Turn on your TV, and click around the various nature, history and science channels, and it will soon become evident that we have an appetite for the bizarre. We take in shows about ghoulish parasites that eat us from the inside out. We watch people consume freakish foods that make us squeamish. We are transfixed by “reality” programs that enter eclectic shops selling shrunken skulls, torture devices and mummified pets. Maybe it is this same attraction to the atypical that draws a guild of marine aquarists to members of the family Muraenidae — the morays.
Although not for everyone, many of the morays make outstanding aquarium pets. In fact, there are a number of species that are a great choice for the beginning marine aquarists. But because this group of eels is quite diverse, care should be taken to get a moray that is right for your aquarium. In this article, I will discuss how to set up a moray tank and detail their general care requirements.
Muraenidae Family Overview
Moray eels belong to the family Muraenidae. This genus is comprised of around 16 genera and approximately 200 species. All are characterized by a lack of pectoral and pelvic fins; gill openings that consist of small holes with no bony cover; large, toothy jaws; and dorsal and anal fins that are continuous around the tail. Morays lack scales, but instead, they exude large amounts of body slime to protect themselves from parasites. A few morays (e.g., yellowmouth moray [Gymnothorax nudivomer]) are known to exude a toxic slime that may dissuade parasites from attaching to them. Morays almost always have their mouths open. Although it looks menacing, it is simply how morays respire. The mouth remains open as they pump water over the gills with the muscles in the gill cavity. While the color of some morays is dull and monochromatic, there are other species that sport dramatic patterns that include bands, spots and/or mottling.
While some morays have fanglike dentition (e.g., dragon moray [Enchelycore pardalis]), there are other species that possess molarlike teeth (e.g., zebra moray [Gymnomuraena zebra]) that are perfectly adapted to crushing hard-shelled invertebrates (e.g., crustaceans, snails, sea urchins). When it comes to their food habits, morays can be classified into one of three general categories: mainly fish-eaters, mainly invertebrate-eaters and those that feed almost equally on fish and invertebrates. A classic fish-eater is the purplemouth moray (Gymnothorax vicinus). This moray has smaller teeth on the sides of the jaws and sharp, daggerlike dentition running along the roof of the mouth. A classic invertebrate-eater is the banded moray (Echidna polyzona). This species uses the pebblelike teeth in its jaws to crush crabs. The stout moray (Gymnothorax eurostus) is a species that feeds on both benthic fish and invertebrates (namely crustaceans). Obviously, it is important to know something about the diet of the moray before you add it to your community fish aquarium.
Recently, a fascinating discovery was made about the moray feeding apparatus. It turns out that morays have a second set of jaws in the pharynx that possess re-curved teeth. When a moray bites its quarry with the main jaws and begins to move it into the mouth, the jaws in the pharynx are extended to grasp the prey item and pull it deeper into the esophagus (like the jaws of the creature in the Alien movies!). It has been speculated that they have these specialized pharyngeal jaws because it is often difficult for them to open their primary jaws fully because they hunt in tight spaces, like in reef crevices and interstices. The pharyngeal jaws enable the moray to transport the food into the gullet without having to achieve full jaw gape.
The size of a moray’s aquarium will depend on the species in question. There are more than 200 species of morays, and they can range in size from 8-inch dwarfs to 10-foot giants. Given that morays are used to living in tight spaces (in coral crevices, among coral rubble, etc.), they can be housed in relatively small quarters. But be aware that if you do keep them in a smaller aquarium, they are more likely to jump out, to rearrange the aquascaping and knock into, and potentially disturb, equipment in the aquarium (e.g., siphon tubes, heaters).
Obviously, the giants of the group should be avoid by the vast majority of home aquarists. This group includes the 93/4-foot-long honeycomb moray (Gymnothorax favagineus), the 7½-foot green moray (Gymnothorax funebris) and the 10-foot giant moray (Gymnothorax javanicus). Few will be able to accommodate their space requirements when they reach their full size. Fortunately, the majority of morays attain a maximum length of between 20 to 48 inches. Those species that attain a length of more than 30 inches are best housed in aquariums ranging from 55 to 135 gallons in size. The smaller species (those less than 30 inches in length) will do fine in a 20-gallon aquarium, while the “mini morays” (those less than 15 inches) can even be kept in 10- or 15-gallon tanks.
