Animal-World > Aquarium Tropical Fish > Knifefish > Black Ghost Knife Fish

Black Ghost Knifefish

Black Ghost, Black Ghost Knife Fish

Family: Apteronotidae (Ghost Knife Fishes) Black Ghost Knife Fish, Apteronotus albifrons, Black Ghost KnifefishApteronotus albifronsPhoto © Animal-World: Courtesy Ken Childs
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Our knife fish did it again... we now have 4 in the tank. We don’t have room for this many knife fish. Now I’m going to have to net one and sell it to the fish... (more)  Martha

The Black Ghost Knifefish is the most well known species of knife fish in the aquarium industry!

The Black Ghost Knifefish Apteronotus albifrons is the most popular knife fish. One reason for this is that they have been imported for decades. Other reasons include being unusual, interesting and amazingly beautiful.

It is readily distinguished from other knife fish by the white and black banded area on the caudal puduncle. It also differs from the Brown Ghost Knife Fish, also called the Long-nosed Black Ghost, because of its shorter snout and the Brown Ghost has only one small white band close to the end of its tail.

This fish is also simply known as a Black Ghost. It is a member of the Apteronotidae Family of 'ghost knifefish'. These knifefish received their unusual name because of a rumor that some tribes in the Amazon jungle believe that the souls of the dead inhabit these fish. No one can substantiate this information. It may just be a story created by the people collecting the fish, but it’s a good story!

Though it can get quite big, reaching up to around 20 inches (50 cm), this is a very handsome fish. Like other knife fish, the Black Ghost Knife Fish has a flat elongated body. It has a continuously undulating fin along the underside formed by a joining of the caudal and anal fin. Although it may appear clumsy, it has a built in ‘radar’ system that uses low voltage electricity to help it navigate. This radar system and the undulating lower fin allow it to gracefully move forwards and backwards through the aquarium.

These fish can be shy initially, but once acclimated to a new home they will generally come out to feed. Some have even been know to take food right from their owner's hand. This is a peaceful fish and will not disturb its tank mates. The Black Ghost Knifefish is somewhat sensitive to changes in the water conditions. It is also a big animal that as an adult it will require a large home of 100 gallons or more. But with its good looks and friendly disposition, this knifefish is a distinctive attraction in a large community aquarium.

Until a few years ago, all offered for sale were wild caught and had been imported from South America, mainly from Brazil. The good news is that they are now being bred in Indonesia by the thousands, so much of the pressure has been taken off the wild populations. Odds are that if you see an individual of 5 inches or more offered of sale, it was collected in the wild. Specimens smaller than 5 inches were most likely produced in and imported from Indonesia.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Actinopterygii
  • Order: Gymnotiformes (Knifefishes)
  • Family: Apteronotidae (Ghost Knife Fishes)
  • Genus: Apteronotus
  • Species: albifrons
Black Ghost Knife Fish Eating

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A young Black Ghost Knife Fish searching their aquarium for food.

Nice fish and nice aquarium! The video follows a young black Ghost Knife Fish as it surveys the various areas of its aquarium and meets its fellow tankmates while in search for food. There are quite a few awesome shots of both sides of the fish as it swims around and the video does a great job showing what this fish is like on a day to day basis.

Black Ghost Knife Fish - Quick Aquarium Care
  • Aquarist Experience Level: Intermediate
  • Size of fish - inches: 20.0 inches (50.80 cm)
  • Minimum Tank Size: 100 gal (379 L)
  • Temperament: Semi-aggressive
  • Aquarium Hardiness: Moderately Difficult
  • Temperature: 73.0 to 82.0° F (22.8 to 27.8° C)
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Habitat: Distribution / Background

The Black Ghost Knifefish Apteronotus albifrons was described by Linnaeus in 1766. They are found in South America throughout much of the Amazon River and its tributaries. The species is not listed on the IUCN Red List. Other common names they are known by are Black Ghost and Black Ghost Knife Fish.

This knife fish lives in swift moving sandy rivers and migrates to flooded forests during the wet season. Like most Knife fish they like heavily vegetated areas with a lot of hiding places. Their natural habitat is normally pretty dark and these fish have poor vision, so they use an organ that produces an electric field around themselves that will detect objects and movements around it. It helps with navigating and hunting and they also use this unique electrical field as a way to communicate with other knife fish. They are nocturnal and prey on insect larvae, insects, worms and small fish.

