Black Ghost Knife Fish (Apteronotus albifrons): Care Guide

Common Name(s)Black Ghost Knife Fish, Black Ghost Knifefish, Ghost Knife Fish
Scientific NameApteronotus albifrons
OriginSouth America
Temperature73-82°F (23-28°C)
Size19 in (50 cm) on average; Up to 23 inches (60 cm)
Minimum Tank Size100 gallons
Food & DietMicro-predator of insect larva
Lifespan15 years
Water pH6.0-8.0
Tank MatesOscar Fish, Silver Dollar Fish, Electric Blue Acara, Bristlenose Pleco, etc.
BreedingEgg spawners
DiseaseMay be susceptible to Ich and fungal infections.
Black Ghost Knife Fish
Black Ghost Knife Fish (Apteronotus albifrons)

The Black Ghost Knife Fish (Apteronotus albifrons) is an interesting aquarium fish that originates in South America. They have a long body that is shaped like a knife. They will grow to a significant size, but they are agile fish that are able to maneuver around objects in the tank. They will also live a long time if they are well cared for. As a nocturnal fish, they will feed primarily at night. These fish are known to have poor vision, but they possess an electrical organ that helps them locate their food. An organ in its tail is responsible for generating electrical energy.

These fish are found in the tropical waters of the Amazon River Basin of South America. Among some of the tribes of the Amazonian jungles, it is believed that the souls of the deceased inhabit these fish.

Black Ghost Knife Fish Care

Black Ghost Knife Fish are moderately difficult fish to take care of. They are fish that grow to a significant size, and they do not tolerate poor water quality. Therefore, a proper tank setup and regular maintenance are important. These fish aren’t reserved for experts only but require more attention and care than other hardier fish in the aquarium hobby.

Another factor to consider is that these fish do not have scales. This makes them susceptible to injuries and infections. Therefore, installing a UV sterilizer in the tank may be wise. One thing to remember about these fish is that copper-based treatments are extremely poisonous to them. If copper-based treatment is administered, the fish may begin to scratch and rub themselves around the tank. There are other proper methods of treating an infection for these fish. With early treatment and an increase in temperature (approximately 86°F), there is a good chance they can fight off the infection.


Black Ghost Knife fish are nocturnal, meaning they are most active at night and sleep throughout the day. Although they have poor eyesight, they are able to search and converse using an electromagnetic field.

They are shy fish, especially when introduced to a new habitat. After settling into the new habitat, they will emerge from their hiding location overnight and swim near the base of leafy plants and other vegetation.

While they can be shy fish, remember that if they are kept with other knife fish, they can become violent and aggressive.


Apart from two white rings on its tail and a white stripe on its nose that often runs along its back, the Black Ghost Knife fish is completely black. It has no caudal or dorsal fins. Hence it has the appearance of a knife.

There are no scales on this knife fish species. Its smooth long body is part of what makes this fish so unique.


The Black Ghost Knife Fish is native to the Amazon River and its tributaries. They can be found in the Amazon River, passing through Venezuela, Paraguay, and all the way down to Peru’s freshwater basins. The river is the perfect habitat for these fish since there are plenty of hiding places between driftwood, rocks, and dense vegetation. The water can be very muddy, have currents, and have poor lighting.

In their native habitat, the water would be warm, with a pH close to neutral.


The tank’s water temperature must be maintained at a constant level between 73-82°F (23-28°C).

Water pH & Water Parameters

The pH range for the Black Ghost Knife fish is 6.0 to 8.0, with water hardness ranging from 5 to 19 dGH.

It is important to note that freshwater fish cannot survive in brackish water.

This river-dwelling species prefers water with a moderate to high current.

Black Ghost Knife Fish Size

The Black Ghost Knife Fish is one of the largest ghost knife fish species. On average, the black ghost knife fish grows 19 inches (50 cm) long, while some grow 23 inches (60 cm) long.

Tank Size

The minimum tank size for one Black Ghost Knife Fish is 100 gallons. Since they are large fish, a large tank is needed to accommodate their size.

Keeping the fish in a tank may cause the fish to become overly aggressive and also cause health issues for the fish. Since the aquarium would be the foundation of their habitat, it is important that the fish is housed in a proper-sized tank.

Food & Diet

Black Ghost Knife Fish require a carnivorous diet of live or frozen foods. Bloodworms, prawns, brine shrimp, and tubifex are some of their favorite foods.

They are known for having difficulty adapting to dry flake and pellet foods.

Feeding them a protein-rich diet similar to what they feed in their native environment is the key to their longevity. In short, the key is to feed them what they desire, at least to some extent.

In the wild, Black Ghost Knife Fish are considered micro-predators of insect larvae.


The Black Ghost Knife fish lives for a very long time. It can survive for up to 15 years if properly looked for.

Care Guide for Black Ghost Knifefish – Aquarium Co-Op

Tank Mates

Black Ghost Knifefish grow large but aren’t the most aggressive fish species. Therefore, many species of fish are suitable as their tank mates.

