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FAQs on Mastacembelid, Spiny Eel Identification

Related Articles: Spiny Eels The truth about spiny eels; A closer look at these popular but problematic oddballs by Neale Monks, Husbandry of the Barred Spiny Eel, Macrognathus panacalus by Marco Lichtenberger,

Related FAQs: Spiny Eels, Spiny Eel Behavior, Spiny Eel Compatibility, Spiny Eel Selection, Spiny Eel Systems, Spiny Eel Feeding, Spiny Eel Disease, Spiny Eel Reproduction,
By Species: Fire Eels, Peacock Eels, Tire Track Eels,

Spiny Eel Identification and Possible Problem    6/7/18
A few weeks back, I bought some Spiny Eels from my aquarium supply store whose supplier identified them as Macrognathus pancalus. They now live in my 55 gallon tank and are the only fish in the tank (I will not be adding any more fish). As they've gotten a bit bigger, I've noticed some differences in their coloring and markings so I've been trying to get a picture of them to send you in the hopes you could help me identify the different subspecies. I finally accomplished that this morning. The pictures aren't that great, but they're the best my camera can do, and when I looked at the picture of the lighter colored eel with the yellow tinge in its tail I noticed what looks like redness around his/her gills.
<These photos are too blurry. One of them, with the oblique dark bands, might be Macrognathus circumcinctus. The other one is much too vague to see anything at all. But I would direct your attention to two additional species, Macrognathus pancalus and Macrognathus siamensis. Macrognathus pancalus has a speckled upper half of its body, plain lower half, and in between a distinctive row of 'dashes'. Macrognathus siamensis is the Peacock Eel, so-named for the series of large eyespots on the dorsal fin
near the tail.>
As soon as I got the picture, the eel dashed off to hide, so I can't get a better look at him/her. The reason I'm concerned is because last Saturday I was watching my neighbor's kids for a while so she could run to the store and while I was outside trying to stop the 4 year old from setting my horses free, the 7 year old dumped an entire almost new 1.2 ounce package of flake food into the eel tank (eels don't like flake food).
It took some work, but I've got most of it cleaned up. I've been testing and the biological filter is handling it well as no ammonia or nitrite has shown up, but the nitrate has climbed up around 30 ppm (very dark orange, but no red), so I've still got some work to do. As a precaution, I put the appropriate amount of Prime in, so even the higher-than-normal nitrate shouldn't be bothering them and all the other eels look and act normal. Is this something to be concerned about and can you shed any light on the differences between these two subspecies?
<Spiny Eels aren't especially sensitive, and a series of water changes should handle the water quality damage here. Assuming you've netted out and/or siphoned out most of the flake food, I'd still change 50% today, and perhaps another similar amount tomorrow. You want to keep nitrate below 40 mg/l with most tropical fish, so that's your danger zone. The addition of a little salt may be helpful with Macrognathus species, particularly if they're stressed or off-colour, but isn't essential by any means. Salt does, however, reduces the toxicity of nitrate a bit, which makes it helpful at times. I'd not go beyond 2-3 gram/litre, though some species can handle considerably more. I will direct you to some useful reading, here:
Cheers, Neale.>

Re: Spiny Eel Identification and Possible Problem    6/7/18
Thank you.
<Most welcome. Neale.>

Abandoned eel     10/27/15
Hi guys. A neighbor of mine was recently evicted, and left their aquarium set up. In it was the eel I'm attaching a picture of. Wondering if you can give me an ID, so I'll know what I'm dealing with? Sorry at the time these are the best photos I can get. This thing is fast!
<Appears to be a "tire track", Mastacembelus armatus.... gets big and is an escape artist.... See WWM re.
Bob Fenner>

Spiny eel confusion      3/27/15
I recently acquired a spiny eel identified as a Zigzag eel. Which I thought topped out at like 8". Well now I have found their are two eels that are sold as Zigzag eels. One that gets 38" and the other that stays under 12".
My question is.. How do I determine which species I have? I have multiple tanks and can home either on appropriately just don't know how to tell them apart. There's no way for me to get a picture of this guy without stressing him to the max. The best description I can give is he's light brown across his back with a darker brown across his middle and is currently about 5" long and thick bodied.
<A photo would help here. There are several species sold as Zigzag Eels.
The two big species are Mastacembelus armatus and Mastacembelus favus, more often called (in the UK at least) Tyre-Track Eels. These get to around 70 cm (27 inches) or so, are intolerant of one another, and are accomplished predators. Then there are various small Macrognathus species including Macrognathus pancalus and Macrognathus circumcinctus. These tend to max out at around 20-30 cm (8-12 inches) and get along well with each other. Being small, they're relatively safe with other fish, though bite-sized prey like male Guppies or Neons are possibly at risk. Macrognathus siamensis is the
Peacock Spiny Eel, and probably the commonest species in the UK trade.
There are some African species, commonly called Afromastacembelus, including some stripy species, but they're expensive and you'd probably know if you had one. I would have you peruse this article:
Covers most of the basics. Don't forget soft sandy substrate and ideally the addition of a bit of salt to the water. Both these extras make these fish massively easier to keep. Once sick, Spiny Eels are notoriously unlikely to recover, so prevention is practically the only "treatment" in your medicine cabinet. Cheers, Neale.>
re: Spiny eel confusion

Thanks, Neale. As soon as I received your email the little guy popped out so here is the very best picture I could get.
<It is one of the small Macrognathus, likely Macrognathus circumcinctus or something similar. Maximum length is around 20 cm; peaceful; does well in groups; needs a soft sand substrate -- never gravel, that'll kill it eventually -- and feeds on small worms and other live/frozen invertebrates.
Medium hard water in preference to soft, with a tiny bit of salt (1-2 gram/litre) used for optimal conditions. Not a brackish fish, but like all spiny eels, a taste of salt seems to inhibit bacterial and parasitic infections that cause serious problems for this family of fish. So ideally keep on its own (certainly not with other bottom feeders) or choose midwater tankmates that won't mind a tiny bit of salt: livebearers, rainbows, hardy barbs, etc. Cheers, Neale.>

