Fish with black light-absorbing skin found at great depths

The skin of some deep-sea fish absorbs 99.5 percent of the light incident on it, making them almost invisible in the darkness.

Sunlight quickly scatters in water, and over 99 percent of its rays do not penetrate to a depth of more than a few hundred meters, and in some muddy seas – even a few dozen. It only gets darker further, and deep-sea organisms often resort to bioluminescence in order to at least slightly disperse this darkness.

However, many local animals use the darkness for shelter. The surface of their skin effectively absorbs even those rare photons that appear at this depth, making them virtually invisible “black holes”. This is described in a new article by Karen Osborn and her colleagues at the National Museum of Natural History in Washington, published in Current Biology.

During the expeditions, scientists used remotely controlled drones, making deep-sea dives in the Gulf of Mexico and Monterey Bay off the California Pacific coast. Among dozens of unusual creatures that biologists observed and caught at a depth of a couple of kilometers, 16 species of fish were found, characterized by “extremely black” skin, absorbing 99.5 percent of the incident light.

Note that this figure is still not a record. The black feathers of some birds of paradise also absorb more than 99 percent of the radiation, and synthetic materials reach 99.995 percent. Nevertheless, scientists were extremely interested in how this mechanism works in deep fish, so they investigated the structure of their skin under a microscope.

It turned out that the cells of its surface layers are densely filled with melanosomes containing the light-absorbing pigment melanin. At the same time, the size and shape of the melanosomes make the photons, not immediately absorbed, not reflected, but sent to deeper layers, where they are captured by additional “deposits” of pigment.