geometric moray (Gymnothorax griseus)

Geometric Moray Eel-Facts and Photographs

Gymnothorax griseus 3

The Geometric Moray Eel (Gymnothorax griseus) is one of the smaller and more docile moray eels. They are relatively common on the Tanzanian coast and are sometimes seen in large numbers in small caves, with up to 15 being sighted in a small area of around 2 square meters. These caves are also inhabited by the Pacific Cleaner Shrimp and the eels seem to always be in the same area over a period of time.

Gymnothorax griseus 2


The geometric moray eel has a grey or lilac coloured head with geometric dotted patterns on it. These patterns extend up the body. The body can be a pale brown to light lilac color with light brown blotches. There are small rounded teeth at the front of the jawswhich can be seen in the image below. The mouth is proportionately small for moray eels. They do not have pectoral or pelvic fins and the dorsal fin runs the length of the body. The geometric moray eels grow up to 65 cm in length making them one of the smaller moray eels.
Gymnothorax griseus 1


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 can take it. After that a good clean with a disinfectant and I have never had a problem. Much of the bite damage occurs when one pulls ones hand back after being bitten. Many experts say 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.

geometric moray (Gymnothorax griseus)


The geometric moray eels are generally seen protruding from a hole or small cave during the day and are seldom if ever seen in the open. Sometimes as in these images, they can be seen hiding in soft leather corals, possibly because their coloration provides excellent camouflage in these corals. They are not aggressive but should be treated with caution because of their teeth. They are nocturnal  hunters.

Moray eels have proportionately small  circular gills, located on posterior of the mouth and as a result the moray is constantly opening and closing its mouth. This facilitates 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. Even a small moray such as the geometric moray can deliver a painful bite.

geometric moray (Gymnothorax griseus)


The geometric moray eel is found across the western Indian Ocean. They are found from two meters in depth down to 45 meters.

geometric moray (Gymnothorax griseus)


The geometric moray eel is carnivorous, and does most of its hunting at night. They feed mainly on small crustaceans and probably small fish.

Moray eels have a second set of toothed jaws in their throat called pharyngeal jaws. When feeding, morays latch onto the prey with their outer jaws. They then push their pharyngeal jaws, which are set back in the pharynx, forward into the mouth. These jaws then grasp the prey and pull it back into the 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 favored food.

geometric moray (Gymnothorax griseus)


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.  Recent studies have shown that geometric moray is synchronous hermaphrodite and that they produce both sperm and eggs.

geometric moray (Gymnothorax griseus)


 Ciguatoxin, the main toxin of ciguatera, is produced by a toxic dinoflagellate and accumulated up through the food chain. With moray eels at the top of the food chain this makes them potentially dangerous for humans to eat. They are fished and do take bait.

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


Because of their attractive looks and small size they are kept in aquariums by specialist aquarists. Due to their size of up to 65 centimetres in length they should only be kept in a fairly large aquarium. They are easy to feed and are hardy. They cannot be kept in a reef tank because they will eat crustaceans and small fish and are likely to push rocks over that are not well anchored.


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