undulated moray (Gymnothorax undulatus)

Undulated Moray Eel-Facts Video and Photographs

undulated moray (Gymnothorax undulatus)

The undulated moray (Gymnothorax undulatus) is one of the larger eels encountered on the east coast of Africa. They are voracious predators on the reef.

undulated moray (Gymnothorax undulatus


The undulated moray eel is a large eel, reaching up to 1.8 m in length. Its serpentine shape body has an undulating pattern of lines that form a pattern down its body. In Tanzania the head is usually a green colour although occasional specimens are seen with a yellowish head. The neck behind the head is thickened, once it reaches its maximum length it tends to thicken more around the neck rather than growing longer. The head of the undulated moray eel is large with small eyes located forward. Undulated moray eels have a second set of jaws known as pharyngeal jaws in their throat which may partially account for their thickened neck.

The mouth is wide with large teeth for tearing flesh rather than grinding . As can be seen in the image above they have a further row of teeth running down the middle of the roof of the mouth. This aids in hanging onto prey to prevent it escaping.They do not have pectoral or pelvic fins and the dorsal fin runs the length of the body.

undulated moray (Gymnothorax undulatus)


Undulated moray eels are usually nocturnal feeders and spend the days in crevices in the rocks. Occasionally one may be seen out in the open during the day. Usually low on the bottom and moving in a snake like fashion between rocks rather than swimming. They will usually take off in the opposite direction when they see you. A very large specimen may stay out in the open and threaten a diver by darting at them if they approach too close.

Moray eels have proportionately small  circular gills, located on posterior of the mouth and the moray is constantly opening and closing its mouth to facilitate sufficient water flow over its gills. In general the opening and closing of the mouth is not threatening behavior but one should not approach too closely. They will bite if threatened. In the video below you can view an undulated moray eel feeding opportunistically on a passing shoal of anchovies. Note how the prey is swallowed whole.


Some researchers speculate that moray eels contain toxins in their mouths and are poisonous.From many years of catching crayfish on the Kwa Zulu Natal coast I have never had a bite go sceptic. After every bite I have soaked the bite area in hot water as hot as I couldd take it. Much of the bite damage occurs when one pulls ones hand back after being bitten. Many experts state that one should not pull back, however they should go try it themselves. The bite is usually sudden and unexpected and it is natural to pull away from it.  I have personally seen one diver who lost the use of his thumb from a giant moray bite but that is unusual.

Morays secrete mucus over their scaleless skin, which in some species contains toxins. They have a thick skin and a large number of cells that secrete  mucus epidermis.

undulated moray (Gymnothorax undulatus)


The undulated moray eel is widespread across the Indo-Pacific area, being found from east coast of Africa from south of Durban northwards, Red Sea included, across to the Pitcairn group, Hawaiian islands and  Polynesia. North to south in Japan and south to New Caledonia, Fiji and Australia.
They are found in rocky reefs, coral reefs and occasionally in lagoons provided there is shelter. They are found from depths of 1 to 50 meters.
undulated moray (Gymnothorax undulatus)


The undulated moray is carnivorous, and does most of its hunting at night. As mentioned above it is not that uncommon to see them hunting during the day. If there are scuba divers in the area this usually causes them to go back into hiding. They feed mainly on small fish and crustaceans but the fact that they are on occasion caught by fishermen using bait indicates that they will scavenge as well. Moray Eels have relatively poor eye sight but they have an excellent sense of smell that they use to detect their prey.

Moray eels have a second set of jaws in their throat called pharyngeal jaws, which also have teeth. When feeding, morays latch onto the prey with their outer jaws. They then push their pharyngeal jaws which are set back in the pharanx, forward into the mouth. They then grasp the prey and pull it into the throat and stomach. Moray eels are the only fish that use pharyngeal jaws to capture prey. Their main hunting tool is their excellent sense of smell which makes up for their poor eyesight. This means that weakened or dead creatures are the moray eel’s favoured food.


Studies have shown hermaphroditism in morays, some being sequential and others  synchronous which can reproduce with either sex. Courtship usually occurs when water temperatures are high. After posturing to each other they wrap their bodies around each other and simultaneously release sperm and eggs. Once they hatch the larvae float in the ocean for around 8 months before becoming elvers and eventually a moray eel.

Gymnothorax 3


 Ciguatoxin, the main toxin of ciguatera, is produced by a toxic dinoflagellate and accumulated up through the food chain, of which moray eels are top, making them potentially dangerous for humans to eat. They are fished and do take bait. There is documented evidence of Ciguatoxin poisoning from undulated moray eels and because of this they should not be eaten.

Once caught they are extremely troublesome to deal with. They wrap around the line and secrete a large amount of mucus. Unless the line is changed, much as with the mucus from puffer fish, no other fish will bite on the line. It is not uncommon for a caught giant moray eel to actually bite its self while it is busy wrapping around the line.


Because of their size, as a rule undulated moray eels are usually only kept in public aquariums but some specialist aquarists keep them in species specific tanks. Gymnothorax 2


Kingdom: Animalia
Phylum: Chordata
Class:      Actinopterygii
Order:    Anguilliformes
Family:   Muraenidae
Genus:    Gymnothorax
Species:  G. undulatus


Gymnothorax 1