By Kirby Adams

As a youngster, I recall being frightened horribly by a photograph of a Moray Eel in a picture book about sea creatures. The monster was emerging, snake-like, from a rocky reef with jaws agape and rows of sinister teeth glistening in its mouth. I always tried to avoid looking at that page of the book.  Twenty years later, I found myself thawing whole squids to feed the six-foot-long Green Moray (Gymnothorax funebris) that I was keeping in a 500 gallon aquarium.  Somewhere in between, Eels made a transformation from frightening to fascinating in my mind.  Today I consider the Moray Eels to be among the most rewarding fish a marine aquarist can keep.  Who would have thought?

Eels have charmed me in many ways over the years.  From the exceptional hardiness of some species to the brilliant and exotic markings of others, the seduction was a simple process once the fears of childhood were cast aside.  As a scientist, I’m fascinated by the history of Eels - the first Morays in the fossil record show up about twenty million years ago in the Miocene period.  As a hobbyist, I’m simply enthralled with these primitive oddities of the sea.

The true Moray Eels have been placed in the family Muraenidae, which comes from Muraena, the Latin word for Eel.  Many of the more well-known Morays belong to the genus Gymnothorax, which is derived from the Greek gymno (naked) and thorax (chest).  This references the lack of pectoral fins on these sleek-bodied fish.  Below, I’ll present a few of my favorites from the Gymnothorax genus and a couple of their cousins.  First, we’ll look at some basic Eel-keeping information.

When designing an aquarium to house Moray Eels, consideration must be given to their well-deserved reputation as escape artists.  All Eels are Houdini-like in their ability to escape from aquariums.  If an opening in the cover is big enough for the Eel to fit through, it is a safe bet the fish will be discovered on the floor sooner or later.  To prevent this, a tight-fitting lid that covers the entire open area on top of the tank is essential.  Any holes around filter intakes or other equipment hanging on the rim of the aquarium must be plugged.  In an aquarium without a sump, this has the unfortunate effect of limiting oxygen and gas exchange at the water surface.  For these aquariums, an excellent solution is the use of egg crate to cover all or part of the top of the aquarium.  This renders the tank escape-proof while still allowing unimpeded light transmission and gas flow.  Egg crate is used as a fluorescent lamp diffuser and can be found in the lighting section of your hardware store.

Attention must also be given to the aquascaping of the aquarium.  Most Moray Eels are cave and crevice dwellers, and will thus not appreciate a tank without adequate hiding places.  A reef tank with live rock stacked to create caves is sufficient for many species of eel, particularly the smaller varieties.  For larger Eels, some engineering of specific caves may be necessary.  PVC pipe makes an excellent eel cave.  Select pipe that is no more than 50% larger in diameter than your Eel.  To allow an Eel more freedom of choice and to accommodate its growth, pipe of several different diameters can be used throughout the tank.  The pipe can be set pointing upwards at roughly a 45° angle and the rockwork of the reef built around it.  For added aesthetic appeal, small rocks and rubble can be glued to the outside of the pipe using silicone sealant or aquarium-safe glue.  PVC can also be used to create a cave in the substrate of a tank.  A length of pipe can be laid horizontally under the sand or crushed coral with a 45° elbow and a short length of pipe emerging from the substrate.  Rubble can be piled around the pipe where it juts out, creating a very natural look which is made all the more striking by the presence of the front end of an eel waving in the current!  A display done by my good friend Anthony Calfo utilized clear PVC for this underground cave.  The pipe was situated against the edge of the aquarium so the eel – a beautiful Honeycomb Moray (Gymnothorax favagineus) in this case – could be seen relaxing in his cave.

While they don’t need an enormous amount of room for swimming, Eels are still big fish with big appetites, so a large water volume is of great benefit.  Very strong biological filtration is a must and aggressive organic waste removal such as provided by protein skimming is also a good idea.  When in doubt, always over-filter a tank with large predators.

Now, without further delay, let’s take a look at my five favorite Eels!

