Scientists at the Monterey Bay Aquarium Research Institute (MBARI) have captured rare 4K video of a barreleye fish, a deep-sea animal whose glowing green eyes sit inside a transparent, fluid-filled head. The fish was filmed on Oct. 20 at about 1,970 feet (600 meters) deep in the outer Monterey Canyon, roughly 55 miles offshore of Monterey, California, FOX Weather reported.
It was only MBARI’s eleventh sighting of the species, Macropinna microstoma, in almost 40 years and about 7,000 dives with remotely operated vehicles. The previous sighting came in 2021, and this is the first time the institute has filmed the fish in 4K.
For viewers, the video offers a clear look at an adaptation that took scientists decades to understand. For researchers, it is a reminder of how little is known about the ocean’s twilight zone, a vast layer of water that sits between the sunlit surface and the dark deep sea.
A Surprise on the Way Up
The sighting nearly did not happen — MBARI’s remotely operated vehicle Doc Ricketts was returning to the surface for recovery at the end of a dive when research specialist Shannon Johnson spotted the fish on the camera feed and called out to the pilots. The team was aboard MBARI’s flagship research vessel, the David Packard, during an eight-day expedition called “Diving Deep for Delicate Drifters,” which studies gelatinous animals.
The team watched the fish for about 20 minutes, filming it with a 4K camera before a pilot switched to the vehicle’s VR camera to capture 3D imagery. MBARI did not collect the animal, so the video is the main record of the encounter.
“Seeing a barreleye fish is a rare treat,” said MBARI senior scientist Steven Haddock. Haddock told BBC Wildlife’s Discover Wildlife that his own last encounter had come nine years earlier, before the submersible carried 4K cameras.
Eyes That Rotate Inside a Clear Shield
The barreleye’s most striking feature is the transparent shield covering the top of its head. Beneath it sit two tubular, greenish-yellow eyes that normally point straight up, scanning the faint light from above for the silhouettes of prey. The green pigment may help filter out sunlight from the surface, according to The Weather Network.
That arrangement once posed a puzzle. With eyes aimed upward and a tiny mouth pointing forward, how could the fish see what it was eating? MBARI researchers Bruce Robison and Kim Reisenbichler solved it after bringing a live, net-caught barreleye to the surface in 2008 and observing it in a shipboard aquarium. They found the eyes can rotate inside the shield, from upward-facing to forward-facing, as the fish moves to feed.
The barreleye feeds on small crustaceans trapped in the stinging tentacles of siphonophores, long colonial relatives of jellyfish. The clear shield appears to protect its eyes from those stinging cells, and its large fins keep it steady while it maneuvers into position. The species was first described in 1939, and adults measure about 6 inches (15 centimeters) long, Sci.News reported.
“Macropinna reminds us of the surprising ways that animals have adapted to thrive in the ocean’s midwater,” Haddock said.
Why the Twilight Zone Stays Hidden
Barreleyes live in the ocean’s twilight zone at roughly 2,000 to 2,600 feet (600 to 800 meters) deep, where light fades almost to nothing. Even within that range, sightings are rare. Bruce Robison told Live Science in 2021 that scientists still had “no handle on population size, except in a relative sense,” meaning nobody knows how many exist.
That uncertainty is common across the midwater — fragile animals like the barreleye are often damaged by nets, and early specimens hauled to the surface usually lost the delicate shield, which is why it was rarely described until scientists observed living fish. Video from robotic vehicles has become one of the few ways to study them undisturbed.
MBARI’s Long Watch on the Deep
MBARI’s archive shows the scale of that effort. Over almost four decades, the institute has logged about 41,000 hours of deep-sea video, and its annotation and research programs turn that footage into data on where species live and how ocean conditions shape them. Johnson logged the barreleye sighting in MBARI’s annotation software, adding it to that long-term record.
The institute, based in Moss Landing, California, runs a fleet of robotic vehicles that can dive thousands of feet into Monterey Canyon, one of the deepest submarine canyons along the U.S. West Coast. Its 2021 barreleye sighting came during a dive with the Monterey Bay Aquarium aboard a different vessel, the Rachel Carson, using the ROV Ventana.
The twilight zone matters beyond curiosity. Animals there move carbon from the surface toward the deep sea as they feed and migrate, and the zone is drawing growing interest from commercial fisheries. Knowing what lives there, and how rare species like the barreleye fare, helps scientists judge how changes in ocean temperature and oxygen could ripple through deep-sea food webs.
For readers, the best way to see the barreleye is the video itself, which MBARI and FOX Weather have shared online. MBARI’s next expeditions will continue surveying Monterey Canyon, and any future sighting would add a twelfth record to one of the ocean’s rarest encounters.
What Readers Want to Know
Where was the barreleye fish filmed? In the outer Monterey Canyon, about 55 miles offshore of Monterey, California, at roughly 1,970 feet (600 meters) deep, on Oct. 20, 2026.
How rare is this sighting? It is MBARI’s eleventh sighting of the species in almost 40 years and about 7,000 robotic dives. The previous sighting was in 2021.
Why is the barreleye’s head transparent? The clear, fluid-filled shield protects its eyes, likely from the stinging tentacles of siphonophores whose trapped prey it eats.
Can the barreleye move its eyes? Yes. MBARI researchers found its tubular eyes rotate inside the shield, from facing upward to facing forward while feeding.
How big is a barreleye fish? Adults measure about 6 inches (15 centimeters) long.
Where can I watch the video? MBARI and FOX Weather have shared the footage online, including the 4K video recorded by ROV Doc Ricketts.
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