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Deep down in the ocean where light is nonexistent, a group of fish with light absorbing skin literally disappears in the darkness. A team of scientists have found that the skin of some deepsea fish absorbs more than 99.95 percent of the light that hits them, making them appear ultra-black.
The team from Duke University and the Smithsonian National Museum of Natural History have now discovered at least 16 species of ultra-black fish. Each of these fish is equipped with specialized skin that allows them to evade detection while hunting or hiding in the dark.
Karen Osborn, the co-author of the new study, first became interested in the skin of these deepwater fish when she tried to photograph some specimens that had been brought back to the surface. “It didn’t matter how you set up the camera or lighting—they just sucked up all the light.”
She set up a Canon DSLR camera with four strobes then tested various lighting setups by taking lots and lots of photographs. Finally, she adjusted contrast and applied a high-pass filter uniformly across the images, the better to bring out the details.
“Over the years I deleted thousands of failed shots of other fish as useless because I couldn’t bring out the details in the photos,” she added. “It didn’t matter how you set up the camera or lighting—they just sucked up all the light. I wish I had a few of them now to illustrate this.”
Because sunlight does not reach more than a couple hundred meters beneath the ocean’s surface, most deep-sea creatures make their own light, called bioluminescence. Bioluminescent glows are used to attract mates, distract predators and lure prey.
They can also expose nearby animals–foiling a predator’s stealthy approach or shining a beacon on potential prey–unless those animals have the right camouflage. “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,” Osborn said.
The near-complete light absorption of ultra-black fish depends on melanin, the same pigment that colors and protects human skin from sunlight. Osborn and her colleagues discovered that this pigment is not just abundant in the skin of ultra-black fish, it is distributed in a unique way.
Pigment-filled cellular compartments called melanosomes are densely packed into pigment cells and these pigment cells are arranged very close to the surface of an ultra-black fish’s skin in a continuous layer. The size, shape and arrangement of the melanosomes cause them to direct any light they do not immediately absorb toward neighboring melanosomes within the cell, which then suck up the remaining light.
“Effectively what they’ve done is make a super-efficient, super-thin light trap,” Osborn said. “Light doesn’t bounce back; light doesn’t go through. It just goes into this layer, and it’s gone.” [EurekaAlert]
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