(CN) — Scientists recently discovered a species of fish that absorbs 99.95% of light hitting its skin, making it appear to be a featureless silhouette. In the dark waters of the deep sea, these fish are effectively camouflaged from predators and prey alike.
The research team found the skin of this ultra-black fish to be among the darkest materials ever discovered, which they detail in a study published Thursday in the journal Current Biology. Mimicking these antireflective properties may contribute to the development of ultra-black materials used in technologies such as telescopes, cameras and camouflage.
Sighted animals see the world around them thanks to reflected lighting; our eyes sense the light waves bouncing off various surfaces rather than the objects themselves. If something can absorb most of the photons hitting it, it will appear nearly black regardless of how much light you shine on it.
The ultra-black fish’s propensity for near-total light absorption stems from the concentration and unique distribution of melanin pigments in their skin, the same pigment that colors and protects human skin. The researchers found a densely packed layer of pigment-filled cellular compartments called melanosomes located directly beneath the surface of the fish’s skin. Rather than reflecting light outward, these melanosomes redirect whatever light they cannot absorb toward other nearby melanosomes which finish the job like an array of black holes. The team found the same melanosome pattern in 16 species of distantly related fish, leading them to believe this is a common survival strategy for deep-sea dwellers.
“Effectively what they’ve done is make a super-efficient, super-thin light trap,” said Karen Osborn, research zoologist at the Smithsonian’s National Museum of Natural History and co-author of the study, in a statement. “Light doesn’t bounce back; light doesn’t go through. It just goes into this layer, and it’s gone.”
Osborn first noticed this fish’s unique light absorbing properties and became interested when she and her colleagues caught one in a deep-sea trawl net and tried to photograph it. “It didn’t matter how you set up the camera or lighting — they just sucked up all the light,” she said.
In an email, study co-author Alexander Davis, a doctoral student in biology at Duke University, added: “In general to capture any of the details of the fish one must use an incredibly bright set of flashes. On one of the cruises, a photographer on board used five or six large flashbulbs just to image a two-inch fish.”
Because sunlight cannot penetrate much further than 600 feet below the surface of the ocean, many deep-sea creatures have evolved to see their world using bioluminescence — a biological process by which they generate their own lighting. Bioluminescence is used to attract mates, distract predators and to lure prey. Fish also use it for defense, like the security lights on a home, to foil anyone trying to sneak up on them. Those that can absorb that light have a distinct advantage in the dark underwater environment, like scaly camouflaged soldiers.
“If you want to blend in with the infinite blackness of your surroundings, sucking up every photon that hits you is a great way to go,” said Osborn.
Other animals also have similar light-absorbing properties. Certain birds and butterflies have been found with ultra-black feathers and scales, sharply contrasting with their colorful surroundings and making them appear more vibrant to potential mates. These animals also employ melanin to absorb visible light, but do so with less efficiency than the unique melanosome arrangement of the fish discovered by Osborne and her team.
Synthetically created ultra-black materials have been gaining prevalence in recent years. This past September a team of scientists from MIT showcased the blackest material known to exist. About 10 times more light absorbent than the fish, this material is crafted from vertically aligned carbon nanotubes and captures 99.995% of all incoming light. An artist working with those researchers coated a brilliant 16.78-caret yellow diamond with the material, which essentially made it disappear before the naked eye.
Vantablack, the previous reigning champ of light absorption, is also crafted from nanotubes and has been used in everything from telescopes and satellites, to car paint and watches.
“We hope that this work will be of use to engineers fabricating new ultra-black materials,” Davis said. “Particularly, the modeling of the effect of the size and shape of the melanosomes may be of use to researchers working on nanoparticle-based materials with synthetic melanin.”