Black Ghost Knifefish Care Guide: All You Need To Know

Black Ghost Knifefish are very popular – they are a mesmerizing and elegant fish that will steal your heart in no time.

From ghost stories of tribes in South America to electro genesis, this fish will be an entertaining conversation starter in your home.

This fish is almost an exception to the rules of nature.

It does not have any scales or fins and its tail looks like a rod.

Read on to find out more about keeping Black Ghost Knifefish in your aquarium, from their ideal tank conditions to feeding and the best tank companions.

Care Level:Intermediate
Color Form:Black and white
Lifespan:10-15 years
Size:20 inches
Minimum Tank Size:100 gallons
Tank Set-Up:Tropical-Freshwater
Compatibility:Medium size peaceful fish

Overview of Black Ghost Knifefish

Black Ghost Knifefish

The Black Ghost Knifefish is one of the most popular Knifefish. It was originally known as Gymnotus albifrons and Apteronotus passan. But today this fish is known as Apteronotus albifrons.

Other common names which it is known by include the Apteronotid eel and the Black Knife.

An interesting story about this fish is one which is told by South American tribes. It is believed among the tribes that live in the Amazonian jungle, that the souls of the dead inhabit these fish.

The common name of this fish, the Ghost Knifefish comes from these stories.

These fish are mainly nocturnal animals and they use electrolocation to navigate dark waters.

This fish has quite a long lifespan and if they are properly cared for they will be your companion for 15 years.

It is readily available online or in pet shops for around $7.


Black Ghost Knifefish are tropical freshwater fish from South America. These are nocturnal fish that are most active at night and rest during the day.

As they are most active at night, their eyesight is not well developed, so they hunt and communicate through an electric field.

They are quite shy and not very social preferring their own company – they can become quite aggressive if kept with other Knifefish. After they settle down in the new environment, they will come out from their hiding place during the night and swim mostly near the substrate or foliage and plants.


Black Ghost Knifefish On Substrate
Black Ghost Knifefish by (Derek Ramsey) Wiki Commons

The Black Ghost Knifefish, as their name suggests, is entirely black except for two white rings on its tail and a white stripe on its nose that often extends along its back.

Unsurprisingly, it is also the shape of a knife – it has no caudal or dorsal fin.

Their body is flat and elongated, reaching up to 20 inches long when fully grown. The anal fin stretches along the body from the belly to the tail. This gives it an elegant swimming style.

This species of Knifefish does not have any scales. For this reason, this fish is very sensitive to water conditions and infections as it lacks the extra protection given by the scales.

Black Ghost Knifefish can both emit and receive electric signals. The electricity is produced by an organ found in the tail. These cells sit on the skin of the fish and are used for both communication and electrolocation.

This electrogenesis is interesting when looking at the differences between sexes. While there is no apparent dimorphism between the two sexes, it has been found that females emits higher frequencies than males.

Habitat and Tank Conditions

Apteronotus albifrons
Apteronotus albifrons by Sarah Beth (Flikr)

The Black Ghost Knifefish is found throughout the Amazon River and its tributaries, from Venezuela and Paraguay all the way down to the freshwater basins in Peru.

These waters are full of vegetation with plenty of nooks and crannies to hide. The waters are usually quite murky with low lighting and moderate water currents.

Tank Setup

As they are quite a shy fish, they appreciate a tank with many hiding places. Smooth rocks and plants are must-have features for them in your aquarium.

Remember, this is a scaleless fish so you should provide a fine substrate to avoid injuries – use sand or a very fine gravel mix. The tank should have low lighting with a strong to moderate water current.

As the water in their natural environment is quite murky, they are tolerant to a range of water conditions. However, the best water parameters to allow your fish to easily settle are a temperature of 73.0-82.0°F, a pH range of 6.0-8.0 and a hardness of 5-19 dGH.

Black Ghost Knifefish are freshwater species and can not tolerate any brackish conditions.

Some hobbyists find their fish hiding in the canister filter or tubing. Make sure that when you are setting up the tank, use pre filters or covers any open inlet tubes to avoid surprises.

Since they are scaleless fish and are prone to infections, an UV sterilizer is a good purchase to avoid complications as it helps to keep the water free of diseases.

What Size Aquarium Do They Need?

Black Ghost Knifefish are large fish and need a large aquarium of at least 100 gallons.

How Many Can Be Kept Per Gallon?

These is not an aggressive species toward other tank mates such as peaceful Cichlids, however, it becomes very aggressive when sharing small spaces with the same or similar species.

If you choose to keep these fish together, you will need to allow a minimum of 80 gallons per fish.

Suitable Tank Mates

Discus make ideal tank mates

Even though they are considered semi-aggressive fish, they are perfect for a community aquarium.

The ideal community for this fish is other peaceful similar size fish such as peaceful Cichlids or Catfish.

Black Ghost Knifefish will start to become aggressive if they are limited to small spaces and if they don’t have enough hiding spots.

They also become quite boisterous if kept with members of the same species or similar species.

Make sure any tank mates that you add are at least 6 inches in size and are quite peaceful.
The perfect community can be created using peaceful Catfish, Angelfish, large peaceful Cichlids, Discus and Corydoras.

Corydoras are great companions because they will also help keep the aquarium clean.

While your Black Ghost Knifefish is growing, you might be able to keep it with smaller size fish such as Tetras, Guppies, Barbs and Rasboras.

Small crustaceans and gastropods (such as shrimps and snails) are not a good match as they are the perfect food for your Black Ghost. They will likely be eaten during night hours.

Don’t keep these fish with other aggressive fish, or fish which are small enough to be considered food.

