Dark Fish

March 7, 2021
By Damond Benningfield

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Many deep sea fish are dark colored or even ultra black to help them blend in to the dark sea around them. Credit: public domain

In the darkness of the deep ocean, the faintest glimmer of light can mean the difference between life and death. It can scare away prey or draw in predators. So remaining completely dark can help a deep-sea fish catch a meal -- or avoid getting caught.

A recent study found some fish that have a big advantage in that area. Their skin is almost completely black -- it reflects no more than one-half of one percent of the light that strikes it. That makes the fish much darker than charcoal, and among the darkest living organisms on the planet.

Researchers collected fish from depths of up to 6500 feet during cruises in the Gulf of Mexico and Monterey Bay in California. They found 16 species that they described as “ultra black.” Most of them are medium-sized, suggesting they need to be especially careful to attract prey and avoid predators. And a few use light-producing “lures” to pull in prey, so dark skin eliminates any reflections that might give them away.

The scientists used electron microscopes to study the structure of the skin of these fish. And they used computer models to understand how the light behaves once it hits the skin.

They found that small organs like those in our own skin contain a high level of black pigment. And the organs are shaped in such a way that the light they don’t absorb is reflected into the surrounding skin, where it can be absorbed by the other organs. The combination makes these “ultra-black” fish almost impossible to see in the deep ocean.