The head of the barreleye fish is translucent.
This unusual footage of a barreleye fish, or Macropinna microstoma, was shared by the Monterey Bay Aquarium Research Institute (MBARI) earlier this month (December 9, 2021). This strange fish has tubular eyes and a translucent skull. The twilight zone, a mid-level ocean region just out of the range of sunlight, is where it lives in the deep sea. Ventana and Doc Ricketts are two remotely operated vehicles owned by MBARI. More than 5,600 successful dives have been recorded, and more than 27,600 hours of footage have been captured. However, they have only come across this peculiar fish nine times!
According to MBARI on YouTube:
The barreleye lives in depths of 2,000 to 2,600 feet in the ocean’s twilight zone (600 to 800 meters). Its eyes scan the sky, searching for its preferred prey, mainly little crustaceans caught in the siphonophores’ tentacles, which it spots by the shadows they make in the hazy shimmer of the sun above.
But with its mouth facing forward and its eyes skyward, how does this fish eat? Under the dome-shaped dome of translucent tissue, MBARI researchers discovered that the barreleye could swivel its eyeballs. To collect and comb jellies for the upcoming Into the Deep exhibit at the Aquarium, When they came upon this unusual critter, aquarist Tommy Knowles and his team traveled on MBARI’s R/V Rachel Carson with our ROV Ventana. Before it swam away, the team paused to gawk at Macropinna.
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The two black dots that the barreleye fish has at the front of its face and which mimic eyes are olfactory organs. The eyes may be seen through the transparent head as green glowing spheres. To search for prey above it, the fish can spin them upward. The fish moves its eyes forward when it wants to see what it is consuming.
The size of a barreleye fish can reach 6 inches (15 cm). The Bering Sea, Baja, California, and Japan are all parts of their ecosystem. The fish hovers beneath their tentacles to steal food from other marine organisms, such as zooplankton and crustaceans.