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Keeping the Moray Eels of the Genus Gymnothorax Moray Eels are some of the most popular centerpiece fishes for Marine tanks and many people are drawn to their looks, size, and predatory behavior. The genus Gymnothorax is a mixed bag as far as...
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Keeping the Moray Eels of the Genus Gymnothorax

Moray Eels are some of the most popular centerpiece fishes for Marine tanks and many people are drawn to their looks, size, and predatory behavior. The genus Gymnothorax is a mixed bag as far as suitability is concerned, containing some of the most desirable species as well as some of the most dangerous (but with all species you should always, always keep your hands out of the tank). These can be difficult fish to keep at home but can be very interesting if kept in the right tank.

Species

Moray Eels (family Muraenidae) is one of the larger families of Eels (order Anguilliformes) and contains about 200 different species over 15 genera. The largest genus is Gymnothorax with a total of about 123 recognized species, of which 12 are native to North America:

The species you are most likely to find for sale at your LFS (in no particular order) are the Green, Goldentail, California, and Spotted Morays. That said, Morays in general are in fairly high demand as centerpieces for Marine tanks and any of these are likely to be available somewhere. Just need to get out there and find/order one.

Conservation Status

Oddly enough for such a well known group of fish, all of these species of Moray Eels are considered “Not Evaluated” by the IUCN.

Distribution

For the most part, our Native Gymnothorax Morays are found on the East Coast of the US. All of those species overlap their range around Florida and into the Gulf of Mexico. With the exception of the Ocellated and Blacktail Morays, they are also found in the Caribbean as well as along the East Coast of Mexico. They are found as far North as Virginia or so (again, with the exception of the Blacktail, which is not found North of Florida). 

The California Moray is the only species found on the West Coast of North America, along most of California and down along the Coast of Mexico.

Description

The genus Gymnothorax contains both some of the largest and some of the smaller Moray eels. On the large side, the California gets up to 5 feet long, the Spotted Moray up to 6.5 feet (though usually closer to 3 feet in the home aquarium), and the Green Moray to a whopping 8 feet. On the other side of the size spectrum, the Goldentail and Polygon Morays are both about 2 feet long and the Lichen Moray to a mere 1 foot. The remaining Morays are all about 3 or 4 feet long.

Moray Eels are not the most active of fish. They typically spend most of their time holed up in caves, waiting for food to float (or swim, or crawl) by. Therefore, if you want to keep your Moray feeling secure, provide a couple of caves in the tank made of liverock and a deep substrate (4+ inches) of mixed sized particles (fine sand, coarse sand, crushed gravel). These fish are strong and are often looking for an exit out of your tank… make sure you have a VERY strong and secure lid! And protect your heater… some Morays get too cozy with them and get burned.

That said, there is a sharp divide between the Morays which are good for aquarium keeping and those which are ill suited for it. The Green and California Morays, for example, are very large and aggressive, attacking most all tankmates and should be avoided. On the other hand, the Goldentail and Spotted Morays are both reasonably tempered and hardy and make very good additions. The majority of the other species never really adapt to captive life, either dying due to stress in transit or refusing to eat once they arrive.

Tankmates can be difficult for these fish to place. On the one hand, smaller fish are likely to be attacked and consumed by sizeable eels. If said fish is a Toadfish or another venomous species, it may cost you your eel. On the other hand, native puffers, triggers, snappers, large Angels are all likely to chew on your Moray… also bad for it. With easygoing species (like the Goldentail and Spotted Morays), you should be alright with much bigger, peaceful species like the various Spadefish or Squirrelfish. Species much too small to be seen as food, like the Killifish and Livebearers, may be doable too.

Looking to mix Moray species? It may be doable, with a few precautions. First, make sure you pick an easygoing Gymnothorax (and NOT one of the more aggressive ones like the Green or California Moray). Second, do not mix Gymnothorax species, it usually does not work well. The Native Echidna catenata (Chain Moray) should be a safe bet, but if willing to go outside the US then any of the Echidna species or Gymnomuraena zebra (Zebra Moray) should be safe. Make sure you have a suitably large tank, a large number of caves, and start your Morays off small. Still, there’s no guarantees and there should also be a plan be for removing an eel that’s getting beat up.

