The Black Ghost Knife fish, also known as Apteronotus albifrons, may not be the brightest and most colorful fish, but their elegant swimming style and eccentric looks make these fish one of the most interesting freshwater species in the hobby!

Caring for this fish, however, is not as straightforward as the others partly due to their size and special needs.

In this article, I will share with you everything I know about the Black Ghost Knife fish. By the time you are done reading, you will be able to evaluate yourself and decide whether or not this species is right for you.

Black Ghost Knife Fish Stats

Listed tank sizes are the minimum
Size: Up to 20″ (49cm)
Tank: 48 inches when small
Strata: Bottom-middle
PH: 6.0 to 8.0
Hardness: Soft to medium. dH range: 5.0 – 10.0
Temperature: 73°F to 82°F (23-28°C)


Order: Cypriniformes
Suborder: Gymnotoidei
Family: Apteronotidae
Genera: Apteronotus
Species: albifrons

– Origin and Distribution

The Black Ghost Knife fish can be found throughout the deep and murky parts of the Amazon River and its tributaries in Venezuela and Paraguay. These fish also inhabit the sandy-bottomed freshwater basins in Peru.

Otherwise known as the African Ghost Knife fish, this species has an interesting tale told by South American tribes. According to the natives of the Amazonian jungle, these fish possess the souls of the departed. Although there is no evidence to back up this story, it is a great one to tell guests!

Physical Characteristics

Unsurprisingly, the Black Ghost Knife fish features a thin, long, and knife-shaped body that is entirely black, except for a white stripe on its nose and two white bands around the base of its tail. The fish can reach up to 20 inches (50 cm) when fully grown, but the vertical width of its elongated body tapers off significantly at its tail.

This interesting fish does not have caudal and dorsal fins, but it has a large anal fin running from the base of its pectoral fins. Since it lacks a caudal fin, this black tropical fish generates momentum from its anal and pectoral fins. When the fish swims, the anal fins look like beautiful flowing drapes.

Due to its knife-shaped body, this fish can swim in reverse as easily as swimming forward. Likewise, the undulating movement brought by its thin frame and long anal fins allows it to glide around decorations with ease. Unfortunately, this species has poor eyesight.

Behavior and Temperament

These black aquarium fish have little consideration for others. Black Ghosts just want to mind their own business. As long as nobody invades their cozy space, they have no reason to pick a fight. Besides, these fish are only active at night when most of the aquarium residents are tired and resting.

– How Do Black Ghost Knife Fish See Their Surroundings?

The Black Ghost Knife fish is an electrical fish. Inside its large caudal peduncle is a specialized electric organ, and embedded in its skin are groups of electroreceptor cells.
Although its vision is close to zero, it shoots out electrical signals to find its way around, locate food, and communicate among its species.

Otherwise known as electric organ discharges (EODs), this continuous electrical wave allows the fish to:

  • determine obstacles and water disturbances
  • detect the presence of a nearby prey or predator
  • negotiate with other Black Ghosts when hunting or mating

According to studies, males will generate EODs at a higher frequency, allowing sex recognition. This species also decreases the frequency of their EODs in the presence of a more dominant Black Ghost Knife fish.

– Can a Black Ghost Knife Fish Shock You?

Fortunately, no. As an electric fish, this species generates weaker bioelectric fields compared to others.

On the contrary, the Black Ghost Knife fish are electrogenic fish. Not only do they receive electrical impulses given off by other species, but they also produce their own electrical field.

More impressively, this black tropical fish is the fastest electric-generating fish in the animal kingdom. This fish is not as powerful as the electric eel, but it can provide continuous discharges of electricity.

Tank Mates

The Black Ghost Knife fish is a territorial species. Other than that, these fish are timid, so don’t put in aggressive fish that might beat up your black tropical fish. Also, don’t add in nano fish; they will become a meal for your Black Ghost Knife fish as they grow bigger.