Orange Zig Zag Eel... ID, care       8/16/13
Good afternoon,
I recently came across a spiny eel labeled as an "Orange Zig Zag eel." 
I'm having trouble finding information on it and was hoping you might have some experience with this species.  Is this simply a color variant of Macrognathus Circumcinctus?  It has very similar barred markings, but is entirely orange where a "normal" specimen is brown with a tan stripe on its back.  If this is the case, should I expect it to have the same adult size/care requirements?
Thank you,
<There are two "Zigzag Spiny Eels" in the trade, Macrognathus circumcinctus and Mastacembelus armatus, and there needs are much different. Telling them apart is not too difficult, and you can use Google Images to find images of the two species. On the whole Macrognathus are smaller and more tolerant of one another, whereas Mastacembelus tend to be bigger and solitary (often aggressively territorial). There's much good stuff about Spiny Eels here at WWM; start here, and follow the links at the top:
There is, incidentally, an Orange Fantasy Spiny Eel, Macrognathus lineatomaculatus, recently described by Ralf Britz; they're all very similar to Macrognathus aculeatus in terms of size and behaviour, and doubtless their aquarium requirements will be very similar too (soft substrate, wormy foods, a little salt added to the water for optimal health). See more at the PFK website:
Cheers, Neale.>
Re: Orange Zig Zag Eel      8/17/13

Upon further review, I noticed the Orange Zig Zag was labeled as "Mastacembelus c. circumcinctus"
<Putting my hat on as a taxonomist, what you've written here means "Mastacembelus circumcinctus, subspecies circumcinctus", which is the normal, regular Macrognathus circumcinctus (this species being part of the genus Macrognathus not Mastacembelus). But, I wonder if there's a mistake made, and what the vendor meant was "Mastacembelus cf. circumcinctus" which would mean "a Mastacembelus species similar to, but not identical with, Mastacembelus circumcinctus". In other words, something similar to what is properly called Macrognathus circumcinctus. Clearly this fish isn't a plain vanilla Macrognathus circumcinctus, though of course it might be an artificially produced form of Macrognathus circumcinctus from a fish farm somewhere in Southeast Asia in the same way that a Koi Carp is a domesticated, highly modified form of Common carp, but a Common carp nonetheless. If that's the case, then your Orange Zig Zag Spiny Eel would have precisely the same requirements as ordinary Macrognathus circumcinctus, but with the caution that inbred varieties tend to be that bit less hardy than the wild-type equivalent. On the other hand, if this fish is Macrognathus cf. circumcinctus, then it's not exactly the same as Macrognathus circumcinctus, albeit very similar, so maintenance assumptions would have to be that bit more circumspect, so while you could assume it'll be a smallish, sociable fish, things like maximum size will be unknown.>
and I managed to find a picture:
(Hopefully it shows up in this email.)
Based on the links you sent me, it is definitely not Macrognathus lineatomaculatus, and it doesn't appear to have the tire track markings of Mastacembelus armatus (though, the ones for sale are only 5 inches, I'm not sure if that affects the pattern).  It's a fine looking eel, very pretty, but the last thing I want to do is buy an eel that will grow 3 feet long in a 55g tank!
<No risk at all if it's Macrognathus circumcinctus or some other species of Macrognathus; the biggest of these is Macrognathus aral, which gets to about 40-50 cm in aquaria, but Macrognathus circumcinctus is small (15-20 cm if I recall correctly) and most other Macrognathus are around that size.>
The seller can't tell me anything about it (naturally), so...would it be wiser to just pick a different species and not take the risk?
<I'd definitely take a gamble on these if they look healthy and the price is right. Macrognathus are lovely fish.>
Thank you,
<Most welcome. As should be clear, Latin names are infinitely more useful with rare/oddball fish than common names, and I do wish retailers would use them more often and more accurately! Neale>
Re: Orange Zig Zag Eel     8/17/13

I just wanted to thank you; I decided to go ahead and buy two "Orange Zig Zags."  They're quite vibrant and appear to enjoy the company of my Macrognathus pancalus eels thus far.
<Given adequate hiding places, this does seem typical of Macrognathus; floating plants like Indian Fern are another useful trick, as they'll often hide (and spawn!) in floating plants where you can see them.>
I really appreciate your help, you always give great (and accurate!) advice.  (100% agree with the Latin names; the hobby would be better off for it, that's for sure.)
Thank you again,
<Glad to be of help, and it's nice to know you've taken the plunge, and hope it all works out well. Cheers, Neale.>

Zig Zag eel, sys., ID  3/29/13
Hi there my name is Anthony I purchased a zig zag eel about three months ago and I was on a bit of a budget when I bought him or her. The eel is currently housed in a 25 gallon tank with a Pleco, the substrate is a small gravel since the store I bought it from was not very knowledgeable on the species as the eel was sold to me as a "fire eel". I am upgrading the tank to a 55 gallon early next week and would like to use sand as the substrate but can't find a clear answer on what sand to use. I was also wondering what exact species of the spinet eel I have, the eel does not have the wavy tire track pattern but it does not have a zig zag pattern either. It's more of a bunch of thick stripes on an angle that run from top to belly, mind you there are a couple of thinner lines that run onto his belly. The back fin is fully connected around his tail so there is no separation in the tail fin, I am hoping I have one of the bigger species of the spiny eel but it's not a big deal if its not. Thank you for your help in advance.
<In the US at least, the common "Zigzag Eel" of the trade is what used to be called Mastacembelus armatus, but may well be Mastacembelus favus or indeed some other closely related species. All are light brown with dark brown markings, but there's a good deal of variation in the exact shape of the markings. Use Google images or some other search engine to look for photos. Do also look at Macrognathus circumcinctus while you're at it; while it isn't normally traded as the Zigzag Eel, it's just possible it might be. Otherwise, send us a photo, and maybe we can help you identify your fish. Cheers, Neale.>
Re: Zig Zag eel 3/29/13
I just quickly did a Google search on the Macrognathus circumcinctus and many of the pictures look very similar, thank you for the help.
Now this brings a another question what is the estimated full grown size of this species?
<Not that big, around 15-20 cm seems typical. Basically a community tank fish, though very small species such as Neons may be eaten, so choose tankmates too large to be swallowed.>
I had mentioned in my other message that I would like to put a sand substrate in my new tank but was unsure what sand was best for the spiny eel. I have read mixed reviews of live sand in a freshwater tank and have read playground sand and pool filter sand work as well, I just want to use the best as I would like to have the best conditions for my spiny eel.
<Smooth silica sand (which is lime-free, so won't alter pH) is ideal. In the UK this is widely sold in garden centres for use in horticulture, and I'm led to believe the same stuff is also sold as poll filter sand. Avoid anything sharp or not lime-free, as both these will be unhelpful, to say the least! Silica sand seems very bright at first, but after a few months it ages nicely, as algae and bacteria coat the grains, so don't worry too much about the colour. If you want though, you can stir in some fine pea gravel to darken it a bit, and your Spiny Eel won't mind. Cheers, Neale.>
Picture of my spiny eel 3/29/13