And you should never underestimate the damage your eel can do to you. All Morays are venomous (not a strong venom, but still) and if you are allergic to animal stings like bees then you may react strongly to it. And, venomous or not, a large Moray can deal a lot of damage to it’s owner with a single bite. Always keep your hands out of the tank when doing any sort of tank maintenance.

Feeding

There are two levels of feeding when it comes to Moray eels: those that will eat most anything meaty that you provide them, and those that generally refuse to eat and starve not long after capture. For those that accept food, your best choices are a mix of squid, mussels, cockles, krill, filets of salt water fish… a variety of foods is the best way to ensure health. Due to their inactivity, you don’t have to (and shouldn’t) feed Morays daily. Two or three feedings a week is plenty.

If your Moray has reservations about eating frozen foods, you can always try using a bait stick to move the food in front of the Moray and this should trigger eating behavior. They should eventually convert, though. It’s always recommended to avoid live feeder fish wherever possible (due to health concerns, ethics) but for long term (several week) hunger strikes, you can try gut loaded Mollies, assuming you have bred them at home and can confirm that the stock is healthy.

Water Quality

Like most reef fish, the Gymnothorax Morays prefer a high specific gravity, somewhere around 1.025-1.026. Morays are messy and you’ll need all the help you can get to keep water clean… large filtration, sizeable regular water changes, and certainly live rock and a Deep Sand Bed. And I highly encourage using a Protein Skimmer in any Marine system. Temperature is somewhat flexible, with 72-82 F working for most all Tropical Species (the Green, Lichen, Blacktail, Sharktooth, and Polygon Morays) with Saddled Morays being lower end, from 73-75 F or so. The remaining species are Suptropical and are best around 64-68 F, or about room temperature for tanks in most houses.

Brackish Suitability

Nope, all of these species of Moray Eels are for Saltwater tanks, only. If looking for a brackish Moray, you’re going to have to look out of the country; both G. polyuranodon and G. tile are brackish Morays of this Genus, but these are fish native to the Indo-Pacific Oceans.

Tank Size

Tank space depends on the size of the Eel (surprise, surprise). Lichen Morays are fine in a 75 gallon tank for their entire lives. For Eels up to about the 2 foot range, something around 100 or 125 gallons should be adequate. 200 gallons for 3 feet, and 300+ for 4 foot long Eels are fine too. On the far end of the spectrum, an average sized adult Green Moray will need 500 gallons and anything larger will likely need 1000 gallons. These are absolutely massive fish. And of course, always consider the pros and cons of using sumps and/or refugiums with your display system. The benefits of extra volume and space to put fish that may not live with the Moray are quite significant.

Note that these are all numbers for a single Moray in the tank. You will have to go larger if you plan on doing multiples as agitated/aggressive Eels do not cohabitate well. 

Breeding

No, not going to happen in the home aquarium, sorry to say. To my knowledge, no Gymnothorax Eel has been bred in captivity.

Final Thoughts

Moray Eels can make wonderful centerpiece fishes in your Native Marine biotope, as long as you know what their needs are and understand that Morays can and do “cross the line”… you should always have a plan B for housing your livestock in a Moray tank. But for those few easygoing species, you should find this to be a low risk and be rewarded with a lovely fish for many years.

Sources

Fish Identification, Fishbase

Gymnothorax conspersus - Saddled Moray, Reeflex

The Moray Eels, Family Muraenidae, pt. 1, Bob Fenner

The Moray Eels, Family Muraenidae, pt. 2, Bob Fenner

Moray Eels Bite - But are they Poisonous?, Marco Lichtenberger (warning! Very graphic pictures)

Moray Systems FAQs, Wetwebmedia

(Image Source: Me!)

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