Barreleye fish: The deep-sea weirdo with rotating eyes and a see-through head

The reason it’s so cool: As their name suggests, barracuda fish have bizarre tubular eyes that can rotate to view upwards through their clear foreheads. While they look green, their lenses have yellow pigment, which aids in helping these fish differentiate between bioluminescence and sunlight.

The twilight zone in the ocean, the water layer that runs between 650 and 3,300 feet (200 to 1,000 meters) underneath the water’s surface, can receive just enough light for animals to cast a shadow. Their silhouettes are seen by predators who lurk beneath, which is the reason particular deep-sea creatures have developed organs for producing light on their bottoms to reflect the light coming from downwelling. However, the ocular trick of barreleyes that works by blocking out sunlight keeps them from being fooled by creatures that try to remove their shadows.

Barreleyes stand motionless in the darkness until they spot a possible dinner passing over. They then hurry upwards to grab it with their mouths and keep their gaze on their target by rotating their head forward.

In 2021, scientists filmed video footage from one of the rarely observed, deep-sea strangers in Monterey Canyon, off the coast of California. The researchers speculated that the barreleye fish feed themselves an abundance of crustaceans and larvae that are caught in siphonophores’ tentacles -jellyfish-like creatures that form strings of up to 130 feet (40 meters) long as per the Monterey Bay Aquarium.

Barreleyes’ transparent helmets might shield them from the infected cells that can sting these tentacles; however, this, along with the other aspects of these creatures’ lives, is undetermined.


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