Fish
Giant Moray
Gymnothorax javanicus · also called giant moray eel, Java moray
The giant moray is the biggest of the moray eels — a thick, spotted, muscular fish that lives wedged in the reef with only its head showing, mouth working open and shut. It is a formidable solo ambush hunter, and, unusually for a fish, a team player.
Overview
Gymnothorax javanicus lives on Indo-Pacific and Red Sea reefs, from East Africa to the central Pacific. It reaches about 2.5–3 m and 30 kg, the heaviest of roughly 200 moray species, patterned with dark leopard spots. It hunts fish, octopus, and crustaceans, mostly at night.
Two sets of jaws
Living in cracks, a moray cannot suck prey down the way an open-water fish does. Instead it has enlarged pharyngeal jaws in its throat that shoot forward into the mouth, grab the prey, and drag it back — the mechanism that inspired the monster in Alien.
Hunting with groupers
On some reefs, a coralgrouper recruits a giant moray to a hunt by swimming to its den and shaking its head, then leads it to hidden prey and even performs a headstand to point it out. The moray flushes fish from crevices the grouper can’t enter; the grouper catches those that flee into open water. Both catch more together than alone — a rare, well-documented case of cooperative hunting between two predator species.
Handle with care
Its constant gaping is just breathing — pumping water over the gills. Bites almost always involve divers hand-feeding or reaching into holes. And large giant morays carry dangerous levels of ciguatoxin, so the flesh is considered unsafe to eat.
Status
The giant moray is Least Concern and stable, common across its range and largely ignored by fisheries because of the poisoning risk.
Giant Moray: common questions
How does a moray eel have two sets of jaws?
Behind the main jaws, in the throat, a moray has a second pair called the pharyngeal jaws, which most bony fish use only to grip and process food already in the mouth. In morays these throat jaws are unusually large and mobile and are mounted on long muscles. When the moray bites prey with its outer jaws, it launches the pharyngeal jaws forward into the mouth, clamps them onto the prey, and hauls it back down the throat. This solves a problem specific to morays; living in narrow cracks, they cannot create suction to swallow the way an open-water fish does, so they use the inner jaws as a grab instead. It is the same mechanism, minus the acid, that inspired the creature in the film Alien.
How does the cooperative hunting with groupers work?
On some Red Sea and Great Barrier Reef sites, roving coralgroupers and giant morays hunt as a loose team. A hunting grouper that has chased a fish into a coral crevice will swim to a resting moray, hover head-down in front of it, and shake its head rapidly. If the moray responds it leaves its hole and follows the grouper, which leads it to the spot. The moray then enters the reef and either grabs the hidden fish or drives it out into open water, where the waiting grouper takes it. Neither predator reliably gets the meal, but each catches more often when hunting together than alone, because the moray reaches places the grouper cannot and the grouper covers the open water the moray is too slow for.
Are giant morays dangerous to divers?
They are large predators with a serious bite and a grip that is hard to break, and a provoked or startled moray can inflict a deep, ragged, easily infected wound. But they are not aggressive toward people and spend the day resting in their dens. Almost all recorded bites involve divers who put a hand into a hole, who spear or grab an eel, or, most often, who hand-feed morays at dive sites, which teaches the animals to associate people with food and to lunge at hands. Left alone, a giant moray simply watches from its crevice.
Can you eat a giant moray?
It is strongly advised against. Giant morays are among the fish most often linked to ciguatera poisoning, caused by toxins that originate in a reef microalga and become concentrated as they pass up the food chain into large, long-lived predators. A big giant moray can carry a dangerous dose, and outbreaks in the Pacific and Indian Oceans have hospitalised many people and caused deaths, with the liver especially toxic. The toxin cannot be removed by cooking, freezing, or cleaning, and there is no simple test, so the flesh is treated as unsafe throughout its range.