This is a picture of my spiny eel looks a lot like the Macrognathus circumcinctus or half banded eel
<Indeed, does look like Macrognathus circumcinctus, or something very closely related. All Macrognathus species are pretty similar in care; do read Marco's excellent piece on M. pancalus, here:
Cheers, Neale.>

zig zag eels, stkg., more   8/1/12
I have just started getting into aquariums about 5 months ago. I am addicted to it now. I have a 15 gallon tank now with some phantom tetras, Kuhli loaches, and a zig zag eel.
<I see.>
I am going to buy a 37 gallon tank soon.
<Good. The Spiny Eel in particular will benefit from the extra space. They aren't easy to keep in the long term. Do read here:
Your species, Mastacembelus armatus, is one of the biggest species and should reach around 60 cm/2 ft in length, if not a little more. Obviously even a 37-gallon tank is a short-term fix, and within a year you should have graduated to something 75 gallons or larger. Do bear in mind Spiny Eels are sensitive; you can't wait to buy the right tank when the fish grows -- you need to buy the right tank before it grows otherwise it'll die. I'm not being overly dramatic here. These fish really are sensitive, and once they get sick, they're almost impossible to treat. The 37-gallon tank should be okay for something like the next 6 months assuming your Spiny Eel is small, and doesn't get bigger than 20 cm/8 inches in that time.>
I will put the eel I've had for about 2 months in this new tank. I am going to buy a black ghost knife which I've read is compatible with the spiny eels.
<Can be, but Black Ghost Knifefish are *even* more sensitive fish.>
I was wondering if I could put a tire track eel with the zig zag eel?
<How big is the aquarium you plan on getting? If we're talking 150 gallons, then sure, you should be able to keep both, provided you understand you need a soft substrate for the Spiny Eel and fast-flowing, very clean water for the Black Ghost. Any aquarium smaller than 150 gallons wouldn't work.>
I really enjoy the eels and would like to add another one but not if they don't get along. I have read mixed reviews and nothing solid to go on.
<See, this is the thing. Lots of people buy Spiny Eels and Black Ghosts, and they keep them (they think "successfully") for a few months or a year.
But then these fish die. They think it died for no reason, but almost always, the fish diet because the aquarium was wrong. Too small,  not enough filtration, and in the case of the Spiny Eel, the wrong substrate (e.g., coarse gravel).>
The local pet store has told me they should be fine as long as i by a tire track eel that is close in size.
<The least of your problems. Mastacembelus armatus is a predatory species, yes, and adults can eat quite large fish --  though as a good fishkeeper you would NEVER use live feeder fish! Likewise, Black Ghosts have the potential to eat small, tetra-sized fish, though they prefer worms and insect larvae. But neither species should view the other as threat.>
If this is a bad ideal i would be willing to try other spiny eels, as long as I keep the zig zag eel. thank you so much
<So long as you have 150+ gallons, it's a fine idea. Neither species is easy to keep though, and I'd recommend you stick with the hobby for a couple years before buying a Black Ghost -- they are extremely delicate fish and easily killed by people who don't understand water quality (including nitrate) and the need for high oxygen levels and under-stocked aquaria, which is why you almost never see adults. Mastacembelus armatus is a little hardier, but easily killed by ignorance, and actually does better in very slightly salty water (around 2 grammes/litre) which would be incompatible with the Black Ghost. But it can be kept in plain freshwater, you just need to understand that the moment the fish gets a bacterial infection, it'll almost certainly die, so you have to make sure it CANNOT scratch itself and is NEVER exposed to non-zero ammonia or nitrite levels.
Make sense? Cheers, Neale.>
Re: zig zag eels  8/1/12

