Moray and Wolf Eels: Intriguing and Surprising Fish Facts
Interesting and Distinctive Fish
Moray and wolf eels are marine fish with intriguing features. Like other eels or eel-like fish, they have greatly elongated bodies. Morays are unusual because they have two sets of jaws—an outer pair in the mouth and an inner pair in the throat. The jaws in the throat move forward to grab prey. Wolf eels have a strange face that some people describe as scary and others say resembles the face of a human.
A moray eel is a true eel (family Muraenidae), whereas a wolf eel is a member of the wolffish family (family Anarhichadidae). Around two hundred species of moray eels exist but only one species of wolf eel. Although they aren't closely related biologically, moray and wolf eels have a number of features in common and are a popular sight for divers.
Both types of fish live on or near the ocean floor in shallow water and are carnivores. When they aren't hunting, the animals hide in rock crevices or in burrows in sand or mud, depending on the species. They can give humans a very painful bite and shouldn't be touched, despite the engaging videos showing divers stroking some of them. In general, though, the animals would rather hide from us than attack us.
Not all fish have as many as three dorsal fins and two anal fins. In some fish, the ventral fin is located further back on the body so that it's behind the pectoral one. It's then known as a pelvic fin.
Moray Eel Distribution and Fins
Moray eels live in temperate and tropical oceans around the world. One species is known as the freshwater moray, but this animal lives in brackish water rather than fresh water. The different species vary considerably in size, colour, and skin pattern.
A dorsal fin travels all the way along the eel's back, from behind the head to the end of the body. Other fish have one or more dorsal fins that are separate from each other. At the back of its body, the moray's dorsal fin joins to the caudal (tail) fin, which in turns joins to the elongated anal fin under the animal's body.
Moray eels don't have pectoral, ventral, or pelvic fins. This makes their body look streamlined and snakelike. The fish swim with an undulating motion, forming an S shape with their body.
Body Size and Skin Mucus
The heaviest moray eel is the giant moray (Gymnothorax javanicus), which may reach 9.8 feet in length and 66 pounds in weight. The longest is the slender giant moray (Strophidon sathete), which may be 13 feet in length.
The skin of the fish contains no scales. The term "slippery as an eel' is very appropriate, since the skin produces large amounts of mucus, or slime. The mucus protects the skin from abrasion against rocks. In morays that burrow into sand, the mucus sticks to sand particles and to the walls of the burrow, making the walls stronger.
The outer jaws of a moray are also known as the oral jaws. They catch the prey. The inner jaws, known as pharyngeal jaws, then move forward from the throat into the mouth and grasp hold of the prey. The paryngeal jaws move the prey to the esophagus, where it's swallowed.
More Facts About Moray Eels
- Some morays have bitten off human fingers when people have tried to feed them, but this is most likely due to the bad eyesight of the fish. They are probably unable to tell where a piece of food ends and where a person's fingers begin.
- Although their eyesight is poor, the fish have a good sense of smell.
- Many moray eels are nocturnal. They usually ambush their prey and catch animals such as fish, crabs, shrimp, and octopuses.
- At least some morays visit cleaning stations. These are areas where an eel allows certain fish and shrimp to pick parasites off its body. The eel's visitors get food, and the eel gets a cleaning, so everyone benefits (except the parasite).
- Unlike many bony fish, moray eels have no gill covers on the surface of their body.
- The animals have small gills. They have to rhythmically open their mouth in a gaping motion to allow sufficient water to flow into their mouth, over the gills (which extract oxygen from the water), and out through the gill opening on each side of their body.
- Because a moray often opens its mouth very wide during respiration, people who don't know how the fish breathes sometimes think that it's preparing to bite when they see it.
In the Red Sea, giant morays have been observed hunting cooperatively with fish called roving coral groupers (Plectropomus pessuliferus). Each animal benefits from this very interesting relationship.
A grouper approaches an eel's hiding place and shakes its head rapidly to indicate that it wants to hunt. The eel recognizes the signal and accompanies the grouper. The grouper leads the eel to a place where prey is hidden and shakes its head again. This place is inaccessible to the grouper, but the eel can enter narrow crevices and chase the prey out. Either the grouper or the eel will catch a particular prey animal, but researchers have observed that each animal gets to eat the prey at different times. It's therefore advantageous for the pair to hunt together.
It's often thought that fish are unintelligent animals. Research is showing that in the case of some fish this assumption appears to be false.
Reproduction and Lifespan
Researchers have found that some moray eels migrate to their spawning grounds. The male and female wrap their bodies around each other during courtship, which lasts for hours in some species. The female eventually releases her eggs. The male releases his sperm on top of the eggs, allowing fertilization to occur.
