Scientists have captured rare 4K footage of a fish with a transparent head. Spotted nearly 2,000 feet beneath the Pacific Ocean, this bizarre little creature looks almost unreal. And at just six inches long, it’s much smaller than you might expect.
Meet the Macropinna microstoma, also called barreleye fish. This one is a deep-sea creature with a fluid-filled dome covering the top of its head. Inside this transparent chamber sit two enormous tubular eyes that normally point upward, helping the fish search for food in the dimly lit waters of the ocean’s twilight zone.
Researchers from the Monterey Bay Aquarium Research Institute (MBARI) recently got an unusually close look at this elusive species. It’s not something that happens often. Across nearly 40 years of deep-sea exploration, the institute has encountered the barreleye just 11 times. This latest sighting gave scientists their first opportunity to record the animal in 4K.
A Rare Fish Appeared Out Of Nowhere
The encounter happened around 55 miles (90 kilometers) off the California coast, during an eight-day expedition aboard MBARI’s research vessel David Packard. The team was actually searching for gelatinous marine animals, including jellyfish and siphonophores, when their underwater robot, Doc Ricketts, began heading back toward the surface. That’s when research specialist Shannon Johnson noticed something unusual on the monitors and asked the pilots to stop.
Word quickly spread through the ship, and researchers rushed into the control room to see what was happening. Soon, crew members were gathered around the screens, watching a fish that looked like something out of a science fiction movie.
“It is such an amazing creature, which looks like it was created by an imaginative child,” MBARI senior scientist Steven Haddock, who led the expedition, told Discover Wildlife.
The barreleye fish (Macropinna microstoma) reveals its bright green, tubular eyes through a transparent, fluid-filled dome on its head. Credit: MBARI
The team spent approximately 20 minutes filming the barreleye, adjusting the underwater lighting to capture its transparent head in detail. Pilot Cameron Law even maneuvered the robot close enough to record stereoscopic 3D footage. According to MBARI, the institute has completed roughly 7,000 robotic dives and collected more than 41,000 hours of underwater video. Its previous barreleye sighting occurred in 2021, making this encounter particularly unusual.
Those Two Dark Spots Aren’t Actually Its Eyes
At first glance, the barreleye appears to have two small, dark eyes sitting just above its tiny mouth. But look a little closer, and things get stranger. Those spots aren’t eyes at all. They’re olfactory organs, which work much like nostrils. The fish’s real eyes are the two large, emerald-green structures visible inside its transparent head. Their barrel-like shape is what gives the species its name.
For years, scientists believed these tubular eyes were permanently fixed in an upward-facing position. But a 2008 study published in Copeia revealed something unexpected. MBARI researchers discovered that the eyes can rotate by as much as 75 degrees, allowing the fish to switch from looking upward to looking forward.
The fish spends much of its time hovering almost motionless, using its large fins to maintain its position while scanning the faint light overhead. Scientists suspect the green pigments in its eyes act as natural filters, helping it distinguish sunlight from the bioluminescent glow produced by other marine creatures. Some deep-sea animals use a camouflage technique called counterillumination, generating light beneath their bodies to blend into the weak illumination coming from above.
A Transparent Head Built For Protection
The barreleye was first scientifically described in 1939, yet researchers spent decades misunderstanding one of its most distinctive features. The reason was surprisingly simple: traditional deep-sea fishing nets often damaged the delicate transparent dome as specimens were brought to the surface. By the time scientists examined the fish, the structure had frequently been destroyed, leaving preserved specimens looking very different from living animals.
Underwater robots eventually let researchers observe barreleyes in their natural habitat without damaging their fragile anatomy. The transparent dome may also serve another purpose: scientists suspect these fish sometimes steal prey from siphonophore tentacles, and the dome could shield their sensitive eyes. This feeding behavior has not been fully documented in the wild.
During the latest encounter, the MBARI team chose to leave the fish undisturbed, returning instead with exceptionally detailed footage of a creature rarely seen alive. Nearly nine decades after its scientific description, the six-inch barreleye fish is still surprising researchers.