Thank you so much for the response.
<Most welcome.>
I have been doing some research and hope  that you don't think I was just jumping into this. I was told that my zig zag eel would only reach 10 inches.
<Not the ZigZag Spiny Eel (Mastacembelus armatus and Mastacembelus favus).
But there is a second species, Macrognathus panculus, that is less often traded but may be sold under the ZigZag name. It does indeed stay relatively small, around 20 cm/8 inches or so, and if you are REALLY lucky, this is the species you have. But it isn't a common species. Do read here:
That article gives you a pretty good rundown on what these smaller Spiny Eels need.>
That is what was recommended for my tank at the time.  The pet store had tire track, peacocks, fire and zig zag eels. They said the zig zag was the smallest. That has been another thing that i have read online that seems to have different answers.  They are either the biggest or the smallest.  What are the easiest ways to tell it is a zig zag eel?
<Mastacembelus armatus is sandy brown with dark brown markings; Macrognathus panculus is similar in basic colour, bit has smaller markings (more like speckles) and has a very distinctive row of specks, like a dashed line, running along the midline of the flank from gill cover to caudal peduncle.>
Its markings seem pretty obvious and the tail was another indicator (it is not separated like some) which i have read is an indicator of the size being of a bigger spiny eel.
<Don't know what you mean by this.>
I have a small pebble substrate that was recommended for the Kuhli loaches and was told it was perfect for the spiny eels.
<Absolutely not! If by some chance you do have a Macrognathus species such as Macrognathus panculus, it MUST have a soft, silica sand substrate (such as pool filter sand). I cannot stress this point too strongly. Spiny Eels do better with sand. Gravel scratches them, and sooner or later (it's a "when", not an "if") they get a bacterial infection on their skin that is always fatal.>
As of now, i only feed my eel frozen bloodworms
<Will need much more than this. Try finely chopped seafood (tilapia fillet, cockles, occasionally prawns or mussels) and very small earthworms.
Bloodworms aren't a balanced diet, and there's also some risk of introducing disease through them.>
and had read not to feed them feeders cause of harmful bacteria.
However, I will definitely stay away from the black ghost knife.
<Wise. Do also notice in Marco's piece he mentions the use of salt as well. Trust me that prevention is better than cure with Spiny Eels. Adding a little salt needn't cramp your style -- most livebearers and Rainbowfish will tolerate the minimal amount of salt needed (2 grammes marine aquarium salt mix/litre) but if you go up to SG 1.005 and sent the tank up as a brackish system (that's about 9 grammes/litre) then you could instead keep him with all kinds of fun brackish species like Mollies, Knight Gobies, Glassfish, even Violet Gobies if you have the space.>
Now i feel pressure to get a bigger tank asap.
<Ah yes!>
The tank size is somewhat of a problem. I could only probably go up to a 55 gallon.
<Too small for BGKs. They are massive fish when mature, and extremely sensitive to pollutants in the water.>
If a tank this size isn't big enough for a zig zag, is there a spiny eel that would work better?
<As it happens, Macrognathus species are quite sociable, so getting a couple more would help. On the other hand, Mastacembelus species are very territorial when mature, so best not kept in groups unless you have a huge aquarium.>
I have a friend with a 120 gallon tank which his had for 15 years.  If you feel the zig zag eel is going to be harmed in a 55 gallon tank, I will move it to his tank. thank you again.
<Do check which species you have. Send a photo if you want a second opinion. Cheers, Neale.>
Re: zig zag eels   8/1/12

This is very disappointing news.  It seems i have been mislead on a bit of information.
http://animal-world.com/encyclo/fresh/Eels/HalfBandedSpinyEel.php this site is where found some information before I contacted you. The eel pictured in this link is identical to the eel I have.
<Well that's a species called Macrognathus circumcinctus. It's one of the Asian Macrognathus, and as stated before, these are fairly small, gregarious, basically easy to keep and feed, but they do need a soft, sandy substrate.>
The fin is the same, color is about the same.  I am aware the name given is different then what I have given, but as you have probably seen, tyre track, zigzag, and banded eels are being confused with each other.
<If you rely on common names, then yes, confusion will be frequent. Best to stick with Latin names with Spiny Eels.>
I appreciate your complete honesty and all the information you have given me.
The substrate is a shock, cause I asked specifically for one that would harm Kuhli loaches and spiny eels.
<Not an expensive fix, so I'd not worry overmuch. I use smooth silica sand (here in England called "silver sand") from a garden centre, and it costs no more than the gravel.>
When I set my new aquarium up, i will use sand.
<Cool. Just be sure you know what you're shopping for, smooth silica sand.
Not sharp sand (obviously!) or coral sand or any of the fancy sands used in planted tanks. Just plain vanilla smooth silica sand. Feel free to add gravel (up to about 10% of the total substrate) if you want to tone down the colour of the smooth silica sand and give it a more natural look, but plain sand on its own looks great and ages nicely, getting much darker than it looks at first.>
I have looked at feeding my spiny eel earth worms, but was told not to until it reached a bigger size.
<For sure.>
I will probably try to feed them as soon I can.  The brackish water idea has never been referred to me. It is a great idea and I am going to look into it.  Is it safe for Kuhli loaches or should i wait to setup my new tank with brackish water.
<Kuhli Loaches cannot be kept in brackish water. Macrognathus circumcinctus isn't a brackish water species, so I'd not keep that species in brackish conditions anyway. Basically avoid water that's too soft or too hard, and if your tankmates allow, add 1-2 grammes salt/litre of water. Kuhli Loaches won't like that, but if you change the aquarium around, bear this in mind and choose species that will tolerate a little salt. It isn't 100% essential, but it can make a big difference to the ease with which they are cared for.>
Please let me know if the link provided helps clear things up or is just more misleading information.
<It's not a bad article at all, though I'd argue with a few minor things, like using "aggressive" when they mean "predatory", and their water chemistry recommendations are the complete opposite of what's stated as their natural habitat on Fishbase.>
Thanks again Neale.
<Cheers, Neale.>
Re: zig zag eels, comp.    8/1/12

Very last time I bother you. Now that the species is known and I feel more confident.  Could you give me just a bit more advice.  Is a 55 gallon take sufficient for this species of eel
and is it safe to add other smaller species of spiny eels?
<Provided the size difference isn't huge, then yes, various Macrognathus species (but not Mastacembelus) species can be combined. Allow something like 10-15 gallons per specimen, not so much because they're territorial, but so they have enough space to find food. Spiny Eels are extremely easy to starve.>
Recommendations on other fish to add with this species.
<Anything that isn't so small it'd get eaten is a good start. But also leave out anything that feeds from the bottom. You will have a hard time feeding Spiny Eels at the best of times! No loaches, catfish, etc. Your Kuhli Loaches may be small enough to be eaten by the Spiny Eels when they get big enough. Good tankmates would be medium-sized, non-nippy barbs, tetras, Rainbowfish and livebearers (and the last two groups especially if you wish to add salt).>
I know the Kuhli loaches are not good tank mates for spiny eels and I always have had the intention of moving the spiny eel or Macrognathus circumcinctus to a bigger tank.
<Cheers, Neale.>

