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Moray Eels

There are many things to consider before placing a moray eel in your home saltwater aquarium.

By Article and Photos Scott W. Michael

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Muraena melanotis
The handsome blackear moray (Muraena melanotis) is an eastern Atlantic moray. It is now more readily available to marine aquarists.
Echidna nebulosa
The snowflake moray (Echidna nebulosa) is a relatively docile species that is often kept in community tanks with other marine fish.
Siderea grisea
The gray moray (Siderea grisea), which is sometimes exported from the Red Sea, feeds on small fish and crustaceans that hide between coral branches.

Let’s consider the issue of size first. Size is an important consideration when it comes to your moray eel and its optimal aquarium dwelling. This family includes some real monsters that are going to outgrow all but the largest home aquarium. For example, the honeycomb moray eel (Gymnothorax favagineus), green moray eel (G. funebris) and giant moray eel (G. javanicus) reach massive proportions (all can reach more than 7 feet in length). But there are moray eels that do not exceed 2 feet in total length — these are obviously the best-suited to the majority of home aquariums. Most moray eels fall between these two extremes, reaching maximum lengths of 3 to 5 feet.

Size is not the only species-specific characteristic that will determine the limitations that a moray eel may impose. Some species are more aggressive and even more predatory than others. The disposition of your eel will determine if you can keep it (or want to risk keeping it) in a community aquarium or if you will be forced to keep it in a tank all its own. For example, the honeycomb moray eel (G. favagineus) is a voracious piscivore that will eat any fish tankmate that will fit into its distensible jaws. But there are other morays that are less of a threat to fish tankmates. The ubiquitous snowflake moray eel (Echidna nebulosa) and the chainlink moray eel (E. catenata) are not as big of a threat to other fish, though they may snap indiscriminately at passing fish when excited by food added to the tank.

If you have a larger tank, you may want to try and keep more than one moray eel in the same tank. But beware that many moray eels will behave aggressively to newly added morays that “invade” their domain. As with other fish species, moray eels are most likely to be belligerent toward members of their own kind. Also, some moray eel species (e.g., blackspotted moray eel, G. insigteena; honeycomb moray eel, G. favagineus) regularly prey on members of their own family. If there is a great size disparity between eels, there is also a much greater likelihood of eel-on-eel predation (the bigger ones will eat the smaller ones). So, it is important to do research before putting eels together (for species-specific details, check out my book, Reef Fishes, Volume 1, printed in 1998 by Microcosm).

There are some moray eels that are a threat to crustaceans. These eel species should not be kept in an aquarium with ornamental shrimp, anemone crabs, small hermits, etc. In some cases, these moray eels will tolerate cleaner shrimp (Lysmata and Stenopus) and will even welcome their cleaning services, but these shrimp should be added to the tank before the moray, and the aquarist should be aware that sometimes a moray will “go bad” and snap up one of these beneficial decapods.

If you want to keep one of the more aggressive or predatory moray eels, you will need to keep them in a species-only tank (on their own, except for sessile inverts and heavily armored mollusks). But be honest with yourself — will you eventually get bored with your solitary eel? If you think you will lose your interest in a solitary moray, you may want to get a more congenial moray eel species or steer clear of the family altogether.

Moray eels are very hardy (i.e., they rarely die prematurely) and their natural life span can extend for a decade or two, or possibly even more. Therefore, if you get a moray, be prepared for a long-term commitment.

I recently read a post on an aquarium club message board from an individual who was trying to get rid of a spotted moray eel (G. moringa). It was getting too large for his tank and was so aggressive that he could not keep anything else with it. Feeding the moray eel was no longer as fascinating as it once was, and he wanted to ditch the eel and set up a more traditional marine fish community tank. If this individual had done his research, he would have known that this is what G. moringa is — a larger, aggressive eel that can live a long time!

The Moray Aquarium
So, you have decided that a moray eel is for you. What does the optimal moray eel home look like? The size of the aquarium will depend on the species in question. Moray eels live in tight spaces. As a result, they typically can be housed in relatively small quarters appro-priate for their body size. But be aware that if you do keep them in a smaller aquarium, morays will be more likely to jump out. Also, in a small tank, moray eels are more likely to rearrange the aquascaping and knock into and disturb equipment (e.g., siphon tubes, heaters) in the tank.

