Black Ghost Knifefish – Care, Diet & Breeding

Breeding Pair of Black Ghost Knifefish


The Black Ghost Knifefish is an unusual freshwater aquarium fish that originates from South America near the Amazonian Basin. It belongs to the Ghost Knife Fish family and is capable of both producing and sensing electric signals in the water.

They are very popular in the aquarium hobby due to their strange shape and movement. The Black Ghost Knifefish navigates itself by rippling its head to tail underside fin in a constant rhythm. Aside from the two white strings on its tail and a white stripe on its nose, the Black Ghost Knife is jet black without scales. Unknown to most beginner hobbyists the Black Ghost Knife Fish demands a very large aquarium and can continue to grow in size until it reaches its maximum length of 20”.

In the wild Black Ghosts Knifes are nocturnal and reside in tropical silty and sandy creeks, rarely seen by humans. Natives in South America believe that their departed loved ones take up residences in these Ghost Knife Fish and they are of strong cultural importance.

Black Ghost Knife with Cardinal Tetras

Black Ghost Knifefish Requirements

Temperature – 73° F to 82° F (23° C- 28° C)

pH – 6.0 to 8.0

Hardness – Soft to medium

Max Size – 1’ 6”

Min tank size – 150 gallons

Diet – Carnivore

Care Level – Moderate

Temperament – Semi-aggressive

Cost – $16 – $19.99

Other Facts and Information

The black ghost knife fish is sensitive to changes in water conditions and is not recommended as a beginner fish. Water stability is key with this species. An adult Black Ghost Knife will need a large aquarium of at least 90 gallons in size, an important factor to keep in mind when purchasing this species in the store.

Black Ghost Knifes are fairly placid and are suitable as a community fish, they do well with other large species. They are less compatible with small, slow swimming fish such as guppies and other livebearers and may be attuned to fin nipping.

Ghost Knife Fish can be very shy when introduced to the aquarium. As mentioned before, they are nocturnal creatures and generally are most active at night. It will take a number of days to weeks for the Ghost Knife to recognize you as it’s food supply, at which point the Ghost Knife should become more active during feeding times. They are infamous for being very tame and ‘pettable’. It is not recommended to touch any of your aquarium inhabitants to restrict disease and injury.


Black Ghost Knife fish are omnivorous and will readily consume a variety of live foods – such as meat and worms, or flaked foods. Since they are nocturnal, these knife fish feed on their food during the night but can be trained to eat at the same time as the rest of the aquarium.

By feeding this species several times a day, they can rotate their sleep patterns to be more active when the lights are on. Consistency is important to ensure your black ghost knifefish are active during the day when you want to see them.

How to Breed Black Ghost Knifes

Very little is known about breeding this species. Tank bred inhabitants are bred in ponds in Indonesia. Due to the large size of the adults (20”) breeding would require an extremely large aquarium. It is not exactly feasible to breed these species without dedicated ponds/aquariums but it is possible.

‘How to breed the black ghost knife fish?’ is a question which has puzzled hobbyists for many years. Successful breeding requires the following:

  • A mated pair of mature Black Ghost Knife Fish (The pair must be compatible and ready to mate, this is considered the most difficult part)
  • A very large aquarium that is in a darkened location away from noise and excessive movement
  • Giant marbles, large pebbles or plants to ensure the parents cannot reach the eggs once they have been laid (This is very important as the parents are likely to consume their own eggs after birth)
  • Water temperature of around 27 degrees is reported to be the optimum breeding temperature.
  • Consistent water changes (Recommended to do these at least every two days, between 25 and 50%). This is thought to indicate ‘wet season’ and increase the chance of breeding.

Consistency in water parameters is also very important. The black ghost knifefish have a much higher chance of successful breeding when they are free of stress in a non-threatening environment. The mother will not lay eggs if she doesn’t feel safe in the aquarium. Ponds have been reported to have a much higher success rate in breeding, however, ponds make it very difficult to control the young and collect the eggs.

Rearing the Fry

Once the eggs are laid the parent should be immediately removed from the aquarium or pond. Black ghost knifefish have little attachment to their own young/eggs in the wild and will readily consume their own spawn. Fry should be raised using infusoria followed by baby brine shrimp and then powdered flake food.

21 thoughts on “Black Ghost Knifefish – Care, Diet & Breeding”

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  2. I have a question. It’s written than minimum tank size for a black ghost knife is 150 gallon. How much can i keep in 150 gallon? Just 1 or as much as i like? Do i need a 300 gallon for a pair?

  3. I breed this fish when I’m still in Indonesia. I only use 55 gallon tank 1 female with 2 males. First batch 500-1000 eggs as they grow older and bigger eggs only between 100-200 eggs. Water change 25% everyday , oxygen level have to be high all the time. I only use sponge filter, at size 8-10 inches they breed already. Keep them in dark place all the time if you want to breed this fish successfully and live food. My ph water is 7.0 . I took the eggs and artificially hatched them , leave the eggs in other fish tank with sponge filter with strong oxygen bubbles.

  4. I am a big fan of the B.G.K.I would love to have more information on this fish and
    I would love to no if I can put it with angles.and where I can g e t them I am having a hard time getting them.and how many can I put I a fish tank

    1. Jeannie, do not put angel fish with the ghost knives. They are quick to eat the big food. You will get frustrated and end up separating or getting rid of the angel fish.

      1. my knife fish shares a tank with one chilid does anyone know why my knife fish is growing lumps on one side of his jaw and now no appetite. The lump started as one 4 months ago and now there are five right in a row I treated with bacterial meds but did not touch the lumps they continue to grow if you know please email at [email protected]

  5. Love you info, fell in awe of the black knife ghost fish upon first sight. I have a 48 gl bowfront with lots of glowfish tetras and 2 dojos.

  6. I have a 375 gallon aquarium community tank I bought two Black Ghost knife fish and about six months ago I noticed little brown egg looking objects on the large driftwood I have in the tank Today I noticed at least one knife fish about an inch long I think there may be more inside the driftwood I’m looking

  7. I have had a black ghost now for three months. He hides so much I really don’t know whether he/she is eating enough. I only put frozen blood worms in the tank twice a week because I’ve read that a steady diet of them is not good for them or the other fish in the tank. There is a log it hides in to eat. I put the bloodworm cube in there and I guess it eats. When he vacates the log the rest of the fish cleanup what is left over. I need to find out what other foods to feed it and how to feed it. It looked healthy the few times I’ve seen it and it is still alive so I know it’s eating something. Any advice would be very much appreciated.

  8. My knife fish has grown a lump under its chin, it has been growing slowly for the last 6 weeks. I don’t think it is bloat as it is still swimming around.
    Does anyone have any idea what it could be?
    Cheers Stuart

    1. my knife fish started off with one lump on side of jaw four months ago and now there are five and he is not wanting to eat bacterial meds do not help if you find out what it is please email me at [email protected]

  9. This is not a reply, but a question. My ghost knife, who is about 6 years old, is no longer looking svelte, but has developed a swollen area that looks like bloat, but the aquarium tech says that it isn’t that. “Jaws,” my knife, is still very active and eats well, but I am worried that he is going to “burst” and that he is quite sick. I don’t know what to do. Any ideas out there? Hospitalization?

  10. I have two black ghosts in my 125. A friend passed and I put theirs in my tank. I also have 11 discus a few cats and Plecos.
    While doing maintenance on my canister filters I found a baby black ghost in one.
    Totally shocked and amazed.

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