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FAQs on Knifefish Feeding

Related Articles: Knifefishes, GymnarchusBlack Ghost Knife, Electrogenic Fishes,

Related FAQs: BGK Feeding, Knifefishes 1, Knifefishes 2, Knifefish Identification, Knifefish Behavior, Knifefish Compatibility, Knifefish Selection, Knifefish Systems, Knifefish Disease, Knifefish Reproduction, Electrogenic Fishes,


Re: Identifying Knifefish; now fdg.      1/8/17
Neal, thanks for such a quick reply. So I have one more question. I feed him live black worms which he happily slurps up. Is there any other foods I can give him?
<Definitely needs more variety than this! I'd be looking at earthworms and gut-loaded river shrimp as staples, and if he takes frozen foods as well, such as krill or Spirulina-enriched brine shrimp, that'd be great.>
Sometimes I have given him blood worms but I know they shouldn't be a everyday food. I won't do feeder fish as they carry parasites but what if I breed guppy's or something similar for him to eat or is this unnecessary?
<In theory home-bred Guppies are safe, but in fact not necessary, if for no other reason they're more likely to encourage him to view fish as food, which could cause problems for tankmates. In the wild Apteronotus are more
micro-predators than anything else, and benthic invertebrates such as insect larvae are probably their main food. They do have substantial appetites though, so do keep an eye on how rounded his belly looks.
Slightly convex is what you're after, rather than bloated, but shouldn't be concave either.>
I just want to give him what he needs and deserves.
<Understood and he looks a great fish! Big adult Apteronotus are impressive, and intelligent, animals that make rewarding pets. They can become quite tame, and electric fish often become rather quirky as they settle in, with distinct personalities. At least some species have brain to body weight ratios similar to mammals, suggesting a high level of intelligence, by fish standards, anyway. Cheers, Neale.>

Knife fish swallowed a rock   10/30/11
Hello, well I have a knife fish that is about 12" long. I was feeding him some live fish and he got a mouth full of rocks.
<Please do not use live feeder fish. Even putting aside the cruelty debate, store-bought "feeder fish" and cheap tropical fish are parasite bombs, and certain sorts, most notoriously goldfish and minnows, are extremely rich in fat and an enzyme called thiaminase that breaks down vitamin B1. There's simply no advantages to using feeder fish, and NO expert aquarist or vet recommends it. Here in the UK you can't even buy feeder fish, but in some countries, notably the US, there are still pet stores that sell them, despite all the evidence damning their usage.>
He spit one large one out but it seemed that he was still trying to swallow another one.
<May be caught in the gill rakers.>
I do not know the size. I know it was not the fish as it was still in the tank.
It's been about a week and I've noticed that it has not passed and stools in the past few days. The fish is not stressed but it seems as though he is "full" in the belly area. What can I do?
<Not a great deal without consulting a vet.>
Should I not feed him?
<I would not feed him for a week or so.>
Do I use Epsom salt?
<Yes, that would be helpful. It's a laxative, so loosens up the digestive tract, and if the stone is in the gut, may help it pass. Do read here:
The Epsom salt bit is towards the bottom of that page.>
I would hate to see this fish die, please help!
<Good luck, Neale.>
Re: Knife fish swallowed a rock  10/31/11

Thank you for the prompt reply. I have a 55 gallon tank and I have a dosage of 21 teaspoons of Epsom salt for the time being.
<Good luck!>
How long do I leave the fish in this solution?
<As long as won't do any harm.>
No signs of any stools passing yet. I will be calling an expert in the morning to see what else I can do.
<Real good. A vet may be able to massage or even remove surgically any obstructions. Do be aware that Goldfish and Minnows as feeders contain fat, and this accumulates around the internal organs, and this could potentially make it more difficult for your fish to get rid of faeces and accidentally-swallowed items like stones.>
Thank you again for the advice,
<Cheers, Neale.>

