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Ultra-black Fish Are “Living Black Holes”

These fish absorb 99.5% of light—making them practically invisible

Karen - Idiacanthus_1450747-8-2_sm
© Karen Osborn, Smithsonian

The ocean is full of mysteries, and nowhere is more mysterious than the deep sea. Because of its intense pressure, utter darkness and freezing temperatures, the deep-sea habitat is not for everyone. But from tube worms that thrive on toxic hydrothermal vents to entire communities that pop up around whale falls, animals have employed all kinds of strategies to survive there.

Scientists have discovered another weird and wild way animals survive in our ocean’s deepest depths: ultra-black coloring. A team of scientists discovered that 16 different species (that we know of!) use deep black coloring to stay hidden in the deep sea. They’re so dark that they resemble Vantablack, the manmade pigment that absorbs 99.965% of light that hits it. (If you want to go down a [black] rabbit hole, check out the MIT-created material that is apparently 10x blacker than Vantablack.)

Why be ultra-black in the dark deep sea?

Sunlight can travel only so far in the ocean. The sun’s rays can penetrate to a depth of about 1,000 meters, but only the top 200 meters—known as the photic zone—get enough light to support photosynthetic plant life. But sunlight isn’t the only light available: Bioluminescence, or chemically-produced light that comes from an organism, is common in the deep sea. The sudden bioluminescent light from a predator  can surprise and stun potential prey or illuminate them for easier visibility. Some animals definitely use their lights as lures in the deep sea to draw prey to them. Doing this can distract or misdirect a predator for a time, allowing the prey to quickly escape. A glowing light can also signal to predators that the potential prey is toxic and also serve as a warning sign for others that a predator is among them.

Ultra-black Fish in black water
© Karen Osborn, Smithsonian

Sometimes, however, animals need to be stealthier. For some species that use lures, like the anglerfish, there needs to be a way that the lure brings prey in without lighting up the waiting predator behind it. That’s where ultra-black coloring comes in. “Ultra-black” means the material absorbs 95% or more of the light that hits it. There are a few other animals that fall in this category, including some insects and birds, but it’s relatively rare to find.

How do they do it?

It’s not easy to achieve ultra-black status which requires lots of energy and special traits. When the scientists looked at the skin of these fortunate fishes under a microscope, they found that their melanosomes, or specialized skin structures that store melanin, had a unique configuration. Rather than supported by collagen proteins, like other animals, the melanosomes in these species were packed incredibly tightly. This means that less incoming light is reflected straight back out to the observer.

Ultra-black Fish in black water
© Karen Osborn, Smithsonian

With much of the deep sea still unexplored, we’re likely only scratching the surface of the strange and unusual ways animals survive there. But just because the deep sea is remote doesn’t mean it’s immune to human influence—help Ocean Conservancy protect the deep sea, and the animals that live there, from climate change and plastic pollution.

Can’t get enough weird and wonderful deep-sea critters? Learn about the dumbo octopus, the deep-sea lizardfish and the Pacific footballfish.

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