The following is a good rule to go by when it comes to housing moray eels. Species that attain a length of 3 to 5 feet do best in aquaria ranging from 55 to 180 gallons; smaller species (less than 30 inches in length) will do fine in a 20- to 30-gallon aquarium, while the “mini morays” (those less than 15 inches) can even be kept in 10- or 15-gallon tanks.

Remember that moray eels produce a lot of waste and can be messy eaters. Therefore, the aquarium will require good biological and mechanical filtration. A good protein skimmer will also help provide better water quality.

Aquascaping is an important consideration in the moray eel aquarium. In order to ensure that your moray “feels secure” in its new home, provide it with shelter sites that are large enough to hide its entire body. This is especially true for more secretive eels, such the zebra moray. 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, aquarium-safe silicone sealant or drilled holes secured with PVC pipe 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, large ceramic flowerpots or a fishbowl with crushed coral attached with silicone to the outside and placed on its side on the aquarium bottom to create moray hideouts.

Moray eels are the Houdinis of the marine fish world. They will find the smallest opening in the back strip or space between glass tops, and they will slip out of their tank to go “crawl about.” Unfortunately, slithering on the carpet or dusty linoleum floor for a while is usually not too good for their health. I have lost a number of morays to jumping. I even had a glass top on the tank that had weights from a dive belt set on top of the cover to prevent the moray from pushing the top off. Even with the added weight, on two separate occasions, an eel managed to push the top to the side and slither out of the resulting opening in their aquarium. (In both cases, these were larger moray eels that were being temporarily housed in smaller aquariums — a situation I now avoid.)

Morays for Nano-Reefs
The larger moray eels are typically featured in nature documentaries and Hollywood movies (The Deep comes to mind), but there are a number of smaller moray eel species that do well in nano-aquariums.

One of my favorites is the golden or pencil moray eel (Gymnothorax melatremus). This is a rather secretive species that attains a maximum length of 7 inches. This moray actually is better-suited to a small species aquarium than a larger reef tank. In a more expansive aquarium, this secretive fish is likely to disappear in one of the many nooks and crannies, and thus becomes difficult to observe and to feed.

Golden moray eels are sometimes sold in pairs. Although I have not observed this species in pairs in the wild, and to the best of my knowledge, there are no easy ways to separate the sexes, some collectors sell individuals captured together as a male-female pair (which they may or may not be). That said, a pair of these morays can make an awesome addition to a nano-reef of 15 gallons or larger. Although not a direct threat to sessile invertebrates, this moray may occasionally knock off pieces of coral that are not affixed to the live rock, which could result in mechanical (abrasion) damage to the corals. Use some of the more popular aquarium cements to make sure corals are attached to the main rockwork in the aquarium. Also, be aware that this moray eel is a threat to small crustaceans.

Moray Parameters
Moray eels are considered to be very durable creatures. However, they are more likely to thrive and live long lives if you provide them with optimal living conditions. As far as water parameters are concerned, they do best when maintained at a specific gravity of 1.018 to 1.024. The tank water should have no detectable levels of ammonia and no or trace levels of nitrite (best under 3 ppm). They can withstand higher nitrate levels (e.g., 50 ppm), while the pH of a moray tank should be between 8.0 to 8.4 (sudden drops in pH can be lethal). A water temperature of 74 to 80 degrees Fahrenheit is perfect for morays, although most can withstand slightly higher temperatures.

Moray eels rarely succumb to disease in the aquarium. They are occasionally parasitized by nematode worms, which appear as squiggly, raised bumps under the eel’s skin. These animals are sensitive to copper compounds and organophosphates. Moray eels kept in aquariums with fiberglass decorations may develop skin lesions, resulting from contact with the fiberglass.

On rare occasions a moray may also suffer from skin tumors, and older specimens may develop cloudy eyes, a condition I have seen in wild and in captive eels.

Make sure you do your research before purchasing a moray eel. While some aquarists love keeping them and will always reserve aquarium space for one or more eels, other keepers get bored with a moray after a year or two. Therefore, you need to make sure you know what you’re getting into before acquiring a moray. For those willing to make the commitment, morays can make amazing aquarium pets. Happy fish watching! Previous Page>>

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