Fish
Gulper Eel
Eurypharynx pelecanoides · also called pelican eel, umbrella-mouth gulper
A gulper eel is mostly mouth: a loosely hinged jaw and stretchy throat pouch attached to a thin, whip-like body, built to engulf whatever drifts close enough in the food-scarce darkness of the deep sea. A small glowing light at the very tip of its long tail may be the lure that brings prey within reach of that oversized mouth in the first place.
Overview
The gulper eel, Eurypharynx pelecanoides, is a deep-sea fish living roughly 500 to 3,000 metres down in the Atlantic, Pacific, and Indian Oceans. Its enormous, loosely hinged jaw, resembling a pelican’s expandable throat pouch, gives the species its alternative name, the pelican eel.
A mouth built for scarcity
Despite the mouth’s theoretical size, stomach contents show gulper eels mainly eat small crustaceans, with the oversized jaw acting as an opportunistic adaptation to an unpredictable deep-sea food supply rather than a tool for routinely swallowing giant prey. A small light-producing organ at the tail tip likely lures curious prey through the darkness.
Status
Least Concern, based on a very wide deep-ocean distribution, though its extreme depth means population size and trend remain genuinely poorly documented.
Gulper Eel: common questions
How does a gulper eel's mouth open so wide?
The gulper eel's lower jaw is only loosely connected to the skull and can swing outward and downward much more freely than in most fish, while the throat and pouch-like tissue behind the mouth is capable of significant stretching, together allowing the mouth and throat to expand dramatically to accommodate prey considerably larger than what the eel's otherwise very slender, elongated body would suggest it could swallow.
Why does the gulper eel have a light at the tip of its tail?
The small light-producing organ, or photophore, at the very tip of the gulper eel's long tail is thought to function primarily as a lure, producing a faint glow in the near-total darkness of the deep sea that may attract small, curious prey animals close enough for the eel to strike. Some researchers have also suggested the light could play a role in deterring or confusing the eel's own predators, though its lure function for attracting prey is generally considered the more likely primary purpose.
Does a gulper eel actually eat animals bigger than itself?
While its enormous, expandable mouth is theoretically capable of engulfing quite large prey relative to its slender body, actual examination of stomach contents from captured gulper eels suggests the species feeds mainly on smaller crustaceans and other modest-sized deep-sea invertebrates rather than routinely swallowing very large prey. The oversized mouth is thought to function more as a flexible, opportunistic adaptation for an unpredictable deep-sea food supply than as a tool used constantly to swallow disproportionately massive meals.
Why is so little known about the gulper eel's biology?
The species lives at extreme ocean depths, typically well over 500 metres and sometimes several thousand metres down, conditions that make direct observation of live, undisturbed gulper eels in their natural habitat exceptionally difficult and expensive to achieve using submersibles or remotely operated vehicles. Much of the existing scientific understanding of the species instead comes from specimens recovered in deep trawl nets, which can damage delicate deep-sea animals and provide only limited insight into natural behaviour, reproduction, and social structure compared with a living, undisturbed animal observed in its own environment.