The Bizarre Transparent Headed Barreleye Fish

The ocean is home to some of the most bizarre creatures on our planet.  Here’s yet another another example of a creature that makes you scratch your head about just how complex and advanced mother nature can be. The deep sea Barreleye fish looks like a, a glass domed submarine with the front top part of its head transparent, showing off its unique eyes.

First discovered in 1939, the barreleye fish had scientists and marine biologists guessing and trying to figure out the mystery behind this unusual sea creature. Earlier the fish had been noticed when it was caught in fishing nets, however, it’s transparent head is destroyed once the fish died, making it hard to study why the creature is as such. It wasn’t until the researchers at the Monterey Bay Aquarium Research Institute captured videos of a live specimen using the institute’s remotely operated vehicles (ROVs) and studied the bizarre fish off the coast of Central California.

Named for its barrel-shaped, tubular eyes which are generally directed upwards, the barreleye fish’s (Macropinna microstoma) eyes were believed to be fixed in place were assumed to provide only a “tunnel-vision” view of whatever was directly above the fish’s head. However, this would mean that it would be impossible for the fish to see what was directly in front of them, and very difficult for them to capture prey with their small, pointed mouths. The ROVs sent down to the depths of 2,000 to 2,600 feet (600 to 800 meters) showed that these unusual eyes of the fish could rotate within a transparent shield that covered the fish’s head. This allows the barreleye to peer up at potential prey or focus forward to see what it is eating. The fish can rotate its tubular eyes as it turns its body literally from a horizontal to a vertical position.

Not very big fish themselves, barreleyes are thought to eat small fishes and jellyfish. The green pigments in their eyes that you can see through their transparent heads is believed to filter out sunlight coming directly from the sea surface, to help the barreleye spot the bioluminescent glow of jellies or other animals directly overhead. When it spots its prey (such as a drifting jelly), a barreleye rotates its eyes forward and swims upward, in feeding mode.

Here’s a video of the strange see through headed barreleye fish by MBARI:

* Photo credits: Monterey Bay Aquarium Research Institute


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