Scientists at the Monterey Bay Aquarium Research Institute (MBARI) in California, USA have been able to collect more information about the elusive barreleye fish (Macropinna microstoma).

The mysterious creature lives at depths of up to 2,600 feet, and has a transparent skull through which it interacts with the world around it. Its eyes resemble orbs, and sit on a pair of long, silvery eye tubes, which is why it is called a "barreleye" fish.

Its beautiful emerald eyes look like two bottle caps fixed inside the transparent head. According to researchers, the fish "can rotate its eyes towards the front to see its food when eating."

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Its eyes allow it to spot sea creatures that use bioluminescence to hide in the deep-sea waters. The emerald color of the eyes allows the creature to differentiate between sunlight and bioluminescence.

As the prey is difficult to spot against the soft blue sunlight trickling down from the surface into the ocean; their eyes essentially work as sunglasses to help spot the prey, explains The Guardian.

Their eyes appear to be fixed upwards and it took scientists years of study to figure out how they go about catching their prey.

Bruce Robinson, a deep-sea biologist at the institute, said that it was when he got to see a living barreleye fish that he realised that the fish can rotate its eyes. "Suddenly the lightbulb lit and I thought, 'A-ha, that's what's going on!'."

The process of understanding the fish has been very slow since it is extremely difficult to spot it. Robinson claims that he has only seen the fish eight times in the last 30 years of his career. The fish was last spotted in December 2021.

"We do spend a lot of time exploring down there, so I can say with some confidence that they're quite rare," he added.

Barreleye fish
Image of a barreleye fish by Kim Reisenbichler, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons