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FAQs on Freshwater Eel Fishes

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A Fire Eel in captivity

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>

Was: What kind of Moray eel is this?, now, pet Anguillid from Borneo      6/16/17
Hello Bob!
<Hey Ben!>
Speaking of edible eels, I just want to share a small video clip of my pet eel. They guy who sold me this eel called it a "Sidat", a river eel. Natives of Borneo (Kalimantan) said that Sidats are edible and tasty.
<Ahh; either Anquilla boreensis or A. bicolor likely>
But I will never eat my pet eel! It is so cute, I love it, it's very intelligent, it could sense me coming to the aquarium to feed it, and it takes frozen worms off my hands.
(pardon the video quality, my cellphone's flashlight is rather weak) I like eels, they are very fascinating in their own way. People said eels are voracious predator, but this one, mine, is very gentle and never bothered any of its tankmates. Except for eating small shrimps every now and then, but that's my eel being an eel, ha ha ha.
Thank you Best Regards,
<Thank you for sharing. Bob Fenner>

Re Mystery eel "Am I simply thinking doom and gloom" (RMF, second opinion on the ID?)   8/25/09
Play slideshow
Hello everyone
These are the pictures Neale requested I send to help him help me identify my freshwater eel ("am I simply thinking doom and gloom?" was the original e-mail). I don't know if it is obvious by the pictures but his head is fairly pointed with very small clear fins (pectoral? the two little ones on each side) just shy of the head, his belly is nearly white with a small amount of the grey colour on top bleeding into the white in the form of small spots. I could not really see gill slits perhaps they are at the bottom of his "neck". I was previously mistaken and he does appear to have both a top (dorsal?) fin that goes around his tail and is at the bottom to.
It is completely clear and barely visible (I doubt you'll be able to see them as they are transparent and I could barely see them without the camera) It starts at about an inch from the head ("eel" is about 6.5" maybe 7.5") and goes all the way around to the bottom stopping about a little more than an inch from where the top one began. He has very small black eyes found close to the snout he burrows tail first into the substrate and burrows all the way in, not any of him is exposed. I have never seen him with his mouth open so can't help with what his teeth are like. Sorry the pictures aren't that great he appears to be camera shy and the camera batteries died, as it was 3 am I thought it might be rather inconsiderate stomping about trying to find new batteries and the little beast has proven highly allusive so I am sending these pics even though they aren't the best, sorry. I have never seen it eat and so far no missing fish but I am worried he is starving to death, he appeared to eat a few marine pellets when I left for a bit but he might have just stirred them into the sand lol he was not at all impressed he couldn't burrow.
<Well, I really do need a good view of the head and pectoral fins to be sure, but I'm fairly confident that this is some Anguilla (True Eel) species, a juvenile specimen at the moment, hence the pale colouration.
Almost without exception, Anguilla offer a pair of characteristics that aquarists should be aware of: they get rather large, and they are highly predatory. They aren't difficult to keep -- we had one at university that
lived in what was little more than a bucket -- but they are notorious escape artists and can be difficult to house because of this. Anything small enough to be eaten will be eaten. They can be kept in big tanks with
similarly robust fish, things like catfish and large carp, and kept properly can live for decades. Water chemistry and water quality are of remarkably little importance. All species are extremely similar in shape,
size and temperament, and telling them apart is consequently very difficult. Although never popular aquarium fish, they are widely traded as food fish, and some end up in the ornamental fish trade. The only other fish you might consider is Pisodonophis boro,
<<I do concur. RMF>>
sometimes sold as the Glass or Rice Paddy Eel, a brackish-water predator that gets to about 90 cm in length and feeds at night on invertebrates and small fish. It isn't commonly traded, but in recent years has been sold with a little more regularity than before. There are some comments on this species on my Brackish FAQ, here:
Telling Rice Paddy Eels from True Eels isn't easy, but Rice Paddy Eels are much more slender, have weaker dorsal and anal fins, and a more tapering tail; Rice Paddy Eels also have thick corneas over their eyes to allow them to dig through the sediment without damaging their eyes.>
I have tried researching Fishbase and other databases however, most pictures are of adults and I just can't quite match it to anything else. I appreciate any help you can give on the matter. I hope you all have a
pleasant evening and thank-you very much for the site it is very helpful I hope I didn't miss a post that would have told me what this guy is. I just don't want him to eat the rest of the tank mates (if he gets giant) or to starve because I am not feeding the right thing, also the concern that the people I got the tank/fish from might have unknowingly bought a saltwater "eel" on accident, they weren't big into research/knowing what the fish were =0).
<Neither eel is a "good" aquarium fish, and if you can't tell them apart, keeping either in slightly brackish (SG 1.003-1.005) conditions would be wise, since that will be appreciated by both. Eels are easily distinguished from loaches (such as Pangio) which have barbels around the mouth and spines in front of the eyes. Spiny Eels are also different, having whopping great spines along the dorsal and anal fins as well as very odd, trunk-like noses. Moray Eels are similar to true Eels, but lack pectoral fins.>
Speaking of starving I am wondering if I am feeding my fish enough, I realize you get this question often and I am sorry to bug you with it again, but I find the pinch measurement confusing as everyone's "pinch" is
different. I have a 90G tank (any suggestions to alterations in stocking would be appreciated)
*1 dwarf Gourami
*4 platies 2- 3" / 2- 1"
*5 1/2 inch white cloud minnows
* 3- 3" turquoise rainbows (might get 3 more)
*3 weather loaches 7", 4" and 3" (plan on getting 3 more)
*2 Plecos one "common at 2.5"(will have a new home at 8inches) and one bristlenose at 8"
I feed them about 1/2 a pea size flakes 2x per day 5 different types alternating days for variety, alternating days they get marine sinking pellets and tropical crumble sinking pellets about 1/4 pea amount fed at the same time as the flakes, 2x a week they get sinking algae wafers 2, 1 time a week they get mysis frozen shrimp 1/2 cube, and than once a week they get sinking bottom feeder pills. I know they say what they will eat in 5 min but the stuff that goes to the bottom dissolves slowly and the loaches and Pleco's can't bite it so they worry it and get it as it dissolves. I don't want to overfeed them because I know that isn't good but they ALWAYS look hungry to me ROFL I know they probably aren't but I want them to get enough. Oh and once a week they get peas that are skinned. I also have a planted aquarium with several plants and duckweed available for casual grazing.
<Provided your fish have gentle rounded, convex bellies, and when viewed from the front the flanks aren't concave, you're feeding them just fine.
Most aquarists over- rather than under-feed their fish. It's a good idea to provide algae wafers a couple nights per week for Plec-type fish, 1-2 being adequate for Ancistrus species, and 4-6 being more appropriate for the larger Hypostomus and Pterygoplichthys species.>
Again thank-you so much for your time and all of your guys'/gal's efforts it is a great help and very interesting to read your articles and answers to questions. Hope you all have a pleasant evening/morning, I am going back to bed lol 4 am is WAY to early lol.
<Cheers, Neale.>

