Fish with ultra-black skin that can swim undetected could help design better cameras, telescopes, says study

When researchers tried to take the fishes' photos, the images failed to provide information on their features despite using sophisticated cameras and only showed up as black silhouettes


                            Fish with ultra-black skin that can swim undetected could help design better cameras, telescopes, says study
(Karen Osborn, Smithsonian)

The deepest parts of the Earth's oceans are home to certain fish that have perfected the art of invisibility through millions of years of evolution. Their skin is ultra-black, helping them swim around undetected in the dark waters. But how does it accomplish this feat? According to a new study, the answer is in the skin of these deep-sea creatures. More specifically, in the cells responsible for color. They are arranged and shaped in a manner that absorbs almost all the incoming light.

These new findings can help humans learn these tricks to design better cameras, space telescopes and even camouflage technologies. "This is the first example we have of an aquatic animal that is ultra-black,"  Alexander Davis, a PhD student from Duke University and the first author of the study, told MEA WorldWide (MEAWW). Researchers have identified at least 16 species of deep-sea creatures with the intense color. Their camouflaging trick is more efficient than other ultra-black animals, such as a few birds and some butterflies.

(Karen Osborn, Smithsonian)

The creatures have developed a super-efficient, super-thin light trap, Duke University biologist Sönke Johnsen said. "Light doesn't bounce back. Light doesn't go through. It just goes into this layer and it's gone." The other researcher involved in the study is Smithsonian's National Museum of Natural History zoologist Karen Osborn. Drawing the team's attention to these deep-sea creatures was a failed art project of sorts, Davis recalled.

"Sonke and Karen Osborn both had attempted to take pictures of these really black fish," he said. The images failed to provide information on their features, despite using sophisticated cameras. They only showed up as black silhouettes. "That got them started thinking about how black these fish were and how they were accomplishing that," he added.

One specimen of the ultra-black fish species Anoplogaster cornuta
(Karen Osborn, Smithsonian)

The researchers studied 39 black fishes roaming in the waters of Monterey Bay and the Gulf of Mexico. Using a light-measuring instrument called a spectrometer, they found that only 0.5% of the light was bouncing off the creatures'skin to reach the eye. A creature's visibility depends on the amount of light it reflects. They then used an electron microscope to view the fish skin in greater detail. Ultra-black fish appeared different from others.

"These fish have a different skin structure than regular fishes, where the melanosomes are in a continuous layer in the skin," Davis explained. The difference was in the shape and arrangement of a skin pigment called melanosomes. They are more tightly packed together in the ultra-black fish, forming a continuous sheet around the body. The ordinary black ones, on the other hand, had gaps. As for shape, the ultra-black creatures have more tic-tac-shaped melanosomes, as opposed to the pearl-shaped ones seen on others. Computer modeling also revealed that these ultra-dark creatures have the best means to absorb light.

There are some aspects of these creatures that remain mysterious. "I would love to know how ultra-black skin changes as these fishes grow. For some of the species, like Echiostoma barbatum, the juveniles are ultra-black but the adults are far less so," Davis said of his future projects. The study is published in Current Biology.

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