The Monterey Bay Aquarium Research Institute (MBARI) recently took a rare video of the strange and uncanny barreleye fish (Macropinna microstoma). The deeper the ocean, the weirder the fish become and the barreleye fish is no exception. This odd creature has a transparent head surrounding its bulbous eyes.
MBARI used two remotely operated vehicles (ROV) called the Ventana and the Doc Rickets to observe the depths of the ocean. Despite over 5,6000 missions collecting over 27,600 hours of footage, the institute has found this fish only nine times.
The Rare Barreleye Fish Caught on Camera
The barreleye fish lives in the twilight zone of the ocean, which is about 2,000 to 2,600 feet deep. They prefer the areas that fall into complete darkness. At this depth, light is scant so different species developed unique attributes to adapt to this level. Even among these creatures, the barreleye still stands out as one of the strangest.
Their eyes are extremely sensitive to light and so they peer through a transparent, orb-shaped head full of fluid. Above the fish’s mouth are two spots called nares that help the creature smell. They are akin to human nostrils. “Two small indentations where eyes might normally appear on a fish are actually the barreleye’s olfactory organs, and its eyes are two glowing green orbs behind its face that gaze up towards the top of its head,” MBARI explains.
The eyes have bright green lenses and point directly upward, which is where the fish searches for food. But when the fish is eating, the eyes point forward.  “Its eyes look upwards 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,” said MBARI. Previously, animal scientists believed that the fish could only look upward. But they have been found to look forward as well.
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“I immediately knew what I was looking at”
The barreleye doesn’t grow very long; adults are estimated to grow to only six inches long. Their habitats include Baja California — where this video was captured — and between Japan and the Bering Sea. At that time, the ROV was swimming about 2,132 feet deep in the Monterey Submarine Canyon, one of the deepest canyons in the Pacific Ocean. Thomas Knowles, a senior aquarist at the Monterey Bay Aquarium, said, “The barreleye first appeared very small out in the blue distance, but I immediately knew what I was looking at. It couldn’t be mistaken for anything else.”
Everyone in the control room grew excited. The ROV pilot Knute Brekke kept the camera pointed at the fish while Knowles kept the lens in focus. “We all knew that this was likely a once in a lifetime experience,” since the elusive creature is seen so very rarely, Knowles said. In the video, the light of the ROV made the eyes of the barreleye glow green easily visible beneath its transparent head. 
Because of their rarity, little is known about these creatures and their Jello-like heads. “We have no handle on population size, except in a relative sense,” Bruce Robison, a MBARI senior scientist. The MBARI team tends to find barreleye fish about as often as anglerfish and whalefish, “which is very rarely,” Robinson said. More commonly-seen twilight zone fish include lanternfish or bristlemouths, which populations are more abundant.
Rare and Unknown
However, based on past research, scientists believe that barreleye fish tend to remain still to wait for unsuspecting prey to swim overhead. This can include jellyfish and zooplankton. These fish can remain motionless without sinking by spreading out their broad fins. Meanwhile, their unique eyes allow them to scope out the silhouettes of potential prey overhead. Once they lock onto their prey, they speed upward while rotating their eyes forward, and snatch the food with their mouths. Some scientists speculate that the fish might steal food from siphonophores, jellyfish-esque creatures that drift together and trap prey in their tentacles. They add that the barreleye fish’s strange head may protect them from the stinging in the tentacles. “Most aspects of their natural history remain unknown and much of what we think we know about them is based on speculation,” Robison said.+
The barreleye fish was first discovered in 1939 by fishermen who caught them in nets that broke their gelatinous heads. Therefore, scientists didn’t know the fish’s true form until they saw them in their natural habitat. Because of their unique anatomy and the limited information on them, MBARI has no plans to capture the barreleye fish. It’s very likely an aquarium would not be able to take care of such a rare and unknown creature.
Check out the exclusive video here: