Bizarre Facts: Deep-sea fish sees through its forehead

MONTEREY一 Parents will say they have eyes on the back of their head to catch unsuspecting offspring amid some transgression to house rules, but I have yet to hear someone say they have eyes on their forehead. A deep-sea fish founded in 1939 coined, the barreleye fish has tubular eyes set into its transparent forehead.

The barreleye fish has extremely light-sensitive eyes capped with bright green lenses that can rotate in the transparent fluid-filled shield on its forehead.

The eyes can point up when the fish is looking for food and forward when the fish is eating. To complete the unusual setup, the bit where it looks like the eyes should go above the mouth are actually olfactory organs called nares, according to the Monterey Bay Aquarium Research Institute.

In 2009 researchers from the institute wrote a paper that filled in the blanks about the animal’s ocular methods, finding that the eyes could in fact, rotate.

Until this point, researchers believed the eyes were fixed in place, which would make it challenging for the fish to see anything in front of it.

The fish falls into the ‘barreleye’ category because of the tubular shape of their eyes; tubular-shaped eyes are great at collecting light which is a neat trick for deep-sea dwellers.

Researchers from the Monterey Bay Aquarium Research Institute, Bruce Robison and Kim Reisenbichler use remotely operated vehicles to study the fish off the Central California coast at depths between 2,000-2,600 feet. After observation, Robison and Reisenbichler developed a hypothesis that the fish spends its time hanging motionless in the water with its eyes looking upward; the green lens filters out the sun, allowing the fish to see the bioluminescent glow of potential prey. The fish can reach up to six inches and is found in the Bering Sea to Japan and Baja California; it feeds on zooplankton, including crustaceans and siphonophores. To learn more, see the Monterey Bay Aquarium Research Institute at


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