Deep in the coldest and darkest parts of the ocean, below 200 m (656 ft), scientists have discovered ultra-black fish that absorbs almost all light that hits them, allowing them to hide effectively. Some other animals use similar methods, but the fish have a more efficient technique, one that could help guide future advances in camouflage and optical technology.
Deep-Sea Survival Techniques
A team led by scientists from Duke University and the Smithsonian were responsible for the discovery, which they detailed in the journal Current Biology. The fish, currently identified in 16 different but distantly related species, were found to absorb up to 99.5% of all light, making them appear as silhouettes even in direct light.
Deep in the sea, beyond the reach of light, animals have adapted to the environment by either producing their own light called bioluminescence, being utterly blind without dependence on light, or blending in with the pitch-black background.
Bioluminescence is used to attract mates or food or to illuminate predators and prey hiding in the dark. The ultra-black fish absorb almost every photon of light that hits them to boost their odds of not being eaten and not to scare off food. All of these adaptions are effective survival strategies.
Meet The Creatures
One of the identified species is an ultra-black ridgehead that uses its camouflage to hide from predators, and if it gets caught, its detachable scales can let it slip away. Another is a scary-looking creature called Pacific blackdragon that combines ultra-black skin with a bioluminescent lure. The best part of all, it has transparent, antireflective teeth!
How Do These Fish Absorb Light So Well?
When the team examined the specimen, brought up from the deep sea in trawl nets, they found that melanin was the critical component. Melanin is a light-absorbing pigment that naturally darkens human skin to various degrees, depending on how often the light is absorbed.
These fish have significant levels of melanin in their skin. The pigment cells consist of densely-packed compartments known as melanosomes, which waste minimum light due to their shape, positioning, and size. Any remaining light that doesn’t get absorbed gets deflected to other melanosomes.
Karen Osborn, the study’s lead researcher, explained:
Effectively what they’ve done is make a super-efficient, super-thin light trap. Light doesn’t bounce back; light doesn’t go through. It just goes into this layer, and it’s gone.
Similar Species
Some other species use similar light-absorbing methods, such as the Birds of Paradise. These ultra-black birds are so black it looks like you’re looking into a cave hole. Their extremely black feathers contrasted with vibrant colors on their chest to attract mates and were found to absorb 99.95% of directly incident light.
Future Ultra-Black Materials
Osborn said:
This is the only system that we know of that’s using the pigment itself to control any initially unabsorbed light. 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.
The fish’s melanin-based system is much smaller and mechanically simpler. Replicating this system could pave the way for future designs of ultra-black materials that are cheaper, more durable, and thinner than what’s currently available on the market.