Brown knife fish... Sys., fdg.,    12/31/09
Hey, I recently (2 days ago) got a brown knife fish,
<Is this Apteronotus leptorhynchus or Xenomystus nigri?>
and it hides in its clear tube all day AND night.
<Both these species are nocturnal, and unless the aquarium is precisely right for the species, they *will* hide away and eventually die from starvation. To recap, Apteronotus leptorhynchus needs moderately warm (25 C) water with a very strong water current and lots of oxygen. Water chemistry should be soft to moderately hard, slightly acidic to neutral (pH 6.5-7, 5-10 degrees dH). Xenomystus nigri needs similar conditions in terms of warmth and water chemistry, but isn't so fussy about water current. Both will be quickly stressed, even killed, by exposure to copper and formalin-based medications.>
I have dropped two cubes of blood worms in the tank, but I don't think its eating them and I'm pretty sure they are making a mess!
<May well be. Do remember neither species competes with catfish, cichlids, etc at feeding time. Apteronotus leptorhynchus in particular should be quarantined first, or at least kept with fish that offer no competition at all (i.e., just small midwater swimmers). Xenomystus is a little more adaptable, but won't feed if it feels threatened or bullied. Neither species is a community fish in the general sense, though careful fishkeepers can keep them with appropriate tankmates.>
Is there a more convenient way to feed frozen blood worms without them dirtying everything because once it breaks apart I can siphon all the worms out... I am going to try buying live worms... If I drop a bunch of live worms in.. Will he hunt them or something?
<These fish are greedy for live and wet-frozen foods including bloodworms, earthworms, brine shrimp, krill, etc. But they won't eat dried or freeze-dried foods, and they won't compete for food. Most critically of all, if conditions are inappropriate, they simply won't feed. Apteronotus spp. are notoriously sensitive fish, and among the first fish to die when conditions aren't right. Cheers, Neale.>
Re: Brown knife fish
Thanks so much!!
<You're welcome. Cheers, Neale.>
Re: Brown knife fish
It is a pteronotus leptorhynchus ..
<Apteronotus leptorhynchus is a lovely fish, a bit smaller than Apteronotus albifrons, but otherwise identical in terms of care.>
dude at pet store said it would be easy to keep..
<"Dude" was obviously making a sale. These fish are extremely difficult to keep. Wild fish live upwards of 15 years, but the vast majority of casual fishkeepers manage less than a year.>
I have a well planted tank (30gallons) with two coconut caves and a clear tube.
<He will need a much bigger tank eventually; I'd be saying a 55 gallon within a year or two. The size of the fish is rather less important here than its need for clean, oxygen rich water; these fish simply don't tolerate stagnant water conditions. They live in and around rapids and waterfalls, and expect not-too-warm, well aerated water.>
water conditions are fine...
<Define "fine".>
Should I not feed him for a couple days then try with live food?
<The problem with electric fish is they tend to need numerous small meals every day to be healthy. Presumably their energy demands are rather high.
In any case, starving these fish does little good, much harm.>
How long do you think it will take for it to accommodate?
<Kept on its own, should settle in within a week. Kept in a mixed community of poorly chosen tankmates, may never settled down at all.>
thanks again
<Cheers, Neale.>
Re: Brown knife fish
Okay well thanks for all the info.... The fish is swimming around now when the lights are off.. So I guess il feed it when its dark..
<Initially, this is probably best. Add modest amounts, and remove any nocturnal species (catfish, loaches) that would compete with your Knifefish.>
What's the easiest thing to feed them? worms? or crickets?
<Earthworms of appropriate size are very popular, as are live or wet-frozen insect larvae (bloodworms, mosquito larvae, glassworms, etc.). Cheers, Neale.>

Re: Brown knife fish... Fdg., using WWM   12/31/09
are earth worms from my yard okay? or do I have to buy them?
<... Read here: http://wetwebmedia.com/FWSubWebIndex/wormsfood.htm
Please learn to/use the search tool and indices on WWM. Bob Fenner>

Black Ghost knife fish ate my Betta?  11/22/05 Hi, <Howdy> I wonder if you can help? <Perhaps> I purchased a Black Ghost knife fish after being very intrigued in him at my local store( and only after being assured by my local fish store that they are a community fish and quite harmless). <...?> I also brought a few Cardinal tetras at the same time. <As food items?> All was well for about 5hrs until I noticed that one of my tetras was dead and had its tail missing.. the next day my Fighter fish was dead and had his fins totally stripped as well as another Tetra. I've checked my water and everything seems in order so I don't believe that bad water quality was to blame for this, I was wondering if my Ghost Knife could have done this? Cheers, Steve. <Yes... Bob Fenner> 

