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Main Index > Detailed Fish Profiles > Miscellaneous species > Black Ghost Knife Fish
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South America



Apteronotus albifrons



    One of the most stunning and odd looking fish we can keep. The black ghost is sure to create a conversation. If you can meet its needs they can live for many years.
Quick stats:
    Listed tank sizes are the minimum
    Size: Up to 20" (49cm)
    Tank: 48 inches when small
    Strata: Bottom-middle
    PH: 6.0 to 8.0
    Hardness: Soft to medium. dH range: 5.0 - 10.0
    Temperature: 73°F to 82°F (23-28°C)
Paraguay River
photo from Turismo Aventura


    Order: Cypriniformes
    Suborder: Gymnotoidei
    Family: Apteronotidae
    Genera: Apteronotus
    Species: albifrons

Common name:

    Black Ghost Knife Fish

Image gallery:

    Additional species photographs


    Badmans' Forum


    Northern, South America in the Amazon river basin

General Body Form:

    An elongated, laterally compressed species with a long anal fin that starts at the base of the pectoral fins. The caudal penuncle is also long, and the rounded caudal fin is very small. The small Dorsal fin is filamentous

    Black Ghost


    The body and fins are a jet Black color, the base of the tail fin is marked with two wide vertical bands. There is a white stripe on the back starting at the head and extending about halfway down the body.


    The aquarium for the Black ghost should be large with a small grained substrate. It should be fairly densely planted with many floating plants. The floating plants will help the fish overcome its shyness as it is nocturnal and sensitive to bright lights. Driftwood is also recommended along with some sort of inert piping for the fish to hide in. The water should be soft, and kept at a temperature of between seventy-five and eighty-two degrees. The pH should be neutral to acid. Feeding should be a mix of live tubifex brine shrimp and meaty frozen foods. The Black ghost is sensitive to water pollutants, changes in water conditions, and medications. Although timid they are aggressive to their own kind but can be housed with other large peaceful fish such as Angelfish, Discus and Gourami.

    Hand feeding
    One of our readers hand feeding his ghost


    Found in fast flowing waters of rivers and streams with a sandy bottom


    Little (or nothing) is known of their sexing and breeding habits. It has been reported that they are being bred in Indonesia

    Note 1/21/2005 here is a report of breeding, the site has pictures of the fry G&S Aquarium

Your comments:


Please remember that the following comments are personal experiences and may or may not apply to your setup. Use them as guide to help better understand your fish, like us all individuals will behave differently under different circumstances.


