Hatchetfish

Natural History

Hatchetfish are well camouflaged. Like many deep sea fishes, they have light-producing organs in rows along their bellies. These organs shine a pale blue light that matches daylight filtering down from above, and hides them from predators below.

Hatchetfish can regulate the intensity and color of light from these organs to match the light filtering down. Each species of hatchetfish has its own particular pattern of lights. 

This use of bioluminescent light is called "counterillumination," a common adaptation in midwater fishes and cephalopods. Some midwater predators hunt by looking up for the silhouettes of animals. Counterillumination makes hatchetfish almost invisible from below.

Conservation

Anything that finds its way into the ocean, whether it's tossed away as trash, washes off a beach or falls off a boat, may eventually make its way to the deep sea. It's important to realize that the deep sea is not so far away that it's beyond the reach of human activities. Living creatures in the deep are affected by what we do at the surface.

Cool Facts

A hatchetfish's eyes can focus close up or far away.