The fertilized eggs hatch into tiny, transparent, ribbon-like creatures known as leptocephalus larvae. The larvae drift in the ocean with the plankton and eventually become young eels, which are known as elvers.
Moray eels seem to live for a long time. The members of some species may survive for thirty years or more.
Wild animals are unpredictable and may be potentially dangerous. It's very important that a diver doesn't approach and handle a moray eel. The interaction between the person and the fish above is interesting to see but is a special case.
Some types of morays are kept as pets in home aquariums. If you encounter moray eels in an aquarium tank or in the wild, don't assume that they'll be as friendly as the fish in the video above. The larger individuals have strong jaws and sharp, rear-facing teeth, although some have flatter teeth that enable them to grind the shells of their prey. Morays can inflict a nasty wound if they decide to bite, which they may do in self defence. It's very interesting to see that the animal in the video appears to like being stroked, though.
Green moray eels are often feared and mistaken for sea serpents.— National Aquarium
Wolf eels are found in the cool water of the North Pacific Ocean. Their scientific name is Anarrhichthys ocellatus. The fish tend to be grey or brown in colour with darker spots. Like morays, wolf eels have a long dorsal fin on the top of their body. They also have a pectoral fin on each side of their body behind their head, which moray eels lack.
Wool eels are famous for their strange and menacing face. They have a large, square head as well as thick lips, fleshy jowls, and a bulbous forehead. Their lower jaw may protrude beyond the upper jaw. The enlarged head is most noticeable in males and may be massive. Despite their fierce appearance and their name, wolf eels are generally not aggressive towards humans.
They've got faces only a mother could love.— Scott Reid from the Monterey Bay Aquarium
Body Features of Wolf Eels
- Wolf eels are orange-brown as juveniles but are grey or sometimes brown as adults. The skin often has spots of a darker colour, which may be outlined in a lighter colour. The scales are invisible. They are tiny and embedded in the skin.
- The Seattle Aquarium says that their staff (and perhaps other people) can recognize a particular wolf eel by its spot pattern.
- Like true eels, wolf eels have long dorsal fins. They also have long anal fins, which are separate from the dorsal and caudal fins. They lack pelvic fins but have a pectoral fin on each side of their body.
- The fish may reach eight feet in length, but most animals are about six feet long. They weigh up to around forty pounds.
- According to the Seattle Aquarium, the fish may have up to two hundred vertebrae.
- Unlike the moray, the wolf eel has a covering called an operculum over the gill openings on the sides of its body.
Daily Life of the Fish
- Wolf eels are usually nocturnal, but they may emerge from their den to eat during the day.
- The fish feed on crustaceans, mussels, clams, snails, sea urchins, sand dollars, and occasionally other fish. They crush their prey with their strong jaws.
- The animals have strong canines and molars to help them break and crush their catch.
- The fish has been found in water as deep as 740 feet.
- In some places, it's illegal to catch the animals because of their importance for divers and photographers.
Feeding wolf eels is a popular activity amongst divers. This is especially true in areas where the animals have become used to human visitors. It's important to be careful if a wolf eel is approached, however. Even a normally placid animal may bite if it becomes overexcited, irritated, or scared.
Mating and Reproduction
Wolf eels generally mate for life, although there may be exceptions to this rule. The female may share her den with her mate. Females reproduce for the first time between four and seven years of age. During courtship, the male butts his head against the female's abdomen. The female lays up to ten thousand eggs. The male releases sperm on top of the eggs to fertilize them.
The parents take turns protecting the developing eggs by curling their bodies around them. Sometimes the females curls around the eggs and the male curls around her. The female rotates the eggs periodically to ensure that they remain oxygenated.
The eggs hatch after about four months. The larvae that emerge are left on their own to swim with the plankton in the ocean. Eventually, the maturing youngsters settle on the ground and enter a den. Wolf eels have lived for more than twenty years in captivity.
The status of the wolf eel population doesn't appear to have been formally assessed. The species is not believed to be in any trouble, however.
It's fascinating to observe the behaviour of wolf and moray eels. Although they aren't closely related to each other and have a number of different characteristics, they are superficially similar. Their shared features help them survive in their habitat on the ocean floor.
There's still a lot to learn about both types of fish. They indicate that the idea that fish are simple creatures is at least sometimes wrong. We may discover that their behaviour is even more complex than we currently realize.
- Giant moray facts from FishBase (an online database of fish information)
- Green moray facts from the University of Florida
- Moray jaws plus comments from a biologist from the Wired website
- Cooperative hunting in moray eels and roving coral groupers from Discover magazine
- Wolf eel facts from the Monterey Bay Aquarium
- More information about wolf eels from the Seattle Aquarium
- Facts about Anarrhichthys ocellatus from the Washington Department of Fish and Wildlife
© 2012 Linda Crampton