Training a black ghost knife fish  9/22/05 Dear Mr.  Fenner, I have a black ghost knife fish that I have had for a month.  He is now about 7" long and very healthy.  He eats flakes in the morning and at  night, occasionally I give him some freeze-dried Tubifex worms.  What I  would like to know is how you teach them to eat out of your hand. He seems to be  a smart one he figured out the flakes were edible on his own.  If you know  how to do this I would really appreciate it. Thanks for your  help, MDM <Try feeding small amounts of meatier foods, more frequently, particularly just with some light on outside the tank (not in... too bright). Takes time, patience. Bob Fenner>

Just general random questions about Knifefish... heh
Hey there! First off, I'd like to say that I'm completely Wowed by your extensive and totally awesome information and help on all sorts of fish and such. It's been a great help to me, and quite interesting to read (heh, I'm a bit dorky =P) <You're in good company here> I've had fish for all my life really, and I'm always trying new stuff, so naturally, when I spotted an odd looking fish, I snatched him up right away. Probably not the most brilliant of moves, but the shopkeeper assured me that he was what I could handle properly. (we've known each other for some time...) He sold him as a "Chocolate Ghost Knifefish". Upon proper research.... I couldn't find a single thing on them, really. ^^" I can't quite determine the species of fish he is (or she really, I haven't found many websites that are too helpful with sexing Knifefish.), but he LOOKS like a Black ghost knife... but with a longer face, brown-ish, and a yellow stripe and a white dot for a tail. He doesn't match up with Brown Knifefish either, he just...isn't. Are there such things as Chocolate Ghost Knives, or is he just a special brown? <Mmm, there are a few species of apteronotids this could be. Most often sold is Sternarchella schotti: http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=48027&genusname=Sternarchella&speciesname=schotti> It's been a good couple months since we got him, and he seems very healthy and quite lively and happy. We've been feeding him frozen blood worms, but I've recently wanted to change it up a bit, too. I heard full grown brine shrimp aren't particularly nutritious though...can we feed just hatched, or is that too small/meager to last them? <The latter> I heard frozen krill was a good choice; compared to blood worms, where does that stand? <A mix of worms, insect larvae, crustaceans... live, or frozen/defrosted will do> When there's a downpour around our area, we often can find earthworms and such wriggling about, and our old fish gobble those up. However, we've been concerned that they may either lack nutrition, or possibly still have chemicals from landscaping/lawn work, is that a concern? <Yes> We often eat shrimp and seafood at my house, and though I know fresh shrimp are quite delicious and probably great for them, are the ones at supermarkets and such fresh enough? <Yes> You know, the ones laid out on ice, that are already dead? <These are fine> Or will only the live ones, until the hour before you eat, okay? <Will learn to take bits of these> Can they OVEReat? <Can, but not common> He seems to bloat really easily while he's eating, and because I'm concerned with him overeating, I normally give the rest to our other fish. However, the few times he does get to try and eat a lot, he seems to stop himself. Do they always stop themselves before they explode =P, or should I be careful with feedings? <One should always be careful here> Since he's been with the same tank for a while now, but I suppose I should check in while I have the chance, right? He's about 7+ inches, in a 46gallon tank. A blue Gourami, a gold Gourami, a red-tailed shark, a Pleco, and 2 angelfish. The fish are all about 4-5 inches in length. He's not terrorized by any of them, never seen a mark on any of them, asides from the gouramis always having spats between themselves. Any problems with these? <Should be fine> The tank is well planted, with aged driftwood, a ton of leafy plants, an excellent & powerful filter, more plants, and err...more plants. =) No little tunnels for the Knifefish like I've read about having, but he seems to like the plants enough anyways. Should we find a suitable tunnel, anyways? <Mmm, not necessarily... I like transparent... glass "chimneys" or plastic... for viewing... but the plants are fine> Wow. Typing wayyyy too much now, sorry! ^^" For now, my mind has run out of pathetically inane questions to pester you with, so until later.... Thank you for all your help! <Thank you for writing, sharing. Bob Fenner>

