Scientists discover fish so black they vanish in light

In a new study led by the Smithsonian National Museum of Natural History, scientists have discovered fish deep in the ocean with skin so black that it is one of the darkest materials in existence. The ultra-black fish absorb more than 99.5% of light, which means that even in the brightest light, they can disappear from view.  

The fish aborb light with so much efficiency that in the bioluminescent light produced by deep-sea creatures, they appear to be silhouettes with no discernible features.

Study co-authors Karen Osborn and Sönke Johnsen report that it is a unique arrangement of pigment-packed granules that enables some black fish to absorb light, and as little as 0.05% of the light is reflected back. 

When the remarkable fish first caught her attention, Osborn was attempting to photograph them in trawl nets used to sample the deep sea. Even using sophisticated equipment, she said, she could not capture any detail in the images. “It didn’t matter how you set up the camera or lighting – they just sucked up all the light.”

Lab experiments revealed that many of the black fish pulled up from the deep sea could absorb more than 99.5 percent of the light that hit their surfaces. This ultra-black appearance greatly improves their chance of survival. 

Most animals in the deep sea create their own light called bioluminescence, which is used to attract mates and lure prey. These biochemical emissions of light can also be used to expose lurking predators – 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,” said Osborn.

The researchers found that the light absorption capabilities of the ultra-black fish skin rely on melanin, which is the same pigment that protects human skin from sunlight. The pigment is contained in cellular compartments, or melanosomes, that are densely packed into pigment cells.  

The pigment cells are arranged very close to the surface of the skin in a continuous layer. The melanosomes direct any light they do not absorb to neighboring melanosomes that take up the slack.

“Effectively what they’ve done is make a super-efficient, super-thin light trap,” said Osborn. “Light doesn’t bounce back; light doesn’t go through. It just goes into this layer, and it’s gone.”

“These pigment-containing structures are packed into the skin cells like a tiny gumball machine, where all of the gumballs are of just the right size and shape to trap light within the machine,” said study co-author Alexander Davis.

The team found the same distinct pigment patterns in 16 species of distantly related fish.

“This is the only system that we know of that’s using the pigment itself to control any initially unabsorbed light,” said Osborn. 

She explained that mimicking this strategy could help engineers develop less expensive, flexible, and more durable ultra-black materials for use in optical technology, such as telescopes and cameras, and for camouflage.

“Instead of building some kind of structure that traps the light, if you were to make the absorbing pigment the right size and shape, you could achieve the same absorption potentially a lot cheaper and (make the material) a lot less fragile.”

The study is published in the journal Current Biology.

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By Chrissy Sexton, Earth.com Staff Writer