Black Ghost Knifefish Care Guide: All You Need To Know

Black Ghost Knifefish Care Guide All You Need To Know Banner

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 electrogenesis, 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.

Black Ghost Knifefish Facts & Overview

Black Ghost Knifefish

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

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 cared for properly 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 emit 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.

The water would also be warm with a fairly neutral pH.

The substrate beneath them would be soft sand that would not scratch, which is important since they are scaleless.

These tropical freshwater habitats are home to a wide variety of insects, which provide plenty of insect larvae for Black Ghost Knifefish to eat.

A captive Black Ghost Knifefish needs an environment that resembles their natural environment as closely as possible. This is simple to do, we outline how to below.

Tank Setup

As they are quite 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 cover any open inlet tubes to avoid surprises.

Since they are scaleless fish and are prone to infections, a 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 are 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.

Tank Mates

Discus make ideal tankmates

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.

Tankmates will of course have to have similar preferences regarding the water conditions too. This rules out species like Goldfish which prefer cooler waters.

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 that 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 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. Your 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 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 a 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 pets with their own hands. 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 about 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.

The parents should be separated from the eggs once they are laid. In the wild, it is common for the parent to eat the eggs; they do not appear to have any strong parental instincts.

Once the fry are released they will need to be fed a selection of small foods. These could be infusoria, baby brine shrimp, and/or broken-up flake foods.

Most aquarists do not reach the stage of raising Black Ghost Knifefish fry. If you manage it, may sure you share your story to help others and shed light on the mystery.


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

Similar to most eels, Knifefish has 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…

About Robert 468 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. Addy says:

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

  2. Gary Crow says:

    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 ?

    • Fishkeeping World says:

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

    • Dallas Marrison says:

      This is absolutely fascinating! I just got my first black ghost knife fish. I’m going to try this to see if I get similar results!

  3. Stuart Allan says:

    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?


    • Fishkeeping World says:

      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

      • Ayun Khan says:

        Ive been keeping a BGK since 14th March, 2020 now. We still havent named her yet. She is my elder brother’s favourite fish along with a Koi we keep in our pond. My bro has a special affinity for her out of the entire tropical lot.

        Ill share some of my observations here.

        The only fish my BGK is aggressive or defensive against is my Common Pleco. Idk why but the pleco is the only fish the BGK attacks whenever the pleco gets too close. Since the pleco is a pretty tanked up fish, I dont worry about it. The pleco has learned to stay away from the BGK’s territory now.

        African Cichlids try to nip at the underbelly and fins of my BGK. She had been shredded like a paper by the cichlids so I gave the stupid cichlids away. She recovered in no time.

        She likes to eat crustaceans. I had an Electric Blue Crayfish in the tank with her. After a molt, the BGK devoured the cray before he had a chance to harden up his shell. Ever since that, The BGK has had quite a growth spurt as she grew 1.5 inches in length in less then a week! I still get amazed by just remembering it

        The only tankmate my BGK is afraid of is my turtle. I have a Brown Roofed Turtle in there with her. The turtle has claimed no lives ever since the day I got him (19th March, 2020). He gives free rides to the shrimp I feed my BGK on the back of his shell.

        In the beginning, the BGK would come to the surface to eat pellets and freeze-dried worms. She did so for quite a few months but then she quit coming to the surface. Now she accepts anything that sinks to the bottom. Every once in a while, I do witness her going to the surface but its a rare event now.

        In a 150 gallons, I keep my BGK with four Tiger Barbs, six Silver Kuhli Loaches, a Common Pleco, a Dwarf Gourami, an Indian Barred Spiny Eel, and a Brown Roofed Turtle (and countless Malaysian Trumpet Snails because of the sandy substrate). Everyone gets along fine with the exception of a few baby snails getting eaten here and there by the fish.

        I hope some of these accounts fascinated you because they def fascinated me!

  4. Sandra says:

    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. Sheridan R Christensen says:

    So kinda new to this, but I got a ghost and I am having problems feeding him. it seems like the other fish eat the food before he comes out and gets it. I have 150 gal tank. could use some ideas please. thank you.

  6. Lunatra says:

    When i was a kid, I had one I my 10gal tank. It grew to about 9-10 inches. But it lived successfully for 10 years. It did die from ick when I introduced a new cave for it though. It had an angel fish and pleco living with it.

  7. Jeffrey Clarke says:

    Bought 3 ghost fish about 3 years ago. A week ago I notice I have a baby about 1-1/2″ long. I’m in shock. Never saw any eggs. I’m very surprised I didn’t suck them up while cleaning the tank. Baby stays near the top on the leafy plants. Eats the tiny pellets and gets very active at feeding. Now what? Anybody got any advice?