Black Ghost Knife Won't Eat I bought a black ghost knife  week back and gave it a small place to hide. Since then it has been hiding inside and very few times, twice in fact, it came out in the night. Apart from this it does not eat anything. I feed it in the night to discover that the food is still floating in the morning. Will it take time to get set in the tank or is it sick? There were small molly fry in it which  I bred and it has not touched them. Is there anything wrong with it ? Is it a strong or a delicate fish? I do water changes once a week. pls advice <Your black ghost knife fish is indeed a nocturnal fish. Try small live invertebrates live worms or shrimp. After awhile you may get him to try frozen foods and then maybe pellet foods. If you can get him over to prepared foods then keeping him will become much easier. If you can't then live and or frozen foods may make him difficult to keep.-Chuck>

Feeding a Black Ghost Hello, <Hi back! MikeD here>     I am a very new aquarium owner.<Welcome to the wonderful world of fish addiction, er, keeping.**grin**>  I am obviously still learning about everything.<50 years later, me too. The learning never stops>  I just found your site yesterday and I'm loving it!!  But I do have a question regarding a black ghost knife that I bought about 3 days ago.  I currently have a 60 gal. tank with 2 parrot fish, 2 black skirted tetras <In the future tetras and often barbs, do better in schools of 5-6 rather than in pairs> 2 catfish, 2 angel, 2 Gourami, and now I just added the BGK.  Is this too crowded??<Not necessarily. My biggest concern is did you give you tank enough time to cycle, and/or that you added all, or most of your fish at one time.>  I am feeding pellets and flakes to the other fish, and got some frozen bloodworms and shrimp pellets for the BGK.<This may work, but some ghosties can be a little demanding on food choices, especially when they are first obtained>  I feed them around noon everyday.  I understand the BGK is shy<Not shy, nocturnal, which are two separate things entirely>, but he will not come out of his hiding spot when I feed the tank.  My other fish not only eat all the flakes and pellets, they also eat the bloodworms and pellets.  I'm afraid they are not leaving anything for the BGK.  Do I need to change my feeding time or habits??<Yes, the Black Ghosts are nocturnal nighttime animals that often are very reluctant to come out into the open during the day. Usually, this will gradually wear off in time, but early on the best thing to do is feed it separate, just after turning off the lights at night. You might also want to keep check and make sure that it's eating what you are offering for food.  The bloodworms will almost certainly be eaten, while the pellets are a big if for now, possibly forever.  They also relish raw shrimp (either cut up pieces of human food shrimp or the small live ghost shrimp sold as feeders in many shops) live or sometimes freeze dried Tubifex worms, daphnia, etc.. Their absolute favorite food is live earth worms like you'd use for fishing!  Some will gradually start consuming "normal" aquarium fare while most others are always somewhat demanding and require special foods>   Thank you for your help and information!!<You're welcome and I hope this helps...the Ghosts are one of my all time favorite freshwater fish species> Mike

Black Ghost Knife Help Hi there from another fishaholic!<Hi Jennifer, MikeD here> Sorry to bother you with petty questions that really don't apply to any of your other visitors, but I *really* need some help regarding my black ghost knife.<One of my all time favorite FW fish> Although I generally research fish species very thoroughly before purchasing them, I only did a little such research before buying a black ghost knife. It was really pretty much an impulse buy, though I was at least somewhat familiar with the species.<They're pretty tough if handled right> At any rate, the manager of my LFS promised me that if I purchased one, he would do just fine in a twenty-gallon, provided he had plenty of coverage and was kept completely by himself. She did say that it was pushing the limits to keep him in a 20-gallon, but that he'd do okay, even as an adult. (He's 7 inches now.)<I'm not sure why they told you to keep it alone, as they do well with many other species if the tank is arranged correctly. As to the adult part, my largest grew to about 15" if that tells you anything> Now, I'm starting to have second thoughts on that. I assume he's okay for *now* in the 20-gallon, but will he really be okay when he grows up? I have an extra 35-gallon that I haven't stocked yet but it's very well planted and decorated, as I tend to pride myself on that. The problem is, it's very hard, brackish water, and it would be a huge inconvenience to redesign and refill the whole thing. Besides, I was really looking forward to the archers and Sailfin mollies I was going to keep... But, if I need to, I'm willing to change conditions if that's what it takes to save my ghost knife. (I simply can't afford another large aquarium for him.)<OK. While he WILL eventually outgrow the 20 (20L or 20H?), they are fairly slow growers so you've got at least a couple of years before it should become a concern.> Wow, you're very patient if you're still reading this.<Still here **grin**> I guess, to get to my point, can my ghost knife stay in that 20-gallon as an adult, or even now? Or will I have to completely revamp the 35-gallon for him? Would a 35-gallon even be enough? Should I just swallow my pride and give that poor fish to somebody that can take better care of him? Just how fast will he grow, anyway? Maybe slow enough that he could stay in the 20-gallon until I could afford a new tank?<I guess I should have waited until I got here to answer, eh? **grin**> Also, the LFS lady told me that black ghost knives can be held and are even intelligent enough to recognize their handlers... is this true? Sounds a little odd...<It depends on what she means by held. If you cup your fingers in the water, they will indeed swim into your hand if you train them.  I don't know what you're currently feeding it, but they also appreciate meaty foods, with their favorite being earthworms. They'll also appreciate ghost shrimp and even a piece of raw shrimp like you'd have for dinner, unbattered, of course.  These are small cousins of the electric eel, and I'm assuming you know that they navigate by true electronic sonar. Because of this, never add another S. American Knifefish or African Mormyrids, such as "baby whales" or "Elephantnoses"...they cross each others electric signals and a true war will result> Thank you SOOOOO much for your help! <You're very welcome>