From: SQ
I live in Calgary, Alberta, Canada. The water is very hard, pH slightly lower than neutral. A member in a local aquarium club has found baby BGKF twice. They are probably 6 months old now and still thriving. The breeding group (5) was kept in low light and the fish were full grown. My BGKF is extremely hardy. It was about 6-7" about 9 months ago and now about 12". It has undergone a battery of antibiotics, antifungals, and antiparasitics and has never been sick. Where it's tank mates have fallen (clown loaches, angelfish, mollies), it's kept going. Currently it's kept with angels (mid-upper tank), Roseline/Denison's barbs (mid-lower tank, fast swimming schools), and clown loaches (lower-mid schooling). Such a neat fish and we're hoping it's tank mates grow big and strong with it
From: Jordan
Thank you to everyone for all the advice offered. Today I took my 9 year old son into one of the 3 pet shops that I know of in Zimbabwe which are extremely limited and we came across these B.G.K fish that we had never seen before and my son said " mum please we just have to get these sometime" I replied," my boy, if we don't get these today I doubt we may ever see them again". Great excitement we bought them in knowing that we knew nothing about them but because they seemed so peaceful and flowing tails I knew or thought I knew that we were able to introduce them to our 150 gallon tank which consists of 6 x 3inch Dwarf Gourami's . So yes this was a great way to start Jordans tank that was a Christmas present (2015) which had very limited fish and we were very unsuccessful due to the wrong types of fish and huge lack of knowledge. So today we bought the only 2 B.G.K fish in the pet shop as well as some beautiful fresh water guppies and were given 3 extra for free as the guy supervising the pet shop advised that they would be great together(no problems) while we acclimated them to the water 0f 24 degrees Celsius, I got onto the Internet and found this web page. 'Wow oh my, we have bought guppies as well and they are going to be live bait for the B.G.K (ha,ha,ha) what fools we are! Cut a long story short we found a tank for the guppies and eventually released the B.G.K 'S. Thanks to all the advice .... they immediately hid behind some drift wood and we turned the lights off and left them for 4 hours, we came back and decided to feed them with a block of blood worms, while I was holding the block under water at the back of the tank hoping for them to sink, My son suddenly shouted out " mum, mum they feeding out your hand". First day and we are so excited, we will not be tempted to throw the guppies into the tank. We have the front of the tank covered with small colorful natural stones, from half way to the back of the tank we have river sand with a lot of plants and big boulders n the 2 back corners of the tank and 1 large drift wood piece in the 1 back corner, this they love. Unfortunately I do not know the P.H of the water but this I do know that we have borehole water which is quite hard water, hopefully tomorrow I am able to drive 60km out of Harare to a well which has softer water until I am able to find a P.H meter. First day am so excited but yes I do realize its only day one, I hope no disappointments. Looking forward to watching and learning from more comments as the days go by.
From: Robert
My ghost knife is 9 inches (I raised him from 3") in a 90 gal. tank and eats black worms from my fingers at the top of the water making a loud slurping sound just like a vacuum cleaner which they resemble he is with 5 adult Discus 5 Clown Loaches, and 2 Glow Tetras and gets along with them great as well as they with him. As soon as lights are out at night he comes out like a storm eating the high protein sinking pellets and beef heart I add just beforehand his name is Shadow, not very creative but appropriate. They are a great and interesting fish and definitely catch the eye of anyone who sees them
From: Carol
I have found out that you can tell the sexes by the position of the eyes. The males will have their eyes sitting higher up to the stripe on their head, where as the females eyes are closer to the mouth and sit lower. I hope this can help others.
From: Shane
The BGK fish is very vulnerable in its juvenile stage until maybe 3 inches where the water hygiene and hiding places matter. In case they get sick (Mostly fungus) a simple half water change takes care of the fungus automatically. But once they grow beyond that, they're unbelievable nocturnal assassins and just thrive in any conditions. Mine grew to 8 inches before I gave it away to the LFS. At night, most of the fish in the aquarium sit down on the aquarium floor motionless and the BGK gets out of its hiding place minutes after the lights are turned off and gets into action. They PLUCK eyes of small fish, which I was surprised to see. Anything that is sick wont survive the night if your BGK is anything beyond 6 inches. The list of victims that were killed include 2 inch Discus, 2.5 inch Algae eaters, 3 inch angels, Chinese suckers, 3 inch crayfish, 3 inch large shrimps and also among the sick fishes of which eyes were plucked out include Mono Angels, Elephant nose fish, pleco, Clown Loaches, Pearl Gourami and what more it even killed its own partner in a fight! I have around 15 years experience in fish keeping and I am absolutely certain that it was the BGK resposible for all the deaths, I caught it plucking the eyes of the algae eater during the day after which I was absolutely sure about my doubts!!.. Also my observation is that feeding Bloodworms and shrimps make the BGK aggressive, although it is necessary to feed them such food once big enough.
From: KG
I have had two of these fish throughout the past 6 months. The first one, ended up dying due to my inability to get food to it. I attempted to feed it blood worms, but it would rarely take it, and died a week after purchasing. A month later, I purchased a large African knifefish, and I enjoyed his presence in my 150 gallon tank. I decided to then give the BGK another shot so this time I purchased one a bit larger (definitely recommenced for a large tank), around 3-4 inches. He is doing great and eating well, as log as I keep the other gouramis, mollies, platys, rasboras, danios, catfish and sharks away. He gets along so well with everyone including the large Africa knife, who is now over 7 inches long. Overall, one of the coolest fish I have owned and a must for any aquarist looking to add a new flair to the tank.
From: Taliera
