Reveal the secret behind the ability of some fish to disappear in deep water

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At the bottom of the ocean, where sunlight barely reaches, the scientists of the Smithsonian and a team of collaborators have discovered one of the materials more blacks are known : the skin of certain fish . These fish ultra black absorb the light efficiently so that even with bright light seem to be silhouettes with no features discernible. In the darkness of the sea, even surrounded by light bioluminescent , they disappear. Literally.

the research findings have just been published in “Current Biology”. A team of scientists led by the zoóloga of the National Museum of Natural History of the Smithsonian, Karen Osborn , along with the biologist of Duke University, Sönke Johnsen , explains how the unique arrangement of granules filled with the pigment allows some fish to absorb almost all the light that reaches your skin, so only 0.05% is reflected . Imitate this strategy could help engineers develop materials ultra-black less expensive, flexible and more durable for use in optical technology, such as telescopes and cameras, or even to camouflage.

Osborn became interested for the first time in the skin of the fish when he tried to shoot some fish black eye-catching that she and her colleagues get caught in the trawls used to study the depths of the sea. But in spite of using sophisticated equipment with the latest technology, failed to capture any detail of these fish. “No matter how configurabas the camera or the lighting just absorbed all the light,” explains Osborn in a statement.

Question of survival

Measurements in the laboratory confirmed why the cameras could not capture their characteristics: many of the fish black found in the depths of the sea absorbed more than 99.5% of the light through the skin . That means that it is ultra black: more black than the black paper, more black duct tape, more black than a new tire. And in the sea, deep and dark, where a single photon of light is enough to attract the attention, that blackness is intense, can improve the chances of survival in an incredible way.

Another view of the black Dragon in the Pacific – Karen Osborn / Smithsonian

Due to the fact that the sunlight does not reach more than a couple of hundreds of meters below the surface of the ocean, most deep-sea creatures produce their own light, called bioluminescence . Glows bioluminescent are used to attract mates, distract predators and to attract prey. They can also expose the animals nearby, thwarting the approach the stealth of a predator or bringing a potential prey, unless those animals have camouflage appropriate.

The absorption of light nearly full of fish ultra black depends on the melanin , the same pigment that colors and protects the human skin from sunlight. Osborn and his colleagues discovered that this pigment is not only abundant in the skin of the fish ultra black, but is distributed in a unique way. The cellular compartments full of pigment called melanosomes are densely packed in pigment cells and these cells are arranged very close to the surface of the skin of the fish in a continuous layer. The size, shape and arrangement of melanosomes make direct any light that is not absorbed immediately into the melanosomes neighbours within the cell, which then absorb the remaining light.

“Effectively, what they have done is to make a light trap super-efficient and super-thin,” says Osborn. “The light is not recovered; the light does not pass. Just go to this layer, and it is gone”.

Anoplogaster – Karen Osborn

“These structures that contain pigments are packaged in the cells of the skin as a small machine of chewing gum, where all the chewing gum are of size and shape suitable to trap the light inside the machine,” adds Alexander Davis , co-author of the study. and phd student in biology at Duke University.

The fish ultranegros are not the only

These fish are not the only animals that they trap enough light to produce a surface ultra black. They have found feathers and scales ultra black in some bird and some butterfly , which contrasted with regions of bright colors, making the colors look more vibrant. These animals produce the effect by combining a layer of melanin structures that capture the light, such as small tubes or boxes. In the deep sea with limited resources, the fish ultra black seem to have developed a more efficient system, ” said Osborn. “This is the only system that we know of that uses the pigment in itself to control any light not initially absorbed”. This ultranegritud based in melanosomes appears to be a common strategy in the depths of the sea: Osborn and his team found the same distinct patterns of pigment in 16 species of fish related distantly.

The adoption of this design strategy could efficiently improve the manufacturing of materials ultra black, which is currently used by a system more similar to that found in birds and butterflies ultra black, said Osborn. Such materials, sought after for optical equipment sensitive, are currently extremely delicate and costly to produce. “Instead of building some kind of structure that traps the light, if you did that the pigment absorbing were the size and shape correct, you could achieve the same absorption and potentially much cheaper and make the material much less fragile.”