According to a study published Thursday in the journal Current Biology, certain species of exotic fish have adapted the shape, size and pigments of their skin to absorb 99.5% of the light that hits them – making them about 20 times darker than common black objects. These fish mark the first time that ultra-black has been discovered in aquatic animals, researchers said.
Scientists at Duke University and the Smithsonian National Museum of Natural History studied 16 species of ultra-black fish, including fang, black pacific dragon, monkfish and black swallow in the waters of Bay of Monterey and the Gulf of Mexico. The fish spanned seven different orders, which are large groups that each have a common evolutionary history, to determine that the changes occurred independently of each other.
Some fish inhabit parts of the ocean as deep as three miles, where very little sunlight can reach. At these depths, bioluminescence – the light emitted by living organisms – is the only source of light.
With organisms illuminating the water themselves to hunt, ultra-black fish have adapted to hide in plain sight. Camouflage is probably the difference between eating and getting eaten, scientists said in a press release.
“In the deep, open ocean there is nowhere to hide and lots of hungry predators,” Karen Osborn, co-author and zoologist with the National Museum of Natural History at the Smithsonian Institution told Reuters at Washington. “The only option for an animal is to blend into the background. ”
Scientists have found that, compared to ordinary black fish, ultra-black fish have uniquely shaped melanosomes, tiny bundles of pigment with their skin cells. The skin of these fish is one of the darkest materials ever discovered – they often appear as simple figures, even in bright light.
“The darkest species they found, a tiny monkfish not much longer than a golf tee, absorbs so much light that almost none – 0.04% – bounces in the eyes,” said the researchers.
The results rank the fish among the darkest animals known in the world: ultra-black butterflies reflect between 0.06% and 0.5% of light and the blackest birds have a reflectance of 0.05% at 0 , 31%.
Photographing the fish proved extremely difficult for the researchers.
“It doesn’t matter how you set up the camera or the lighting – they just sucked in all the light,” said research zoologist Karen Osborn from the Smithsonian National Museum of Natural History.
Researchers say the discovery could lead to the development of light-trapping materials with practical applications on earth – ranging from solar panels to telescopes – like Vantablack, the ultra-black coating designed for defense and space applications.