Black Ghost Knife Fish (Apteronotus albifrons)
Tue, Jun 17, 2008

Black Ghost Knife Fish Photo © phrakt
The Black Ghost Knife Fish (Apteronotus albifrons) is nearly blind and uses harmless electrical pulses to navigate through water.
Introduction
The Black Ghost Knife Fish hails from the Amazon River basin in South America. They are one of the most interesting tropical fish to watch due to their strange features.
In the aquarium, Black Ghost Knife Fish are known for their flowing movement and their unique body shape. They are similar to a graceful, rippling black curtain as they swim through an aquarium. You might also notice that their eyes are very beady, and they do not resemble “normal” tropical fish eyeballs. This is due to the fact that Black Ghost Knife Fish have a difficult time seeing.
In fact, Black Ghost Knife Fish have developed electrical organs that allow them to send out electric pulses to navigate through water. Aquarists should avoid placing other fish species that use similar electric navigation and Black Ghost Knifes together because their electrical pulses will interfere with each other confusing themselves in the aquarium.
Size
Otherwise, Black Ghost Knife Fish are very peaceful to other tropical fish in the aquarium, and they make great centerpieces for community tanks. That is, if the fish aren’t small enough to fit inside of their mouths. The Black Ghost Knife Fish are gargantuan beasts that grow up to 20″ (50 cm), and they should not be placed with smaller tetras or community fish because the Black Ghost Knife Fish will eat them. Not out of maliciousness, but they are small, moving objects that fit in the mouth; the fish doesn’t know better. Speaking of their large size, they should not be kept in tanks less than 75 gallons. Although their maximum size is 20″, they usually do not get to be this big in aquariums, and the average size in aquariums is just over a foot (12″+).
Water Parameters
Other water parameters that factor in the well-being of the Black Ghost Knife Fish are pH and temperature. The pH that can accommodate this fish is pretty forgiving, and it ranges from 6.0 to 8.0 (from slightly acidic to neutral to slightly alkaline). The temperature this fish can be kept at is forgiving as well, 76ºF to 82ºF (24-28°C). It can cover an array of water qualities, but this doesn’t mean the fish is necessarily hardy. The nitrites and ammonia should always read 0 ppm for this fish, and the nitrate should never rise too high.
Characteristics
When one first introduces a Black Ghost Knife Fish into an aquarium, the result can be pretty disappointing for the owner. They have been known to hide behind aquarium decorations, but owners should not remove the decorations in order to view their fish because it will only stress them out even more. They should be given time to adjust to their new environment which can take up to a couple of weeks. One idea is to use a large, plastic, see-through bottle that will allow the Black Ghost Knife Fish to enter and feel safe but still allow its owner to watch him from outside of the glass. Another way is to increase the amount of hiding places, and lower the lighting in the tank.
But after the Black Ghost Knife is accustomed to his tank, it can develop a strong relationship with its owners. Black Ghost Knife Fish owners are known to hand feed their Black Ghost Knife Fish beefheart. Additionally, owners are able to pet and stroke the fish, and the fish will actually run through its owner’s hands. A real interspecies relationship!
Food
Besides beefheart, Black Ghost Knife Fish can accept frozen bloodworms, shrimp pellets, brine shrimp, tubifex worms.
Medicine
Owners should be careful when medicating their fish tanks with Black Ghost Knife Fish inside. Since the fish are scaleless, they react differently to medication than fish with scales. They are more sensitive, so the doses of medication should be halved as to not endanger the Black Ghost Knife Fish.

November 24th, 2008 at 10:14 pm
i just got a new black knife ghost fish and put it in my 55 gallon tank with others and its not eating the frozen food i give it???
November 24th, 2008 at 11:56 pm
Hello justin,
The BGK fish is going to take a few weeks to adjust to new living conditions. I just got one during the summer, and I remember that it took around 2-3 weeks before it actually came up for food and was active in the tank. It’s probably scavenging for week at night, but you never see it. I would try to get a flashlight and drop some frozen food in the tank since that is when the BGK is most active. Don’t put too much in, since the BGK is still shy, and putting in too much food will only pollute the tank. It will be a slow transition before the BGK is well-adjusted.