Re: Mystery eel "Am I simply thinking doom and gloom" (RMF, second opinion on the ID?)  8/25/0Thank-you for the help identifying the eel it appears to be the Pisodonophis boro (rice paddy eel), well maybe lol.
<Indeed, maybe.>
It will have a new home at my LFS. They will keep it as a display fish in their new 300+G tank.
<Let's hope it's a brackish water aquarium, or it won't do particularly well.>
It will stay in my 20 G tank till then. If you would like I will try and get a better picture, when I move him (it), for your archives?
<I would certainly like such a picture for my Brackish FAQ, and I'm sure Bob would happily put a copy up on WWM as well.>
He might be a little bigger in a few months when he is relocated and easier to photograph. If you don't want another pic than no worries, just let me know please. Wishing you all safe journeys.
<Thank you.>
Have a good day.
<Cheers, Neale.>

Eel  ID, probably no moray eel  2/28/07 Are there any moray species that stand on their tails and have their throats inflated? I have heard of tulip eels doing this which are supposed to be very aggressive. I do not have any good pictures of my fish to help determine if he is a moray or not, but the LFS sold him as a moray. <Moray eels rather hide instead of standing on their tails. They inflate their throats while breathing. To get an idea of the ID a good picture is necessary. Without a picture you should try looking at http://www.wetwebmedia.com/congridae.htm and http://www.wetwebmedia.com/ophichthidae.htm and http://www.wetwebmedia.com/morays.htm for marine eels. Have a look at http://www.wetwebmedia.com/FWSubWebIndex/anguillids.htm and http://www.wetwebmedia.com/FWSubWebIndex/matacembelids.htm for freshwater eels. Check the related FAQs, too. Also check FishBase by entering the family names you found on WetWebMedia and selecting 'all fishes' to get a link to photos. For the swamp eel check Monopterus alba. It has a very typical head much unlike a real moray.> I do not know growth rates of the swamp eel but my fish has not grown but little in length but he has gained some girth and he has eaten quite a bit for a year now. He also no longer has a pointed tail it is rounding out with possible fins can not see close enough. Am I in a bad situation if mine is a swamp eel with my Gymnothorax tile? <I would not recommend keeping any of them with other fishes maybe except their own species. May work for years, but even the scat is potential prey. Read the freshwater moray articles on WWM.> So far they are both sharing the tree root ornament to hide in peacefully. I have my toad fish and red scat and the G. tile has no problems with them either and even lies on top the toad fish when out. I have seen people with swamp eels on monsterfishkeepers.com, but they are in fresh water. I have a brackish setup. The main question I have if this is a swamp eel should I be looking into finding him a new home at some point? <Yes. Swamp eels need fresh water to lower end brackish water, the moray eel needs high end brackish or full strength marine water, both are incompatible.> Thanks for your advice on this. <You are welcome. Cheers, Marco.>