  • Scientific Name: Apteronotus albifrons
  • Social Grouping: Solitary
  • IUCN Red List: NE - Not Evaluated or not listed


The Black Ghost can reach up to around 20 inches (50 cm) and has a lifespan of 15 years. Its body is flat and elongated. The caudal peduncle gets very thin, almost 'rod-like'. It has a continuous fin along the underside formed by a joining of the caudal and anal fin and moves with an undulating motion. Although they appear clumsy, they have a built in ‘radar' system that uses low voltage electricity to help them navigate. This and their undulating lower fin allow them to gracefully move forwards and backwards through the aquarium.

True to its name, it has a black body, though occasionally there is a white stripe starting from the tip of its nose and running along the top of its back. It has a broad whitish band just in front of the caudal fin (tail fin) and another narrower white band just before the tip of the tail.

  • Size of fish - inches: 20.0 inches (50.80 cm)
  • Lifespan: 15 years

Fish Keeping Difficulty

This knife fish is really best for an aquarist with some fish keeping experience. The Black Ghost is a scaleless fish and and can be more prone to disease. Because of the lack of scales they are extremely sensitive to a lot of medications such as cooper. Those that are wild caught can carry parasites. It is highly recommended to have a UV sterilizer in the tank, this will aid in killing many diseases that the knife can get. They are very sensitive to water condition changes as well.

As with many knife fish they are very shy when they are introduced to the tank. It can take time to get them to eat what they need. Being nocturnal by nature makes it even more of an issue and feeding at night may be necessary.

  • Aquarium Hardiness: Moderately Difficult
  • Aquarist Experience Level: Intermediate

Foods and Feeding

The Black Ghost Knifefish are carnivores. In the wild they are nocturnal, when the sun sets and throughout the night they feed on insect larvae, insects, worms and small fish. In the aquarium this is a fish that prefers fresh or fresh frozen foods such as bloodworms, brine shrimp or blackworms.

Once acclimated to their new home, they should come out of hiding at feeding time. Some have even been taught to feed from their keeper’s hand. These fish are known to create such a bond with their owners that they will eventually lay in their owners hand and eat. Make sure to have no soaps or perfumes on your hands if you do this and sanitize before handling the fish.

  • Diet Type: Carnivore
  • Flake Food: No
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Most of Diet
  • Meaty Food: All of Diet
  • Feeding Frequency: Daily - When acclimating the Black Ghost Knifefish, offering it several feedings a day can help it get comfortable with coming out more.

Aquarium Care

This fish is scaleless and as with most scaleless fish, it is very sensitive to water condition changes. A high quality filter is a must. Weekly water changes of 30 - 50% are needed, depending on bio load. Water condition tests should be done weekly to make sure levels are not spiking.

  • Water Changes: Weekly - Do a 30 - 50% water change weekly.

Aquarium Setup

The Black Ghost Knife Fish will spend most of its time near the bottom. But a full sized Black Ghost Knifefish is a big animal which requires a big home. You will need to eventually provide a tank containing 100 gallons or more if you plan on keeping one of these beauties into adulthood. A high quality filter is a must. A UV sterilizer is a smart thing to incorporate into your tank as well, as these fish are very sensitive to medications. The UV sterilizer will kill many diseases.

Provide them with a dimly lit tank and you will have a happy Black Ghost. A fine gravel substrate and many hiding places with plants, smooth rocks or aquarium safe wood is a necessity. Some aquarists will use a clear tube for the fish to hide in. This makes it feel secure, but also the aquarist can see it. They are nocturnal and will spend most of the daylight hours hiding in a safe and secure location. They do apprecaite a moderate to strong water flow as well. Once acclimated to their new home, they should come out of hiding at feeding time. Some have even been taught to feed from their keeper's hand.

  • Minimum Tank Size: 100 gal (379 L)
  • Suitable for Nano Tank: No
  • Substrate Type: Sand/Gravel Mix - Needs a fine gravel substrate.
  • Lighting Needs: Low - subdued lighting
  • Temperature: 73.0 to 82.0° F (22.8 to 27.8° C)
  • Range ph: 6.0-8.0
  • Hardness Range: 5 - 19 dGH
  • Brackish: No
  • Water Movement: Moderate - This is a species that will apprecaite a moderate to strong water flow.
  • Water Region: Bottom - This species of knifefish spends most of its time near the bottom.

Social Behaviors

This is a peaceful fish and will not disturb its tank mates. However Black Ghosts can become aggressive with members of their own species and members of other, similar species. Other than that, they are usually quite timid. They do have a large mouth so small fish or invertebrates kept in the same tank may eventually become a meal for a hungry Black Ghost.