Keeping Black Ghost Knifefish Together

Keeping Black Ghost Knifefish together is not the best idea unless you can provide a tank large enough to let them establish and develop their own territory.

Black Ghost Knifefish Care

Black Ghost Knifefish are recommended to more experienced aquarists as they can be challenging to keep.

This fish has no scales and is quite sensitive to diseases and chemicals in the water. This is why you might want to consider investing in a UV sterilizer.

One thing to keep in mind for this fish is to never use copper-based medicines as it is very toxic to them.

Knifefish are prone to skin flukes such as the Ich disease. You fish will start to itch and rub themselves around the tank, however with the right treatment they should heal quickly. Raise the temperature up to 86°F if you spot any infection. Higher temperatures interrupt the parasite life cycle preventing reproduction and growth.

They are commercially bred in Indonesia which is great for the wild populations of South America.

When you are buying one, look at the size of it. If you get offered an individual bigger than 5 inches, it’s likely to have come from the wild.

If an individual has come from the wild, it might carry parasites and diseases. Make sure you place them in quarantine to ensure no unwanted organisms enter your pristine aquarium.


Ghost Knifefish Swimming
Ghost Knifefish Swimming by ProjectManhattan (Wiki Commons)

Black Ghost Knifefish are a carnivorous species. In the wild, they feed on insect larvae, juveniles and small fish and worms.

In your tank, this won’t change much and they should be fed with fresh or frozen food such as bloodworms, brine shrimps or blackworms.

Other alternatives are tubifex worms, krill, prawns or crickets. You can also try to feed them pellets or flakes, however, it might take a while for them to get used to this these.

They tend to avoid dry food.

It is important to keep a varied and balanced diet to ensure that your fish will receive the right vitamins and minerals for a healthy immune system.

They should be fed daily with an amount of food that they can eat in few minutes. They are nocturnal animals and should be fed in the evening or at night.

Initially, they might struggle to feed. Black Ghosts are quite shy and will take a while to come out from hiding.

Some hobbyists have also been successful to feed their pet from their own hand. This might be something that you want to try, but you will have to be patient. It can take a while to train your fish, but it will be very rewarding.


Black Ghost Knifefish are not commonly bred in tanks. Whilst there are claims from some hobbyists that they have managed to breed them, the methods are sometimes disputed.

Some specialized commercial fisheries in Indonesia have managed to breed them. However they are quite secretive of their success, so this still remains a mystery.

The most common factors to encourage breeding are:

  • Large tanks (at least 100 gallons)
  • Densely planted aquarium
  • Lots of hiding places
  • Flooding and draining the tank

Eggs are laid in a cave or a similar sheltered area. The eggs are yellow and about 0.08 inches in diameter; they usually take 3 days to hatch.


Black Ghost Knifefish are very popular, they have a mesmerizing swimming style and can be very friendly once settled in the tank.

Similarly to most eels, Knifefish have an electro-sensory system used for location detection and communication.

As they are quite sensitive to diseases and can be a bit picky with food it is recommended that you gain some experience before keeping these fish.

This is a nocturnal fish and will be most active at night. They are carnivores and will mainly feed on worms, brine shrimps and insects.

Over the years, aquarists have successfully trained their Knifefish to eat from their own hands – if you want to dedicate some time to this adventure, maybe you can get them eating from your hands too!

Have you already kept a Black Ghost Knifefish? Tell us about your experience in the comments section below…

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About Robert 329 Articles
Robert Woods is the creator of FishKeeping World, a third generation fish keeper and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America and the Nature Conservancy.


  1. A peaceful and shy fish. I am keeping it with some jewel cichlids, angelfish, bala shark and a silver arowana.

  2. I keep a Ghost knife in a tank close to the sofa. It Hid all day until I turned on a blue tooth speaker close to the tank and played music through it . I looked round to see it swaying about on its tail next to the glass in the middle of day. It started moving about the way they do mimicking an underwater ballet in reverse. It’s picking up the Bluetooth signal from the phone . This excited it and makes it feel it more at ease when it senses it . I turn off the blue tooth and it’s back into the log . I keep the phone and speaker on all day now so it can groove to the sounds. Could these Bluetooth signals mimick other fish in it natural habitat ?

    • Hi Gary, thanks for sharing this, this is fascinating! I have no experience of this happening before. Many thanks, Robert

  3. My knife fish has a bulge under its chin? It has been growing slowly over the last 6 weeks.
    Would you have any idea what this could be?


    • Hi Stuart, it’s difficult to tell without being able to see it, but a single lump is most likely a cyst. Probably lymphocystis which is viral. To treat this you will need to do all you can to reduce stress, make sure water parameters are perfect, feed regularly, remove any fish which are causing stress etc. Thanks, Robert

  4. Have had my ghost thats his name for 2 months sleeps in the canopy of the plants i stroke him to wake him up and feed him by hand love this fish

  5. My ghost fish started hiding by the filter nut as it likes to sleep I didn’t think it was a problem.
    Today I cleaned the tank but after some minutes I saw that it wasn’t moving.
    I tried moving it with my fingers but it won’t move.
    It is dead?

  6. I had my ghost knife for about 10 years, he was already around 25 cm when he was given to me. He was a part of the family loved by everyone but unfortunately we lost him about a month ago. John was his name and he was very friendly eating out of our hands and always rubbing his cheek against our fingers for a pat before taking his bloodworm. He was amazing to watch and would always make our day by putting on little performances for us whenever he knew we were watching. I highly recommend a ghost knife to anyone with a love of unique fish. I will be purchasing a new one eventually when i am ready.

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