The most suitable tank mates for the Black Ghost Knife fish are:

  • Alligator Gar
  • Arowana
  • Bichir fish
  • Cory Catfish
  • Clown Loach
  • Electric Blue Acara
  • Freshwater Stingray
  • Oscar fish
  • Paroon Shark
  • Plecos
  • Silver Dollar fish
  • Rope fish

There are in fact several compatible species you can pair with your Black Ghost Knife fish because they mind their own business. As long as there is enough space, these fish will not get grumpy.

– Can Black Ghost Knife Fish Live with Other Electrical Fish?

Oftentimes, many people want to mix the Black Ghost Knife fish with other species of the same family. Unfortunately, doing so tends to produce a lot of problems.

Having several fish that can emit electrical signals will upset your Black Ghosts. While this may work in mammoth tanks in wholesale facilities, it won’t work in a home aquarium with limited space.


Until recently, all Black Gold Knife fish offered for sale from fish stores and specialist dealers were taken from their natural habitat.

Fortunately, there now exist numerous hatcheries in Indonesia breeding this particular species for the aquarium trade. As such, the risk of depopulation has reduced.

However, the precise method of breeding has not yet been documented. Until now, these commercial fisheries have remained secretive about their success.

Captive-raised specimens available on the market tend to be much smaller than their wild-caught cousins, but they are more tame and in far better conditions.

Black Ghost Knife Fish Care Guide

If you are a rookie in the aquarium hobby, you might find these guys too much to handle. For one, the Black Ghost Fish diet can get pretty expensive.

– Diet

The freshwater Ghost Knife fish is a carnivorous species. Although these predators may accept sinking pellets, you don’t want that to be their staple food.

As with other carnivores, the Black Ghost Knife fish will need 50% to 75% protein in their diet. Additionally, these fish need a small amount of fat for insulation.

In their natural environment, these fish feed on insect larva, worms, fry, small fish, and whatever live food that fits in their mouth. Their protein-rich diet won’t change much when they are kept in captivity.

To replicate their natural diet, offer your pet:

  • bits of steamed fish
  • a variety of live or freeze-dried foods (brine shrimp, blood worms, white worms, tubifex worms, and micro worms)
  • daphnia

It is vital to provide your fish with a varied diet to ensure they are well-nourished. Since these fish are nocturnal, feed them in the evening and later at night.

Why Won’t My Black Ghost Knife Fish Eat?

Black Ghosts are coy, especially when they are still adjusting to their new environment. When it is chow time, these fish would just dart out of their hiding place and grab food, then dart back down, and vice versa.

Don’t worry; these black aquarium fish will grow confident as they grow. In fact, they become too confident that they would hunt down smaller fish. Thus, you should carefully consider which species to add to your tank. As soon as they have settled into their new home, Black Ghosts will head out to feed during the day.

Also, these fascinating fish are notable for taking food from their owner’s palm. While it is possible to hand-feed your pet, you will need to be extremely patient.

– Water Conditions

Don’t get your water acidic. The freshwater Ghost Knife fish cannot endure brackish water. Stay within PH 6.8 to 7.8 PH range with a water hardness of 5 to 19 dGH. As far as temperature goes, 75° to 82° F is ideal. You can go a little lower or higher than the recommendations, but nothing too extreme.

You’ll need to run a high-quality filtration system that produces a fairly strong current, as well as include a UV sterilizer to help kill pathogens that could harm your fish. Depending on the bioload of your aquarium, you’ll also need to carry out weekly water changes of at least 30%. By doing so, it ensures ammonia and nitrate levels are kept to a minimum.

– Diseases

The Black Ghost Knife fish can be your companions for up to 15 years if you provide them the correct diet and appropriate water conditions.

But because they lack the scaly armor that other species have, they are more susceptible to certain diseases, including:

1. Ich

Ich is a disease caused by the Ichthyophthirius multifiliis, a protozoan parasite that attacks fish with compromised immune systems.

The disease manifests as tiny white spots resembling sugar or salt grains on the gills and body of the fish. The affected fish will scrape themselves against tank decorations in an effort to get rid of the parasites. Eventually, the fish would lose their appetite and exhibit abnormal hiding behavior.

Ich has a high mortality rate. Fortunately, you can treat it using an over-the-counter product or by raising the temperature to 86° F for four days. Carry out a water change thereafter and put the water temperature back to normal. Only by doing so can you disrupt the lifecycle of the parasite.

