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FAQs on Mastacembelid, Spiny Eel Stocking/Selection

Related Articles: Spiny EelsThe 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 Identification, Spiny Eel Behavior, Spiny Eel Compatibility, Spiny Eel Systems, Spiny Eel Feeding, Spiny Eel Disease, Spiny Eel Reproduction, By Species: Fire Eels, Peacock Eels, Tire Track Eels,


Mastacembelus pancalus    6/30/13
Hello again!
A few weeks ago I emailed you regarding information on Macrognathus aral eels.  I have since decided that they may get a bit too large to have a pair live comfortably in a 55g tank.  After searching for other eels, Mastacembelus pancalus ("Yellow Tail Spiny Eel") seems like a fine alternative.
<More properly, Macrognathus pancalus.>

From what I have gathered, they only seem to get up to 7" in length, aren't particularly aggressive, and are good community fish overall. 
<Yes. Tricky to feed and great at escaping from tanks, but those are about their only tricky aspects.>
Do you happen to know if this species is sociable towards it's own kind?  I would like to get two, ideally one male and one female, and I'd rather not have one constantly picking on the other.
<Oh, pretty much all the small Macrognathus species are good. There's a nice Burmese species traded ("Red -Fin" or "Mekong Spiny Eel", Macrognathus mekongensis) that seems to be small (~20 cm) and sociable enough. But for most folks, you just buy what's available. They're all good. It's the
Mastacembelus species that tend to be big and much more territorial.>
If it's not too much trouble, I was wondering if you would take a look at my planned stocking list as well:
Harlequin Rasbora x 15  (Already quarantined and stocked)
Yellow Tail Spiny Eel (Mastacembelus pancalus) x 2 (Would not introduce new stock until they eat confidently.)
Praecox Rainbowfish x 12 (4m, 8f)
Pepper Corys x 8
Vampire Shrimp (Atya gabonensis) x 2  (Only to be added after tank has matured.)
Essentially I'd like to stock these fish in this order; I already have the Harlequins and I'd like to get the eels next if you think they're compatible with the rest of the stock.  Is this an overstocked tank and/or can you spot any problems I might encounter housing these fish together?
<Should be fine. Avoid soft water with Spiny Eels though; they seem most hardy in medium-hard, around neutral to slightly basic water chemistry, and in some cases with a little salt added (e.g., Macrognathus aculeatus) if skin parasites are a problem.>
Thanks for your time and sorry for the long post!
Have a good evening,
<You too, 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.>

65 gallon stocking. Fish in planted sys.    11/28/11
Hey there folks, I'm back again with a question pertaining to stocking my 65 gallon planted tank!
I've sent an email before regarding Archer fish identification and how many Toxotes microlepis to keep in my tank. So here is what I have so far in terms of ideas.
1. 5-6 Toxotes microlepis
2. Some sort of spiny eel (what species might you recommend? I don't particularly care for the peacocks but i know fire eels are out of the question with this tank size and water requirements)
<Yes, can work; one of the Tyre-Track Eels should be okay, but do also look out for Macrognathus aral, the One-Stripe Spiny Eel, an attractive fresh and brackish water species that would allow you considerable flexibility should you decide to keep the tank slightly brackish to allow other oddball
3. Would some sort of knife fish work? I was looking at some info on the African Knife fish, Xenomystus nigri I believe? If i kept the water chemistry stable and a pH that is fairly basic might this work?
<Yes, that's a good species. Hardy, adaptable, and quite peaceful.>
If not any other recommendations are welcome! I really love oddballs when it comes to fish!
<Would get the Spiny Eel first, get it feeding, and then introduce the Knifefish if you want to keep that species as well. These two compete for the same sort of food, so getting them both feeding properly may be tricky.>
<Cheers, Neale.>
Re: 65 gallon stocking., Spiny eel stkg./sel.  11/29/11

Would a Black Spot Spiny eel (Mastacembelus dayi ?) be an appropriate spiny eel, for my tank long term? I was looking up/ trying to find info and some say they get to about 12" max while others say 20"...any input on this? Its a beautiful species!
<If you can get this species, then yes, I'm sure it's nice enough. FishBase reports maximum length of 30 cm, but the estimates on FishBase are sometimes rather low, reflecting the biggest size reported in the scientific literature rather than the maximum possible size. In any event, Mastacembelus are all rather similar. Territorial towards one another and other Spiny Eels; predatory; prone to skin infections; benefit from the addition of a little salt in the water, around 2 g/l. Cheers, Neale.>

