The following resource was first published by the National Aquarium in Baltimore's Department of Education in the winter of 1995 as a "Puffin Report" to schools Posted here 12-7-2002.
During the day, the reef is filled with activity as colorful animals move about in search of food and shelter.
The daytime world of the reef is fascinating, but it is at night that it really comes alive. Nocturnal creatures emerge from burrows, ledges and other hiding places within the coral to search for food. As dusk approaches, coral polyps spread their delicate tentacles to capture tiny planktonic animals which dart through the water. Squirrelfish with pale red bodies and giant black eyes swim around the reef, also looking for a meal. Along the sandy bottom, the long body of a moray eel slithers from a dark ca ve. With beady eyes and snaggle-teeth, this fish has been labeled as a vicious predator that attacks both fish and people.
Morays are nocturnal animals that inhabit the waters of the Indian, Pacific and Atlantic oceans. All eels belong to the order Anguilliformes which contains 20 families. Morays are members of the family Muraenidae. The 100 species identified by scientists range in size from 2-10 feet. The largest is the giant moray which reaches 10 feet in length and weighs 75 pounds. Many have beautiful color patterns which help to camouflage them in the reef. Because morays keep their mouths open almost all of the time, the insides of their mouths are camouflaged also. The common morays in the Caribbean reefs include the spotted, goldentail and green morays.
Morays have muscular, snake-like bodies with thick skin. They have no scales, but a layer of mucus covers the body and protects the skin from germs and parasites. These fish are also missing the two sets of fins that are normally found on the belly. The p elvic and pectoral fins are not found on morays. Instead, they have one long dorsal fin (back fin) which curves around and connects with the short caudal fin (tail fin). The only fin found on the belly is the long anal fin. In the moray, the dorsal, caudal and anal fins are all connected.
The moray has poor eyesight but a very good sense of smell. Like most fish, it has two nostrils on each side of its face. Because it is a night hunter with poor eyesight, the moray relies on its keen sense of smell to locate prey such as damselfish and cardinalfish hiding in the coral. Scientists have found that morays cannot locate food if their nostrils are plugged. One inhabitant of the reef which outsmarts the moray's nose is the parrotfish. Before it sleeps at night, the parrotfish covers itself with a mucous cocoon to hide its smell. In eels, the first pair of nostrils may stick out like little tubes. The ribbon moray, which is found in the Pacific Ocean, has front nostrils which look like leaves.
Ledges and caves within the coral reef are the favorite dwelling places for the eel. Although it does not usually emerge during the daytime, divers often see the pointed face of a moray sticking out of a cave with the jaws open wide! While it may appear t o be hungry and looking for a tasty morsel, this is hardly the case. A moray must keep its mouth open constantly to take in water so that it can breathe. It has small spiral-shaped gills which pick up oxygen from the water. By opening and closing its mouth, the eel is able to pump water over the gills. After the water passes over the gills, it leaves through the gill slits which are two small holes on the face. Since both the gills and gill slits are small, the eel must take in the extra water to get enough oxygen.
With its jaws agape, it is easy to see the jagged teeth of the moray which curve back into its mouth. Some eels, such as the Atlantic green moray have a third row of teeth located on the roof of the mouth. This gives the animal a "snaggle-tooth" appearance. The curved teeth help to make sure that the slippery fish goes only one way - down the hatch! The chain moray and its close relatives are an exception. These small morays have flat teeth for crushing the shells of crabs, sea urchins and other invertebrates.
Morays: Past and Present
In the past, morays have been feared for many reasons. Tales of giant sea serpents and schools of man-eating eels have made even the bravest swimmers a little scared. In ancient Rome, rulers like Nero were said to throw disobedient servants into pits fill ed with hungry morays. Even today, divers tell of being held in a bulldog grip by eels who "attack" for no reason. While it is true that some morays are aggressive, it has been found that many of the "attacks" were the fault of the divers! Some divers were injured while searching for lobsters or shells when they poked their hands inside of caves occupied by eels. In other cases, the animals were attracted by freshly cut fish which the divers carried into the water. Most of the encounters between people an d moray that have occurred recently have not ended in injury to either. Instead, divers have been able to observe the true behavior of morays which they describe as being gentle and curious. Therefore, it is not quite true that all morays are vicious man- eaters. Instead, it is just the opposite. People have been eating eels for hundreds of years.
The first fish breeding tank was developed in ancient Rome where European morays were raised. In 1966, 46,000 tons of morays were caught in the Mediterranean Sea. They are also very popular in Japan and China. During that year, Japan alone captured 32,700 tons. Because five types of morays are known to be poisonous, the fishermen cut off the heads as soon as the eels are caught. The poison is thought to be contained in special glands in the mouth. Even so, more people have probably died from eating the me at than actually being attached by the animals.
One reason why morays have been misunderstood for so long is that people did not know very much about them. For many years, no one saw any baby eels, only adults. Most of the information on morays came from their relatives, the freshwater eels. (Freshwater eels are in the family Anguillidae.) Morays are now thought to begin life as a tiny planktonic larva called a leptocephalus. The larva is shaped like a leaf and is so thin that you can almost see through it. The leptocephalus is about 3 inches long and drifts in the currents with other plankton for abut 8 months. After this time, it will suddenly change its appearance and begin to look like a miniature adult. It then continues to grow until it reaches the length of the adult.
Octopus Encounters
The octopus and moray are deadly enemies. These two animals often encounter each other because they both like to live in the same kinds of caves on the reef and they are both nocturnal hunters. If a moray smells an octopus nearby, it will poke its nose in to dark holes until its prey is found. Once located, the octopus is surprised by the moray's powerful jaws, which promptly clamp onto its soft body.
The octopus will wrap its many tentacles around the head of the eel but to no avail. The slippery moray will tie a knot in its tail and move the knot up its body until it has pushed the tentacles off. If the octopus is too big to swallow whole, then the moray will eat it tentacle by tentacle. If the poor octopus is able to escape with some tentacles left, the missing ones will grow back.
Morays can be quite efficient predators on a variety of prey. In addition to hunting for octopuses, they are good at squeezing their heads into small openings in the coral where small fish hide. They have also been known to hide in eelgrass beds and ambush unsuspecting reef animals. While they do not eat people, if provoked, they can do serious damage with their powerful jaws. Even though divers continue to report stories of "friendly" morays, scientists still have much to learn about these secretive and unusual animals.
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