Deep beneath the ocean, where the sunlight barely reaches its darkness, lives 16 species of ultra-black fish that each has its specialized skin to evade detection while hunting or hiding, Science Alert reports.
Scientists have discovered that these fish have blacker-than-black exterior absorbing 99.95% of all photons that create an invisibility cloak against the ocean's dim backdrop. These creatures appear as mere silhouettes even under a harsh spotlight.
The new study is published in the journal Current Biology.
Ultra-Black Fish Discovered in the Ocean's Darkness
Karen Osborn, a research zoologist at the Smithsonian's National Museum of Natural History, said that she grew frustrated trying to photograph a striking black fish that had been caught from the deep sea.
"It didn't matter how you set up the camera or lighting-they just sucked up all the light," Osborn said.
This piqued her interest, and so she and her colleagues analyzed the skin from 18 species of black fish they collected during their searches in the Gulf of Mexico and Monterey Bay, California.
These creatures all had ultra-black skin that reflected less than 0.6% of available light, while 16 of the species reflected less than 0.5%. Moreover, the researchers found that the ultra-black skin of the fish probably evolved in the near-complete darkness of the deep to absorb bioluminescent light coming from prey or predators.
"This low reflectance puts deep-sea fishes on par with the blackest known animals," the researchers write, "surpassing the darkness of ultra-black butterflies (0.06%-0.5% reflectance) and equaling the blackest birds of paradise (0.05%-0.31% reflectance)."
The black skin of these species is almost the same with Vantablack, which absorbs 99.96% of light and is once recorded as the blackest material known to science.
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Light-reflecting Pigment
After analyzing its skin, the researchers found that the pigment cells of the fish were tightly packed together with very few gaps that almost looks like a gumball machine. In one of the species, they found the pigment in its guts, probably used to hide the bioluminescent from its recent snack.
Osborn explains that this mechanism of the black fish makes a super-efficient, super-thin light trap as it only bounces back and does not go through. "It just goes into this layer, and it's gone," she said.
Although other ultra-black animals on land use the same light-reflecting pigments, they also utilize other light-capturing structures in their skin.
According to Osborn, this is the first time they found an animal that uses only the pigment alone to control unabsorbed light. This ability seems common in these animals. The researchers said that among the 16 distantly-related fish, the light scattering is due to the melanosomes themselves without any other structures that allow their skin to absorb light.
Understanding this mechanism will help scientists improve their camouflage technology, which has become increasingly sought after.
"Instead of building some kind of structure that traps the light, if you were to make the absorbing pigment the right size and shape, you could achieve the same absorption potentially a lot cheaper and [make the material] a lot less fragile," Osborn says.
