In filling in for Henry this month, I thought
I'd present an overview of a few exceptional reef-safe fish,
specifically some of the moray eels. With their unmistakable
appearance and mode of locomotion, moray eels provide a unique
presence in an aquarium. Many people ask if there are any
reef-safe eels that will not consume their fishy tank mates.
As morays have no interest in corals or other sessile invertebrates,
they are technically "reef-safe." Only a few, however,
are fish-safe. All morays are carnivorous and feed on either
fish or moving invertebrates. However, there are a small number
of them that are generally fish-safe, and these may fit into
hobbyists' aquarium plans.
1. Moray eels, such as this snowflake, can
make a wonderful and unique addition to a reef tank,
given some qualifications. Photo courtesy of Skip Attix.
This month I would like to highlight the
moray eels that I consider to be both reef-safe and fish-safe.
Additionally, I will as discuss specific husbandry issues,
tank requirements, and potential compatibility conflicts.
I should mention that this is not a complete listing or description
of morays which could fit into a reef tank. For example, I
will not discuss in detail a group of dwarf sized morays that
are known fish eaters, but have mouths too small to easily
consume most common reef fish. These eels, exemplified by
species such as the dwarf golden moray (Gymnothorax melatremus),
are rare and very expensive [Figure 2]. Rather, I wish to
identify a few commonly available eels, ones you might see
in your weekly excursions to the pet store, and provide background
and husbandry information so you can decide if a fish-safe
eel would be a candidate for your aquarium.
2. G. melatremus-the dwarf golden moray.
These rare morays are known fish eaters but have mouths
too small to eat many of our common reef fish. Photo
courtesy of anilabbasi.
Moray eels are true eels in the taxonomic
Order Anquilliformes. They are found in the family Muraendae
that comprises 15 genera and approximately 200 species. Approximately
12 of these 200 species are suitable for the home aquarium,
and Fenner (1995) considers only five species to be safe with
other fish. These particular eels range in size from eight
inches to about two feet long. Eels are readily identifiable
by the lack of pelvic fins, pectoral fins, and having elongated
bodies, and have a snake-like in appearance. They do not have
either gill cover openings and scales. Additionally, their
dorsal and anal fins are continuous around the body. This
body design requires the fish to maneuver with long flowing
wave-like strokes. Because morays lack scales, they protect
their skin from abrasions by shedding a constant covering
of mucus. Morays possess lateral line pores only on their
heads, and this unique adaptation allows them to live in caves
and crevices with only their head displayed, and still be
able to sense movement in the water.
The vast majority of morays can be found
in coral reefs in tropical waters, with a few members found
in all oceans as far north as the west coast of North America.
Interestingly, morays are the second-most represented fish
group (after the wrasses) in the Hawaiian Islands, with more
than 40 species found locally, suggesting they play an important
role in the local food chains (Gonzales, 1976).
Moray eels possess a menacing appearance,
with their mouths constantly agape. While an opened mouth
display appears frightful, especially when coupled with pointed
fangs, the eel's physiology requires this behavior. The mouth
must remain open to allow water to be pumped into the oral
cavity, then over the gills by muscles located in the gill
cavity and attached to the mandible or lower jawbone. Juvenile
morays often appear differently colored, often with more pronounced
color patterns, and with different bodily proportions than
are found in the adults. As the animals age, their body proportions
become thicker, and the bold color patterns fade to a more
diffuse coloration (Michael, 1998).
Many moray eels have limited vision and
instead, they rely on a highly evolved sense of smell. This
sense of smell, combined with the head-localized lateral line
system to sense vibration makes these eels formidable hunters
of any prey items that pass near their cave-like opening.
Morays can detect sick or injured fish hiding in the reef,
and as they possess wedge-shaped heads and bodies, they can
squeeze into tight recesses to extract a hiding food item.
Many eels have nutritional preferences
and these eels are easily divided into two groups (Axelrod,
1990). Morays with pointed teeth, the fang-toothed morays,
use these fangs to hold and tear their fish prey. In my experience,
almost any captive fang-toothed moray will eventually eat
its fish tankmates. Even tough fish like triggers, quick swimming
groupers, and puffers, may fall prey to a moray, especially
at night. The fang-toothed eels will even eat cleaner wrasses.