Flower Pattern eel - What kind of Spiny eel? 04/03/10
Hey Crew,
<Howdy Matt>
I recently purchased a flower pattern eel from my LFS. I asked the owner if he knew of any other names that this eel went by when he ordered it. He said the only name he could find was flower pattern eel.
<And... it's a Mastacembelid?>
I can not find any info on this type of spiny eel and was wondering if you knew what I had.
<Nope... but I have an idea of where to look next>
I'm mainly interested in how big he will get. I currently have him in a heavily decorated 55 and he is amazing. Since day one "Rocky" has eaten from my hand. He loves earth worms. He will come up to the glass and greet me when I come home and loves to relax in one of his many caves during the day. He and a striped peacock eel get along OK, but the striped peacock eel is much more passive. I've seen the flower eel scare him off a few times but no damage is ever done and 90% of the time they are indifferent of each other. An amazing super smart spiny eel. Any ideas on max length on this fellow? Thanks, love the website, read and learn something new everyday.
<Mmm, take a look on Fishbase.org
Information by Family
At bottom left, Show species
Do you see a pic of your specimen?
Click on it and
Read on!
Bob Fenner>
Re: Flower Pattern eel - What kind of Spiny eel?   4/5/10

<The "Flower Pattern Eel" is a new species of Mastacembelus from Southeast Asia. I don't know anything specific about it, but you can assume it's much like the others in the genus. Expect a size around 60-75 cm, predatory
towards fish up to the size of Swordtails, territorial towards its own kind, and extremely sensitive to bacterial infections. The use of small amounts of salt, 1-2 grammes per litre, is often recommended and may be wise at least for the first couple of months. Feeding is problematic, and healthy fish have large appetites. Not suitable for community tanks, but in tank with a sandy substrate and lots of floating plants could be kept alongside Silver Dollars, Kissing Gouramis and other large, non-aggressive community species. Avoid anything likely to damage its skin, e.g., cichlids. Bumblebee gobies would be nothing other than live food. Cheers, Neale.>
Re: Flower Pattern eel - What kind of Spiny eel? Fdg. "Tiger" Bumble bee gobies ID, Neale    4/5/10

Bob, thanks for the website. Unfortunately I wasn't able to make a 100% positive identification from there, no biggie. To me he looks like a big zig zag eel, but I always thought they were the smallest of the spiny eels.
<There are at least four species of Mastacembelids commonly labeled as such>
He looks a little bigger than most zig zags I've ever seen. I'll keep watching and make sure he doesn't out grow his home. Maybe if I can snap a good picture of him sometime I'll send it in, he is not a very colorful fellow nor does he have an elaborate pattern so it is hard to find any distinguishable markings to compare with. He's very brown with some black markings along the top half of his body all the way back. Tough to ID with some of the small and black and white photos they have.
I do have a few other question if you don't mind. I feed both my eels mainly earth worms. About a 1/4 to a half inch piece once or twice a week.
I've read spiny eels "reuse" their food and don't have to eat for 2 weeks sometimes.
<Mmm, ones in good condition, health, can go this long w/o eating... but better to offer food every other day at least>
What kind of schedule do you recommend. They look very healthy and have never seemed too thin or overly bulging so I figure I am doing good. What else should be a staple in their diets?
<Please read here:

Spiny Eel ID  2-9-08 Hi, I was wondering if someone from the WWM Crew might be able to help me figure out the sort of Spiny Eel I have. <Hello! Merritt here!> When I got the eel I have (it was more then a year ago) she (or he) was very timid, very small, and wanted to hide all the time, as I would assume that most eels do. I was told at the time that she was a Black Leopard Eel, as I couldn't actually find anything on that being even a real name of a fish I tried to find out what she was on me own. <Smart move> For the first few months I never saw much of her or what she looked like. Now that she's gotten used to her surroundings, I've been able to get a good look at her markings almost every day now for the last few months, and was finally able to get a good picture, but I cant find anything that looks like her. Im starting to wonder if Im either not looking in the right spot, or if her markings are just to light? <They will develop as she matures.> If it helps here's some info on how she acts and her growth. She went from about 5 inches long and just under and inch tall in the middle when I got her, to just under 14 inches long and about an inch and a half tall in the middle in about a year. She loves frozen blood worms and likes frozen brine shrimp, and her favorite seems to be ghost shrimp (but I only give the ones I breed so its not to often she gets those). <Nice variety in diet, keep it up!> She gets along great with the two (about 8 inch) Plecostomus that have. But she did attack one of two angel fish (They were about 6 inches tall at the time when she was still little) during the night of the first day after they got in the tank after quarantine. I clearly dont plan on adding anything else to the current tank or when I get a bigger one for them. During the day she will come to the surface and take cubes of food from my fingers and oddly (never had another fish do this) likes her sides rubbed. <Many species of eels like to be touched.> She will also try and attack the fish in the tank next to hers. I assumed the first time she was hungry but even when she has leftovers that she doesn't eat she still attacks, similar to a Betta. Hopefully between the picture, and her temperament someone might be able to tell me what exactly it is I've been keeping in there. And also please dont think that I was irresponsible for getting something without knowing what it was first. Normally I make sure to know exactly what Im going to be putting in my tank long before I get it. However when I had gone on my trip that ended up with the eel, I had just finished cycling a new 30 gallon tank set up, and my list was for a Betta, and few swordtails as I was planning on just having a well planted tank. But there was a 5 year old with his dad and one of those 2 gallon Betta bowls not even big enough for a Betta who was looking at picking out the eel. And I had enough common sense about eels that it needed something bigger then that to live in. <I can understand the saving a fish from death story, I have done it a few times at pet stores. From the picture I think you might indeed have a spiny eel (Macrognathus siamensis) but here is a link to FishBase if you want to be 100% positive. http://www.fishbase.org/Summary/SpeciesSummary.php?id=50400> The link to the picture is http://i107.photobucket.com/albums/m304/yuugana/dessy.jpg if the attachment didn't work. Thanks much Jacob <You're welcome! Merritt A.>

Re: Spiny Eel ID, Neale's further input to Merritt and querior    2/10/08 Hi Merritt, From the photo of the spiny eel in Sunday's FAQs, my best guess would be that is not in fact Macrognathus siamensis but actually one of the species in the Mastacembelus armatus/favus complex. The size of the thing is one clue; if the plants are Amazon Swords, then that spiny eel has to be a good 30 cm long, way too big to be Macrognathus siamensis. The colour markings are quite close to Mastacembelus armatus, just restricted to small spots instead of  squiggles. In any case, it's a large Mastacembelus spp of some sort, will get to about 70-90 cm in total length, and is predatory. I've made the mistake of keeping these fish with things as big as swordtails, and they get eaten! Cheers, Neale