Moray’s are messy. As a result, they require a good filtration system, which should include mechanical, chemical and biological filtration. There are a number of different filtration methods that can be employed to manage the accumulation of nitrogenous waste products. The popular wet-dry (trickle) filters can be used to maintain excellent water parameters. Canister filters, filled with materials that provide good substrate for nitrifying bacteria growth, will also furnish adequate biological filtration. The filter media should be cleaned every two weeks or so with water from the aquarium to remove accumulating detritus. Just fill a bucket with tank water and agitate the canister media in the bucket. Some canister filters have a foam pre-filter that will allow you to clean the media less frequently. A foam fractionator, or protein skimmer, is also a good idea for the moray aquarium. Get an external skimmer as internal models are likely to be displaced by an active eel. Hang-on-the-back skimmers also can present a problem due to the hole in the top required for them to function. This may provide a way of escape for the eel (more on this later).
Aquascaping is an important consideration in the moray aquarium. In order to ensure that your moray “feels secure” in its new home, you will need to provide it with shelter sites that are large enough to hide its entire body. You can construct a coral head or reef wall out of live rock or artificial corals, but make sure your reef structure is stable. It may be necessary to use cable ties to attach rocks together so that they are less likely to be displaced by your moray. These eels often dig under decorations and could potentially topple pieces of live rock or coral that are not fixed into position. This could result in injury to the eel. If you are using live rock or other heavy objects as the base of the aquarium decor, make sure that they are resting on the glass bottom of the tank, not on the surface of the sand substrate. You can also use PVC pipe, a large conch shell, a fish bowl with crushed coral attached with silicon to the outside and placed on its side on the aquarium bottom or large ceramic flower pots to create moray hideouts.
Morays can be kept in a reef aquarium, but most species will eat smaller fish and ornamental crustaceans. Larger individuals will regularly knock unattached corals off of reef structures, which can damage the invertebrate. This is particularly true for those morays that get more rambunctious at feeding time. All of that said, one advantage in placing an eel in your reef tank is that when it moves behind and between your live rocks, it will stir-up some of the detritus that collects in these hidden areas. This not only puts the decomposing material into suspension, where it can be removed by mechanical filtration, but it also helps some soft corals to feed on the detritus.
Cover it Well
One of the most important components of the moray aquarium is a suitable top. A moray will escape from an open tank in no time. They are curious animals that cover extensive home ranges, so it should not be surprising that their forays (often nocturnal in nature) end in their slipping over the edge of the uncovered aquarium to see what is going on beyond the glass walls. This, of course, does not usually end well for the exploring eel. But you can have a top on your tank and still end up with a dried up eel on your fish room floor. These animals have a special sense that enables them to find holes in the top, and when located, they will then deftly slide through and out of the tank. They will even use their muscular bodies to push the top off a tank if they can and make their escape. I have placed heavy dive weights on top of tanks in an effort to prevent escapes only to have large morays successfully push their way out. Morays can become particularly frisky when being fed and are most likely to jump out of the tank when feeding stimuli are present. They are more likely to evacuate their aquarium home after the rock work in the tank has been rearranged or when crowded in an undersized aquariums. Morays will even slip into corner overflow boxes — removing an agitated moray from such tight confines can be a real joy! Attach plastic-mesh screening along the top edge of the overflow box to try and preclude such incursions. There is no doubt that these suicidal tendencies kill more morays than anything else.
OK, now that you have the moray tank ready, how do you keep your moray alive and well? Let’s start with one of the most important aspects of muraenid husbandry — feeding.
As far as their dietary preferences are concerned, morays can be divided into two groups. Group one consists of those morays that eat primarily fish but will also eat crustaceans and cephalopods on occasion. Group two is comprised of those species that feed almost entirely on crustaceans and other hard-shelled invertebrates.
Whether a member of group one or two, in captivity, it is important to feed your moray a varied diet. Although it is interesting to watch morays chase and capture live feeder fish, it is important to include frozen or fresh squid, marine fish flesh and crustacean meat in their diet as well. If you feed your eel frozen food, make sure the food is completely thawed first. Most morays can be enticed to eat non-living food by impaling it on the end of a feeding stick (I use a piece of rigid airline tubing with a sharpened end) and moving it in front of their head.
It is important not to feed your moray too frequently; over feeding a moray can lead to fatty infiltration of the liver, which impairs the functioning of this organ. It is not uncommon to see animals that have excessive fat deposits on the head and body in public aquariums, probably as a result of being overfed.
Field studies suggest that morays eat infrequently (in some species, once every three or four days). Therefore, in order to prevent your eel from becoming too fat, I recommend feeding your eel to satiation twice a week. An overfed moray may regurgitate its partially digested meal, which can make a mess of your tank.
It is not uncommon for a moray to refuse to eat on occasion. This may occur if the eel is being overfed, if the water quality in the tank has deteriorated or the water temperature drops significantly. Sometimes, a moray will stop feeding for no reason at all. This problem can usually be rectified by performing a partial water change, offering your eel different types of food and by being patient. It may just take some time (e.g., several weeks or more) before your eel regains its appetite.
