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FAQs on the Aba Aba, Upside Down, Feather Back Knifefish

Related Articles: Gymnarchus niloticus, Knifefishes

Related FAQs:  Bony Tongue Fishes, African Butterflyfish, Arapaimas, Arowanas, Featherfin Knives, Mormyrids, New World Knifefishes,

Aba aba knifefish; Trauma       7/1/17
Good morning, I had a accident with 2 fish that I had separated. In preparation of transitioning my 20" Aba aba knife to its own tank, it was in a divided tank opposite a single Caribe piranha.
Aba somehow ventured over the wall last night and was bitten pretty badly on the back end. His entire tail, and an additional several inches of body/flesh is gone. The Aba actually seems fine, and I have made other arrangement for housing. How much should I expect to grow back?
<Hard to state (as I only have limited first and other hand... reading, experience with this species). I will state that like many related species, this one does have "remarkable powers of regeneration". And that depending on how far forward the actual vertebrae, distal nerves are gone, may mark the limit of regrowth. To summarize, one can only keep up good conditions (water quality, nutrition) and hope for the best here.
Am sharing w/ Neale Monks here for his independent input. Bob Fenner>
<Thank you for sharing. Please send me/us follow-ups with your thought processes, experiences. Bob Fenner>
Aba aba knifefish; injured. Neale's go      7/2/17

Good morning, I had a accident with 2 fish that I had separated. In preparation of transitioning my 20" aba aba knife to its own tank, it was in a divided tank opposite a single caribe piranha.
somehow ventured over the wall last night and was bitten pretty badly on the back end.
His entire tail, and an additional several inches of body/flesh is gone.
The aba actually seems fine, and I have made other arrangement for housing.
How much should I expect to grow back?
<Assuming excellent water conditions, frequent water changes (ideally daily) until the flesh heals over, and immediate use of a good quality antibiotic medication against Finrot, there's a good chance your fish will survive. Whether it'll actually regrow its tail completely is harder to say. Most likely it'll end up with a skin-covered stump of some sort.
Cheers, Neale.>
re: Aba knifefish     7/2/17

Thank you!!
<Welcome. BobF>

aba knife fish; fdg.   /RMF      5/21/15
I have recently purchased a aba aba knife fish of 15 inch and kept it with my black Arowana in 3 ft tank on temporary bases
<Dangerous.... inappropriately small. MOVE ASAPractical to larger quarters>

and the fish is only eating live fish. Is there any way that I can change her diet to dry shrimps.
With regards,
Mehandi Shaikh
<Perhaps mixing in some of the same sort/s of fish/es (dead) w/ the dried shrimp... SEE/READ on WWM re Feeding Knifefishes of all kinds (the FAQs).
Bob Fenner>
aba knife fish; fdg. /Neale         5/22/15

I have recently purchased a aba aba knife fish of 15 inch and kept it with my black Arowana in 3 ft tank on temporary basis
<I'll say! aba (Gymnotus niloticus) get extremely large and are very aggressive. Expect an adult length of over 1 metre. They are very territorial, and usually vicious, biting anything else kept with them. An Arowana could easily be killed by one, whether directly or by being so frightened the Arowana damages itself.>
and the fish is only eating live fish.
<Very bad idea. Do NOT do this. All you are doing is introducing parasites and diseases.
Is there any way that I can change her diet to dry shrimps.
<Dry shrimps would be only occasional treats. Shrimps (and prawns and other crustaceans) contain Thiaminase. Over the long term this leads to a vitamin B1 deficiency, the cause of many problems with carnivorous fish. Do read here:
Many safe foods will be taken including tilapia fillet, earthworms, and cockles. You may need to starve your aba for a few days, but that isn't a problem. aba will take frozen foods without fuss, and some also take carnivore pellets (such as Hikari Massivore).>