Also, be careful that the BGK does not get ich. I remember mine got ich a few days later, but after I used CopperSafe, the ich subsided, and my BGK came out to eat voraciously seeking food.
November 25th, 2008 at 7:13 am
The Black Ghost Knife really prefers live foods , you will find it will make your bgk more active , also to sex the bgk the female will reach 25cm and stop growing her head will stay small like a juivinilles, while the male will reach 30cm and his head will protrude. They really are a great and interesting fish.
December 24th, 2008 at 6:36 pm
I have a black ghost knife who is very active but has a white slim type on his body can anyone suggest a treatment please
December 25th, 2008 at 3:34 am
What do you mean by “white slim type”? Like small, white spots?
January 6th, 2009 at 10:50 pm
Just bought a Black Ghost best thing I have spent my money on… adds a nice flavor to my tank. My one question is i set up a few places for him to hide out in a couple of clear tubes is he going to find those pleace on his on or do i have you guide him in there cause currently he is just hangin out in the back behind my plants. Can anyone give me some info about the Black Ghost and what to do and what not to do ? Thank you
January 21st, 2009 at 11:47 pm
My father in law game a BGK a month ago, about 10 cm long. is it ok to put in a 10 gallon tank?
January 25th, 2009 at 9:10 am
for fungus or finrot with these fish, use melafix – a herbal remedy (smells like teatree oil)
– it works great i have used it for several years now – other heavy metal based remideys cure the fungus but then the fish seems to die of poisoning from the medication later. i had to learn the hard way before i got this tip from a Zoo The same goes for the long-nose elephant fish; hope this helps!!
January 27th, 2009 at 11:53 am
ive had one for the last year mine eats anything you put in including flake but hes not frendily to my hand he bites it lol other than that hes never touched another fish and id say there pretty hardy fish he lives with a green terror 8″ and a 6″ jack dempsey, and a 9″ birchir and ive had no problems at all very slow growing tho i got a 65 uk gallon jewel tank with 2 filters getting a flu val fx5 sooon so i can tAKE the internals out and another point mine used to live with rummy nose tetras with no problems even tho it could of ate them just keep them well fed n they will be ok with anything!!!!!!!!!
January 27th, 2009 at 12:08 pm
dont beleve everthing you read on the net everyfish is different eg my tank a huge male gt with blue and gold gouramis n other ciclids some people say they should be in a species tank only :S supose big bobs just a pussy lol
January 27th, 2009 at 12:10 pm
he takes his agresion out on me wen im in my bedroom he attacks me for been in there lol hes only happy when he sees the red bag of hikari cichlid gold lol
March 3rd, 2009 at 5:45 pm
My light is apparently too bright for my BGK. I don’t use an aquarium light b/c my old one broke and I’m saving up to buy a new one. I walk in to the room with the lights off and can just make out its form, so I turn on the lights and it darts behind the plants. I am trying to train it to associate light with feeding time, so I can work towards hand-feeding it. Until I get a new light, how can I dim the room light?
March 25th, 2009 at 11:55 am
about that white slim you have on your knife fish, if you have any angelfish in your tank i would go to a another site and look it up but i think that maybe it could be angel fish virus. or you could just try stree relif products or vitamin supplements and keep a close whatch on you ph levels and keep that ghost knife away from your other ones for a while till you know what it is and treat it.
April 5th, 2009 at 9:26 am
I just got a small BGK, about 4 inches. For now I keep in a 35 gallon tank with 2 tetras, a blood parrot, and an angel. None of the fish bother eachother other then the tetras invading the bloods space. But I’m concerned because the BKG isn’t eating. He seems lively enough but I feel like he’s going to die. So far I’ve tried freeze-dried bloodworms and regular tropical flakes. He doesn’t even look at either. How long can he go without eating before I should get worried? Any suggestions?