The Snowflake Moray is (no disrespect intended) the Comet Goldfish of the Moray Eels.  Most aquarists get their feet wet (pun definitely intended) in Eel collecting with the purchase of a Snowflake.  This popularity is well deserved, as Echidna nebulosa is ideally suited to even a novice hobbyist with a modestly-sized aquarium.  Reaching a maximum size of less than 30 inches, the Snowflake can be kept in tanks as small as 40 gallons.  They are primarily crustacean eaters and aren’t inclined to nip at larger tankmates.  Smaller fish however, should be considered at risk with a Snowflake Moray since they are not completely devoted to a crustacean diet and are known to take fish when the opportunity arises.  It’s always fun to watch Eels preying on live food, but the aquarist must avoid the temptation to train a Snowflake (or any marine eel) to feed on freshwater feeder fish such as Goldfish, Guppies, or Minnows.  These are all lacking in nutrients essential to the Eel’s health, can harbor diseases and harmful enzymes, and are generally not suitable foods except in an emergency.  Ghost Shrimp or common marine bait shrimp can be used as treats, as can Fiddler Crabs or very small Crayfish.  Again, many of these lives foods will be deficient in fatty acids that are an essential part of any marine fish’s diet, so they should be used only as the occasional treat.  The regular diet should consist of Silversides, uncooked shrimp, krill, pieces of squid, or other marine meat of suitable size.

Next, we’ll examine my personal favorite, the Zebra Moray (Gymnomuraena zebra).  Among the many qualities of this animal is its finicky taste for crustaceans that makes it one of the few large predatory fish that is almost completely save to house with small fish.  “Almost” is the key word in the preceding sentence, as there are no absolutes in life or Eel-keeping, but I’ve never seen a Zebra hunt and/or eat healthy fish in an aquarium.  The only notable drawback to Zebras is their tendency to be somewhat shy and occasionally unwilling to take food.  When first introduced to an aquarium it is often difficult to induce a Zebra Moray to feed.  When a newly introduced Eel refuses proper frozen food, it may be necessary to train it on live food first.  In the case of Zebras, live crabs or Crayfish are a good choice for initial live food.  Crayfish are inexpensive and easy to obtain, but should only be used with “problem” Eels that refuse to feed since their nutritional value for marine fish is low.  Once a Zebra is accepting live crayfish it is usually no problem to get them to accept shrimp from a feeding stick.  I have found uncooked, shelled shrimp to be the best regular food for Zebra Morays. 

The next two Eels on the list are often confused with each other.  These are the diminutive Golden Moray of the Pacific and its larger cousin, the Golden Moray of the Atlantic.  Both are seen in the aquarium trade under the common name “Golden Moray”.  The Pacific Golden (Gymnothorax melatremus) is one of the smallest of the true Moray Eels, reaching an adult length of less than eight inches.  The Atlantic Golden (Gymnothorax miliaris) is more than 24 inches as an adult, but is still small enough to be a good candidate for many home aquariums.

G. melatremus is somewhat reclusive and spends a lot of time hiding in crevices.  In the wild they will even occupy larger holes in sponges.  In most cases, even when hiding, the Eel’s head will be apparent protruding from the rocks.  At such a small size, this eel is only a threat to tiny fish and small crustaceans.  Coloration varies, but the most prized (and expensive!) specimens are a striking golden yellow.  These Eels are collected primarily from Hawaii.  If you want to make sure you’re ordering a G. melatremus and not a G. miliaris, be certain that the fish is arriving from the Pacific Ocean!

G. miliaris is the more commonly encountered an much less expensive “Golden Moray” and also makes a wonderful reef fish.  Unlike many Gymnothorax, they are not overly aggressive.  Their natural habitat is sandy flats and rubble zones, a condition easily replicated in an aquarium with some decent floor space.  Unfortunately, at two feet long, the Atlantic Golden Moray can’t be trusted with small fish or most crustaceans.  The best looking G. miliaris are collected in the waters off the coast of Brazil.  Again, keep in mind that if you are getting a Golden Moray and it is coming from Brazil or the Caribbean, it will be the bigger Golden, not the tiny Pacific variety.