We have had a lot of success with Ghost Knives in the past, having kept 4 at various times, which all died due to stupid accidents which I blame myself for. No, seriously, we have had a lot of success. They've taken to our water conditions like "a duck to water" (bad analogy), and grown incredibly quickly. I have one now, and he/she has grown in 3 months from 2 inches to 8 inches - pretty impressive! I think it's because of our daily feed of bloodworms... When I put a frozen square in, the ghost knife thrashes it back and forth, gobbling up as much as it can before the bloodworms disperse and the angelfish begin eating. I have also fed my ghost knife with high quality flake and pellets, as well as live food (which it loves - mosquito larvae and pantry moth grubs - both a good thing to get rid of!). They have very poor eyesight, but a keen sense of smell and a large mouth. On the few occasions I've seen it open its mouth, it looks like a moray eel. I think there are a few other things that make our tank such a good environment for them: having a hollow log (which it can swim in and out of, on whim), keeping an acidic pH (between 5 and 6), soft water and many plants (our large Amazonian Sword is perfect - makes it feel like it's its natural habitat). And I strongly feel that ghost knives are of a superior intelligence to most other fish. They don't just swim around and eat - they seek activities. Our ghost knife takes a slumber in the hair-grass, or a spa from the bubbles coming from an air stone. It rubs itself against soft plants. It even twirls around the electrical cables like a dolphin! Pretty cool.
From: Ashley
I've had my bgk for about 6 months now. I named him Rufus because he has the personality of a dog -- very friendly and I swear he even wags his tail! He shares a 90 gallon tank with 4 angelfish, 3 blood parrots, 2 cory cats, and a pictus cat. He's very friendly with the blood parrots, often snuggling up to them in their little caves. He's very social and comes out every time I feed the other fish to eat his portion out of my hand. He currently eats freeze dried blood worms and tubifex, but I'm looking to try new foods since he doesn't appear to have grown much. I'm also afraid he isn't getting enough food because the angelfish come over and steal the food from my hand when Rufus is trying to eat. I just bought some frozen beefheart and brine shrimp today and will try that. Our water is very hard, even with a water softener, and the pH is pretty high at 8.2, but he seems to tolerate it just fine. I did acclimate him very slowly, but he actually lived in a bucket with just a heater overnight after I bought him because I didn't come home from my mom's until the following day. We really bonded during that time and he took food right from my had after only a couple of tries. Rufus is definitely my favorite freshwater fish. (I also have a 110 gallon saltwater reef aquarium.) I would highly recommend this fish to anyone with a big enough aquarium who is dedicated to hand feeding daily, because otherwise the knife might not get enough food if the other fish eat it first. Remember, they are practically blind and operate on electrical signals to swim around. They actually like the dark better, and I need to get a lunar light for my tank -- especially after reading some of the other posts.
From: Melissa DeHaan
My BGK lives peacefully with a variety of Rainbowfish, a Clown Loach, an Orange Flame Rio tetra,a couple of Black Skirted tetras, and 4 Nerite snails. All the fish live peacefully in a 90 gallon planted tank with large rocks, driftwood, and a root system from a tree, creating a "tunnel" effect through the center of the tank, providing plenty of hiding places during the day. Water changes are performed around 30% once a week, temp. is maintained between 74-78F, and pH between 7.0-7.2. A high-flow power filter keeps the water moving quickly, with additional mechanical pre-filtration to keep particles out of the water with the high-flow rate. The BGK was about 4 inches when we brought it home 4 months ago, and is now at least 7 inches long. The BGK reacts very well to both live and prepared foods. Each day at least one White Cloud feeder (from a reliable supplier) disappears, freeze-dried bloodworms are added as the daylights go out (watch the feeding activity under led moonlights!), and Hikari Sinking Carnivore Pellets during the morning. It is somewhat shy with the daylights, but is the most graceful and amazing mover under the led moonlight! This fish has easily become one of my favorites in the tank, with its gentle demeanor and quick vertical, horizontal,and diagonal traversing across the tank under the moonlight.
From: David Billingsley
I have a breeding pair of BGK,There seams to be very little information about the breeding of them in captivity. I will give you some information on my tank set up as we have had 2 babies survive in the last 3 years. They seem to breed around this time of year. My thank is 6 foot,with 9 Discus fish sharing the tank. PH is around 6.2, Temp varies from 26 to 36 during summer as I live in central Queensland. I do half tank water change every 2-3 weeks. I feed them Fish Fuel Co Discus cubes twice a day. They contain Beef heart, blood worms and spinach. The tank has many places to hide on the bottom including tree roots,rocks and ceramic structures. The tank is situated on my veranda and receives plenty of sunlight and has many plants growing around the structures. I will take a photo of the tank setup and post it at a later date.
From: Christina
I recently purchased a 4 inch BGK about a month ago and placed him in my 55 gallon tank. I have an old resin vintage car wreck and a large chunk of driftwood with holes and openings along it and he seems happy to alternate between the the two when going about his business. He currently shares the tank with a pair of 3 inch Discus, 3 swordtails, 2 angels, 4 Tiger barbs, an 8 inch Pleco and half a dozen zebra danios. All get on really well together and I haven't had any casualties as yet. The BGK seems to prefer the bloodworms to the flake food and freeze dried blackworms which the others eat. All in all he is a fascinating fellow to watch but I think I might have to purchase one of those moon lights for better observation.
From: Christina
I have had my BGK for about a year and it is one of the most interesting fish that I have had. At the moment he is in a 75 gallon with an elephant nose, dinosaur bichir, dragon goby, angelfish, gourami's, and a stripped peacock eel and they all get along great. The best thing that you give for food are bloodworms, brine shrimp, and mysis shrimp in the short time that I have had him he has significantly grown in size. This unique fish is a must for anyone who wants a real looker in there tank.