Spiny Eel questions... ID, sys., comp.   2/26/07 Hiya, WWM. This is Ashley again; the paranoid person with the two spiny eels named Hope and Doom. <Hi Ashley, spiny eel keeper Marco here.> I'm pretty sure they're what I've seen called yellow-tailed spiny eels. (Mastacembelus armatus) <I just had a look at your older mails with pictures and hesitate to agree, because the second picture seems to show that they have a separate tail fin in contrast to an unbroken fin. If that's right, they are not M. armatus, but a smaller species, probably Macrognathus pancalus (max. 7 inches). Have a look at the tail fin to verify.> They're still going strong, eating like pigs, and uprooting my plants. I have been considering "downsizing" in the fish department, since I have 5 tanks to keep up with now, along with tons of fish, and many other pets. <Thats just the beginning, you are already addicted> I was wondering if the two eels would be okay in a 10 gallon together (alone). I read somewhere that they stop growing at about 6 inches <Not if they are healthy M. armatus.>. I was thinking about either keeping them in a 10 gallon, or keeping just them, the gold dojo loaches, and the Pleco(s) in the 30 gallon. Which would be better? <If they are M. armatus, both tanks are too small in the long run, since these fishes will get 90 cm (35 inches) long. If they are a M. pancalus or another Asian species with separate tail fin, the 30 gallons would ok.> I'm also wondering if the activity of the other fish (various guppies, mollies, platies, the loaches, and the Pleco) affects the eels' activity level. They are fairly active during the day, and I'm wondering if I take the other fish out, will the eels' activity level go down? <To me it seems their activity is high, when the tank mates are peaceful, and low, when they are intimidating the eels.> Or do I just have some really weird eels? Thanks in advance for your reply, Ashley. <You are welcome.> Oh, and since they're fairly little, and don't even bother messing with anything bigger than a bloodworm, do you think they would harm 2 two and a half-inch Kuhli Loaches? I was told that they would attack them like worms... <They are probably safe with M. pancalus, but would be eaten by M. armatus>.

Re: Spiny Eel questions...   3/1/07 Thank you so much! I have never noticed that there was any difference in the tails of the different species...They look most definitely like Macrognathus pancalus to me, now that I've looked it up. They do have separate tail fins, not one whole one. Thanks again for your help! Ashley. <I am glad we could help. Good luck with your eels. Cheers, Marco.>

Spiny Eel IDing...and a few other questions.   1/27/07 Thanks again for your quick reply. I looked at the FishBase pictures and descriptions, and didn't find anything that looked like them, but on one of your Spiny Eel pages, I found a letter from another reader who had what they called a "Yellow-tail Spiny Eel" and it looks exactly like what mine looked like in the store I rescued them from. (Wal-Mart... They were sold to me as Fire Eels. <M. erythrotaenia they are not> I knew that wasn't what they were, but they had no idea what the difference was between Fire Eels and other Spiny eels... They were $9 each! It was worth it, though.) I'm not sure if it's the lighting, or if they just changed their colors, but they're both more grayish now. Doom's fins are still yellow, but you only notice it when she burrows in the gravel and when she's up against something. They have these square/rectangle spots all over their bodies, if that helps at all. And right now they're 4 or 5 inches long, give or take a bit, since they never sit still unless they're eating.   And on the subject of eating, how much frozen bloodworm should I give them? <Mmm, not too many...> The LFS was out of the kind that's cubed, so I bought the other kind, the frozen slab-looking thing. I break off about an inch long piece, and thaw it, and they greedily gobble it down. I try to satisfy the other fish with frozen Brine Shrimp so that the eels will have a fair chance at the bloodworms, and it seems to work. I just don't want to overfeed them, but I also have had trouble with previous eels and underfeeding. How often should I feed them? I feed them about 2 or 3 times a week, with a good amount.   Thanks again!   Ashley <Really a matter of subjective evaluation... a look/see at how full... they appear... look up the term "index of fitness" on WWM. Bob Fenner>

Mastacembelus ID and Wild-Eyed Angel - 01/23/2007 Hi, it's Ashley again. <Hi Ashley, Sabrina with you today.> You may remember me as the person with the overstocked tank suffering from some sort of poisoning (new sponge, possible chlorine)...Well, they're (the fish) all just fine now, no more deaths, and they're all in the other tank. They seem to be back to normal except for Jack, the Angelfish. He is fine physically, but he hides at the back of the tank when I come anywhere near the tank, (before the incident, he'd beg for food at the front, or just show off his fins) and he also has a 'wild' look in his eyes. And at first I thought he wasn't eating, but he does eat a little. Just not when I'm around. He almost seems as though he's had some sort of brain trauma...is that even possible??? <Mm, possible, but more likely the animal is still recovering from whatever issues they dealt with....  Without seeing the previous correspondence, though, I don't know what troubles they had.> And I have some pictures of my two Spiny Eels, and I was wondering if you could help me ID them. I believe they are some sort of ZigZags...I am attaching the pictures. The one in the gravel is Doom, as well as the one under a plant, and the paler one is Hope. They have the same markings, but Hope seems paler, and Doom's fins are more yellow. <The images aren't clear enough for a definitive ID, but I'd wager that they're Mastacembelus armatus, tire-track or zig-zag eels.  You might also consult Fishbase's listings of Mastacembelidae: http://www.fishbase.com/identification/specieslist.cfm?famcode=432&areacode= > Thanks for all you guys do! <And thank you for your kind words! Ashley And I scanned the pictures of the eels, no viruses. :) <All the best to you,  -Sabrina>

