Anglerfish have light-absorbing skin to keep hidden while they attract prey with a glowing lure.
Introduction
Anglerfish are the Harry Potters of the deep sea: They have both a luminous wand and an invisibility cloak. They wield these weapons to eat and not be eaten in the dark depths.
There are more than 200 species of anglerfish. Most are dark gray or brown and less than 1 foot (30 centimeters) long, though the largest can reach 40 inches (100 centimeters). They have huge heads and mammoth mouths filled with sharp, translucent fangs. They dwell far below the surface of the ocean, where sunlight no longer penetrates and the ocean fades to black. Here, female anglerfish have evolved body features to manipulate light—to lure prey with it and simultaneously to avoid illuminating themselves and becoming prey.
There are some 200 species of anglerfish. Female anglerfish have evolved body features to manipulate light—to lure prey with it and simultaneously to avoid illuminating themselves and becoming prey.
The Strategy
In the vast, dark, open spaces of the ocean, bacteria, tiny zooplankton, shrimp and other crustaceans, jellies and other gelatinous animals, and many fish produce and emit their own light. They use this bioluminescence to attract mates, communicate with kin, or blend in with light flowing down from the surface. But every time a creature lights up, it risks being seen by predators.
A female anglerfish works both ends of this paradox, using two remarkable s. Instead of expending energy to search for food, she coaxes food to unwittingly come to her.
The first adaptation is a long, movable spine sticking out of the top of her head. At the tip of the spine hangs a fleshy sac called an esca. Inside the esca, bioluminescent bacteria settle in to live. They emit light in blue wavelengths that aren’t absorbed by water. The bacteria gain a protected place to live. The anglerfish gets a glowing orb to attract prey. The spine is her fishing rod; the glowing esca is her bait.
An anglerfish dangles her spine just above her cavernous mouth to mimic the movements of smaller, glowing organisms. She keeps the rest of her body still and hovering. That’s when she makes use of the second key adaptation: her skin.
To lure prey, anglerfish use a spine that they dangle above their fanged jaws. At the tip is a sac filled with bioluminescent bacteria, whose light attracts prey.
Anglerfish (Bufoceratias wedli)
Many anglerfish have ultra-black skin that absorbs nearly 100% of the light that hits it. They blend completely into the blackness surrounding them, rendering everything invisible but their luminous escas.
This capacity comes from structures within cells called melanosomes, which contain the same light-absorbing as human skin: melanin. The outermost part of an anglerfish’s skin is lined with a continuous thin layer of large melanosomes that are densely packed in a way that leaves no unpigmented gaps. The melanosomes are also ideally shaped and positioned so that they scatter light sideways within the layer, increasing its time within the pathway of light-absorbing melanosomes. One species of anglerfish has skin that reflects a mere 0.04% of the light shined on it.
Together, the skin-and-esca system makes the anglerfish simultaneously seen and unseen. The esca glows like a solitary beacon, attracting prey. When victims draw near enough, the anglerfish engulfs them. The maw, encircled with inward-pointing stiletto teeth, is an inescapable cage.
The Potential
Scientists have taken a lesson from anglerfish, exploring ways to harness bioluminescent light. Applications range from glowing biochemical “tags” used in medicine and scientific research to new bioinspired lamps and the development of bioluminescent trees that could replace streetlights.
Researchers are also investigating the properties of ultra-black skins to explore new ways to make light-absorbing materials for solar panels, telescopes, and camouflaging textiles.