April 13th, 2009 at 1:21 pm
CJ,
I am interested in any follow up experience you have. Two days I got a BGK (about 4 inches) and hides in a narrow gap between some driftwood and the side of the tank. I can still see OK. When I throw blood worms to land where he is other other fish come by and eat them – even if I feed at night befoer going to bed. So my concern is whether any food will be left for him.
I will try feeding him live worms directly. I would not try flakes as others claim BGK might not take to that too easily.
April 20th, 2009 at 9:40 am
i have the same problem as cj, i have had a BGK for a week now. it is only 4 inches. i spends all day hiding in my plants (despite placing 4 caves in the tank) and hanging around the air pump. sometimes it just doesn’t move for hours so i have to turn off the lights to get a response as they are nocturnal. I haven’t ever seen it it. even at night i put frozen brine shrimp and float it in front of it an wait but it still wont eat. this is in the day and night. i’m not too sure if it is eating if it going to starve. everything else in the tank is fine, ph, temp, minerals and water hardness are all fine and it s pretty clean too. Any suggestions?
April 22nd, 2009 at 5:34 pm
Great work.
May 1st, 2009 at 11:34 pm
Hi All
just wondering how to breed the TGK fish .
May 3rd, 2009 at 9:08 am
@CJ, Karl and Dapo:
Every BGK is a little different food-wise, it probably depends on how they were raised.
Remember that these guys are carnivores in the wild, they like meat. Mostly you can feed them on frozen Bloodworms, Brine Shrimp but I think their favourites are Misys Shrimp. Live Brine Shrimp and worms ocassionally also go over well. Make sure you keep the diet varied – bloodworms by themselves, for example, are not very nutritious. Some of my BGK’s will take flake food, but only if its based on fish meal. I’ve never seen one take a second sniff at vegetable wafers, algae wafers nor Catfish chips (which are largely vege-base with added cellulose fiber for rasping catfish).
Make sure that you don’t overfeed – siphon out any food that’s left over after an hour or so otherwise you’ll foul the tank.
Although BGK’s eyes don’t work very well they don’t like brightly-lit tanks. Make sure there’s plenty of plants and hiding places. Put your tank lights on a timer switch, if you can, for less than six hours per day then use Moon Lights (blue) or red lights to observe them feeding. I’ve found red lights work better because the other fish don’t see it and will go into night mode themselves.
BGK’s are scale-less fish like loaches. They’re sensitive to ammonia and especially nitrites in the water. Keep the tank clean. If you use any medicated treatments for white spot or fungus make sure you use half-doses or you run the risk of poisoning your BGK.
Good luck!
May 11th, 2009 at 11:58 am
I had the same issue with feeding mine when I got it about three months ago (at about 3.5 in) with other fish getting all the food before he had a chance. I found that feeding him with an aquarium plan gripper works great. I hold a piece of frozen bloodworms or brine shrimp in front of his hideout and he comes out and attacks it with great vigor. He is now over 6 inches long and is quite active, at times even during the day.
He will also eat flakes, sinking shrimp pellets, occasional earth worm, and even comes up to the top to nibble at the blanched squash that I put in for other fish. Apparently some BGK’s like to add veggies to their diet!
May 27th, 2009 at 7:59 am
I’ve had my BGK for about 8 days now and so far, I can amuse myself spending countless hours watching the tank for him (since he never turns up, even at night!) I guess he’s just getting used to the tank (either that, or he’s avoiding the stupid human ;P). He pops up every other day or so, just to remind me he’s alive!
I’ve had the same problem with the frozen bloodworms and other fish – but he’s still alive, so I’m guessing he’s living on more than water and universe juice
I think he took a snap at a shrimp pellet tonight.
He’s only a little one at 2.5 inches… hope he grows up soon… anyone know how fast BGK’s grow?
addit: lol as soon as I wrote all that stuff about him never coming out, Knifey came out for the longest he’s ever come out before, he’s dancing all over the tank as if to say “haha told you so” – *sighs* ^.^
July 4th, 2009 at 3:25 am
I have 3 BGK’s ~5″ long living harmoniously together & with 3 baby Bristlenose Cat’s, African Cichlid & lionhead goldfish for last four years.