Do not treat the disease using copper-based medications.

2. Stress

Some sources say that the Black Ghost Knife fish is super sensitive. The truth of the matter is, any fish can endure one stress factor. Your fish could handle a slight variation in the temperature to cater to other species within a community tank. But if other problems start stacking up ― aggression, acidity, and so forth, then your pet will get ill.

You don’t want to take that chance. Therefore, you will need to optimize the water quality and prevent fluctuations in water parameters as much as possible. An excellent strategy is to invest in a water test kit to ensure the levels and readings you are getting back are accurate, so you can treat the water accordingly.

To avoid running into more problems, you need to quarantine new fish before introducing them to a community tank for at least two weeks. Watch out for potential infections during this period and treat diseases accordingly. Likewise, you should always wash and sterilize decorations before adding them to your aquarium.

Tank Setup: Size, Decor, and Equipment

The definition of a cozy home for the Black Ghost Knife fish equates to a long to-do list. Therefore, they are not recommended for the novice fishkeeper, unless of course, you are willing to go the extra mile.

– Tank Size

A 55-gallon tank is a little too small for the black tropical fish, particularly because these guys need a ton of stuff to stay comfortable.

The Black Ghost Knife fish size will shoot up 8 or 10 inches during the first year, then grow a couple of inches each year until they reach their full potential of 20 inches.

Start with a 125-gallon tank so that you can have a few years to save up for a much larger tank. If you want to keep several Black Ghost Knife fish in one tank, you need to make sure it provides enough space for each fish. Better yet, cap the number at two per tank.

– Decorations

These fish will appreciate a well-decorated aquarium filled with lots of nooks and crannies they can escape to. So before you get the Black Ghost Knife fish, make sure you already got some caves and rocks piled up to give them a sense of security. You may also use coconut shells, pleco caves, and terra cotta pots.

Take note; these fish will need larger caves as they grow. Equally important, there should be no competition for your black tropical fish. If you are getting this fish, then do not add other cave-dwelling species. The goal is to ensure your new pet feels protected.

– Plants

The Black Ghost Knife fish are not interested in plants, but they do appreciate the shade these plants provide. Since these fish do not nip plants, you can add whatever plants you see fit for your aquascape.

– Substrate

The Black Ghost Knife fish spend much of their time chilling in caves or swimming near the bottom of the tank. Since these fish do not have scales to protect them, any coarse substrate could nick their fragile skin. With that in mind, fine sand would work best as a substrate for these guys.

– Lighting

These nocturnal beauties prefer subdued lighting, as they originally live in dark, deep rivers. If your tank permits, how about you try fitting a moonlight mood light system? This will replicate a nighttime environment, thereby allowing them to come out to feed during the day.


The Black Ghost Knife fish is one of those peculiar animals that could either haunt you in your sleep or make you fall in love with its amazing attributes! From ghost stories to electrogenesis, this species will make for a killer conversation starter among your friends.

But before you make this black tropical fish a showpiece in your aquarium, take note:

  • The Black Ghost Knife can grow more than a foot. You will need a 125-gallon capacity tank to cater to this enormous fish.
  • Black Ghosts couldn’t care less what the other fish are doing, as long as they keep their distance. However, they can get scrappy towards other electrical species other than their own.
  • Invest in a high-quality filter and a solid water test kit to ensure the water parameters you are getting are accurate.
  • Feed this black tropical fish as you would feed other carnivorous species. These fish will thrive on a diet consisting of live and freeze-dried food. As they grow bigger, they will start hunting down smaller fish.
  • The Black Ghost Knife fish emit electrical signals to navigate and communicate. The electric charge these species produce is not enough to kill other fish or stun your hand.
  • These exotic beauties will appreciate plenty of shade and places to hide.

The Black Ghost Knifefish might not be suitable for a novice hobbyist. I hereby encourage you to be honest and evaluate yourself if you are ready to care for this marvelous fish. If you believe you are prepared, then devise a proper plan before you decide to bring one home.

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