Which <FW Spiny> eel do you suggest?   3/25/11
Hi, I emailed the other day asking about the diet of a Fire eel. She's eating now, thank you.
I'm thinking about getting another eel for my other tank, 20 gallons.
Which do you suggest?
<Mmm, perhaps one of the smaller species of Mastacembelids sold as "Peacocks". Read here:
The tank has loose substrate with plenty of hiding places.
Oh, and two 3.5" Oscars
<Oh! Then no Eels... and I'd be moving these Oscars to at least twice this volume now>
and a Pleco. I'd like an eel other than a Fire eel, since I already own one. Maybe a Tire Track eel?
<Mmm, no; gets too large>
Can you please list a few pro's and con's of popular eels?
<See the Spiny Eel article linked to where you've been directed. Bob Fenner>
Thank you very much for your time.
Tire Track Eels VS. Zig Zag Eels   3/25/11

Hi, it's Sherry again.
Can you please do a comparison between those two types of eels? I'm getting very confused by all the sites online...
<Search by their scientific names on sites of authority... Fishbase.org...

Tiger Barbs and peacock eels, comp., Mastacembelids gen.    1/5/08 Hello WWM! <Hello.> I am new (2 months) to freshwater aquariums. <OK.> I was wondering, will 2 Tiger Barbs and 2 Peacock Eels get along when in the same 10 gallon tank with limited places to hide and some live aquatic plants? I'm concerned since both are aggressive species. Will they fight? <Won't work. Tiger barbs are schooling fish and become nothing but trouble when kept in groups of less than six. They nip at other fish. So, get six Tiger barbs before you start fussing about other species. Six tiger barbs need more than 10 gallons of tank space. At least a long 20 gallon tank to get the room to swim and play they need.> Also, will Peacock Eels eat spikes (fly larvae), sinking shrimp pellets, freeze-dried blood worms, Tubifex worms and worms you use as bait when fishing? This is what I've been feeding them, but can't tell if they are eating or not. <Peacock Eels, by which I assume you mean Macrognathus siamensis, will eat live and frozen worms/insect larvae happily enough, but ignore dried foods, pellets, etc.> I just got my Tiger Barbs yesterday and they just seem to hang out together. <Why did you buy just two? That's mean. These are social animals and as they mature they create a pecking order. Denying them this leads to problems. Besides, they're too big for a 10 gallon tank. If you have access to January's edition of TFH Magazine, I have an article in there all about stocking 10 gallon tanks. Consider this essential reading!> So far, I've had 3 Striped Peacock Eels (one died when it was exploring its new home and it was eaten by my filter) they get along fine. <Please let me make this very clear: Peacock Eels are not easy to keep. For a start, they CANNOT be kept in tanks with gravel. Putting them in a tank with gravel is giving the eel a death sentence. These eels dig, and gravel scratches them, and then they get secondary bacterial infections, and then they die. I have seen this and heard about this too many times over the last twenty five years of my keeping tropical fish. Secondly, they are difficult to feed. Live foods are preferred, and they CANNOT be kept with any night-time bottom feeders. Neither catfish nor loaches. You must feed the eels at night, and they must be the only fish in the tank eating the bloodworms or whatever. Otherwise they starve to death. Finally, they jump out of tanks. Again, this is incredibly common when people keep these eels. The tank must be almost airtight. Block any holes big enough for the fish to squeeze through.> I also had 2 Pictus Cats and a Pleco not survive, any ideas why? <Your tank is insanely overstocked. A Plec will reach 45 cm, probably longer than your aquarium! Pimelodus pictus is a schooling, riverine catfish that needs to be kept in groups in a tank with lots of water current and swimming space.> I took a peek at your FAQ's and noticed there were quite a few articles about eels! Good Job!!! Just out of curiousity, how long have you been studying eels? <Studying them may be overdoing it a bit, but I kept my first Mastacembelus armatus back in 1988, and have been keeping and writing about them ever since.> Also, how are you supposed to determine the sex of Peacock Eels and Tiger Barbs? <Spiny eels are universally sexed by looking at their body shape: females are dramatically more deep-bodied than the males. Tiger barb females are rounded at spawning time. If you have a group of six or more mature fish, it's usually not a problem to identify the males and females.> Any advice would be greatly appreciated. Thanks, a curious newcomer. <Good luck, Neale.>