Huge tank, heavily planted with anubias, much bogwood++, ceramic vases. I use Tahitian moonsand as substrate as all these fish love various ways to burrow in it, it’s darkness seems to assist them all to different levels of camouflage.
They are all active all the time. I use moonlighting during evening hours and combination blue/white light during day for plant oxidation. They all have very unique personalities and are so energetic.
The best advise (being a nurse also) is that one manages the water quality (PH, GH, KH, NO2, NO3, NH4) more than one feeds the fish. This is MORE important. Get in there and do water changes frequently! It is a little to ask from these magnificent beasts that tantalize our senses so much.
Pls do your water changes and learn basic biochemistry! It is mega fun & definately a worthwhile challenge. Enjoy the fishies.
July 6th, 2009 at 2:24 am
Hi I have my second BGKF and he just won’t grow. i have had him now for over a year and he is still just 3 inches long. my last kf grew to be over a foot and lived a very long time. will this one ever grow and do you have any suggestions on how to help him on his way…?? he eats normally and is active day and night. he lives in a 70gallon tank so it isn’t that he doesn’t have room to grow.
thanks
ashley
August 28th, 2009 at 2:19 am
It is a good idea to know how to care for BGK or any fish BEFORE you get it. Its not hard to do an internet search and you will find at least a few reputable sources for info on how to care for these beautiful fish. They are already stressed enough being shipped all the way from South America. Help them out by doing a little research before you bring it home and don’t know how to care for it.
August 28th, 2009 at 2:24 am
BTW, my comment was not directed toward any recently posted comments. I saw a few from a year ago and read the date wrong. Cheers!
December 8th, 2009 at 11:12 pm
I just got a BGK for a christmas gift along with two dinosaur fish. They all get along great and each has their own hiding rock to sleep in. But I noticed today that my BGK has one side with what looks like white scratches. It seems it could either be that he is scratching his side on his hiding rock when he sleeps. so i could fix that. or maybe it is ich? Im not sure what ick looks like or if it can only be on one side of the fish? These arent dots, and dont protrude. they just look like he scratched himself, but like i said, im not sure what ick loks like. if anyone knows what this is please advise. thanks!
December 9th, 2009 at 2:50 pm
why do people keep these fish in small tanks (even when they are little)? they need to be in a 75 gallon or 100 gallon tank MINIMUM. no less… not even as a juvenile. bigger tanks can ensure great water quality which in turn allows the growth for fish to be as natural as possible. the smaller tank, the more build up of hormones and other various minerals and fluids… which can stunt fish growth and harm the health of the fish.
you may be experiencing a timid BGK because your tank water isn’t up to snuff, there aren’t enough empty hiding places, the tank isn’t big enough, or you have fish that scare it. then again, it could just be the fish itself.
December 22nd, 2009 at 4:51 am
We just got a BGK. They are a really neat fish. It is still in the hiding mode so we hope to see more later. We have ours in with a dragon fish,chilids,crabs,sharks,and kissing fish. They are all roughly the same size so hope they all get along. We cant wait untill we can interact with our BGK.
December 28th, 2009 at 12:45 pm
Hi! I got my BGK about two weeks ago and my tank has come down with ich! I asked around at differint pet stores and they recomended Rid-Ich. So I added the right dose and did two treatments, but now my BGK is on the bottom of the tank, has white lines and the tip of its tail is red. I did a 45% water change and checked the condition of my water. pH and everything is fine. Also i noticed the rosy barb i have was picking on the BGK tail. I need advice please, I really don’t want to loose my BGK.
January 3rd, 2010 at 6:51 pm
@ peter if he dose not find 1 week after you got him/her slowly and carefully push him to the tube he will go inside by himself
January 3rd, 2010 at 6:58 pm
BGN hate hate frozen worms and a lot of them hate flakes
January 3rd, 2010 at 6:59 pm
srry i ment BGK