Finally, I complete the discussion of my favorite Eels with a fish I must concede is terrible choice for the vast majority of aquarists.  This is the large and often fearsome Green Moray (Gymnothorax funebris).  Greens are common sights for divers who frequent the waters of Florida and the Caribbean, but an unwary hobbyist who hasn’t seen an adult in the wild might be tempted to purchase a small Green Moray.  Don’t be that unwary (and ill-informed) hobbyist!  Even a half grown G. funebris can cause serious damage to an aquarist.  An adult can easily mutilate the hand that feeds it, or deliver a bite that leads to severe infections and potentially the  loss of a hand.  They are aggressive, bite without provocation, and eat any tankmates that are small enough to be ripped apart.  In short, they make extremely poor aquarium subjects unless you are willing to devote a huge aquarium solely to one specimen.  I kept a 6.5 foot Green Moray in a 500 gallon aquarium, and I consider that to be the smallest tank suitable for these eels.  The tank was fitted with a completely escape-proof locking lid.  The Eel was fed whole whitefish and squid from a fresh seafood market.  Long feeding tongs were obviously used, as hand-feeding a Green Moray is simply lunacy.  Tank maintenance and cleaning that required human hands and arms to enter the tank was quite an adventure and only attempted when absolutely necessary.  The normal procedure involved a “spotter” who kept an eye on the eel and warned the cleaner to quickly remove himself from the tank if the Eel showed any signs of emerging from the rocks.  Needless to say, this is not something any normal aquarium hobbyist needs to get involved with.  I thoroughly enjoyed my experience with G. funebris and I have to admit that the site of the Eel resting with its jaws open, allowing an Eel-cleaner shrimp to probe for tasty debris amongst its razor-like teeth is one of the most stunning things I’ve witnessed as an aquarist.  Unfortunately I had to relocate the aquarium and – fortunately – came to my senses and decided it was time for the moray to move on to more suitable conditions.  Even with my connections at various zoos and aquariums, I found it nearly impossible to find someone willing to take a huge Green Moray off my hands.  Once again, I implore you not to follow in my footsteps by purchasing this fish.  If the Green Moray eel is also on your list of favorite Eels, get to your local dive shop and book a trip to the Cayman Islands to see one! [Editor's note:  Being a conscientious aquarist requires being prepared to take care of an animal for it's entire life and at it's adult size!  However, even in the case of an honest mistake or changing circumstances, Zoos and Public Aquaria have strict policies against accepting overgrown or no longer welcome animals, and releasing them into the wild (especially in non-native habitat) is serious ecological problem.  Please plan well when keeping large animals!]

One final note concerns a potential tank mate for Eels – the common cleaner shrimps mentioned above.  Lysmata amboinensis of the Pacific and its Atlantic look-alike cousin, Lysmata grabhami have been dubbed “Eel cleaners” because of their habit of climbing inside the gaping mouth of Eels and cleaning debris from amongst the teeth.  This behavior is not hard to observe in captivity, provided your eels don’t eat your shrimp.  The best method of avoiding this is to introduce the shrimp first and then put the eel into the shrimp’s environment.  There is always the possibility the Eel will still consume the shrimp, but in most cases the shrimp are recognized as being cleaners rather than prey.  Even the crustacean-eating Eels will usually allow a cleaner shrimp to perform its service.  Witnessing an Eel relaxing while a brightly colored shrimp scavenges between its teeth is one of the many wonders of the ocean an aquarist can have the pleasure of enjoying right at home.

Selected Reading

Fenner, Robert. The Conscientious Marine Aquarist. Microcosm Ltd. 1998.

Michael, Scott W. Reef Fishes Vol. 1.  Microcosm Ltd. 1998.

Purser, Philip. Moray Eels in the Aquarium. TFH Publications. 2005.