Take A Look Inside the Barreleye Fish: The Marine Animal With Transparent Skull

An extremely rare fish with a transparent head is found in the depths-the fish swimming in the ocean with big green eyes peering up through its transparent head.

(Photo : Image from Kim Reisenbichler licensed under the Creative Commons Attribution-Share Alike 4.0 International license)

Barreleye Fish

The fish, with translucent heads and eyes resembling mesmerizing green orbs that peer upward through the darkness of the ocean's twilight zone, lies between 600 and 800 meters below the surface. The barreleye fish (Macropinna microstoma) gets its common name from a pair of enormous spherical domes attached to long, silvery eye tubes.

They use the green hue, a yellow pigment, as a type of sunglasses to assist them in finding their prey. In the wide waters of the deep ocean, where there is nowhere to hide, many species have luminous bellies that conceal their silhouette and provide protection. Bioluminescent prey is difficult to notice against the soft blue sunlight trickling down. However, barreleyes have a step up.

According to Bruce Robison, a deep-sea biologist at the Monterey Bay Aquarium Research Institute in California, the fish's eye pigment allows them to discriminate between bioluminescence and sunlight. Seeing the creatures as they work to vanish their shadows is beneficial to barreleyes.

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Evolutionary Advantage

(Photo : From Brauer, A., 1906 )

It is advantageous for the barreleye to have tubular eyes since they are susceptible and can take in a lot of light in the murky twilight zone. However, Robison was initially perplexed by the fact that their heads seemed to be fixated upward on the tiny pool of water.

The fact that their eyes were directed upward but their mouths were not visible in the field of vision has long perplexed Robison. Consider trying to focus on the ceiling while consuming food scraps floating in front of you.

But with the high-definition cameras of a remotely driven vehicle, Robison and colleagues finally got a clear look at a living barreleye after years of only seeing dead, net-caught species. "All of a sudden, a lightbulb went on, and I realized what was happening. He says, "The fish can monitor prey drifting through the water until it is just in front of their mouths because "they can rotate their eyes."

Robison discovered another thing scientists had previously missed when he found a barreleye swimming in the deep. He refers to the transparent front portion of the barreleye's body, which had been severed from all the specimens he had previously brought to the surface, saying, "It had this canopy over its eyes like on a jet fighter."

Potential Defense Mechanism

The siphonophores are creatures that float across the deep sea in long, lethal strings, much like drift nets. He believes that this canopy likely helps protect their eyes as they gather food from among their stinging tentacles.

In addition to siphonophores' tentacles, bareleyes have also been discovered with organisms that siphonophores eat, such as copepods, in their stomachs. They might use the transparent shield to protect their green eyes from stings when they swim up to siphonophores and munch on the little prey caught in their tentacles.

Extremely Rare

However, it's difficult to come across barreleyes in the wild. Robison claims that he has only seen these 15 cm long fish alive perhaps eight times in his thirty years of work. He adds with some confidence that they're fairly unusual because we spend a lot of time exploring there.