Freshwater moray eel help    4/10/06 Hi, my name is Connor and i have 3 questions: <Hello, my name is Bob and I have many more> (1) I have been looking for a freshwater moray eel everywhere and  i cant find one anywhere near me i live in Clearwater FL. and have a 20  gallon tank (2) if I have any more room in my tank would another  moray have space and if not is there any other fish that can be put into the  tank with it. (3) is there somewhere were i can find more about like what it  eats. thank you so much for your help. <Please read here: http://wetwebmedia.com/FWSubWebIndex/fwmorayeels.htm and the linked file above... and use the scientific names there to look elsewhere on the Net, particularly fishbase.org Bob Fenner>

Eel suitable with goldfish   2/13/06 Hi there, what a fantastic website. Just need some answer for my questions. I have 70 litres aquarium (not sure) but it is 75cm length, 60cm depth and 40cm width. And full with 13 fantail goldfish. <Too crowded... This volume is suitable for 2-3> Seems like it is too crowded, and having plan to get rid some of those goldfish and get couple eels and could sucker fish (not sure what you call them). Any idea, what kind of eels that suit my goldfish? <None> OR any other animal looks like snake that suit my goldfish? How many fish are better to stay in my aquarium? Thanks heaps. -Stephanie- <The coldwater species get too large, eat goldfish... Bob Fenner>

Freshwater eel ?  12/21/05 Hello Bob, My name is Seth and I have (a what the store owner called) an African eel. <There are a few possibilities here> He lives in my freshwater aquarium that hosts a small community. He has a striped/spotted pattern that gets lighter and darker or more defined as he hides. Recently I noticed that upon coming out of the sand, the front half of his body was light colored and the rear half is darker (more defined pattern). I figured that maybe its his chameleon way of camo. but it hasn't changed back to one solid consistency. He still eats regularly and is very responsive to my movement as well as other fish. Is there reason for concern or is this two tone a natural tendency?   Thank you ~Seth. <Hard to say w/o actual identification of the species. Is this a spiny eel (family Mastacembelidae), or does it appear to be a "true" eel (lack spines in its fins)? Can you send along an image? Bob Fenner>
Re: Freshwater eel?  12/24/05 Its fins appear to be transparent. I have not seen a photo on the web that looks like this one. There is a poor quality photo attached that maybe you will recognize. <Yes, is a spiny eel... member of the family Mastacembelidae. Please see this family's African members on fishbase.org. Bob Fenner>

Monopterus / Swamp "Eel" - 08/09/2005 I recently purchased this cutey from a local fish store. They had the poor guy in a too-light tank with no hiding spaces. <Poor feller!> I have always wanted eel-like creatures in my 75-gallon, and I thought anything would be better than where he was now. <Likely so.> I waited a week, checked in on him twice, tested my tank, and took him home.   <Keep in mind all the possibilities that a quarantine tank offers you.... ! > After researching almost fruitlessly on the internet for care articles for this species (which you can find by the handful in Asian rice paddies), <Also by the handful on Google....  Just search on "Monopterus".  Seems "alba" is almost as commonly used as "albus".  Fishbase has it as "albus".  http://www.fishbase.org/Summary/speciesSummary.php?ID=4663&genusname=Monopterus&speciesname=albus > I decided the best thing to do was go fishing for public advice.   <No pun intended, I'm sure?  <gfin> > It's been about a week. He seems as comfortable as possible, and I have provided him a few small feeder fish whenever he gets the urge to have a bite (as well as about a thousand tiny snails). <Does he eat the snails?> He has no aggressive tankmates. <As he grows, he may EAT his tankmates.... all....> I have been keeping the tank lights off until he has time to adjust. <Good.> He's got plenty of hiding spaces.   <Also good.> I would like advice any of you have with this species - actually not a true eel. He hasn't eaten anything yet (that I know of), <BAD.> but I will not worry for another week about that. <Begin worrying right away.  Food is of the utmost importance with new wild imports - try everything you can get your hands on.> Any suggestions for meaty foods besides tiny feeder fish? <Frozen "Formula One" cubes by Ocean Nutrition, bits of thawed frozen raw shrimp or other fish/seafood, live shrimp....  just anything you can get into him, for starters.  'Course, I'm not sure if he is "eel-like" in that he can go for many weeks without food, so this may not be as urgent as I see it.  I'd be shaking in my shoes in a few days, if it were my fish.> Will they eat dead food? <Uncertain.  Eventually, he should.  You may have to start him on strictly live foods.  Perhaps even insects, like crickets?> Should I purchase a feeding stick? <Couldn't hurt.  I prefer a very long, clear straw, myself....  cheaper, and comes in packs of 100 ;) > Any advice would be golden. Thanks!! ~M <Wishing you and your new, very interesting pal well,  -Sabrina>

