Physicists Investigate How Hatchetfish Camouflage in the Deep Sea

The midwater region of the ocean is the largest habitat by volume in the world, making up 99 percent of Earth’s livable space. It’s home to a myriad of occupants, many of which have evolved peculiar abilities to allow them to survive.

“They spend their whole lives sort of suspended in the middle,” says Alison Sweeney, an assistant professor in the Department of Physics & Astronomy. “Because they live in this three dimensional void, they have to deal with being potentially visible from every angle. There’s literally nothing to hide behind and so they end up hiding within the light itself. The deep sea is a really amazing place to look for cool biological optics because so much of the ecology is driven by light.”

Hatchetfish, so named because the shape of their bodies resembles the blade of a hatchet, are one of the “classic-example weirdo fish denizens of the midwater.”

Because many deep-sea creatures hunt by looking up and seeing shadows or silhouettes, hatchetfish's large flat bodies keep them relatively well hidden. Their skin is somewhat metallic-looking, resembling the dull side of aluminum foil.

Hatchetfish also have a line of photophores on their belly that produce light, or bioluminescence. This is useful for when the fish are swimming in waters shallow enough for sunlight to dominate. By producing their own light with the same intensity as the faint sunlight coming from above, the hatchetfish make themselves invisible to predators.

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