Moray Eel: Identification, Second Jaws and Bite Risk

A moray is a true eel with no pectoral or pelvic fins at all, a laterally compressed body, and dorsal and anal fins that run continuously into the tail as a single low fringe. That absence of side fins is the quickest way to separate a moray from a wolf eel or an eelpout, which do have them.

The green moray, the big one on the US Atlantic and Caribbean coasts, is described by the Florida Museum as often 6 feet long and reaching 8 feet and 65 pounds. Its colour is a trick: the skin underneath is dark grey-brown, and the green comes from a thick layer of yellow mucus over it.

Other working marks:

• A round gill opening behind the head instead of a bony gill cover
• Skin with no visible scales, always coated in mucus
• Eyes set well forward on a pointed head
• Long jaws lined with backward-curving teeth

If you have a photo from a reef or jetty and want the species, photograph it and the app identifies it.

A moray sitting in a hole with its mouth gaping looks like a threat display, and people read it as aggression. It is breathing.

Morays have small round gill openings and no bony gill cover to pump water across the gills the way most fish do. So the mouth opens and closes constantly, mechanically pumping water through the head and out the gill pores. The Florida Museum describes exactly this for the green moray.

A moray with its mouth open is doing what it does every second of the day. It is not a warning, and there is no version of it that means the animal is about to strike.

Most bony fish capture prey by suction: they open the mouth fast, water and prey rush in, and the food is carried back to a set of pharyngeal jaws in the throat, derived from the gill skeleton, which process it.

Morays cannot do that. Their bodies are long and narrow with a reduced gill cover, so they cannot generate the pressure drop that suction feeding needs. Mehta and Wainwright showed in Nature in 2007 that morays solve this a different way: the pharyngeal jaws themselves lunge forward — in one filmed eel reaching 3.5 cm, more than the eel's own 3.3 cm head length — grab the struggling prey, and haul it back down the throat.

The mobility comes from elongated muscles controlling those jaws and a reduction of the neighbouring gill-arch structures. The authors described it as the first known case of a vertebrate using a second set of jaws both to restrain and to transport prey.

This is also why a moray bite is worse than the tooth size suggests. The animal is built to hold and pull rather than to bite and release.

Green morays occupy rocky shorelines, coral reefs and mangroves in the western Atlantic from New Jersey to Bermuda and the northern Gulf of Mexico, south to Brazil, including Ascension Island, with occasional strays as far north as Nova Scotia. They also use tidal creeks, harbours, seagrass beds and soft bottoms, and generally stay shallower than 100 feet.

They hunt at night and rely heavily on smell rather than sight, working prey out of reef crevices. The diet is fishes, crabs, cephalopods and shrimps.

In daylight a moray is normally jammed into a hole with only the head showing, which is how most divers meet one.

Morays are not aggressive toward divers, but the Florida Museum states plainly that bites from green morays can be painful and sometimes life-threatening. Nearly all recorded bites involve hand-feeding, reaching into a hole, spearfishing, or handling a hooked eel.

A moray bite tears rather than punctures, and the wound is heavily contaminated with bacteria. Any moray bite needs medical attention promptly: irrigate the wound, control bleeding, and get to urgent care or an emergency department for cleaning, a tetanus check and a decision about antibiotics. Do not try to pull free if an eel has a grip, which makes the tearing worse.

The second risk is food, not teeth. Large reef predators including morays can accumulate ciguatera toxin, and the Florida Museum specifically notes that eating green moray risks ciguatera poisoning, which causes gastrointestinal upset and weakness in the limbs, sometimes lasting a long time. Ciguatera is not destroyed by cooking. If you suspect ciguatera poisoning, contact a doctor and call Poison Control at 1-800-222-1222 in the United States.