Black Ghost Knife Feeding Hello fine fishy folks, GREAT website.  I have spent hours and hours here for the past couple of years and learned more than I ever thought possible.  Thanks for the effort you all put forth. I have a simple (probably paranoid) question for you. I have had a Black Ghost Knife (Apteronotus albifrons) for the past 2 years and he is a big boy!  Looks great and is my favorite fish.  He is health, velvety black with brilliant white markings on the tail (starting to fade on the head - from age?).  He is currently sharing a tank with 3 clown loaches, 1 fire eel, and 2 black Kuhli loaches. My question is, what I feed the tank is Tetra flakes and shrimp pellets in the morning, and frozen cube (thawed of course) enriched Mysis and frozen blood worms in the evening.  Since the BGK is approximately 14 inches long, is this fare big enough for him to get enough to eat?  Should I try switching to larger shrimp/worms, etc.? Any input/opinions you care to share would be much appreciated.  I am probably just being paranoid, but can't stand the thought of him being hungry all the time and risk slowly starving him. Thank you and keep up the good work! Tom <<Dear Tom; What a great job of fishkeeping you are doing there! Your ghost is large enough to warrant more food, yes. Keep in mind this usually means more water changes :P You can try a few new things: Earthworms are a great source of protein, bought from your local fish 'n tackle bait store, or you can grow your own http://www.thekrib.com/Food/, live ghost shrimp from your LFS, chopped seafood from your local grocery: buy frozen shrimp, etc, and chop into bite sized pieces for him. It's also a good idea to soak your sinking shrimp pellets in some liquid fish vitamins, like Selcon or VitaChem (also sold at pet stores) so he is getting a decent staple. Have fun! -Gwen>>

Black ghost Knifefish  hi, I need some advice concerning my ghost Knifefish, I've got a 5ftx3ftx2ft tank(400 litres) I have 1 rather large goby an Arowana 2 angels and 1 Geophagus brasiliensis a few Kuhli loaches and a bristle nosed Plec, lol of which seem to get on fine. last week I fell in love with a ghost Knifefish but since he's been in the tank I've hardly seen him, or seen him eat anything. the goby that I've got is very greedy and I'm worried if the Knifefish getting any food, what should I do???? any advice would be greatly appreciated, thanks Julie < Your knife fish is nocturnal and will only come out a night. If you put on a red light bulb at night you will see him out an about. To make sure he is eating I would turn out the lights and then feed the tank. They can be very picky and sometimes only eat live food. I would place some live black worms in the tank after I turn out he light at least once a week. If you ever got an elephant nose then I would recommend the same thing. -Chuck> 

Black Ghost Knife Feeding Have you ever known a Black Ghost Knife to eat flake food because odd as it sounds mine just did... usually feed him on freeze dried Tubifex worms and brine shrimp and was shock not only to see him come out in the light and feed but to snag some flake away from my gourami's and clown loach. <Have seen these intelligent fish eat most everything... do need meaty foods to sustain themselves though. Bob Fenner>

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