Obviously these fang-toothed morays are suitable only for
tank dedicated only to them. It pains me to see any hobbyist
adding Clown triggers to a tank containing a two-foot long
Tessellata eel (Gymnothrax favagineus); the outcome
of such a placement surely known well in advance.
Fish-Safe Eels: The Pebbled-Toothed Morays
The pebbled-toothed morays feed primarily
on crustaceans and hard-shelled invertebrates. These morays
are found in the genera Echidna, Gymnomuraena,
and Siderea, and are known for having blunt molar-like
teeth that are designed for crushing the shells of their prey.
They tend to have small poorly-developed eyes, short head
and mouth structures, and a highly developed olfactory system
that compensates for their poor vision. Not surprisingly,
the pebbled-tooth morays rely heavily on locating their prey
based on smell, rather than by sight. Additionally, these
eels have adapted their behavior to pinpoint prey based on
angulations of their head. When a prey item approaches the
eel's sensing perimeter, the moray will move its head from
side to side to better acquire scent intensity, and to determine
the signal strength based on its head orientation. To place
a definitive confirmation on their location, these eels will
often "bump" items with their nose before they strike.
Taste and touch receptors located in the lips and nose of
the eel help determine if the item is an appropriate food
(listed according to most "reef safe")
Common name: snowflake eel, starry eel
Maximum length: 30", minimum tank size:
Snowflake morays are found commonly on
reef slopes and reef lagoons. According to Michael (1999)
this eel is common in the tidal zones and has been observed
slithering out of the water at ebb tide. Snowflake eels feed
primarily on shore crabs, spider crabs, and rock-dwelling
xanthid crabs. Additionally, mantis shrimps and small bony
fish remains have been found in the stomach content analyses
of these eels and adult snowflake eels have been observed
eating small cephalopods. In general, snowflake eels are excellent
reef-safe morays [Figures 1, 3, 4, 5]. They adapt quickly
to tank life, readily accept prepared marine-based foods,
and are much less of a threat to fish than members of Gymnothorax.
Snowflakes remain fairly small, under 30 inches, and it is
not uncommon for a juvenile snowflake to take up to two years
before adult sizes are reached. However, one word of caution
is needed when keeping snowflake eels: when food is in the
water, these eels may become aggressive. It is not uncommon
for a medium-sized snowflake eel to attack a fish when chasing
a scent trail though the water column, and it is also not
uncommon for an adult snowflake eel to take a bite out of
a nearby fish when food is in the water. As a way of preventing
this type of feeding behavior, snowflake eels can be fed using
a feeding stick, a rigid tube on which the food item is attached
to the lower end and placed within inches of the eel. Stick-fed
eels tend to wait for food on the stick and don't exhibit
the frenzied feeding response described above. As with most
morays, juvenile snowflake eels will spend the majority of
their time with their head protruding from the rockwork. When
they become more familiar with their surroundings, they will
actively explore the tank. Snowflake eels tend not to be as
shy as chainlink eels.
4. An adult snowflake eel peering from a cave in
Kona, Hawaii. Apparent in this photo is the head structure
of the eel and a very unique splotchy pattern specific
for snowflake morays. This dive photo courtesy of Linda
5. Another dive photo of a snowflake moray peering
from its hole. Notice how different the body pattern
is compard to Figure 4. Each snowflake moray has a unique
body pattern and coloration scheme. Photo courtesy of
Common name: zebra moray
Maximum length: 3 feet, minimum tank size: 40
Must have a strong reef rock structure for these eels (Michael,
Zebra morays are found primarily in rocky
and coral reefs on the east coast of Africa to the Red Sea.