ZigZag Eel question, ID and more    1/20/07
 I've been looking for an excuse to E-Mail you all, <Heeeee! No need> First question, I'm curious, are you all biologists with extensive schooling or are you just extremely dedicated hobbyists? <Mmm, a mix... we are all volunteers (I am the common progenitor)... a bit of our backgrounds is posted... http://wetwebmedia.com/WWMAdminSubWebIndex/wwmcrew.htm Some of us have an academic background in related "life sciences"...> Anyways, I'll move onto the real question. I need help identifying this Spiny Eel I bought at a local fish store. It was listed as a "ZigZag Eel" and I had just assumed it was a Tiretrack Eel, but I'm not completely sure. <Mmm, there are quite a few Mastacembelid eels sold as such...> I've seen a few images of comparable fish but they're all listed as "ZigZag Eels" with little solid information. I mainly need to know if this is one of the big ones or will it max out at (hopefully) 6'' or so? I'm sorry if I'm being an idiot, I'm just having trouble finding a clear line between a "ZigZag Eel" and many of the Spiny Eels commonly found in fish stores. <You/we're in good company... the best simple course of action is for you to go to Fishbase.org here... insert the above family name (Do you see the tray to drop down?)... look at the nominal species images for an ID... read re the species posted there> How is their disposition? Will I have trouble with it hurting any of my fish? How about dietary requirements? <Most Mastacembelids, even the ones that get quite large, are easy going... only trying to eat even small, slow fishes if trained to do so, and/or very hungry... they eat worms of many kinds, insect larvae... can be trained to take meaty foods...> Ok, about the last question. I know they prefer live food, I've read this everywhere. The thing is, I bought this one maybe two or three weeks ago and he seems fat and healthy. I feed the Needlefish that he shares an aquarium with 'Rosy Reds', which I'm sure, are far too big for him to eat. I also throw in Ghost Shrimp occasionally; however, I'm sure they're also too large for a fish this size. Its mouth seems tiny. I feed my fish various foods, trying to find the right combination. Here is the (not so complete) list. Frozen, cooked shrimp (Treat for the Dragon Goby), Algae Wafers (Stopping these right away, they're discoloring my water), Freeze Dried Tubifex worms, Freeze Dried Krill, two brands of flakes and Shrimp Pellets, along with the live foods, the Ghost Shrimp and the Rosy Reds.. Is it possible he is eating and thriving on one of these foods? Which is most likely so I make sure to feed him often enough? <Small worms and insect larvae (often labeled as "worms" of various sorts) are best for small specimens, species...> Like I said, it's been 3 weeks since I bought him so I don't think he's starving; he has to be eating something. Now I need to know about the temperament of this fish. So far everything has been alright, of course he only comes out when the lights are off (it's getting better about this); however, I noticed something alarming the other night. My Dragon Goby shot to the other side of the tank; he's usually calm and never moves quickly for anything. A fish this big is noticeable when he does something like that so I turned on a nightlight to see what was going on. The Dragon Goby was sitting in its 'hole' like it always does but the ZigZag Eel was inside... of him... The ZigZag Eel had about half of its body inside the Goby, the other half through the left gill. I turned the lights on to scare off the ZigZag Eel and it worked. The Goby is fine, he immediately came to the top of the aquarium looking for a treat and a day later is just as healthy as he has ever been. <Yikes!> Should this be something I should be concerned about? Or do you think it was a freak accident on the part of the ZigZag Eel? <I would be concerned... that the Goby try to consume the eel...> Maybe even an aggressive move? This is the kind of information that the internet rarely provides except for with the more popular species. I appreciate any help you can offer, thanks. -WJ <Perhaps you will pen an article re your experiences here... In discerning the spiny eel species, determining their habitat, foods/feeding, and temperament. Bob Fenner>
Re: Forgot to attach picture. (ZigZag Eel question)   1/20/07 Unbelievable, I knew I would do that. <Heeee!> Here is the picture of the Eel I'm trying to have identified. I apologize for the bad picture quality, I had to do this in the dark. Thank you, -WJ <Mmm, does look like a Mastacembelus armatus from what I can make out: http://fishbase.org/Summary/speciesSummary.php?ID=10140&genusname=Mastacembelus&speciesname=armatus BobF>

Spiny-eel Hi, regarding one of the photos on WetWebFotos.com, specifically the one depicting "Macrognathus siamensis", appears to be of Macrognathus aral, sometimes referred to as the striped spiny-eel. I don't know if you're aware of this, but I thought I would bring it to your attention, I hope you don't mind. Apart from this, I find it to be a very good site, and should improve as more species are added. All the best, Dave Curran <Thank you for this. Will send off to Zo for amending. Bob Fenner>

Yellow spiny tail eel I have had difficulty finding info on the yellow spiny tail eel. I bought one from PetSmart a few months back, and they were unable to give me any info on it aside from the name. This particular store has been known to label their fish wrong, so it could be the wrong name. <Am sure this is a member of the spiny eel family Mastacembelidae, but fishbase.org does not list the common name, even w/o the "tail" in it...> All I know about it is that it's from the same family as the peacock eel and fire eel, right now is 3 inches, cost me $2 (a lot cheaper than my peacock eel), and that it likes live worms instead of commercial fish food. <Most Mastacembelids do> If you could supply me with any info at all, such as how big I can expect it to get (it is currently living with my girls guppies and mollies), I would be extremely thankful. My email is XXXX.                                                             Thanx,                                                                   Josh <Josh, what little we have on this group is posted here: http://www.wetwebmedia.com/FWSubWebIndex/matacembelids.htm and the Related FAQs (linked, in blue, at top). Bob Fenner>

Why does my fire eel have yellow markings? >Hi, >>Hello, Marina tonight. >I have had a fire eel (now about 9") for almost a year.  He was about 4" when we got him. He used to live in a 25 Gallon Eclipse (eel proof) until I bought the new 90 gallon tank back in March. Quick cute story- thought I lost him last winter. Went missing for about 2 months.  Turns out he was living in the hidden compartment eating bloodworms as they got sucked up the tube. No worse for were, but bigger. Didn't suspect a problem until the water level on the filter was way too high. Anyway, he lives with a couple of zigzags, a black ghost, a golden Gourami, 4 pearl Gouramis, 5 red Serpae, and a tiger barb. Normal for the tank is flake, frozen beef heart and frozen bloodworms. The big question. Whenever I see a photo of a fire eel it has red markings. Mine is dull yellow.  Any ideas?  Thanks in advance either way.  Great site! >>I've seen them both ways, and have always assumed that it's just a variance on coloring.  Try this link for some ideas http://www.wetwebmedia.com/FWSubWebIndex/matacembelids.htm >>I hope this helps.  Marina

