Overview
The barreleye is one of the most amazing fish ever discovered. The top of its head is a clear, see-through dome filled with fluid, and you can look right inside it. Floating within that dome are two bright green, tube-shaped eyes.
For a long time scientists were puzzled by this fish, because its eyes seemed to be stuck looking straight up. Then researchers filmed a living barreleye and learned the truth: its eyes can actually rotate to look forward, all while safe inside their transparent shield.
| Where it lives | Cold, dark water in the twilight zone of the deep sea |
| Range | The northern Pacific Ocean |
| Adult size | About 6 in (15 cm) long |
| Diet | Small animals and drifting jellies |
| Lifespan | Not well known |
| Depth or habitat | About 2,000 to 2,600 ft (600 to 800 m) down |
| Keep at home? | No, it lives in the deep sea and has a fragile see-through head |
Its weirdest feature
The barreleye's whole forehead is transparent, like a window into its skull. Its two green eyes are shaped like barrels, which is where the fish gets its name, and they sit inside that clear dome of clear fluid.
Surviving the dark deep
In the dim twilight zone, the barreleye points its ultra-sensitive tube eyes upward to catch the faint light and shadows of prey passing overhead. The green color inside its eyes may help it tell real sunlight from the glow of living creatures.
How it hunts
When the barreleye spots a meal above it, it can swivel its eyes from looking up to looking forward. That lets it keep its prey in sight as it turns its body upward and moves in to feed, possibly on small jellies.
Life in the deep sea
This little fish drifts almost motionless in cold, dark water, saving energy where food is scarce. Its see-through dome is so delicate that it usually gets destroyed when fish are pulled up in nets, which is why it stayed a mystery for so long.
An amazing fact
For decades scientists did not even know the barreleye had a clear dome, because it always popped on the way to the surface. Only in 2009 did deep-sea video finally reveal the fish's intact see-through head.
Fun facts
- The top of its head is a clear, see-through dome.
- Its green, tube-shaped eyes can rotate to look up or forward.
- The two spots above its mouth are not eyes, they are smell organs.
- Its delicate dome usually breaks when it is brought up in nets.
- Its see-through head was first filmed intact in 2009.
Frequently asked questions
Why is the barreleye's head see-through?
The clear dome protects its eyes while still letting light pass through, so it can look up and see prey overhead.
Can it really see through its own head?
Yes. Its eyes sit inside the clear dome and look up through it, and they can also swivel to point forward.
How big is the barreleye?
It is small, only about 6 inches (15 cm) long.
Can it live in an aquarium?
No. It lives in the deep sea and its fragile head does not survive being brought to the surface.