  8. Mary says:

    Hi Robert, I’ve had Hoover for 3 years now in a 20 gal tank. She’s a stunner and super responsive. Eats during the day with the other fish but I notice lately she eats at night as well as the population in the tank has dwindled to only 4 quests left. I have been planning to get a larger tank but was waiting to finish a remodel. Moving a 20 gal tank as opposed to a 75 gal tank is easier.
    Just in the last few weeks I noticed Hoover had a whitish film on her and wanted to deal with this organically. After some research I choose to go with a salt treatment as the article said this is like electrolyts and would help the tank. As soon as I started the treatment I noticed Hoover in a panic. Back to more research, I found your page and read that Ghost Knives are intolerant to brackish water. I have flushed the tank twice so far taking out 75% of the water and replacing with fresh. Hoover has settled down with a more regular breathing pattern but is still in shock and not swimming. I am watching closely and am debating whether to do another flush….what would you suggest and hope you get back to me soon.

    • Mary says:

      Hoover is alive and swimming today! I am so delighted! I only did two flushes on the tank figuring that would be enough disruption for her. So lucky to still have her. They are a special fish! Thank you for all the info concerning ghost knives! What would you suggest to use to rid the tank of the white fungus on her body?

  9. Cynthia Leigh says:

    I had two black ghost knifes. The first one, which I think was a male, became very friendly. I could pet him and he began to rest inside my hand. I got a second one, which I suspected to be a female. I noticed what I suspected was mating behavior consisting of swimming around “dancing” with their bodies. Low and behold, one day when I was cleaning the tank, I picked up a rock and a baby knife swam out. I moved some sub strata and saw another one, that was much younger. The female had been guarding the first baby. Sadly, I think one of the adults ate the babies. These fish are amazing! Their undulating swimming motion is beautiful to watch as is their ability to swim both forward and backward.

  10. Gigi DuPont says:

    Hi, I have a pair of clown knife fish measuring approx 20cm long. I have had them for over 2 years now. The power was out at home and being winter in Cape Town the temperature of the water dropped. The fish were acting very strangely before I realized what the problem was. They were vertical (nose down)and not moving at all, like really dead still. I thought they had died. I added some warm water and they recovered in about an hour or so. They, however developed a slimy coating much like a mucous all over their bodies. The mucous was clear but visible and slowly came off their bodies as the temperature increased. I scooped off the mucous that was now floating on the surface. I am guessing that this mucous protected the fish while the temperature was too low and the fact that it was in a stasis form was its way of protecting itself. I just need some clarification.

  11. Christine says:

    How black ghost knifefish swimming method improved their function in the environment and survival?

  12. Scotty says:

    They sleep alot i agree and allways hide i got 3 on one 110 gallon

  13. Aysha Sara says:

    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?

  14. leonie says:

    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.

  15. Robert says:

    I have 8 Ghost knife fish in a 4ft tank. The largest fish is around 12 inches long. They don’t have any special care and the other month I noticed a smaller fish around 2 inches long…. upon further investigation I have seen a few other baby fish about 1 inch long, so I assume they are breeding. Reading ghost fish articles I am led to believe that these fish are difficult to breed. I dispute all the claims that tank breeding is almost impossible.

  16. Beverley Graham says:

    Hi. I’ve had a black ghostknife fish for about 11+ years which is why I just checked their lifespan. His name is Avraham but not sure if he’s a male. He’s beautiful to watch and I have a couple catfish in with him plus a couple goldfish. They all get along really well but it is a large tank.
    Black Ghostknife are my favourite fish…

  17. Jeannie Holman says:


  18. Gaynor says:

    Hi I’ve had my knife fish for about 2 1/2 years it was about 3 inches long now he’s just under 13 inches he’s very tame takes meal worms from our fingers and is so beautiful and very loved its shame I can’t leave a video of him how big he is

  19. Robert says:

    I have been keeping Ghost Knifefish for aeound 6 years and they breed quite happiy. I get 2 or 3 new fish every year. There are no special conditions as you say in your article, they just get on with doing what they do

  20. Fadillah says:

    Funny you mention we Indonesian keep secrecy about breeding which in reality we don’t, most hobbyists probably can’t breeding is due wrong setup or let parents on the tank after they lay eggs which not good idea since they will love eating them.
    Keep look at hard leaves plant because ussually they put their egg on that and makes sure the fry get good amount of oxygen

Leave a Reply

Your email address will not be published.