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FAQs on Synbranchids, Swamp Eels

Related Articles: Freshwater Anguillid Eels,

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Swamp Eels, Family Synbranchidae, are often looked on as true eels by the trade. They are not. Sure, they have a lot of eel-like traits, being long of body and tapered, lacking pectoral and pelvic fins, possessing only vestigial dorsal and anal fins, reduced or absent scales and small gill openings...

    These widespread (Africa, Asia, Mexico, Central and South America) fishes are interesting aquarium specimens in their own right. Not to add to the common name confusion, but one Swamp Eel (Monopterus alba) is often referred to as a/the Freshwater Moray Eel.

    Bear in mind the synbranchids can get to more than a meter long, jump out like no tomorrow, and eat tankmates they can get their capacious jaws around if you intend to try them.  

Mystery "Tiger" Eel... ID     6/19/17
Hello Neale,
Thank you for the fascinating exposition about the world of fishes. My knowledge of fish's sensory organs does not extend beyond knowing what are lateral lines on fishes. So it's good to hear more details from you in regards to this matter.
<Glad to share.>
As an Indonesian, I feel blessed to live in a country with such rich biodiversity, especially concerning fishes. At the same time, I often stumped by the very diversity that my country's fishes exhibited. Take this fish (picture attached), for example. Is this a Gymnothorax Polyuranodon?
<Quite possibly; but I do think Gymnothorax reevesii more likely.>
<<Thought this looked more like a Synbranchid... RMF>>
Such a lovely skin pattern, but it must served a purpose, maybe to confuse predator fishes into thinking that it is a snake?
<Interesting thought. One issue is this though: Morays are nocturnal, and hide by day, so their predators (if there are any!) wouldn't really see their colour patterns easily, and more likely hunt by smell or vibration.
Still, who knows? Your idea definitely makes sense, and many animals mimic venomous snakes.>
Strange and beautiful eels often got fished out of our rivers and canals by unsuspecting locals, and oftentimes I cannot even tell what species are they. Local Indonesian, when shown the beautiful eel in the attached picture, will say "that's Belut Macan Tutul!" (means: Tiger Eel), but there are lots of other species which also being called "Tiger Eel". It's like the Pleco catfish, so many different species and yet to local Indonesians, they're all "Ikan sapu sapu". One name fits all :D.
Well, again thank you for the chat, and have a nice day!
<And likewise to you, too; Neale.>

What kind of Moray eel is this?      6/15/17
Good afternoon Neale and all the good people at WetWebMedia;
<Howsit Ben?>
In an Indonesian discussion forum, I found this picture, the guy who posted it said that he fished this moray eel in a river, several kilometres from the river mouth/estuary. I wonder what Moray eel is this? It does not looks like "freshwater" moray (Gymnothorax polyuranodon, we call it belut muara), so it might be a new species?
<Mmm; I do think this is a Synbranchid eel (not a Moray): Ophisternon bengalense
Best Regards,
<Cheers, Bob Fenner>

Re: What kind of Moray eel is this?      6/15/17
Hello Bob! Thank you for the reply. That was quick! And very informative too. I never heard about this fish. We learn something new everyday. It's a very fierce-looking fish, no wonder we all confused it with the moray!
<Synbranchids do look very similar... Neat animals (and tasty!)
Again, many thanks! *bowing*
Best Regards,
<Sama sama my friend. BobF>

Eel not eating and strange behaviour 9/13/08
hi. my eel is refusing to eat.
<I can't really tell what the eel is from your photos. Is it some sort of Synbranchus?>
i have read the information about the rearing of eels on your website. however, i still cannot understand the strange behaviour of my eel so i decided to write you this e-mail.
my eel is about half a metre long and i have been rearing it for almost half a year. it lives in a tank (39.8cm x 25.4cm x 28cm) but unlike the other eels which i read in your website, it lives in the light and the surroundings are only dark at night when i turn off the lights. there is no sand or stones on the bed of its tank and besides a filter, 2 small red coloured fish and 5 prawns, there are no rocks or shelters where it can hide itself in. however, it does not show any symptoms of escaping. it is gentle and even allows me to touch and carry it in the water for awhile before swimming out of my hands slowly. of course, i treat it gently and carefully.
<If this is a Synbranchus, this nice behaviour is VERY unusual. They're usually incredibly aggressive and predatory.>
previously, i fed it tiny blood worms but then changed to frozen prawn as it grew bigger. i feed it by dangling the food above its eyes and it eats at least one small frozen prawn everyday.
<Do try not to use Prawns exclusively; they contain a lot of thiaminase, and so can cause Vitamin B1 deficiency if used on their own.>
Occasionally, it will not eat for at the most 2 days. then it will start feeding again. However, for the past 5 days, it has not been eating at all and has been pushing its body against the corner of the tank to great heights and putting it's whole head above the water level when previously it was only his nose. i have tried to feed it countless times, but to no avail. i am afraid it may starve as it normally eats everyday but now its not eating at all continuously for 5 days.
<By all means leave him without food for a few days. Then offer something different. Earthworms are very popular with carnivorous fish, and provided you collect them from somewhere not sprayed with pesticides, they're cheap and safe. I collect mine from the garden, underneath rocks and pots. Alternatively, get a bag of mixed from seafood; these contain squid, prawns and mussels, all of which your eel should enjoy.>
Please help me and my eel as it is really very dear to me. for example, if i stand in front of the tank, it will swim towards me and put its head above the water and look at me even if i am not feeding it. sometimes, when i ask it to shake its body, and shake my body to demonstrate, it will really do so! it has really brought much joy to my family and i really hope that you will help me bring it back to normal. i have attached some pictures of it as i do not know the species. (sorry if the file size is too big! ) I eagerly await your reply. thank you!
<He sounds a nice pet! Do research Synbranchus, particular Synbranchus marmoratus, which is what I suspect your eel to be. Cheers, Neale.>

