the amazing fish with the transparent head

the amazing fish with the transparent head

the amazing fish with the transparent head

In the twilight zone of the ocean, between 600 and 800 meters below the surface, there are fish looking up through their transparent heads with eyes like fascinating emerald spheres. These domes are huge spherical lenses that sit on a pair of long, silver-colored eye tubes – hence its common name, the barreleye fish (Macropinna microstoma).

The green tint (which actually comes from a yellow pigment) acts as sunglasses, in one species, to help them track their prey. There is nowhere to hide in the open waters of the deep ocean, and many animals that live here have glowing bellies that mask their silhouettes and protect them – it’s hard to spot bioluminescent prey against the dim blue sunlight dripping down. But the barreleyes are a step forward.

The ocean is one of the last truly wild spaces in the world. It is teeming with fascinating species that at times seem to border on the absurd, from fish looking up through transparent heads to gilded snails in iron armor. We know more about deep space than about deep oceans, and science is only beginning to scratch the surface of the rich variety of life in the depths.

As mining companies push to industrialize the seabed and global leaders continue to squabble over how to protect the high seas, a new Guardian Seascape series will feature some of the weird, wonderful, majestic, ridiculous, hardcore and mind-blowing creatures recently discovered. They reveal how much there is still to be learned about the lesser-known environment on Earth and how much there is to be protected.

Their eye pigment allows fish to distinguish between sunlight and bioluminescence, says Bruce Robison, a deep-water biologist at the Monterey Bay Aquarium Research Institute in California. Help barrel eyes have a clear view of animals trying to erase their shadows.

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The barreleye’s tubular eyes are extremely sensitive and absorb a lot of light, which is useful in the ink depths of the twilight zone. But Robison was initially confused that their eyes seemed to be fixed upward on the small patch of water, right above their heads.

“It always baffled me that their eyes pointed upward, but the field of view didn’t include their mouths,” says Robison. He imagines trying to eat leftover food floating in front of you, while staring at the ceiling.

But, after years of seeing only dead and caught specimens from the net, Robison and colleagues have finally gotten a good look at a living barrel eye through the high-definition cameras of a remote-controlled vehicle. “Suddenly the light bulb went on and I thought ‘A-ah, that’s what’s going on!'” He says. “They can roll their eyes.” This means that the fish can follow the prey as it descends into the water until it is right in front of their mouth.

Seeing a live barrel eye in the depths, Robison saw something else that scientists had previously missed. “He had this canopy over his eyes like on a jet fighter,” he says, referring to the transparent front of the barreleye’s body, which had been ripped off from all the specimens he had previously brought to the surface.

He thinks this canopy likely helps protect their eyes as they steal food between the stinging tentacles of siphonophores, animals that float deep in the sea in long deadly threads, like driftnets.

Barreleys have been found with a mix of food in their stomach, including the tentacles of the siphonophores, as well as animals that the siphonophores feed on, including small crustaceans called copepods. Their tactic might be to swim up to the siphonophores and nibble on small prey entangled in their tentacles, using the transparent shield to protect their green eyes from stings.

But meeting barrel eyes in nature is not easy. In his 30-year career, Robison claims to have seen these 6-inch-long fish alive only eight times. “We spend a lot of time exploring there, so I can confidently say they’re quite rare,” he says.

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