Moray eels bite – But are they
by Marco Lichtenberger
Moray eels without a doubt are among those fish you’d call oddballs if
they were from freshwater. Most specimens usually hide their long bodies
in narrow gaps and holes all day, but if they leave them for food or
explorative purposes, they are definitely eye catchers. Not only will
they catch our attention, sometimes, if given the possibility, they will
also catch our fingers, hands and arms with varying success.
In the last moray related article I composed for Conscientious
Aquarist, I stated: “Own experience with regard to moray bites are
luckily not available.”
Well, things have changed since then and I had an unfortunate meeting
with the teeth of one of my moray eel. Accordingly, after the “wound”
was treated, I searched literature with regard to moray toxins and moray
bites and, aside my own little experience, came across several reports
of hobbyists, scientific studies with regard to moray physiology and
cytology, as well as toxicological studies on substances from morays.
Therefore, an overview about moray related substances and the results of
moray bites are given here.
State of knowledge
There is quite a divergence in published books for hobbyists with regard
to the toxicity of moray eel.
Most interestingly there is also a divergence with regard to the
language these books were written in. Searching German books (and online
sources) one often stumbles over the (here translated) statements “Moray
eels are poisonous. Among all moray eel five species even can give a
deadly bite. One of them is the Mediterranean moray Muraena helena.”
By contrast, English sources often state: “Moray eels are not poisonous”.
Comparing these statements to scientific literature, both have to be
Mucous toxins produced by moray eel themselves
Studies as well as personal reports confirm that the bite of a moray eel
can be much more painful than the bite of other predatory fishes of
similar size. This cannot be explained by a “pulling back effect”, which
means that one automatically pulls back a bitten limb and thus increases
the wound by driving the moray eel’s teeth through the flesh forcefully.
Such happens with other fishes, too.
Secondary infections also fail to explain strong pain immediately after
a moray bite. Such infections can likely occur if wounds are not treated
properly, but will need several hours to spread.
In addition to the pain, wounds from moray bites often bleed unusually
It was suggested that bleeding and pain are related to a toxin in the
slime coat of the skin and the mucous of the mouth. And truly, the
mucous of moray eels was analysed and not only one, but also several
toxic substances were found. One of these substances is hemagglutinin.
This is a glycoprotein that makes red blood cells clump. Another yet not
too well understood toxin found in the mucous coat of moray eel was
shown to be haemolytic. That means the toxin destroys red blood cells.
These toxins are produced by glands in the skin of the eel, and a
category of toxins known as crinotoxins.
Closer examination of the Starry or Yellow-mouth moray eel
Gymnothorax nudivomer, (formerly Lycodontis nudivomer)
have shown that it has specific club shaped cells in its thick (up to 2
mm) skin that produce these toxins. So, in contrast to many other toxic
marine animals (e.g. pufferfish) that ingest poisonous critters and
store the ingested toxins in their own tissue, morays are capable of
producing crinotoxins themselves.
Those club shaped cells have not only been found in the Yellow-mouth
moray, but also many other species. It is likely that the majority of
the approximately two hundred known species of moray eel can produce
toxins, but this has not been subject to scientific research yet.
What is known is that the number and distribution of the club cells
varies among species. In addition, it was suggested that moray eels with
serrate teeth (e.g. G. nudivomer; G. albimarginatus; G. chlamydatus;
G. ocellatus) could transfer more mucous into the wounds and thus
deliver the most painful bites.
Germane to this point it the belief that the crinotoxins of morays are
not particularly dangerous to man, but rather lead only to increased
pain and bleeding. Even allowing for this, allergic reactions may be
possible and are just one more reason why you don’t want to be bitten by
a moray eel.
In short, those crinotoxins underline two general rules of tank
maintenance: Don’t put your hands into the tank if you have open wounds,
and don’t touch your moray eel. Both of these could make you vulnerable
to crinotoxin poisoning even without the moray biting you.
In common with other members of the eel order Anguilliformes, moray eels
have blood that contains proteins that are toxic to humans. These
proteins are usually referred to as ichthyotoxins, a word that simply
means “fish poisons”.
Ichthyotoxins were among the first toxic substances identified,
fisherman having long known that certain fishes have to be heated about
75˚C before they are safe to eat (high temperatures destroying the
toxins). Because of these ichthyotoxins, making moray eel sushi is not a
Ichthyotoxin poisoning can lead to spasms and heavy breathing;
ichthyotoxins are also haemolytic and should not touch your eyes, mouth
or open wounds. Because of this bleeding moray eels should be handled
Aside from mucous and blood toxins, moray eels (like many other
predatory fishes) can accumulate additional toxins in their flesh and
internal organs. The two most prominent of these are ciguatoxin and
maitotoxin; these toxins are not destroyed by cooking, and cause a type
of food poisoning known as ciguatera. Fortunately for the aquarist,
these toxins are not transferred by bites.
Ciguatoxin is not produced by the moray eel itself, but by microscopic
algae dinoflagellates such as Gambierdiscus toxicus.
