Fish
Moray Eel
Muraenidae · also called moray eels
A moray eel hides a second set of jaws in its throat, and when it finally strikes, that hidden jaw shoots forward into its mouth to grab already-caught prey and haul it straight down — a feeding trick found in almost no other fish. The rest of the time it just looks like it is threatening you, mouth gaping wide from a reef crevice, when it is actually only breathing.
Overview
Moray eels, family Muraenidae, are reef-dwelling ambush predators found on tropical and subtropical reefs worldwide. Lacking pectoral and pelvic fins, they move with a smooth, snake-like undulation and hunt mainly at night, relying on smell over weak eyesight to find fish, octopuses, and crustaceans hidden in crevices.
Jaws within jaws
A moray’s pharyngeal jaws, a second toothed set deep in the throat, launch forward to seize prey and drag it down — a substitute for the suction-feeding most fish rely on, which works poorly in tight reef crevices. Despite being capable predators, many morays hold still for cleaner shrimp and fish picking parasites from their mouths.
Status
Least Concern — common and widespread across reef habitats globally, with only localised pressure from reef degradation or targeted collection in some areas.
Moray Eel: common questions
How does a moray eel's second set of jaws actually work?
A moray eel's pharyngeal jaws sit further back in the throat and normally rest in that position, but when the eel bites down on prey with its main jaws, the pharyngeal jaws are launched rapidly forward into the mouth, grab the prey item directly, and pull it back down into the throat and gut. This mechanism largely substitutes for the strong suction-based feeding that most other fish rely on to swallow prey, which works poorly in the tight, confined reef crevices where moray eels typically hunt and would otherwise make swallowing captured prey considerably more difficult.
Why does a moray eel keep opening and closing its mouth?
This repeated open-mouthed gaping is not a threat display but a basic breathing behaviour, since moray eels lack the large, muscular gill covers that most fish use to actively pump water over their gills. Opening and closing the mouth in this way helps draw water in and push it back out over the gills, allowing the eel to keep breathing effectively even while remaining almost completely still and hidden within a rock or coral crevice for extended periods.
Do moray eels really let shrimp and small fish clean them?
Yes, many moray eel species regularly visit or tolerate cleaning stations where small cleaner shrimp or cleaner fish pick parasites, dead skin, and debris from the eel's mouth, gills, and body surface, and the eel will often hold remarkably still with its mouth open throughout the process. This is a genuine mutualistic relationship, benefiting the eel through improved health and parasite removal and benefiting the cleaner species through a reliable meal, and it occurs despite the moray being an entirely capable predator of similarly sized animals in other contexts.
Is a moray eel dangerous to divers and swimmers?
Moray eels are generally not aggressive toward humans and typically retreat into their crevice when approached, but they can deliver a painful and sometimes serious bite if provoked, cornered, or, especially, if a diver's hand is mistaken for food while hand-feeding, which is why hand-feeding wild morays is strongly discouraged. Most reported moray bites on humans occur in exactly this hand-feeding context or when a diver reaches into a crevice without seeing the eel sheltering there, rather than from unprovoked attacks on swimmers simply passing by.