Interesting Fish Facts - Moray and Wolf Eels
What are Moray and Wolf Eels?
Moray and wolf eels are marine fish with fascinating features. Like other eels or eel-like fish, they have greatly elongated bodies and a long fin extending along their backs. They live on or near the ocean floor in shallow water and are carnivores. When they're not hunting they hide in rock crevices or, in the case or some morays, in burrows in sand or mud.
A moray eel is a true eel (family Muraenidae) whereas a wolf eel is a member of the wolffish family (family Anarhichadidae). There are about 200 species of moray eels but only one species of wolf eel.
Moray and wolf eels can give humans a very painful bite and should never be touched, despite the engaging videos showing divers doing this. In general, though, the eels would rather hide from us than attack us.
The Giant Two-Jawed Mouth of a Moray Eel
Moray eels live in temperate and tropical oceans around the world and are generally found in shallow water. There is a species known as the "freshwater moray", but this actually lives in brackish water rather than freshwater.
The different moray species vary considerably in size, colour and skin pattern. They are unique fish that have a pointed snout and two pairs of jaws. When a moray is eating, the inner jaws, which are normally located in the throat, temporarily move forward to grab the food and move it into the esophagus.
Fins of a Fish
Some Moray Eel Facts
- A dorsal fin travels all the way along a moray eel's back, from behind their head to the end of their 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 the moray's body look streamlined and snake-like.
- The moray swims with an undulating motion, forming an S shape with its body.
- The heaviest moray eel is the giant moray, which may reach 9.8 feet in length and 66 pounds in weight. The longest is the slender giant moray, which may be 13 feet in length.
- The skin of morays 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.
Moray eels have two sets of jaws. The outer jaws, or oral jaws, grab hold of the prey. The inner jaws, known as pharyngeal jaws, then move forward from the throat into the mouth and grasp the prey. The paryngeal jaws move the prey to the esophagus, where it's swallowed.
The Pharyngeal Jaws of Moray Eels
How Moray Eels Eat - Two Sets of Jaws
More Moray Eel Facts
- Some morays have bitten off human fingers when people have tried to feed them, but this is most likely due to their bad eyesight. The fish are probably unable to tell where a piece of food ends and where a person's fingers begin.
- Although their eyesight is poor, morays 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 moray eels 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).
- Moray eels 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 morays often open their mouths very wide during respiration, people who don't know how moray eels breathe sometimes think that the fish are being aggressive and are preparing to bite.
Japanese Dragon Moray Eel
Cooperative Hunting in Moral Eels
In the Red Sea, moray eels have been observed hunting cooperatively with fish called roving coral groupers. 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.
A Moray Eel and a Grouper Hunt Cooperatively
Moray Eel Reproduction and Lifespan
Researchers have found that some moray eels migrate to their spawning grounds. Male and female morays 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 fertlization to occur. The fertlized 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.
A Diver Strokes a Captive Green Moray Eel
Green moray eels are often feared and mistaken for sea serpents.— National Aquarium
Pet Moray Eels
Some types of moray eels are eaten by humans and some 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 moray eels 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 is very interesting to see that the moray in the video appears to like being stroked, though.
A Male Ribbon Eel
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 moray eels, 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 bulging, bulbous forehead. The 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, however, wolf eels are generally not aggressive towards humans.
They've got faces only a mother could love.— Scott Reid from the Monterey Bay Aquarium
Some Wolf Eel Facts
- 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 are embedded in the skin.
- 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. Unlike true eels, wolf eels 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, a wolf eel may have up to two hundred vertebrae.
- Wolf eels are usually nocturnal, but they may emerge from their den to eat during the day as well. They feed on crustaceans, mussels, clams, snails, sea urchins, sand dollars and occasionally fish. They crush their prey with their strong jaws. The back teeth are flattened to help with this task.
A Wolf Eel Near Vancouver Island
Feeding wolf eels is a popular activity amongst divers. It's very important to be careful if this is done, however. Even a normally placid animal may bite if it becomes overexcited, irritated or scared.
Wolf Eel Reproduction and Lifespan
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 fertlize 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.
Helping an Injured Wolf Eel Survive
It's fascinating to observe the behaviour of wolf eels and moray eels. Although they aren't closely related to each other they have developed similar body forms, which helps them survive in their ocean bottom habitat. There's still a lot to learn about both types of fish. We may discover that their behaviour is even more complex than we realized.
Further Reading - Cooperation Between Two Fish Species
© 2012 Linda Crampton