These passive eels have remarkable patterns of deep black
to chocolate brown interspersed with vertical white stripes
[Figures 6, 7, 8, 9]. Their head is designed to crush hardened
crustacean shells. The primary foods of zebra morays are crabs,
shrimp, and occasionally snails and urchins. Zebra morays
employ a unique hunting style for finding food: they intentionally
bump the prey item to first see if it moves, and second to
taste the prey item, to determine its food worthiness. Small
prey items are usually swallowed whole, while larger food
items like crabs, are held down by their body coils as the
claws and legs are broken off and eaten. A zebra moray's jaws
will easily crack crab claws, and in the home aquarium, one
can hear the equivalent of a nutcracker sounding off when
a crab claw is cracked. Zebra morays do much of their hunting
behind the reef structures and rarely venture out into the
open. These fish often refuse take prepared foods, but after
a lengthy starvation period will generally wean over to stick
feeding. However, initially I would recommend feeding them
live fiddler crabs, small blue crabs, and small shrimp to
establish the fish.
6. A head shot of a zebra moray. Obvious
in this photo are the nostrils placed high on the head.
Photo courtesy of www.exotictropicals.com.
7 (background). The full monty. A full view of a
34" adult zebra moray. Notice how thick and muscular
the adult body is. Photo courtesy of J.E. Randall www.Fishbase.org.
Figure 8 (insert). A zebra moray extended out
of its hiding spot. Photo courtesy
of Kpeterson of Monterey
As they grow to adult size, zebra morays
become relatively much thicker and more muscular, which emphasizes
their apparently clumsy demeanor. Reef structures must be
large and strong to withstand the body movements and contortions
these eels exhibit when feeding. My only reservation in recommending
these eels as a wonderful, reef-safe eel is that at adult
size they are guaranteed to renovate your rockwork, toppling
corals in the process. Most reef fishes are safe with a zebra
moray as long as the eel is regularly fed. These eels are
too large and "clumsy" to be kept with most sessile
invertebrates and they definitely should not be kept in small
reef systems. They will eventually eat all of the ornamental
crustaceans in their tank.
9. A shot of a zebra moray in the author's tank.
Photo courtesy of Frank Marini.
Common name: chainlink moray, chain moray
Maximum size: 30", minimum tank size: 40
Chainlink morays inhabit coral and rocky
reefs in the warm tropical waters of Brazil (Michael, 1999).
The attractive body coloration of these fish varies considerably
with each individual having a unique color pattern [Figures
10, 11, 12]. Juvenile chainlink morays have attractive green
banding patterns with alternating yellow stripes, however,
these colors tend to fade and run together as the animal ages.
These eels are extremely reclusive and hide under the rockwork.
They are nocturnal hunters and feed primarily on crabs. According
to Michael (1998), they will frequently pursue these crabs
out of the water and onto the shore to capture them. Chainlink
eels readily adapt to aquarium life if provided with plenty
of hiding places and adequately sized caves. These eels remain
reclusive even after an adjustment period in captivity and
tend to remain this way until hungry. Fortunately, chainlink
morays readily wean onto prepared food after they are initially
established on live fiddler crabs and small blue crabs. After
some training, these fish will learn to take food from a stick.
These morays are an excellent choice for a reef safe eel,
as they are moderately sized, attractive, and wean readily
onto prepared foods. However, they are a secretive fish that
spends much of its day out of sight.
10. A head shot of an chainlink moray. Photo courtesy
of Dick "Fishdaddy."
11. A full body shot of a chainlink moray. Obvious
in the photo is how thickly muscled the body of this
eel is, and the unique color pattern. Photo courtesy
of Dick "Fishdaddy."
12. Shown here is a 4.5 year old captive raised
chainlink moray. While the maximum published size
of chainlink morays is 30", this moray is 32".
Apparently, he couldn¹t read the fine print.
Photo courtesy of Musipilot.
Once you decide that a moray eel could
fit into your tank situation, there are a few requirements
that will ensure a perfect home for your eel. In general,
you want to provide a rockwork structure in which the eels
can find a number of good hiding spots and areas where the
eels can peer out into the tank. The good news is that in
a reef tank, this is a typical rock structure. To ensure that
an eel has the appropriate home when you are designing the
reef, adding a PVC pipe three inches in diameter and two feet
long will provide an adequate home [Diagram 1]. Eels will
often dig under structures and can topple any loose rockwork,
so "eel proof" your reef structure by using heavy
or tightly fitting rock arrangements. When considering a zebra
moray, in particular, the lower rock structures must be large
and firm, thereby preventing any movement of the lower rocks
by the eels when they are feeding. Adult zebra morays are
very muscular and will readily topple any weak supporting
structures as they use these structures to push against while
ingesting shelled foods.
