Barreleye fish shows a transparent head

The Monterey Bay Aquarium Research Institute (MBARI) shared this rare video of a barreleye fish, or Macropinna microstoma, earlier this month (December 9, 2021). This unusual fish has a transparent head and tubular eyes. It lives in the deep sea, in a region scientists call the twilight zone, a mid-level ocean region just beyond the reach of sunlight. MBARI has remotely operated vehicles Ventana and Doc Ricketts. They have logged more than 5,600 successful dives and recorded more than 27,600 hours of video. But they have encountered this bizarre fish only nine times!

As MBARI said on YouTube:

The barreleye lives in the ocean’s twilight zone, at depths of 2,000 to 2,600 feet (600 to 800 meters). Its eyes look upward to spot its favorite prey – usually small crustaceans trapped in the tentacles of siphonophores – from the shadows they cast in the faint shimmer of sunlight from above. But how does this fish eat when its eyes point upward and its mouth points forward? MBARI researchers learned the barreleye can rotate its eyes beneath that dome of transparent tissue. Aquarist Tommy Knowles and his team were aboard MBARI’s R/V Rachel Carson with our ROV Ventana to collect jellies and comb jellies for the Aquarium’s upcoming Into the Deep exhibition when they spotted this fascinating fish. The team stopped to marvel at Macropinna before it swam away.

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Barreleye fish: A chubby fish in shadow with a see-through head and glowing green eyes inside.
The barreleye fish’s light-sensitive eyes rotate within the transparent, fluid-filled shield on its head. The fish’s tubular eyes have bright green lenses. The 2 spots above the fish’s mouth are not part of the eyes but similar to human nostrils. Image via MBARI.

The barreleye fish

The two dark spots at the front of the barreleye fish’s face that resemble eyes are actually its olfactory organs. The green glowing orbs that you can see through the transparent head are the eyes. The fish can rotate them upward to look for prey above it. When the fish wants to see the food it’s eating, it rotates the eyes forward.

Barreleye fish can grow up to 6 inches (15 cm) in size. Their habitat ranges from the Bering Sea to Baja California to Japan. The fish hovers below the tentacles of other sea creatures to steal their food, such as zooplankton and crustaceans.

Watch the barreleye escape a scientist’s trap in the video below.

Bottom line: On December 9, 2021, the Monterey Bay Aquarium Research Institute shared this rare video of a barreleye fish, or Macropinna microstoma.

December 17, 2021

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Kelly Kizer Whitt

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