Some fish that live in the deepest reaches of the ocean have evolved skin so dark it absorbs more than 99 per cent of all light, rendering the animal almost invisible.
The animals are so efficient at soaking up light that they appear as mere silhouettes, seemingly devoid of any features.
Academics from the US have identified at least 16 species that use the ultra-black form of camouflage to avoid predators, including the dragon fish and fangtooth.
In the ocean’s depths, no natural sunlight penetrates and some predators have the ability to glow using bio-luminescence to hunt their prey.
Being able to hide in plain sight and absorb all this light without being spotted is a major survival advantage.
Some of the species with the ultra-black skin also have their own bio-luminescent lures, or headlamps, but their skin is so dark that none of the light bounces off their bodies, allowing them to attract and ensnare their food.
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This deep-sea dragonfish has ultra-black skin capable of absorbing the bioluminescent light that might blow its cover
Pictured, a specimen of the ultra-black fish species Anoplogaster cornuta. This fish was so lively after being sampled and documented that the research team released it back to the deep via submarine the day after being caught in a trawl net
The darkness is created by melanin, a pigment which also gives human skin its colour. More melanin creates a darker skin tone.
In these fish species however, they have evolved to maximise production of melanin and have melanosomes, specific cellular pockets packed with the dark pigment.
They are arranged close to the surface of the skin and lie in such a way as to maximise light absorption.
Co-author Alexander Davis, a co-author of the study and doctoral student in biology at Duke University, says: ‘These pigment-containing structures are packed into the skin cells like a tiny gumball machine, where all of the gumballs are of just the right size and shape to trap light within the machine.’
Pictured, the ultra-black ridgehead (Poromitra crassiceps ).These fish are also commonly known as bigscales because of the few giant scales they possess. Their ultra-black skin covers their scales, but the skin and scales detach easily when a predator tries to grab them
Pictured, the ultra-black Pacific blackdragon (Idiacanthus antrostomus), the second-blackest fish studied by the research team. These fish have a bioluminescent lure that they use to attract prey, and if not for their ultra-black skin and transparent, anti-reflective teeth, the reflection of their lure would scare prey away
The Pacific blackdragon (pictured) has light-producing organs below their eyes that scientists expect might be used as a searchlight to spot prey
Dr Karen Osborn, of the Smithsonian National Museum of Natural History in the United States, adds: ‘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.’
Soaking up light, whether from the sun or from bioluminescent creatures, is an effective technique to avoid being eaten in the bleak world of the deepest oceans.
The team caught and analysed 40 black fish swimming up to a mile below the surface in Monterey Bay and the Gulf of Mexico using a trawl net and unmanned marine vehicle.
They measured how much light was being reflected off each fish using a spectrometer.
This revealed 16 species reflected less than half a per cent of light, making them 20 times darker than everyday black objects like paper and tires.
Anglerfish, which are about the size of a ‘golf tee’, were found the darkest species, reflecting just 0.04 per cent of light.
Only one other animal in the world is known to be as dark, the birds-of-paradise of Papua New Guinea.
Dr Osborn said: ‘Mimicking this strategy could help engineers develop less expensive, flexible and more durable ultra-black materials for use in optical technology, such as telescopes and cameras, and for camouflage.’
The findings were published in the journal Current Biology.
Pictured, the ultra-black fish species Anoplogaster cornuta being sampled before it was released back into the ocean