A Very Good Fishy Story (well-adjusted Fire Eel) I have a fire eel, quite a crazy and yet good story, just though I'd share it.  I bought a fire eel the other day in Fort Wayne, IN, from a retailer who had it in an aquarium with green terrors, jack Dempseys, Flowerhorn cichlids, African Synodontis, and an EXTREMELY AGGRESSIVE banded Headstander.  Fort Wayne is about 5 hours from where I live, and due to traffic, it waited 6 hours in a bag for me to get it home.  When I got it home, it acclimated instantly.  I have read stories on your website about them getting diseased easily and those refusing food, but mine is completely disease-free, and ate so much beef heart that his stomach swelled to the size of Chicago.  He is fat and happy, and even likes to come out and lurk around during the day.  Just thought I'd share the story. <Thank you for sending this along. Bob Fenner>

Freshwater eel Hi there, crew.  It's been a while since I've written.  Last we "spoke" I had gone freshwater only.  I found good homes for my SW fish and corals, and now have a 180 oceanic with a huge sump and bio balls.  I keep the tank at 80 F, and I am using an Iwaki RXLT 40 full blast for sump return.  I do a 30 gallon water change once a week, and clean the overflow sponges at that time.  I run a 40 Watt Aqua UV light on the tank, and use a diatom filter once a week at water change time.  The gravel is a little on the large side, and not really conducive to burrowing.  There are a lot of rock caves, though.    I have four clown loaches (2 are 8+ inches [13 years in my care, so far] and two are 2 inches); 2 small Corys, 9 glass catfish, 2 Plecos.  I was thinking about adding a spiny eel (after lengthy quarantine, of course).  What do you think?  I have read your FAQs, and would like to know what kind of eel might go well in that tank.  I also have another tank (80 gal) with just a couple of dwarf Gouramis that I could place the eel in (he's going to start there, anyway).  Would be interested in recommendation for a fish that did not grow too large and would not eat any tankmates.  I feed frozen bloodworms, mysis shrimp, flake food and sinking pellets.  My loaches are pretty old and hefty, so I assume that they're happy with the diet. thanks for your help, tom Dear Tom; Tire track eels grow to two feet, and will eat any tankmates that fit into its mouth. Likewise fire eels. There is a pretty eel that grows to around 4 inches called the Short finned spiny eel (Latin name is Mastacembelus zebrinus) if you can find one for sale. Many other eels are either aggressive, grow large enough to eat your other fish, or are brackish/marine. Here is a link for ya: http://saltaquarium.about.com/cs/eelprofilesindex/a/aa082901.htm -Gwen

Purchasing some spiny eels I was thinking about purchasing some spiny eels from an online store. Is it wise to have a striped peacock, a Zig Zag, and a fire eel all in the same tank? <Not problematical in terms of them getting along, feeding/foods, having different habitats if this is what you mean> Also, the site I was planning on ordering from said that spiny eels eventually needed 29 gallon tanks... but I read about people having to put them in 100 gallon tanks, what's the minimum size I can have for one and does it affect what size of tank I need if I have one of each of the aforementioned spiny eels? <Mmm, at least a hundred for the Fire Eel... gets quite large over time, in good health... the others could live in 29 gallon systems (well-covered!). Please read here: http://www.wetwebmedia.com/FWSubWebIndex/matacembelids.htm and the Related FAQs (linked, in blue, at top)>   I read that the eels will eat crustaceans, so I assume a blue crayfish would be a bad tank mate...  Is it wise to order online?  Or would you suggest going to a local breeder or distributor?  Thanks in advance. <Both sources could work... or be trouble. The spiny eels are quite tough if cared for well, and doomed if not... Seeing them ahead of purchase is definitely a bonus, better start if you can find, order them locally. Bob Fenner> Fire eel purchase in the GWN >I would like to buy a fire eel but I do not find any store of fish which has some can you help me please >>> What city do you live in? It is hard to find you a store without knowing where you live. Oliver sorry, I'm living in Montréal >> Try Nature Pet Center on Newman in Ville LaSalle, they can likely order it for you if they do not have them, speak to Robert. If not, maybe Big Al's Aquarium Services on Boul. Des Sources. Speak to Daniel. Keep in mind that fire eels will get four feet long... Good Luck, Oliver.

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