7 Facts About the Black Ghost Knifefish


The Black Ghost Knifefish is a unique looking fish that is found in various freshwater habitats in South America. Its long body moves by undulating a long fin on the underside of its body. This fin allows the knifefish to maneuver very dynamically allowing it to easily navigate crevices and caves where it can hide and hunt.

Black Ghost Knifefish – Image Source: Science.org

In addition to its unique body shape, this fish has a very unique ability. For navigation and defense purposes, this fish has an electric organ discharge capability or an EOD. This organ allows the fish to emit a small electrical discharge which helps them to navigate, hunt, defend itself and communicate with other Black Ghost Knifefish. In this blog post, we will take a deeper look at this unique species and learn about its care needs in the aquarium hobby.

How Big Does the Black Ghost Knifefish Get?

This species is on the larger end of the size spectrum that tops out at 20 inches in length or 1 foot and 6 inches in length. When I say “larger end of the spectrum” I am referring to keeping them in the aquarium hobby. The Black Ghost Knifefish is one of the most popular “oddball” species in the freshwater aquarium hobby. At purchase size they are typically around ¾” to 2” in length.

Black Ghost Knifefish – Image Source: Josh’s Fish

So at first, it can appear that this species can thrive in smaller aquariums, however, their growth rate is a bit faster than one would think. The Black Ghost Knifefish grows between 4 and 5 inches in length per year. Within the first year of keeping one of these as a baby will have you caring for a ~9 inch long fish. That’s why if you are thinking about keeping this species, you plan ahead and make sure that you will have a suitable aquarium, already cycled and ready to be inhabited, for it.

Black Ghost Knifefish Aquarium Size and Set Up

Taking into consideration this specie’s maximum size and any additional species that you would like to keep with it, at least a 200 to 250 gallon aquarium would be a suitable size. Without getting too much into the specifics of other types of species that you can keep with the Black Ghost Knifefish – here is a general rule of thumb: Any tank mate needs to at least be big enough to not be able to fit into its mouth when both species are full grown – In addition to suitable temperaments of the tankmates. Depending on the sizes of the tank mates plus the Ghost Knife Fish, this will determine the minimum aquarium size that will be needed to keep this species.

In order to have this species thrive in your care, you will need to build your aquarium around its needs. One of the biggest issues with this species is ensuring that they are able to feed with other tank mates. They are nocturnal and they do not like strong lights. So they will come out to feed at night or when the tank lights are off. The Black Ghost Knifefish can swim forward and backwards very easily. This allows them to graze on food while making sure that they are not vulnerable to other species while they feed. So be sure to give them a good space where you can easily feed them.

Black Ghost Knifefish – Image Source: AquaticArts.com

Since they are a nocturnal species, they like a well decorated aquarium that has plenty of hiding spots, caves, etc. So be sure to provide them with lots of spaces to hide that they can easily navigate through. As this species grows, be sure to upgrade their hiding spots so that they can easily swim in them, comfortably hang out in them with them and make sure that they can easily exit them whenever they want.

What Do Black Ghost Knifefish Eat?

In the wild, this species eats insects, small crustaceans and fish that are small enough to fit into its mouth. In captivity this species is known to eat all kinds of live foods such as daphnia, brine shrimp, worms and feeder fish. They will also eat a variety of frozen foods as well as pellets and flake foods.

Black Ghost Knifefish – Image Source: AquariumDomain.com

How Long Do Black Ghost Knifefish Live?

In captivity the Black Ghost Knifefish has been known to live as long as 10 to 15 years.

Black Ghost Knifefish Temperament

Although this species is commonly referred to as a community fish, it has a semi-aggressive temperament. So this species will eat anything that will fit in their mouth. They are also susceptible to getting picked on by other, more aggressive species.

Black Ghost Knifefish – Image Source: Bad Mans Tropical Fish

Black Ghost Knifefish Diseases

While this species is known to be extremely hardy and will typically stay disease free in a well maintained aquarium with good water parameters, they do not have scales. This makes them susceptible to diseases like Ich. Keep in mind, if you are planning on keeping this species, or you already have one, be sure to maintain proper water parameters and temperature in order to avoid a potential Ich outbreak. Here are the recommended water parameters via LiveAquaria:

  • Temperature: 73° – 80° F
  • KH: 0 – 10
  • pH: 6.5 – 7.0
Black Ghost Knifefish – Image Source: Mori Aquatics

Black Ghost Knifefish Tank Mates

Let’s address the species itself first, you cannot keep 2 Black Ghost Knifefish in the same aquarium due to their electric organ discharge capability or an EOD abilities. In an aquarium there is just not enough space for them to have their own territories without causing an issue with one another. Bummer – I know. As for other species, AquariumSource.com recommends the following:

  • Electric Blue Acara
  • Silver Dollar Fish
  • Cory Catfish
  • Rope Fish
  • Bichir

They also recommended an Oscar Fish with a note that these 2 species will need plenty of space in order to cohabitate. So I would personally recommend avoiding it if that’s the case as the Oscar fish is known to be very aggressive at times.

And there you have it! 7 facts about the Black Ghost Knifefish. If you are interested in learning more about other species of marine life, be sure to check out the Fish Facts section of this website.

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