With regards,
<Cheers, Neale.>

Gymnarchus niloticus with white eyes - 6/12/10
Dear Crew,
Amazing website - the wealth of information has certainly helped so many of us to care for our fish better.
<Nice of you to say so.>
I purchased a young 14 cm Gymnarchus niloticus two months ago,
<Still a baby.>
and it has been housed in a 180 litre tank with plenty of cover and filtration. I know it grows to an enormous size and I'm making preparations for a much larger tank for it.
<These fish are gigantic and notoriously aggressive. They are not really suitable for home aquaria.>
However, it's eyes have recently turned white. Nitrites and Nitrates are at a low but not completely zero, which I fear may have been the cause of the disease.
<Correct. Chronically poor water quality will cause skin infections, including damage to the cornea, which is the issue here. But I suspect physical damage is the aggravating factor, e.g., by throwing itself into the glass walls of the tank. Also be aware that live feeder fish can introduce a variety of parasites and infections, including Eye Fluke, so
should never, ever be used. Other possible causes include exposure to chlorine (i.e., incorrect/no use of water conditioner) and poor diet (specifically, vitamin A deficiency).>
I first thought it was a cotton wool-like fungus that grew over its eyes, and I have added some medication for external fungal and bacteria.
<Unlikely to help without establishing the causes.>
But after a week of treatment, it has not shown signs of getting better.
After closer examination, it seems that the lens itself are white, and thus I now suspect that it could be Cloudy Eye Disease. I want to hear your opinion on it from the photos attached before I treat with different medication.
<You really do need an antibiotic -- not an antibacterial -- and you also need to optimise water quality. Zero ammonia, zero nitrite.>
If it is cloudy eye, I understand that I will have to use antibacterial medications. As Gymnarchus are similar to Mormyrids, do you think I will need to lower the amount of medication added?
<Avoid malachite green, formalin and copper. Antibiotics and Methylene blue should be fine.>
The fish is still eating and moving around well.
<And will likely lose its eyes, unfortunately.>
Thank you for your comments,
<Cheers, Neale.>

Re Gymnarchus niloticus with white eyes -- 08/22/10
Dear Crew,
I am pleased to inform of you good news regarding the same fish that I emailed you about two months ago. After heeding Neale's helpful advice on care and medication, the baby Gymnarchus niloticus has recovered fully after treatment and quarantine.
<Excellent news.>
It's been moved to a new, properly cycled 4ft tank for it to live by itself.
<Cool. Will need more space eventually, as you realise.>
It's been a great joy seeing it recover and grow healthily, excitedly begging to be hand-fed pieces of market prawns
<Do use these sparingly because of the thiaminase issue; would use tilapia instead, if you can.>
and carnivore pellets every time the fishroom's lights are turned on. I know how huge Gymnarchus can grow to, and thus I have made plans for it to be moved to a large display tank at a friend's place. Till then, my family and I will be enjoying the care of this beautiful and surprisingly resilient fish.
<Certainly a fish with lots of character!>
<Do look out for the excellent 'Jurassic Fishes' book from TFH. Been out of print for many years, but I suspect if you can find a used copy online or in a second-hand bookstore, you'll enjoy much of the content. Cheers, Neale.>

Gymnarchus niloticus, gen... & cramming Loricariids, other madness    4/28/10
Hi guys,
<Hello Craig,>
Thanks for such a wonderful site.
<Kind of you to say so.>
I'm picking up an Aba knifefish tomorrow that is very young and small, about 4 inches, that I ordered from my LFS.
<I hope you know what you're getting yourself into here. These fish are insanely aggressive and require huge tanks.>
I currently keep two freshwater tanks, a 135 gallon and small 10 gallon.
<Neither of which is suitable for Gymnarchus niloticus.>
I know that the will require a massive tank by himself as he grows,
<Understatement if ever there was one.>
but will he be ok in my 10 gallon as a baby?
I currently keep some small Plecos in the 10 gallon, a "vampire" Pleco L007( 4"), an albino Bristlenose Longfin Pleco (3" including his long fins), a royal Pleco (3"), and a very small "snowball" Pleco (2").
<You are wildly overstocked already. Even if water quality is acceptable now, it won't be for long, and the Royal Plec alone needs a tank upwards of 55 gallons once it matures. As juveniles these Plecs might be kept together
in a 30 or 40 gallon tank, but these catfish aren't necessarily friendly fish, and Royal Plecs especially are notoriously intolerant of other Suckermouth catfish, to the degree they can kill potential rivals.
Leporacanthicus cf. galaxias gets to about 25 cm, Baryancistrus L142 to 25 cm, Ancistrus to 12 cm or so, and Panaque nigrolineatus to well over 30 cm. Bear this numbers in mind, and choose aquaria accordingly.>
I also have two snails in there to help keep the bio load balanced.
<What? Snails don't "balance" anything, and pray tell me what "bio load" might be. If the pet store told you adding snails makes the tank cleaner, then they took you for a ride.>
It has worked well for about 6 months now and the tank is doing excellent.
<Not for much longer. After six months these catfish will have grown appreciably, and really do need to be moved into a proper sized aquarium..
My goal has been to raise some of these Plecs for my 135gal tank, but only the L007 is near acceptable size for a transfer. The 135 gal has a Ruby Oscar (12"), Green Scat (she's been in freshwater for 6 years now, 9"),
BGK (10"), Jardinei Arowana (12"),
<Do you have any idea how aggressive this fish will be when it becomes sexually mature, which isn't far off.>
Jack Dempsey (7"), Common Pleco (15"), Orange Spot Plec (8"), and a "chocolate albino" Pleco. Can I raise my in this small tank for a little while?
Will he and the L007 clash? There's lots of hiding places, but am thinking I may need to move the L007 to my 135gal, or just obtain a new small tank to raise the in for now. Also as far as food goes, I was thinking live
Tubifex and frozen krill to start. Is that an acceptable well rounded diet for this young knifefish?
<Least of your problems. Gymnarchus niloticus eats anything, and provided you avoid fat and thiaminase, you'll be fine. Earthworms are good treats for new specimens, but any fresh or wet-frozen fish fillet and seafood should do.>
Thanks in advance for your help, you all are Godsends!
<Craig, you have some seriously insane ideas on mixing fish. I know it's tempting to buy one of everything, but you really can't, and just as you can "win" at Russian Roulette for a while, that doesn't make Russian Roulette a safe game. Think very carefully about what you're doing here, and what you're trying to achieve. Some of these fish are among my personal favourites, so I sense we share much in the way of taste. But there are limits to what we can do when combining oddball fish in the same tank.
Read, reflect, and act accordingly. Cheers, Neale.>