Re: Eel not eating and strange behaviour 9/13/08
thanks for replying me.
<Not a problem. But please, do try and use capital letters in your messages.>
however, the fact that it has not been eating at all for six day and still counting worries me immensely.
<Six days without food won't harm a Neon tetra, let alone an adult eel. However, when fish go off their food it can mean something is wrong with the environment. Review water chemistry and water quality. I really do need to know what sort of "eel" this creature is. Did you look at photos of Synbranchus marmoratus? This is a big (150 cm) eel-like animal that needs a big tank with lots of hiding places. If it's out in the open all the time because there aren't any caves, it will be stressed. In the wild they live in complex burrows.>
what should i do to get it to eat again. it really hurts me to see it get weaker and weaker each day and its skin colour pale.
<If it's getting sick, I doubt this is because of lack of food. Review its tank, particularly water quality. Don't tell me the water is "fine" -- tell me at minimum what the nitrite concentration is. Also how stable is the pH?>
what do you suggest it should do? would putting an enclosed place for it to hide itself help?
otherwise should i switch back to feeding it the worms (a ball of bloodworms which are each not more than 1cm long) like i did previously?
<Insect larvae of all types will be good. So also earthworms and river shrimps. Avoid Tubifex worms though, and never use feeder fish. Both of these things cause much more harm than good.>
i have been feeding it prawn for quite some time now. how can i let it regain the vitamin b1 which it has lost overtime?
<By varying the diet. In particular, offer suitable sized pieces of mussel. This herbivorous mollusk contains lots of algae, and this is a rich source of vitamins. In the wild, carnivores get a lot of their vitamins from the gut contents of prey animals.>
my eel once ate a small red coloured fish (live) and i read on the Internet that eels eating goldfish/rosy-red fish and eating everyday would cause liver problems. is it true?
<Yes, feeder fish and goldfish are bad. Minnows and Goldfish contain thiaminase and ALSO lots of fat, and it's the fat that damages the internal organs. One rosy-red minnow won't have done any harm, but don't use any more of them. Even putting aside nutritional problems, cheap fish are a source of parasites.>
if it is, what should i do? please help me! thanks. :)
<Let me know about the water chemistry and quality, and also either identify the "eel" or send me a SHARP photo so I can identify it for you. Cheers, Neale.>

Re: Eel not eating and strange behaviour, Synbranchnid    9/16/08 Hi again! <Hello,> Thank God! My "eel" is finally eating again after starving for a whole week. Actually, i didn't really do much. I just draped a piece of black cloth over half of the tank to replicate the dark environment of a cave, seeing if it would help. After i came home from school, as per normal, i stood over the tank and called its name. Miraculously it looked up and swam towards me, swaying its body happily. Noticing that it seemed like it had got well, i fed it and fortunately, it ate. :D <Ah, success! Does seem that environment was the factor.> Can i feed it shellfish and squid? are they detrimental to its body? You mean that i can feed it prawn but not everyday right? <Squid is excellent, and so are molluscs of all kinds, mussels, clams, etc. Small pieces of lean white fish (such as tilapia) are good, too. Avoid oily fish though (salmon, tuna, etc.)> Would putting pipes in its tank instead of rocks be ok? <PVC pipes or ceramic pipes are both fine.> And would you recommend me to put sand on the bed of the tank? As the fact that i am afraid that cleaning a tank with sand would not be easy and there would be a lot of dirt caught in sand causing bacteria to multiply which may cause internal or external fungal or bacterial infections. <Smooth silica sand is fine in aquaria. I use it all of mine! Avoid "sharp" sand though. Silica sand is sold in garden centres and is very cheap. It's actually very clean, because dirt can't sink in between the grains. So you can see the dirt, and easily remove with a net, or better still, a turkey baster. Use a thin layer, maybe 1 cm or so, in tanks without plants. Add a few burrowing Melanoides snails if you like, and they'll keep it spotlessly clean.> Just sent this e-mail to tell you the good news and ask some questions. I will send clearer and sharper pictures soon! thanks! :D <Look forward to the pictures! Cheers, Neale.>

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