Dinoflagellates are at the base of the food chain and are eaten by
herbivores such as snails and clams. Small predators such as crabs eat
these herbivores; these get eaten by bigger predators like fish; and so
on up the food chain. With each step up the food chain the concentration
of the toxin becomes greater because of a process known as
bioaccumulation. The amount of ciguatoxin in organisms at the lower end
of the food chain is small enough not to be poisonous in most instances,
but the tissues of predators at the top of the food chain, such as giant
morays like Gymnothorax javanicus can contain dangerously toxic
amounts of ciguatoxin.
Ciguatoxin is a neurotoxin; it inhibits the sodium channels needed for
signal transmission in the nerves. Symptoms are sickness, spasms, skin
irritations and partial paralysis. In terms of its effects it is not
unlike the pufferfish toxins tetrodotoxin and saxitoxin, but luckily it
is slightly less effective and usually occurs at lower concentrations.
Consequently ciguatoxin poisoning is rarely lethal, with less than 1% of
those so poisoned dying. Even so, it is often recommended that moray
eels larger than 1.5 m should not be eaten because the precise amount of
ciguatoxin in the tissues of fish that size is unpredictable and
While the physiological effects of moray eel crinotoxins are not fully
understood but seemingly not usually serious, and the toxins in the
blood and tissue hardly likely to cause harm if you are bitten, the
secondary infections that can set in after a moray eel bite are very
definitely known to be a serious threat to your health.
Moray eels don’t have pectoral fins let alone hands, but even if they
could be trained to use a toothbrush, they’d have major problems
cleaning the numerous spaces between they multiple rows of pointed
teeth. Rotting food provides a perfect environment for bacteria to live
and multiply. Among the bacteria known to inhabit moray eel jaws are
species of Vibrio, known to cause septicaemia, and species of
These bacteria will be very happy to go from the jaws of a moray eel
onto a nice fresh piece of meat like your hand, and a moray eel bite is
the perfect way for this to happen. Although there seem to be no
fatalities from secondary infections caused by moray bites, there
certainly have been fatalities caused by Vibrio infections from
The most important thing when bitten by a pet moray is to clean the
wound with painstaking care. Hold your hand under the tap and thoroughly
wash out the wound. Disinfect the wound. Be sure to visit a doctor if
you see your wound is heavily swelling or turning red. Septicaemia is
extremely dangerous and requires immediate medical attention.
Larger wounds can be dangerous due to the loss of tissue and blood. They
will need medical care. It’s a good idea to ask someone else to drive
you there because dizziness often accompanies these types of injuries.
Make an emergency call if necessary. If you are loosing lots of blood,
because some larger blood vessel has been cut open, the affected limb
will need to be ligatured until further help arrives.
To summarise, pet moray bites are far from inevitably lethal, but there
are some nasty, potentially dangerous effects nonetheless, so situations
where a moray could bite you should be avoided as far as possible.
Some general rules to help you and your moray eel to get along follow;
with these in mind you can enjoy your very special pet (and your moray
eel will be spared the problem of digesting mammal long-fibre meat).
1. No hand feeding
It may be daring to show to friends that such a wild animal can be fed
by hand, it may also seem like hand feeding could somehow improve your
relationship with your pet, but hand feeding obviously puts you at a
very real risk of being bitten by a moray eel.
Hand feeding is widespread among hobbyists, with many aquarists having
done so without incident for years. But that is no guarantee that your
moray will never decide to taste human flesh one day! Even if your
specimen seems to take food very carefully out of your hand, this can
change from one day to another. Especially the supposedly “tame”
Snowflake eels Echidna nebulosa that are known to suddenly make
up their minds when feeding, as well as being unpredictable with regard
to considering their tankmates as potential food.
2. No large species
It is one thing to be bitten by a twelve-inch juvenile Snowflake eel
with quite small teeth; being bitten by a 5-foot Green moray
Gymnothorax funebris is an entirely different experience.
Moray eels of that size are capable of tearing out large pieces of flesh
from your arms; they can rip off entire fingers and mutilate careless
owners. Only people who really know what they are doing should only keep
such animals; they are best left to public aquaria or perhaps insanely
Among the large and potentially dangerous species seen in trade too
often are the Tessellated or Honeycomb moray eel Gymnothorax
favagineus; the Green moray eel Gymnothorax funebris; and
the aptly named Giant moray Gymnothorax javanicus.
WetWebMedia.com lists some more potentially dangerous moray eel species
unsuitable for most fishkeepers.
In fact all species that exceed a body length of more than three feet
(except the Zebra, Chainlink and Ribbon moray eels) should be considered
potentially dangerous with regard to the wounds that they can inflict.
There are also some rather small species equipped with long and curved
teeth that should also be handled carefully as well, including the
various Dragon and Viper morays (Muraena spp. and
3. Use tools for maintenance
One of the basic rules of marine fishkeeping is to keep your hands out
of the tank as much as possible. Usually this refers to the possible
transferral of non-beneficial substances such as oils, fats and soap
into the water, but in case of a moray eel aquarium it also refers to
Numerous long tools are available for almost anything that needs to be
done in a tank. Feeding sticks, long pliers, tweezers and other items
are widely available in the shops. This arsenal can be extended with
basic DIY abilities and a little imagination.
