Ultra-black skin allows some fish to lurk unseen
Packed pigment granules help them blend in without blowing their cover


Date:
July 16, 2020
Source:
Duke University
Summary:
Scientists report that at least 16 species of deep-sea fish have
evolved ultra-black skin that absorbs more than 99.5% of the
light that hits them, making them nearly impossible to pick out
from the shadows. These fish owe their disappearing act to tiny
packets of pigment within their skin cells called melanosomes. The
melanosomes of ultra-black fish are differently shaped and arranged
on a microscopic level, compared with regular black fish, says a
new study.



FULL STORY ==========================================================================
If there were a stagehand of the sea, wearing black to disappear into the darkness backstage, it might be the dragonfish. Or the common fangtooth.


========================================================================== These fish live in the ocean's inky depths where there is nowhere to
take cover. Even beyond the reach of sunlight, they can still be caught
in the glow of bioluminescent organisms that illuminate the water to
hunt. So they evade detection with a trick of their own: stealth wear.

Scientists report that at least 16 species of deep-sea fish have evolved
ultra- black skin that absorbs more than 99.5% of the light that hits
them, making them nearly impossible to pick out from the shadows.

These fish owe their disappearing act to tiny packets of pigment within
their skin cells called melanosomes. The melanosomes of ultra-black fish
are differently shaped and arranged, on a microscopic level, compared
with regular black fish, says a study led by Duke University and the Smithsonian National Museum of Natural History.

The researchers say the work could lead to new light-trapping materials
for use in applications ranging from solar panels to telescopes.

For the paper, to be published July 16 in the journal Current Biology,
the team used a trawl net and a remotely operated vehicle to scoop up
39 black fish swimming up to a mile deep in the waters of Monterey Bay
and the Gulf of Mexico, and bring them up to a ship to study.



========================================================================== Using a spectrometer to measure the amount of light reflected off the
fishes' skin, the researchers identified 16 species that reflected less
than 0.5% of light, making them some 20 times darker and less reflective
than everyday black objects.

"Ultra-black arose more than once across the fish family tree," said
first author Alexander Davis, a biology Ph.D. student in Sonke Johnsen's
lab at Duke.

The darkest species they found, a tiny anglerfish not much longer
than a golf tee, soaks up so much light that almost none -- 0.04% --
bounces back to the eye. Only one other group of black animals, the birds-of-paradise of Papua New Guinea with their ultra-dark plumage,
are known to match them.

Getting decent photos of these fish onboard the ship was tough; their
features kept getting lost. "It didn't matter how you set up the camera or lighting - - they just sucked up all the light," said research zoologist
Karen Osborn of the Smithsonian National Museum of Natural History.

The team found that, when magnified thousands of times under electron microscopes, normal black skin and ultra-black skin look very
different. Both have tiny structures within their cells that contain
melanin -- the same pigment that lends human skin its color. What sets ultra-black fish apart, they say, is the shape and arrangement of these melanosomes.

Other cold-blooded animals with normal black skin have tiny pearl-shaped melanosomes, while ultra-black ones are larger, more tic-tac-shaped. And
ultra- black skin has melanosomes that are more tightly packed together, forming a continuous sheet around the body, whereas normal black skin
contains unpigmented gaps.

The researchers ran some computer models, simulating fish skin containing different sizes and shapes of melanosomes, and found that ultra-black melanosomes have the optimal geometry for swallowing light.

Melanosomes 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," Davis said.

Their ultra-black camouflage could be the difference between eating and
getting eaten, Davis says. By being blacker than black, these fish manage
to avoid detection even at six-fold shorter ranges.


========================================================================== Story Source: Materials provided by Duke_University. Original written
by Robin A. Smith.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alexander L. Davis, Kate N. Thomas, Freya E. Goetz, Bruce
H. Robison,
So"nke Johnsen, Karen J. Osborn. Ultra-black Camouflage in Deep-Sea
Fishes. Current Biology, 2020; DOI: 10.1016/j.cub.2020.06.044 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200716111636.htm

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