Green Moray (Gymnothorax funebris): Facts, Size and Habitat

Why is the green moray green?

The green moray is not really green. Its thick, scaleless skin is dark brown to gray, and it is covered by a layer of yellowish mucus made by special mucus-producing cells in the skin. Yellow over dark brown looks green to our eyes, so a living eel ranges from olive and bright green to brownish green.

Museum specimens give the trick away. Once the mucus is gone, a preserved green moray is drab and dark, and that somber color explains its scientific name: funebris is Latin for “funereal”. The mucus is not just for show. It protects the skin against parasites and infections, and it helps the eel slide in and out of tight holes in the reef without scraping itself.

The color is even from head to tail, with no spots, bars or other markings on the body or fins. Young green morays are uniformly dark and do not have the white chin seen in juveniles of some related morays.

How to recognize a green moray

Like all morays, the green moray has a long, muscular body that is flattened from side to side, a large mouth full of smooth-edged teeth and small eyes. Moray eels have no pelvic or pectoral fins. A single long fin starts just behind the head, runs along the back, wraps around the tail and continues underneath, so the eel looks like a thick ribbon.

Look closely at the snout and you will see a pair of tube-shaped nostrils. Morays have poor eyesight and rely mainly on smell, drawing water in through these tubes. The gill openings are small round holes on the sides of the head, far behind the mouth.

In Florida and the Caribbean, divers see several other morays, but none is plain green:

• Spotted moray (Gymnothorax moringa): pale whitish or yellowish, densely covered with dark spots.
• Goldentail moray (Gymnothorax miliaris): small and dark brown with tiny yellow spots and a yellow tail tip.
• Chain moray (Echidna catenata): dark with a bold yellow chain-like pattern.

Morays are true eels, members of the order Anguilliformes, like the European eel. They are fish with gills and fins, not sea snakes, a difference explained in eel vs snake.

How big do green morays get?

The green moray is one of the largest morays in the world and the biggest in the tropical Atlantic. The maximum reported size is about 2.5 m (8 ft) and 29 kg (65 lb), but such giants are rare. Most large adults top out at around 1.8 m (6 ft) and 13 kg (30 lb).

Worldwide, the giant moray (Gymnothorax javanicus) of the Indian and Pacific oceans is the heaviest moray, while the slender giant moray is longer but much thinner. Among morays the green moray stands out for its thick, heavy build.

Habitat and range

Green morays live in the warm western Atlantic Ocean, from the coasts of New Jersey and New York and from Bermuda, through the Gulf of Mexico, Florida, the Bahamas and the Caribbean Sea, south along the coast of South America to Brazil. A stray, probably carried north by the Gulf Stream, has been recorded as far north as Nova Scotia, Canada. The species is common in the Florida Keys, the Bahamas and throughout the Caribbean.

This is a bottom-dwelling, solitary fish of shallow water, usually found shallower than 30 m (100 ft) and reported down to about 40 m (130 ft). It lives on coral reefs and rocky shorelines, but also in mangroves, seagrass beds, tidal creeks and harbors, and over sand and mud bottoms. During the day it hides in a crevice, a hole in the reef or a gap under a ledge, often with only its head showing.

Why does a green moray open and close its mouth?

The constant gaping that makes morays look so fierce is simply breathing. Most fish push water over their gills by working their gill covers. A moray’s gills are small and round, and the gill openings sit far back on the head, so the eel pumps water through by opening and closing its mouth. The water passes over the gills and leaves through the small gill holes behind the head.

Morays are fairly sedentary animals with modest oxygen needs, and small gills are enough for them. So when you see a green moray showing its teeth from a crevice, it is not threatening you. It is breathing.

What do green morays eat?

Green morays are nocturnal predators of fish, crabs, shrimp, octopuses and squid. They hunt mainly by smell, sliding through the narrow holes and tunnels of the reef where small animals hide at night. Their slim, flexible bodies can follow prey into spaces that larger predators cannot enter.

Morays catch prey with a quick bite and then use a remarkable second set of jaws in the throat to drag it down, a system described in Why do moray eels have two sets of jaws? They swallow prey whole and do not chew.

Morays sometimes hunt alongside other predators. In Brazil, snappers have been seen recruiting green morays while foraging among mangroves, and in the Red Sea groupers team up with giant morays, a partnership explained in Do moray eels hunt with groupers?

Behavior and daily life

Green morays live alone. By day they rest in a favorite shelter, sometimes visiting cleaning stations where cleaner gobies, wrasses and cleaner shrimps pick parasites and dead skin from their bodies. At night they leave the den to hunt.

A tracking study published in 2021 followed 16 green morays fitted with acoustic transmitters in the mangrove estuary of Salt River Bay, St. Croix, in the US Virgin Islands. Most were active mainly at night. The eels used home ranges averaging about 5.8 hectares (14 acres), and an eel’s size did not predict how far it roamed. Six of the eels left the bay for offshore reefs and rocky canyons, each making the move in a single night in winter or spring, and these travelers were larger than the eels that stayed.

Reproduction and life cycle

Surprisingly little is known about how green morays breed. Like all true eels, they lay eggs, and fertilization takes place in open water. Spawning has rarely been observed in morays, which are active at night and breed in places divers seldom see. One female about 1.1 m (3.6 ft) long was found with many ripe eggs about 1 mm across.

Moray eggs hatch into leptocephali, transparent, leaf-shaped larvae that drift in the plankton for months. This larval stage lets young morays travel long distances on ocean currents before they settle on a reef and turn into small eels. Oddly, moray larvae have pectoral fins, which disappear when they change into juveniles. The larva of the green moray itself has never been formally described.

Predators, threats and lifespan

Large green morays have few natural predators. Morays in general are eaten by large groupers and barracudas, and smaller green morays are at more risk than the big adults.

How long green morays live in the wild is not well documented, because wild eels are hard to follow over many years and are rarely aged, so there is no reliable maximum age for this species.

The IUCN lists the green moray as Least Concern in its 2015 assessment. It is widespread and common, it is rarely eaten, and the only threat noted is occasional collection for public aquariums. Like all reef animals, it depends on healthy coral reefs and mangroves, which face warming seas, pollution and coastal development.

Are green morays dangerous?

A large green moray is a powerful fish with big teeth, and a bite can be severe. Even so, unprovoked attacks are thought to be very rare. Green morays often stay put when divers approach and may even allow close contact, and most bites happen in two situations: when divers hand-feed morays, or when someone pokes a hand into a reef hole where an eel is resting.

The safest approach is simple: watch morays from a respectful distance, never feed or touch them, and keep hands out of crevices. If someone is seriously bitten, seek emergency medical help immediately (call 911 in the US or 112 in the EU).

Green morays are also not good to eat. Big predatory reef fish can build up ciguatoxin, a natural toxin made by tiny algae that passes up the food chain, and large green morays are a well-documented cause of ciguatera fish poisoning.

Myths and facts

Myth: morays are aggressive sea serpents. Their snake-like shape and gaping mouths gave morays a fearsome reputation, and they were once mistaken for sea serpents. In reality, a green moray is a shy, sit-and-wait predator that retreats into its hole when it feels threatened.

Myth: the green moray is green all the way through. The green is a mucus coat over dark skin, as preserved specimens show.

Fact: morays are true eels. Unlike the electric eel, which is a knifefish (see Is an electric eel really an eel?), morays belong to the same order as the European and American eels. The moray family has about 200 species, and the green moray is one of its giants.