1. Elaborate tunnels for your moray to hide
in can be created by simply burying PVC in the substrate.
Diagram courtesy of Kevin Carroll from The Book of
Coral Propagation by Anthony Calfo.
Moray eels are the escape artists of the
fish world; they can exit through any hole in the cover of
your aquarium. Adult eels can push against the top to open
the cover. To prevent any Houdini-like escapes, I recommend
covering your tank and weighing the cover down. A tight fitting
top that is locked or clipped into place is mandatory. Just
be sure to allow for the fact that if you do decide on a tight
fitting top and you are using an air stone or under gravel
filter, that carbon dioxide may build up in this upper air
space and this buildup needs to be frequently removed. If
you do happen to find your moray has escaped and has partially
dried on the floor, don't give up hope, moray eels secrete
a thick slime layer that will protect them for a few hours
outside of water. Some juvenile morays and the dwarf morays
have been known to swim down under gravel lift tubes and get
beneath under gravel plates (Michael, 1998), so if you have
an under gravel filtration system, it should have screens
over all the intakes.
It is critical that moray eels be fed a
varied diet, one that replicates their natural prey items.
In the case of the morays discussed here, crustaceans and
hard-shelled invertebrates should be an integral part of the
diet. A close inspection of the seafood counter at your local
grocery store will yield all the food items you'll need. Fresh
gulf shrimp with the shells on, whole blue crab, octopus or
squid will all be eaten with great delight. Most morays must
be trained to eat dead food items and this is a lengthy, albeit
critical, process for survival of your moray. Many pebble-toothed
morays will take live shrimp and fiddler crabs as starter
foods. Juvenile snowflake eels will readily eat ghost shrimp,
and small freshwater feeder fish; however, these starter foods
are just that, "starter food." After a period of
establishment in your tank (say, two to three weeks) you need
to wean these eels off the live foods and onto these prepared
meals. I find it easiest to entice the eel by using a gulf
shrimp on the end of a feeding stick [Figure 13, 14]. I buy
a three foot long, three quarters inch in diameter hard plastic
airline tube and impale the thawed gulf shrimp onto the end.
I then use the stick to gently bump the food item onto the
nose and mouth area of the eel. Do this gently once or twice.
Do not try feeding it repeatedly; the eel will decide within
a few seconds if it wants the food. If the eel refuses, then
try again later or even the next day. From experience I've
found that these eels can be stubborn. It took my zebra eel
eight weeks before it fed on thawed gulf shrimp. So for eight
weeks this eel did not eat a thing. In fact, according to
starving this fish for extended periods replicates its natural
feeding cycle. You need to tailor your eels feeding schedule
to the eel. When you do feed, try to feed until the eel refuses
food; this is usually a few shrimps worth or a quarter of
a small blue crab. The next feeding should occur when your
eel has digested this meal and is out looking for food. My
eels tell me when they are hungry and this usually occurs
approximately 2 times per week. So, how often should your
moray be fed? Morays do not have to eat very often, and overfeeding
them simply adds to water pollution and growth/size problems.
Overfeeding in eels is a major health problem; overfed eels
accumulate fat at an unhealthy rate, and it's not uncommon
to observe a fat eel at a public aquarium where the handlers
feed the eel as part of an hourly display. If your eel refuses
food, consider giving the eel some time off from feeding to
allow the animal to utilize some stored fats. In my experience
eels stop feeding for two reasons. First, the water quality
in your tank has become compromised, and doing frequent partial
water exchanges easily rectifies this. Second, overfeeding
will cause your eel to stop eating; it may take several weeks
before your eel resumes feeding again, so be patient.
13 & 14. The feeding stick (above) with an impaled
fresh gulf shrimp getting ready to feed the eels(below).
Photo courtesy of Frank Marini.