From: Tian
I've had my Ghost Fish for about three years now and kept it in some very hard water indeed. The Ph is usually in the region of 8-8.5 and although he has only grown to about five inches he appears to be in very good health and is very hardy indeed.
From: Jeff
A very interesting fish, often hiding at day, but if you spend the couple bucks on a moonlight, this fish will really wow you. I have one that is fully grown now, easily over a foot and I got him when he was only 4" or so. He's with my 3 foot silver arowana, 8" pleco, and 14" oscar. They all get along fairly well, and over time they will learn to accept pellets. I never feed feeder fish, and unless they are quarantined for over a month there is no need to. Feeders contain very little nutrition, try and get your BGK on a good quality pellet like Hikari, as well as tubifex, blood worms, brine shrimp and earthworms.
From: Joseph Otley
Just thought I'd throw in my own input. My own Black Ghost Knife has been living happily in a tank alongside a small school of Phantom Tetra's (red and black) and so far hasn't eaten any of them! The way I get my BGK to come out is by having numerous hiding places, as mentioned above. This seems to make him happy, and he will come out to swim more. As they are a nocturnal fish, they tend to only come out when the tank lights are off...which means you don't get to see much of them. You can get around this by having a UV light, or moonlight bulb, or just a desk lamp with a red light bulb...pretty much anything that doesn't give out a harsh light. Another thing to be careful of is when medicating your tank should, for example, a case of whitespot occurs amongst your other fish. Remember that the BGK is a scaless fish, so be very careful when medicating the tank. Your best option here is to remove him from the tank, and medicate him separately. Feeding - they love bloodworm, though you can ween them onto pellets and flakes. To really see him grow to his biggest, try and get hold of some beefheart. If you're in the UK, check out for people selling this. Hope I have been able to give some advice to anyone looking into getting their own black ghost knife fish in the of luck! Joe
From: Art Bell
I bought my black ghost knife when it was 1 inch. It is now 6 inches. Its tank mates are 4 silver dollars, pinkish Chinese algae eater, brown African knife fish. They all get along just dandy probably because their sizes are close. My BGK absolutely loves frozen blood worms. It also likes high protein pellets, frozen brine shrimp. I would like to give it live blood worms but its hard to find in this area. I saw a tank with a dozen BGK. They seem to be over active with each other swimming around at different angles back and forth. When they fight they bite each others tails. I don't recommend putting more than one. I clean my tank once a week. They do seem to appreciate quality water conditions.
From: Jeff
Great tip if you own this fish! I purchased lunar lights for my 55 gallon tank and the second they flip on "Jack Knife Killer" is out and about. The lights make the tank look incredible and make the nocturnal fish very active and easy to watch. He ate out of my hand for the first time last night and it was amazing. Get the lights trust me they are inexpensive.
From: Vinny D
I came across black ghost knife fish quite by accident at the pet shop one day and just had to buy one. I was lucky to deal with the owner who understood its needs and told me to watch out for really small fish, and how some of these knife fish can be aggressive and some can be totally peaceful. So I picked a little guy (about 2 inches) and took him home. At the time I had a fairly new set up that I was slowly introducing fish to. I wanted fish that did well with a strong current since I cant stand cloudy tanks or dirty tanks and have fairly aggressive filtration in place. I bought a hollow "log" for him to make home and already had a huge roman coliseum in the tank for my smaller fish to swim in and out of. Turns out he preferred the latter and the little fish (and my tiny pleco) were forced to use the log instead of the roman ruins. I tend to hear a lot about how people go to sleep only to find a fish missing in the morning, usually something small like a tetra or guppy, in the beginning I lost a couple fish to (99.9% sure) "Mr. Wiggles" but after that he never touched another fish and I've had him now for almost 5 years. If kept comfortable they will almost always be really passive and tolerant to other fish, its also a good idea to keep him fed on a regular schedule to keep his mind from straying to nasty ideas of sneak attacks on one of his neighbors =) I've always been concerned about keeping him in good health and have found that ghost knifes can be quite hardy. I sold my home after a few years and had to move my fish (A nightmare!) to my new home and that meant putting everyone in a small container and setting up their old aquarium in its new location and hoping that they survive the stress of it all. I was pleased to find that I didn't lose a single fish, though the ghost knife didn't seem to appreciate not having his home in the moving container. One thing I love about this fish is that it has "personality", sometimes I wonder if we train them or they train us! He's learned now that I find it cute when he gets in his log and rolls upside down and just stares out the glass at me, usually he's rewarded with a few shrimp pellets and more and more I've noticed that when he's looking for a snack he'll keep an eye for me to enter the room, when he knows I'm watching he'll leave the coliseum and swim over to the log, wiggle into it (hence the name, Mr. wiggles) and then proceed to roll over and roll over till I get the hint and drop a few pellets into the water (often times I just put my hand in there and drop a couple right in front of him) after he's had his snack he'll leave and go back to his bigger home and nap the day away (if that's what he actually does in there lol). All in all I found my ghost knife to be a great few dollars spent, long lived, peaceful, smart and more hardy than often credited for. A good choice for anyone with a decent size aquarium. Oh and they're a very clean fish too! probably produces half the waste of my pleco that's 1/3 his size!







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