Monopterus / Swamp "Eel" - II - 08/16/2005 Good morning crew! <Good morning!> I wrote in last week concerning the Monopterus Albus/Alba (swamp "eel"). I was worried a bit that he didn't seem to be eating. <Yes, I recall.> I have tried everything I can get my hands on to entice him... I tried a makeshift "feeding stick" a few times and wiggled some shrimp in front of him - no response, not even negative. None of the remaining feeder fish have disappeared. I bought frozen brine shrimp cubes and he isn't even curious. He MAY be eating the tiny snails littering the tank (they seem fewer in number, and they ARE slow), but I cannot be sure. I sit and watch the guy for hours in the dark, and he just seems to be hanging out. He'll travel the length of the tank, but slowly. Sometimes when the light is on and he's out and about, he seems very weak (may be his sensitive eyes, but I'm more concerned that it's lack of nutrition). <Yeah, I'd be pretty concerned, as well.> I plan on trying some type of worm (maybe earthworms or caterpillars), <Skip the caterpillars!  Or at least research the caterpillar species, first.  Some are toxic.  Earthworms are a great idea....  Drop 'em right in front of him, perhaps just after lights-out....> but beyond that, beyond force-feeding the guy, I am at a loss.  Any last-ditch suggestions? <DEFINATELY try live ghost shrimp.  I would be surprised if he wouldn't chow down on a couple.> Should I isolate him in a smaller area? Tie a live fish to his head?? I am getting very worried, as I don't want this creature to suffer. I'll do ANYTHING to help the poor guy out! <If the ghost shrimp are a hit, keep in mind that they're easy to breed - if you have the space, this may be an option to keep in mind.> Thanks so much ~M <Got my fingers crossed for him....  Wishing you both well,  -Sabrina>

What FW eel do I have? and do you have any advice for me? Hi I recently got a moray eel from my friends fish shop they got them in freshwater and I have a fresh water tank. Today I went to another fish shop and asked about him they told me that I should put him in salt water. So I spoke to my friend and he said that it was the first time they ever got a "freshwater" moray eel and he really doesn't know. He's at least 1 meter long and 3cm thick (1.5inches I think). He looks very much like this picture but no one knows his species. Any advice you have would greatly be appreciated (before it dies) which i hope it doesn't. Thank you. Argyris Papageorgiou. >> I can not see the photo you have sent. You are in South Africa, so I am assuming that this is a marine species. Some young eels go into the estuaries of rivers. E-mail me the photo of your eel to this address, especially a close up of the head: eel@belowwater.com, Thanks, Oliver

Freshwater Eel, maybe Hi. I just bought a Moray eel from my local pet store.  They have it listed as a freshwater eel and recommended I keep it with other freshwater fish. So I put him in my freshwater tank. Later that night I did some research on the internet and even chatted with a few moray hobbyist.  What I found was that there is no such thing as a freshwater Moray.  The hobbyists I chatted with recommended I put the Moray in a separate tank and slowly introduce sea salt. They also recommended I email you with any further questions. So, my first question is, who do I believe, the guys at the pet store, or the hobbyists? My next question is, given that the Moray does in fact need salt water, what is the desired level of salinity, and how fast (or slowly) should I introduce the sea salt to my tank? Thanks for your time! Josh <Hi Josh, Don here. This all boils down to what kind of eel you have there. If it's a real Moray Eel he needs be kept in full saltwater conditions. Conditions that would kill a freshwater species. How about doing a Google image search and try to ID him. Send us a picture or link so we can figure out what he is and what he needs>      

