Deep Sea Mystery: Ultra-Black Fishes Absorb Light and 'Disappear' Into the Darkness

How do the blackest fish in the sea suddenly disappear? Many have tried to pictures of these ultra-black fishes, and only ended up taking a picture of the creature's silhouette. In the darkness of the ocean, even surrounded by light, they literally disappear. This certain "ultra-black" creature is known as the Pacific blackdragon, and its "ultra-blackness" renders the creature almost invisible.

The Pacific Blackdragon's ultra-black feature

In the darkest parts of the ocean's water, bioluminescence from other deep-sea creatures is the only light source. These bioluminescent glows are used to misdirect predators, lure prey and expose nearby animals. According to scientists, the Pacific blackdragon absorbs light so effectively that they appear to be silhouettes with no features noticeable to the human eye. The fish's "ultra-black" skin traps light, giving this creature the ultimate camouflage. 

Researchers explained that this specific feature could help engineers develop and im prove more ultra-black materials for use in optical technology, such as camera and telescopes. Currently, Vantablack is one of the darkest substances known, for its super-black coating that can absorb up to 99.965% of visible light. If light strikes Vantablack, instead of bouncing off, it becomes trapped and eventually becomes absorbed, dissipating into heat.

Much like how some have tried to capture an image of the Pacific blackdragon, "It didn't matter how you set up the camera or lighting - they just sucked up all the light." said Dr Karen Osborn, a Smithsonian National Museum zoologist. "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." Dr. Osborn also described the skin of these fish as something very strange. "Every picture I took was really bad - it was so frustrating," she told BBC News. The frustrated scientist admitted that it took a lot of lighting and even a lot of Photoshop.

Also read: US Pledges to Protect Territory of Endangered Humback Whales in Pacific Ocean

Other ultra-black fishes

So far scientists have been able to identify 16 other species of ultra-black fishes. These fish have ultra-black skin to protect them from being eaten, or to help them sneak up on fish they want to eat. Ultra-black is defined as reflecting less than 0.5 percent of incoming light.

Scientists collected deep-sea fish specimens from 18 different species and used a special black-reflectance light probe to measure the amount of light that was absorbed. Out of those 18 species, 16 were qualified. "It's a splendid exercise in quantifying blackness," says Peter Herring, Marine Biologist. "Deep-sea fishes are routinely described as inky black or velvet black, so it's nice to have some numerical basis. On an intuitive level one might think that just two percent reflectance would be good enough, but if you get a six-times improvement then no doubt an evolutionary advantage could have occurred." 

These fishes were then classified as having 'expert-level camouflage'. They have unique patterns in the pigment cells of their skin that compose of melanosomes. These cells that hold the pigmenting chemical, which are important in many ways. "So basically, by changing the shape and the size of those granules, they control it so that the light goes into the layer and side-scatters into the granules next to it." says Osborn.

Also read: Clownfish in Coastal Reefs Could Be Dying From Artificial Light Sources