There are some moray species that perpetually present feeding problems in captivity. This includes the banded moray (Echidna polyzona), the zebra moray (Gymnomuraena zebra) and the ribbon eel (Rhinomuraena quaesita). All these species are likely to require special attention when it comes to food selection and presentation (the latter species is an especially tricky eel to keep). This may include feeding live prey. In the case of the banded or zebra morays, fiddler crabs or crawfish are sometimes required. Live feeder damsels, mollies or guppies may be needed to get a ribbon eel to eat. These species are also likely to have difficulty competing for food with other predators.
An aquarium with a number of morays can make a fantastic display. But keeping morays together does present some challenges. A moray already residing in an aquarium may not be too happy with having its area invaded. This can lead to chasing and biting. In most cases, rather than engaging in more lethal combat, morays will attempt to defend a preferred hiding place by pushing the intruder away with the side of its head or by placing its open mouth on the body of the other eel. In any case, you should be aware that members of the same species are more likely to fight, and larger individuals may bully smaller morays. Whenever you put two morays together, keep a close eye on them for an hour or so to see if fighting breaks out. In most cases, if a moray melee is going to occur, it will do so shortly after the morays first come into contact. If fighting does break out, you will probably have to remove one of the eels (or the newly introduced moray if it is added to an eel community tank). Dispersing individuals, by providing numerous hiding places, will also help to diffuse the potential for those rare aggressive interactions. Of course, the smaller the tank, the more likely these encounters are likely to occur as well.
Morays are not above cannibalism. For example, I had a small snowflake moray (Echidna nebulosa) regurgitate a slightly smaller conspecific. Some morays are also regular predators on other moray species. The honeycomb (Gymnothorax favagineus) and blackspotted morays (G. insigteena) regularly prey on other muraenids. I had a G. favagineus that ate two eels that were about half its length. Small eels will often stay out of the way of larger individuals, but in smaller aquariums, they will have a difficult time avoiding a hungry relative. To avoid these types of predation events, keep individuals that are similar in size and avoid keeping adults of those species that are known eel-eaters with other morays.
You can house morays with larger fish, but there are inherent risks, especially if the muraenid you’re keeping is a fish-eating species. Morays have a surprisingly large mouth gape, therefore, if you keep fish with a piscivorous eel, make sure that their bodies are several times deeper than the girth of the moray, and introduce them to the tank before the moray is added. It is also possible that a moray, if it catches a larger fish, will tear chunks from its body by employing knotting behavior. I have had eels capture fish, swallow them tail first and successfully separate the body from the head, which was too large to ingest. With all that said, I have also kept piscivorous moray (e.g., dragon moray [Enchelycore pardalis]) with a community of larger angelfish, surgeonfish, fusiliers etc. without the eel ever harming its tankmates (but this is certainly not without risk). If you have a larger moray in a tank on its own, you may want to add an assortment of smaller fish to add color, interest and a supplemental food source. The company I work for takes care of a 300-gallon aquarium that contains a 4-foot honeycomb moray. The technicians that take care of the tank add a variety of small damsels and flagtails (Kuhlia). It takes the moray a while to capture these small fish. There are loads of small cracks and crevices for the damsels to hide in, while the flagtails are fast and can evade the eel, at least for a while!
Although morays are often kept in tanks containing other large predators, like sharks or groupers, these animals will occasionally injure or kill an eel. Sharks have been known to bite or maul moray tankmates, while larger groupers and snappers will slurp up smaller morays like a piece of spaghetti! In some cases, groupers will ingest morays that measure as long as they are.
Morays are frequently serviced by cleaner wrasses, certain cave-dwelling pipefish and cleaner shrimp in the genera Stenopus, Periclimenes and Lysmata. They are the favored client of some cleaners, not only because they harbor crustacean and trematode parasites, but because of the copious amounts of slime they produce, which is rich in nutrients. Cleaner wrasses and cleaner shrimp will also clean food scraps and parasites from the teeth of moray eels, which open their mouths wide to enable the cleaners to do a thorough job. Although it is very interesting to watch these cleaners work over morays in the aquarium, be warned that in some cases, morays may eat these benefactors in captivity. It is always best to add the cleaner fish or shrimp before the moray(s). If the moray is already in the tank when the cleaner is introduced, the eel is more likely to see it as food.
Well Worth the Effort
I hope this increases your appreciation of this magnificent group of eels and facilitates your efforts in selecting a moray for your aquarium. Although they do have some special care requirements, most morays are very hardy fish that will provide their caretakers with many years of pleasure. Happy fish-watching!
Scott W. Michael is an underwater photographer, author (he has written 13 books about marine animals) and veteran fishkeeper. He manages the aquarium service company, Reef Tectonics.
Featured Image: By Scott W. Michael