  • Venomous: No
  • Temperament: Semi-aggressive
  • Compatible with:
    • Same species - conspecifics: Yes - Adults may quarrel if they don't have enough space and hiding places to accomodate each fish.
    • Peaceful fish (): Monitor - While it is not necessarily aggressive, it will eat anything small enough to be considered a meal.
    • Semi-Aggressive (): Monitor
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Monitor
    • Large Aggressive, Predatory (): Threat
    • Slow Swimmers & Eaters (): Safe - They are peaceful with larger tank mates that are big enough to not be considered food.
    • Shrimps, Crabs, Snails: Threat - is aggressive - In the wild, this fish hunts at night for worms, crustaceans, insects and snails.
    • Plants: Safe

Sex: Sexual differences

Sexual differences are unknown.

Breeding / Reproduction

This species is being bred commercially in Indonesia but the method used is unknown. There are hobbyists that claim to have successfully bred the Black Ghost Knifefish in an aquarium but they seem reluctant to share the details. There is some information on this subject, scattered reports, but there is nothing yet documented from reputable sources so it will not be reproduced here. One thing for certain is that if you want to give it a try, you’ll need a big aquarium, probably containing 100 gallons or more.

  • Ease of Breeding: Difficult

Fish Diseases

These fish are hardy and disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won't have to deal with health problems or disease. The Black Ghost does not have scales which make it more prone to disease. Black Ghost are normally the first fish in a tank to show signs of ick and will twitch and rub around the tank. They respond well to most medication and normally heal quickly. NEVER use copper in a Black Ghost Knife Fish tank.

Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance.

When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your fish the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish is more likely to acquire disease.

As with most fish the African Knife are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The Black Ghost Knifefish are available all year long, especially now that they are being bred in captivity. Odds are that if you see an individual of 5 inches or more offered of sale, it was collected in the wild. Specimens smaller than 5 inches were most likely produced in and imported from Indonesia. Large specimens may command a high price, mainly due to the higher costs of shipping them. Smaller specimens are quite affordable.


Author: Ken Childs, Clarice Brough CFS, Jeremy Roche
Lastest Animal Stories on Black Ghost Knife Fish

Martha - 2020-04-17
Our knife fish did it again... we now have 4 in the tank. We don’t have room for this many knife fish. Now I’m going to have to net one and sell it to the fish store that we purchased the original 2 from.

Martha - 2019-11-10
We just learned that we accidentally bred our ghost knife fish. We got 2 about 1.5 - 2 years ago with absolutely no clue of their genders. About a two months ago we got home late and happened to notice that both knife fish were out of hiding, so we sat to watch them for a bit since they are so cool and we don’t get to see them frequently. They began swimming together in what I can only describe as a dance. We joked that they were mating, but never expected it to be accurate. We never saw any eggs, we never saw any fry, but today during a water change we discover a new knife fish - about 2-3 inches compared to the original two being about 6-9 inches. Details of our tank: 150 gallons, 78 degrees F, we shoot for weekly water changes of 20% but often in ends up be closer to two weeks. We have a large variety of other inhabitants in the tank, so we feed frozen brine shrimp, frozen blood worms, tropical flake, and algae wafers. We increased the food amount over the past few weeks since many of the smaller fish have been disappearing and we assumed it was due to night hunting. I honestly have no other details since this was completely by chance. From what I have read of the knife fish, this little guy should have died at every single stage, but he made it so we have three of these beauties now!

Gina - 2012-05-10
I have bought 2 bgkf and I have a 125 gallon tank. Both fish have died within a day of me buying them. I have 2 red tips a black shark and a rainbow shark. My water always tests fine pH is 7.0. I am confused and disappointed. I don't know what's causing the fish to die. Any help would be nice.

