Researchers at the Monterey Bay Aquarium Research Institute have captured their first 4K footage of a rare deep-sea fish with a transparent head, offering an unusually detailed look at the animal nearly 2,000 feet below the surface of the Pacific Ocean. The institute announced the encounter Oct. 28 after an expedition off Central California.
The fish, known as a barreleye (Macropinna microstoma), was spotted about 55 miles offshore during a trip aboard the research vessel David Packard. Scientists used an underwater robot called Doc Ricketts to observe it for about 20 minutes, changing the lighting to reveal the clear covering around its eyes.
Pilot Cameron Law maneuvered the robot close enough to record 3D images with a virtual reality camera. Researchers left the fish in the water, saying the footage could help them better understand its vision. It was only the 11th time the institute had encountered the species in nearly 40 years of deep-sea exploration.
A surprise as the underwater robot returned
The sighting came as the robot was heading back toward the ship after a day of research. Research specialist Shannon Johnson noticed the fish on a video screen and asked the pilots to stop. Scientists and crew members gathered in the control room to watch the encounter.
A fish with a transparent head was discovered over 2,000ft deep in the ocean. It can rotate its eyes to track prey
Known as the barreleye fish, this unusual deep-sea species lives where sunlight barely reaches, using its unique vision to survive in the dark waters of the ocean pic.twitter.com/20EZ0s7FJa
— Nature is Amazing ☘️ (@AMAZlNGNATURE) June 11, 2026
Most of the researchers had moved to a laboratory to prepare specimens for cataloging and hurried back when they heard about the sighting.
“Seeing a barreleye fish is a rare treat,” senior scientist Steven Haddock said in the institute’s announcement. The expedition, held Oct. 13-20, had focused on jellyfish, siphonophores and other drifting sea animals. Finding the barreleye was unexpected.
Why this rare deep-sea fish has a transparent head
The fish can reach about 6 inches long. Its green, tube-shaped eyes sit under a fluid-filled shield and can move from looking upward to facing forward. The two dark spots above its mouth, which may resemble eyes, are actually organs used for smell.
The eyes help the barreleye spot potential food against faint light coming from above. Scientists suspect the clear shield also protects its eyes near the stinging tentacles of siphonophores, which can trap small animals the fish may eat.
The species was first described in 1939, and earlier underwater videos helped scientists establish that its eyes can rotate. MBARI recorded another sighting in 2021. The latest encounter is significant for its sharper imagery, not because the fish was discovered or filmed for the first time.
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