In general, more than one pebble-toothed
moray can be kept in the same aquarium, provided that you
have more than one cave or PVC pipe. As juveniles, snowflake
eels will cluster in the same cave for protection; however,
as adults this is often not the case. If a new moray is added
to a tank with an established eel, you should expect the new
moray to be chased and harassed until a dominance hierarchy
is arranged, especially if you are introducing the same species.
In many cases with the pebble-toothed morays, they will usually
attempt to defend invasion of their hole and surrounding space
by head butting and pushing or by open mouth pushing the new
eel away. According to Michael (1998) some morays can be cannibalistic,
as he has reported seeing regurgitation from a snowflake eel
containing the remains of smaller snowflake eels. The good
news is, in general, smaller eels will stay out of harm's
way in the presence of larger eels.
One of the main reasons to acquire a pebble-toothed
moray is to keep this eel with reef community fish, and, in
fact, the majority of these pebble-toothed morays have no
interest in fish at all. If it were not for the large muscular
size and clumsy nature of zebra eels, I would recommend them
as a perfect moray for a reef tank. The better choice is a
snowflake eel as they adapt readily to tank life, prefer to
feed in their holes, and only get rambunctious when food is
in the water. These eels start fairly thin, reach a maximum
size of 24", and will learn to take prepared foods from
a feeding stick. Juvenile snowflake eels grow quite slowly,
and it's not uncommon for them to achieve adult size in 2+
While these crustacean feeding eels do
not show much interest in fish, they may inadvertently take
chunks out of them at feeding time. I have seen many a snowflake
eel or zebra eel blindly thrash in the water column or actively
pursue what they think is food, when it is really a tankmate
that happens to be in the eel's scent trail. One thing to
consider is that if you feed your eels live freshwater feeders
for extended periods, it will increase the likelihood of these
fish chasing and eating fish, since you have trained them
to eat fish. So, again, my recommendation is to not feed these
eels live feeder fish.
A Sick Moray
Most moray eels are very durable fish.
The two keys to success with morays eels are 1) excellent
water quality and 2) a varied and nutritious diet. I have
found that zebra eels in particular require good water quality
and any decline in water conditions results in them "going
off feed". This problem is easily resolved by frequent
water exchanges and once the water issue is resolved, the
eel is back to its normal self. According to Michael (1998),
he has yet to see a moray succumb to disease or parasites
and only on rare occasions has he noted external parasites
or nematode infections. It is important to remember that when
treating moray eels with medications is that moray eels are
exceptionally sensitive to copper-based and organophosphate-based
medicines. Therefore, Ich treatments should be done in hyposalinity
and not copper.
Additionally, no treatments should be undertaken
using medications with the tradename: Masoten, Dylox, and
Dipterex. According to Fenner (1990), if your eel appears
to be developing a bacterial or fungal infection, check for
a decline in water quality. Should any parameter be suspect,
perform water changes, or remove the eel to a quarantine tank
and treat with an antibiotic. Water quality issues will also
trigger a starvation response from many eels. When refusal
of food is first observed, try performing water exchanges
to alleviate the situation; however, if your eel continues
to refuse food for more than a few weeks, attempt to find
the source of the problem. This could range from bacterial
infections to overfeeding. Don't fret over morays which have
fasted for short periods; my eels have refused food for over
2 months with no loss of body condition or apparent health
In conclusion, the pebble-toothed morays
make an excellent tankmate in reef tank style aquariums. The
snowflake eel is probably the best-suited eel for this tank
as it is small, compatible with other fish species and adaptable
to captivity. It is certainly one of the most passive, sociable,
and desirable moray species. Just remember that snowflakes
may mistakenly strike at other fish when food is in the water.
Zebra eels would be the next choice, as they have no interest
in fish at all, but their large size and clumsy demeanor makes
them more likely to destroy reef structures. Finally, the
chainlink moray are the least preferable of these eels as
they get larger than zebra morays, have an equally clumsy
demeanor, compounded with an exceptional shyness. If you want
the coolness of an eel in your reef tank, then seriously consider
a crustacean eating moray. Remember that fanged teeth equals
a fish eater, pebbled-tooth equals fish safe.