Elongated bristlemouth

About the Elongated bristlemouth

If you spend some time poking around in the twilight zone (or on this website), chances are you will bump into a bristlemouth. These small, dark—and yes, toothy—fish are right up there with lanternfish in abundance. The family’s most prolific genus, Cyclothone, are believed to be the most abundant vertebrate on earth, with estimates in the quadrillions. But not all bristlemouths are the same. Unlike many Cyclothone or even its deep-sea cousin Sigmops bathyphilus, the elongated bristlemouth migrates each night from its daytime abode of 500-1500 meters (1600-5000 feet) to the ocean surface, as part of the largest daily migration on the planet.

Flexibility may be the key to the elongated bristlemouth’s success. It’s a hermaphrodite that changes from male to female over its two-year life cycle. They’ve been found in temperate and tropical oceans around the world. As juvenile fish get bigger, they sprout light-producing organs on their bellies that create counter-illumination. This tactic is used by a variety of twilight zone creatures to blend in with dappled light coming from above, confusing predators that attack from below.

With its needle-like fangs and long lower jaw, the elongated bristlemouth lives up to its name. Judging from the stomach contents of fish that come up in scientific nets, researchers hypothesize that elongated bristlemouth opportunistically feed on smaller fish, grabbing them from the tail with those bristling teeth. Otherwise, they seem content to snack on small crustaceans and zooplankton—especially ostracods and copepods. Best not to be choosy when you’re just one in a quadrillion.