  • Jeremy Roche - 2012-05-11
    Could be the place you got them from. How did you acclimate them to the tank? They stress very easy so a slow acclimation is best.
  • Anonymous - 2012-05-11
    I allowed the bag to float for 15 minutes and than released them into the tank. They were active and found a hiding place. Next morning they were fine and a couple hrs later they died.
  • lauren - 2012-07-19
    Try buying them from a different place.
  • Fred - 2012-09-01
    Maybe cause there was two of them, they couldn't really identify anything cause they were both sending electrical waves that kept intercepting the others.
  • peggy - 2012-10-13
    i had gotten my first black ghost knife from petsmart on sale for 8.60 somethin like that anyway he died two days later also bought other fish and put them all togather i noticed an outbreak of ick so i treated with ick- out he must have died from that i took him and the others to be replaced and got a big run around like they didnt want to exchange for another id wasnt takin no for the answer now two days ago once i brought new one home along with others i exchanged but did not put them in the same tank since im battling ick from the outbreak from the fish i brought home that also killed my few others i had in the tank a few months before i bought the black knife and others from petsmart anyway i put the newer fish in i exchanged in a qaurintene tank 20 gallon just untill the ich clears from my 30 when i put him and the other fish in the qaurintene tank i noticed white spots on them so i put ick out in right away and the next day spots seemed to be almost gone but i lost the ghost knife , i geuss ill be takin him back and exchanging him im sure with alot of disagreeing i did call next morning to petsmart in benton harbor, mi and told them about the ick and they probley have it the guy said he diddnt but i know they do but he told me to pick up some thing called ick-attack by kordon wich cost 11.00 so before i exchange themim makin sure the ick is gone but other then that can someone please e-mail me on what i can do better or whatnot so i can enjoy the black ghost knife for a long time my e-mail is thanks and im sure ill get grief from petsmart takin back the ghost knife for the second time within 3 weeks but oh well its not my fault for the outbreak they will just have to replace him, so here is my story of my losses hopefuly no more after this woud be nice so i geuss im not the only one out here that has lost a ghost knife but maybe two wich i believe it the stores of there non knowledge of ick in there tanks that customers dont kow about or them for that matter, peggy
  • MsMonique - 2012-11-06
    I bought my first Black Ghost fish about a month ago from Petsmart and I fell in love, however about 2 weeks later I could not find it in the tank. I have a 150 gallon tank and I looked everywhere in the tank and cold not find it. No remains indicating he was dead. I just recently bought 2 more less than a week ago and they seem fine. You do have to watch the fish you get from Petsmart. I suggest not purchasing anytime from Thursday thru Tuesday as they get a new shipment in on Thursday and therefore you run the risk of disease and the fish being stressed out from the shipment. I experienced 2 bouts of ick from my fish there, before I realized it was best to have a quarantine tank set up for new fish and not to buy fish when they first get them in. I did however by my ghost fish 2 days later only because they don't keep them more than 2 days in stock due to the high demand. Thankfully my 2 have survived for 5 days today. Good luck!!
  • Breezy - 2013-03-16
    Ick is due to stress. All fish carry the ick virus, it's when they are stressed it comes out. It's like a common cold for us. Immune system is down bam we get sick. To blame it on pet stores is ridiculous. It could have been the stress from being transported to your tank,or the stress of being shipped to the store. you should be checking the fish out before you purchase it anyways, never rely on someone else even if they claim to be 'experts.' When medicating you should use half the dosage because they are a scaleless fish they cannot handle a full dose.
  • kye turnbull - 2013-04-04
    White spot is not carried by all fish! A parasite, ichthyophthirius multifilliis, it comes on plants, fish that have it, gravel or water! It's not in every fish!
  • kye turnbull - 2013-04-04
    Although you are right about the scaleless dosing.
  • k. - 2017-05-17
    That's the coolest thing I've heard in a long time!
    I can't believe that little guy lived in your filter!
    This story made my day. Thanks. Good luck with the breeding! Don't give up. .
  • Bijay B - 2018-07-08
    i had 4 black ghost .firstly i bought 2 ghosts and while im feeding the size of one earth worm exceeds its mouth size and next day morning one of them died due because stuck in day another one got white spot ich and during treating i think water temperature increased lot and it died i have only one which has white spot ich also ...i tried with with yellow medicine,methylene blue and tettra cyline also but no channge in white spot ..can someone help me ...
  • A guy - 2018-06-26
    BGK fish does not go well with sharks. They are semi agressive and they always fight. They are probably too stressed, seeing that there were sharks in the tank which caused them to die
Alvin Ong - 2018-08-06
Hey, I am getting a 85 gallon tank (largest tank I can find in Penang, Malaysia) to replace my 48 gallon tank, which is seriously small. Inside got 6 clown loach, 1 B.G. Knife fish (already 30cm, had been kept for 2.5 years), 2 bearded pleco and 5 cories. Can I add another small B.G. Knife fish? I am fascinated by the B.G. Knifefish.

  • violet - 2018-09-17
    it is not a good thing to do ;with my B.G Knife fish it was defensive and the new B.G Knife fish was gone by the next day
Sophie - 2010-02-12
Hi, I've just bought a 4inch knife fish, it's in my 190lt tank. He's with a clown loach, yoyo, pleco, cardinal tetras, harlaquins, and minnows. Was it a bad idear everyone seems fine at the momment. Please messege me sophie=price at symbol msn . com many thanks