Eel ID hi  my name is Maryanne we have just brought a eel and no one knows what type of eel it is, it has brown coat and dark brown spots and a long head can you tell me what sort of eel it is please. thank you < Hi Maryanne I would need to see a picture of it to say for certain.  It is best to learn about the animals you are going to bring home before you bring them home.  Does it look like either of the eels at the link below? http://wetwebmedia.com/FWSubWebIndex/matacembelids.htm You could also try using Google.com to search for freshwater eels, or marine if that is what you have. -Gage>

Peacock Eel average questions/conflicting answers I just discovered your website and I LOVE IT! I've been a constant freshwater fish fan for years and I have just purchased a peacock eel (Mastacembelus erythrotaenia <<This is a/the Fire... perhaps Macrognathus siamensis? RMF>) and I was just wondering if there was any way to tell the difference between the sexes. Also I have done as much research as I can and I have found so many conflicting reports it makes me dizzy. I just want to make sure I have the basics right so that he/she can live long and happy. For now he's in a 29 gallon (and in about 4 to 5 months to be moved to a 75 gallon) and the temperature goes from 70 (at night) to 75 (in the day). He is in something the pet store called "red sand" but it isn't red and looks like normal sand. The pH sometimes varies from 7.1 to 7.4. He seems to love the sand and only 5 minutes after releasing him he had found a perfect spot to dig and stick his head out. Some of the websites I visited said that they could eat flakes or pellets, is this true? for now he seems happy just to eat bloodworms that come out of this feeder when they are unfrozen. I was thinking (because I know in general spiny eels like live food) to add 1 male guppy and 2 female guppies so that when they mated he could eat the fry. My brother has a soft shelled turtle that he does this with and it seems to work rather well. In a couple of websites they said it would be ok to put him with a knife fish. My knife fish is very friendly and for the short time I had a sting ray in there (babysitting for a friend who's bacteria had all died after his younger brother poured in a bunch of VERY old fish medicine) the knife fish actually made friends with him and would swim just above him and tickle him with his lower fin. These are a lot of questions but I really want him/her to be happy. (I also like to know whether they are male or female so I can name them). >> Your eel should be called "fire eel" by its common name. The peacock spiny eel is another species, that does not have the red lines on its body. If it is a fire eel, it will get to a very large size, that means over three feet long, and he will need a tank large enough to live as he gets older. They do like live food, especially live earth worms. He should be fine with a knife fish. You may want to make sure that your temperature is more stable, best between 74 and 80 degrees Fahrenheit. Good Luck, Oliver

FW Eel  1/16/06 Hi, there! First off, I will begin by thanking whomever is reading/answering this e-mail. I am a relative newcomer to keeping FW eels. I currently own two such specimens. One 7" striped peacock eel, and one 4" zig-zag, or tiretrack eel. I purchased the tiretrack eel from Arizona Aquatic Gardens (azgardens.com) whose incompetent 'staff' told me that the zig-zag eel would grow no more than 10" or so. I have found since that my eel may grow to 3', which poses a dire problem to me. < Fire eels, Mastacembelus erythrotaenia, gets big, like three feet long. I have seen them in public aquariums at least that big. But the tire track eels that I am familiar with, Mastacembelus circumcinctus, stay around eight inches or so.> <<There are other "tiretrack eel" species. RMF>> However, there is an even bigger dilemma I am confronting today: is there such a fish as a dwarf starry night eel (*Caeco**Mastacembelus spp.), *and what size does such a specimen attain? Is it a strictly FW fish? What, pray tell, is the recommended pH and aquarium size of such a specimen? I have tried to Google this one out, and have even gone through the German and French websites, with very little success. I am contemplating the purchase, but I am cautious, as the seller (AAG) states such a specimen will not grow past 6". Is this even possible, in your opinion? Thanks again for answering my question and I bid you good day. George < While diving in Lake Tanganyika a few years ago we saw many eels. Some were only 4 inches long and swam like little seahorses while others were at least a foot long. Look at Caecomastacembelus, Afromastacembelus and Aethiomastacembelum on fishbase.org. These are the three genera of eels from Africa. All that I know of get up to a least a foot and a couple get up to two feet. The Lake Tanganyikan ones require hard alkaline water with the others probably tolerating almost any kind of water. The eel you are looking for may be in these groups.-Chuck>

Hello!  I have an eel-related question. Mastacembelid ID, Sys.  7/9/06 Hello!  I've been frequenting your site for the last little while once I started getting fish and realizing that what the pet stores told me was for the most part completely wrong.  Your site has helped me tremendously with my Fire Eel (who I've had now for almost 3 months and he's doing extremely well :-) ) <Ah, good> but I've noticed there is a general lack of information on the "yellow-tail spiny eel". <Mmm... is sold under a few other common names... Most often as the Zig Zag eel on the U.S. west coast... Old scientific name is Mastacembelus panculus, now Macrognathus panculus: http://fishbase.sinica.edu.tw/Summary/speciesSummary.php?ID=10147&genusname=Macrognathus&speciesname=pancalus> I bought one of those about a month ago (he is also doing well, so whatever breed of eel he is, the care is much the same of that of a Fire eel.) <Yes> and he's grown a lot. <Good... though won't get as large... 9 inches is about maximum>   I got him when he was about 2 inches long.  I've looked at various pictures and he seems to resemble a zig-zag eel? <Ah, yes> Albeit slightly yellower, perhaps.  Anyway, I've included a picture so perhaps someone can tell me what it is, or if I'm completely wrong in my thinking that he is a type of zig-zag.  Thank you for your help, and I look forward to hearing from you! -Becki- <Does appear to be this species to me as well... Can make very interesting, long-lived pets... given initially healthy specimens, good care, consistent maintenance and feeding... As with all spiny eels, do pay particular attention to keeping the top entirely enclosed to prevent them exiting. Bob Fenner>

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