Adapting "Freshwater" eel to marine Hi, First off, thank you for creating such an informative site, your information has been of much assistance to me in looking after my Freshwater eel. <Okay> I have a question for you which I have not really seen answered in any detail anywhere.  I would like to know if it really is possible to adapt a freshwater eel to a marine environment. <Some species, yes... please read here: http://wetwebmedia.com/FWSubWebIndex/fwmorayeels.htm Do you know the species you have? Try inserting the common or scientific name in fishbase.org>   If so, what would be the proper way to go about doing so without causing any harm to it's health? <Slowly... a few hundredths of specific gravity change per week... taking out a volume of existing water and adding more salty to replace it> I ask because I am in the research and planning stages of switching my current freshwater tank to marine, and while I know I will have to give up most or all of my current fish, if it is possible to keep my eel without causing it harm then I would like to take the extra effort to do so.  The information I have seen on your site indicates that they are a freshwater to brackish to marine species, and another site (aquariacentral.com) flat out states that they can adapt to marine conditions, but that is about all I have found on the matter.   If you have any information on this that you could share, I would appreciate it.  Thanks! -Mark C <Read re this animals habitat, life history on fishbase... if it is a marine species as an adult, it will likely be easy to convert. Bob Fenner>

Fresh, marine, brackish eels escaping? I just purchased an eel for my 55 gallon tank.  The lady I spoke with when purchasing it told me to block off all holes in the top of my tank because it could try to escape.  If it did escape, how far could it "slither" before dying, or would it just fall near the tank?                                                                                Thanks,                                                                            Angie... <Depending on the species, how hot, humid the area is, the type of flooring... a few to several feet, a few minutes to several hours. Keep that tank covered. Bob Fenner>

Unknown Eel hi, my name's Dean I have had my eel for about 5 months he is very healthy but I have wondered for awhile what kind it is I have a pic attached I hope you can help in identify him. <Neat... looks like a synbranchid eel to me... maybe Monopterus alba... maybe give a read on fishbase.org re... or place the scientific name in your search engines. Bob Fenner>

Fish Jumping out of Tank!  8/7/04 My name is Abby.   <Hi, Pufferpunk here> I have a 29 gallon fish tank (freshwater).  My eels are acting kind of strange.  It all started when my snowflake eel jumped out of the tank, he was fine for a few days, but then he died. <Snowflake eels are high-end brackish to saltwater fish.  Most of the time, when a fish jumps out of it's tank, it is because it is too small, or the water conditions/quality is poor.> That's when my 2 remaining eels started being weird.  My peacock eel's eyes have turned this translucent white, like he's sleeping, but he swims around like this.  He is breathing fine, and swims a lot.  However, he also stand up on the bottom of his tail for hours on end, if that makes sense.  Then, my fire eel has just been hanging upside down off the heater.  Again he's breathing right and sometimes swims around.  I have been feeding them ghost shrimp and worms from the pet store as advised.  This is all very new to me and I don't like for my animals to die.  I have looked on many websites for answers, but came up empty handed.  Any information is greatly appreciated.  Thanks Abby <How long has the tank been set-up?  Was the tank cycled before adding these fish?  How often are you doing water changes?  Are you aware that fire eels grow to 24"?  I would check the ammonia, nitrItes & nitrAtes.  Add Melafix for the cloudy eye.  Ghost shrimp by themselves, are mostly water.  I would gut-load (feed) them something nutritious, like to use algae wafers, so my fish get their veggies.  ~PP>

FW Eel for 20g Tank?  7/26/04 Hello <Hi, Pufferpunk here> I am sorry for sending you this letter but I have looked for days to find out about something.  <You don't have to apologize for asking questions, if you can't find the answer somewhere.> That something would be that I am looking to buy an eel and I only have a 20 gallon tank.  Would that be enough to have a eel.  If so you tell me which one or ones would be good to get.  If not could you tell me of something similar. <Most eels grow fairly large--way too large for the tank you have.  The only smaller eel that comes to mind is a spiny-nosed eel. http://www.aquariacentral.com/species/db.cgi?db=fresh&uid=default&ID=0603&view_records=1 Even this eel will grow to 6".  Eels will only eat live foods, so be prepared to spend some $$$ on worms & such.>  Thank you Tyler I would really appreciate it if you would write back. Thanks <Good luck finding the eel you want.  ~PP>

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