If you really need to work in a tank with your hands, be sure the lights
are on, know where your moray eels are in the tank, and have a net
available to keep their heads away from your hands. Ideally, have
another person with you to keep watching the moray and reporting what
its doing and where it is.
4. Keep your attention focused
Probably this is the hardest rule to stick to. Maintaining tanks for
months and years leads to a certain complacency that inevitably drains
your attention. This is widely known among keepers of venomous snakes,
who often have a fear of forgetting to lock their pet’s quarters once
they’ve become too used to the routine.
My own moray eel biting experience was also caused by a lack of
attention. I got up 6.30 AM and just had a quick look at one of the
tanks. One of the new Sarcophyton cuttings had left its place
and not even half awake I put my hand into the tank to put the
Sarcophyton where it should have been and ended up with a moray eel
attached to my little finger!
The moray released its bite quickly and hid for the rest of the day. It
was very shy for the next few days as well, so I guess this was not a
nice experience for the moray eel any more than it was for me.
By not being attentive and not using the right tool for the job, I ended
up being bitten. Of course the positive thing for me is that I’m now a
lot more careful about paying attention, and hope this painful reminder
will have this effect for quite a while yet!
In summary, moray eels are poisonous in several ways. Their bites can be
poisonous, although the exact toxicity is so far unknown and considered
to be rather low. However, secondary infections following any moray
bite, as well as the loss of tissue and blood from large moray bites,
both constitute a more probable and potentially more serious health
With this said, the fact that morays can bite is no reason why aquarists
should not keep small or medium sized species and enjoy them as the
wonderful aquarium pets that they are. What moray bites do constitute is
a good reason for being careful when handling them and paying attention
to any work in the aquarium, two attitudes that make for better
fishkeeping anyway, whether you are keeping moray eels or not.
Böhlke, E.B. & Randall, J.E. (2000): A review of the moray eel
(Anguilliformes: Muraenidae) of the Hawaiian Islands, with descriptions
of two new species. Proc. Acad. Nat. Sci. Philad. 150,
Erickson, T.; Vanden Hoek, T.L.; Kuritza, A.; Leiken, J.B. (1992): The
emergency management of moray eel bites. Ann. Emerg. Med.
21, p. 212-216.
Fenner, R.M.: The Moray Eels, Family Muraenidae, pts. 1 & 2 - The
Diversity of Aquatic Life Series. published at
Lewis, R.J.; Sellin, M.; Poli, M.A.; Norton, R.S.; MacLeod, J.K.; Sheil,
M.M. (1991): Purification and characterization of Ciguatoxin from moray
eel (Lycodontis javanicus, Muraenidae). Toxicon
29(9), p. 1115-1127.
Mebs, D. (1989): Gifte im Riff: Toxikologie und Biochemie eines
Lebensraumes. 120 p., Wissenschaftliche Verlagsgesellschaft
Stuttgart. (In German)
Randall, J.E. ; Aida, K.; Oshima, Y.; Hori, K.; Hashimoto, Y. (1981):
Occurrence of a crinotoxin and hemagglutinin in the skin mucus of the
moray eel Lycodontis nudivomer. Marine Biology
62(2-3), p. 179-184.
Randall, J.E.; Earle, J.L.; Pyle, R.L.; Parrish, J.D., Hayes, T. (1993):
Annotated checklist of the fishes of the Midway Atoll, Northwestern
Hawaiian Islands. Pacific Science 47(4), p. 356-400; p.
Riordan, C.; Hussain, M.; McCann, J. (2004): Moray eel attack in the
tropics: a case report and review of the literature. Wilderness
and Environmental Medicine 15, p. 194-197.
Schäfer, F. (2005): Brackish water fishes. Aqualog
Suzuki Y. & Kaneko T. (1986): Demonstration of the mucous hemagglutinin in
the club cells of eel skin. Dev. Comp. Immunol. 10(4),
- The aggressor: an almost adult Gymnothorax tile (© Marco
- The victim after cleaning the “wound”. Two similar scratches from
the lower jaw were on the other side of the finger (© Marco
- Intraoperative photo showing segmental tissue loss from a bite of a
large Green Moray Gymnothorax funebris (Photo with kind
permission of Dr. Colin Riordan)
- The same wound one year after the attack (Photo with kind
permission of Dr. Colin Riordan)This baby Green Moray Gymnothorax
funebris is only 7 cm/2.75 inches now but can reach a length of 2.5
m/8 feet; quite clearly a species not suited to average home aquarium (©
- The Tessellated Moray Gymnothorax favagineus is potentially
dangerous, so unless you’re a clearer shrimp keep your limps out of the
tank! (© Marco Lichtenberger)
WWM on Morays
Related FAQs: Moray
Moray Eels 2,
Zebra Moray Eels,
Freshwater Moray Eels,
Other Marine Eels,
The "Freshwater" Moray Eels,
by Marco Lichtenberger,
Other Marine Eels