Re: Gymnarchus niloticus -- 5/17/10
Hi Neale,
Thank you so much for the speedy reply. I'm a big fan and am humbly following your advice :)
I decided to wait on the Aba and take care of my Green Spotted Scat instead (Her name is Ruby because the LFS sold her to us as a Ruby Scat)
<Plain vanilla and ruby scats end up looking the same as adults anyway.>
I REALLY want to raise an from juvenile to maturity one day, but I've been meaning to switch Ruby to brackish water for quite some time and obviously its very important.
I cycled a new 55 gallon aquarium and have Ruby in it now. I just found a WWM article, authored by none other than yourself, that says she should be slowly acclimated to SG 1.010, and to do water changes that raise the SG by
no more than SG .002 at a time. How much of a water change should I do each time? 25%? Also, what should the SG of my new water be to only raise it .002 on each change for a 55 gallon?
<Oh boy, none of this is necessary for the fish. You can dump a scat from freshwater into seawater and it'll be fine. But the problem is with the filter bacteria. If you've cycled the new aquarium as a freshwater tank, then yes, it's best to do small salinity changes so the bacteria aren't shocked. So if this was me, I'd add the Scat to the newly cycled freshwater aquarium, then do a 20% water change that day with SG 1.003 water, and then another similar water change the next weekend, and so on until the tank is SG 1.003. I'd then do weekly 20% water changes with SG 1.005 water, and again, after 4-5 weeks of this, you should find the tank is at SG 1.005.
That's fine for a good long while, six months or more, but eventually you can do a similar set of weekly water changes nudging the salinity to SG 1.008, and then again to SG 1.010. Why such small increments? Because the
freshwater filter bacteria have to die off and be replaced by saltwater ones, which they do around 1.005, and if you rush, you'll end up with the Scat in an uncycled aquarium.>
I have a bit of explaining to do on my choice of the Jardinei in my 135 gallon tank. I bought her when she was a juvenile and shortly after I brought her home one of her eyes fell out! So she has one eye and was raised in my 135 gallon "knowing her role" amongst the larger fish. I do understand she reaches sexual maturity soon, and have been keeping an eye on her, so to speak. There are plenty of hiding spaces and territories for everybody. I also realize the Plecs in he 10 gallon need to move as they grow, and am hoping to keep them in the 135 when they start to get larger, and then on to their own species tank. I'm a Plec fanatic!
<Join the club.>
Thank you for the info about the Royal Plec being aggressive. So far he has kept to himself always, I've had him for about a year and a half, but will keep this in mind when monitoring them.
<Does likely depend on the specimen. But if you spend a little time on Google, you'll find some Panaque nigrolineatus horror stories.>
Again, thanks so much for all that you do in the aquaria community and your responses!
<Glad to help. Cheers, Neale.>

Re: lungfish and love! Gymnarchus   7/29/07 WOW! Thank you so very much for this information. I better get right on building this "bullet proof" tank.. can't abandon him now! :) Thanks again, you all provide an amazing website packed with so much information, the most reliable as I can tell.. Love and light Kimmy <Good luck, Kimmy. A lovely fish, a real treasure, and one that will bring you many years of enjoyment. Cheers, Neale>

Aba Can you tell me everything you know about the Gymnarchus niloticus? I need as much info as I can find about these guys. Thank you <Please insert these names in the Google search tool on our homepage: www.WetWebMedia.com Bob Fenner> Bruce

Query re Gymnarchus Could you give me any information on the Upside down Knife fish (aba Gymnarchus), and possibly a guide price? <Gymnarchus niloticus? Please look up on fishbase.org> Could you include: length, water parameters, compatibilities, possible size & age and any other information you can get. Thanks, < http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID= 4519&genusname=Gymnarchus&speciesname=niloticus Bob Fenner>

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