Moray Eels: Behavior, Species, and Safe Encounters

Why Morays Look Threatening (But Usually Aren't)

A moray eel resting in its hole, mouth opening and closing rhythmically, looks like an animal displaying aggression. It is not. Moray eels breathe by pumping water over their gills — they lack the gill plates that fish use to create suction without moving the jaw, so they open and close their mouths continuously as the primary breathing mechanism. The teeth visible during this process are real (sharp, curved, and numerous) but their display is incidental to respiration.

Moray eels are not predators of divers. They are predominantly hunters of fish, octopus, and crustaceans, and they locate prey primarily by smell rather than vision. Their eyesight is poor in open water; in the dim crevices they inhabit, it is nearly useless. The risk of a bite comes almost entirely from two scenarios: a diver placing their hand in a crevice occupied by a moray, or a diver hand-feeding a moray (which trains it to associate human hands with food, with unpredictable consequences).

Anatomy: The Second Jaw

Moray eels possess a unique anatomical feature discovered in 2007 that changed how biologists understood their predation: pharyngeal jaws — a second set of jaws deep in the throat that can be shot forward to grasp prey already held in the front teeth, and then retract to move prey backward into the digestive system.

Most predators that seize prey in their jaws use suction, head-shaking, or tongue action to move prey down the throat. Morays, whose narrow bodies and small mouths prevent the suction feeding used by most fish, evolved this independently-acting second jaw instead. It is the same adaptation used by the Xenomorph in the Alien films, though the film's creator drew on different inspiration.

Common Species

Giant moray (Gymnothorax javanicus): The largest moray species, reaching 3m and 30kg. Mottled brown-grey with a paler face. Throughout the Indo-Pacific; the most frequently encountered large moray on reef dives. Despite their size, they are typically docile unless provoked or hand-fed.

Green moray (Gymnothorax funebris): The Caribbean's largest moray; actually brown in body — the green colour comes from yellow mucus coating the brown skin. Can reach 2.5m. Rocky reef and coral rubble throughout the Caribbean.

Snowflake moray (Echidna nebulosa): Small (to 75cm), bold white-and-black mottled pattern. Does not eat fish — specialises in crustaceans, with rounded teeth designed for crushing crab shells rather than piercing fish. Common throughout the Indo-Pacific, often found in very shallow reef zones.

Zebra moray (Gymnomuraena zebra): Striking brown and white bands. Another crustacean specialist — crushing teeth, completely harmless to fish or divers. Indo-Pacific reefs, often in areas with abundant sea urchins.

Ribbon eel (Rhinomuraena quaesita): Not a moray in the traditional sense (different genus) but in the same family. Juveniles are jet black; males are brilliant electric blue with yellow fin margins; females are entirely yellow. Changes sex from male to female over its lifespan. One of the most visually dramatic reef fish.

Cooperative Hunting

Giant morays have been observed in cooperative hunting partnerships with roving coral groupers (Plectropomus pessuliferus) — a behaviour documented in the Red Sea and occasionally in the Indo-Pacific. The grouper signals to the moray (with a head-shaking shimmy near the eel's hole) that it has located prey sheltering in a crevice. The moray enters the crevice and flushes the prey out into open water, where the grouper can pursue it. Both benefit from the arrangement, and it is one of the very few documented cases of active cooperative hunting between two unrelated vertebrate species.