all have these spectacular optics, they don’t all look the same. Some are short, others are thin, some can even bioluminesce. Generally speaking, however, these fish are rather small, with the species most commonly referred to as “the” barreleye reaching lengths of just four inches (10.16 centimeters). They’re almost always found at least 300 feet (91.44 meters) below the ocean’s surface, though they tend to spend their time in what’s referred to as the twilight zone of the ocean where very little light can reach. As deepsea fish biologist Dr. Jeffrey Drazen put it in his interview with WhaleTimes.org, the ocean’s twilight zone is like being out in the country on a cloudy night… and I might add, without a flashlight.

Many of the first described specimens of barreleyes were found unknowingly damaged. The translucent domes covering their eyes are fragile and these were often destroyed before observations could be made. That’s why many older drawings of barreleye fish don’t include the transparent domes we now know to exist. This is just another example of how new data can change the truth we know of the world. That’s why it’s so important to always keep learning, and in regards to barreleyes there’s still lots to learn!

Though we don’t have enough data to know how barreleye’s breed, when they reach maturity, or even how long they can live, one inference based on the number of eggs found within a female barreleye lead to the suggestion that barreleyes spawn, potentially during a predetermined breeding season, and do so multiple times within that breeding season. It will take more observations to confirm or disprove this, but that’s what makes science so much fun!

For more facts on barreleyes, check out the links in the description. Give a thumbs up for deep sea creatures, and thank you for watching Animal Fact Files.