Here’s a list of potentially suitable tank mates for Black Ghost Knifefish:

  • Oscar Fish
  • Silver Dollar Fish
  • Electric Blue Acara
  • Bristlenose Pleco
  • Corydoras Catfish
  • Dinosaur Bichir
  • African Rope Fish
  • Saddled Bichir
  • Geophagus
  • Angelfish
  • Sailfin Molly
  • Green Swordtail
  • Balloon Molly
  • Glass Catfish
  • Pictus Catfish
  • Rope Fish
  • Angelfish
  • Discus
  • Severum Cichlid
  • Mono Sebae

Since Black Ghost Knifefish aren’t particularly aggressive species, it should not be too difficult to find suitable tank mates for them.

As juveniles, Black Ghost Knifefish can be kept in the same tank with smaller aquarium fish such as tetras and danios. Some fishkeepers have successfully kept juvenile Black Ghost Knifefish with small fish such as Neon Tetras, Green Neon Tetras, Celestial Peral Danios, and Zebra Danios. However, keeping fully grown Black Ghost Knifefish with significantly smaller fish is not recommended since they may try to eat them.

Are Black Ghost Knife Fish Aggressive?

Despite their large size, Black Ghost Knife Fish are not particularly aggressive. In fact, they tend to be peaceful fish that keep to themselves.

That said, when Black Ghost Knifefish are kept in aquariums that are too small, it can trigger aggressive behavior. Therefore, providing a tank size of at least 100 gallons is important.

If adequate space is provided, and they are kept with other peaceful fish of similar size, there should be little risk compatibility issues.

Tank Setup

A tank setup for Black Ghost Knifefish should have medium to low lighting, plenty of hiding places, and open spaces to allow them to swim freely.

Regarding the lighting requirement, Black Ghost Knifefish are native to environments with limited lighting. Their limited eyesight and enhanced electric receptors are signs of their adaptation to such low-light environments. When setting up a low-light tank, consider its effect on other tank mates and the overall setup. For example, aquarium plants that require strong light may not be suitable.

Regarding the hiding places, this can be created with a combination of hardscapes and low-light aquarium plants. Hardscapes such as rocks and driftwood would be great since they would mimic their natural environment. Remember that Black Ghost Knifefish do not have scales, and sharp objects can easily injure them.

If you have rocks, driftwood, and other hardscapes that may be sharp or too rough, you can cover them with Java moss. Java moss are low-light plants, so they will be suitable aquarium plants in their tank.

Another great option is Java fern. This is another aquarium plant that thrives in low-light environments. Java fern has large overhanging leaves, which will help provide cover and a sense of security for the fish.

Regarding the aquarium substrate, smooth gravel or sand is recommended. Sharp or overly rough substrates should be avoided since they can cause injury to the scale-less Black Ghost Knifefish.

Do Black Ghost Knife Fish require a hiding tube?

A hiding tube for Black Ghost Knife Fish is not required, but it is highly recommended.

Of course, if the tank is set up with plenty of hiding places, the Black Ghost Knife Fish can find cover elsewhere. However, the hiding tube provides a snug hiding spot that is often difficult to replicate with natural rocks and driftwood.

Another advantage of a hiding tube is the fact that it is clear, allowing the fishkeeper to view the fish even when it is in hiding. Since they can spend long hours in hiding, this can make a significant difference to the fishkeeper. Even though it is clear and visible from the outside, the Black Ghost Knife Fish will still feel safe, based on senses from their electroreceptors.

What does the Black Ghost Knife Fish habitat look like in the wild?

Black Ghost Knife Fish are native to the upper basin of the Amazon River in South America.

The water current is usually fast-flowing, and the river can be deep. While most fish species prefer calm waters, Black Ghost Knife Fish would be the exception. It can thrive in rivers with relatively strong currents.

The river usually consists of a sandy floor.

Since this is a tropical environment, the water temperature remains relatively warm, averaging mid 80’s (Fahrenheit).


Black Ghost Knife Fish are egg spawners, and they are known to spawn during the rainy season.

Most spawns occur during the night (11 pm – 2 am). This makes sense since they are nocturnal fish.

A pair of one male and one female would spawn in areas of dense vegetation. The eggs typically hatch within a week of spawning, and the parents will not look after the fry.

Black Ghost Knife Fish – breeding (eggs)

How to Breed Black Ghost Knife Fish

Breeding Black Ghost Knife Fish is considered to be difficult, but it is possible. They have been bred in captivity and are currently being bred commercially for the ornamental fish trade.

In order to breed Black Ghost Knife Fish, place a breeding pair in a very large tank or pond. A breeding pair would require a minimum tank size of 200 gallons. Unfortunately, this requirement can make it difficult for the average hobbyist to breed this fish.

The breeding pair must be mature enough to breed. Black Ghost Knife Fish reach sexual maturity at 1.5-2 years, so this would be considered the minimum.

In addition, the male and female must be compatible in order to mate. Not all pairs are compatible and will show aggression towards each other instead of mating. In order to successfully find a mating pair, multiple attempts of pairing males and females may be required.

An alternative to choosing a mating pair is to allow the Black Ghost Knife Fish to choose their mates on their own. Of course, housing a group of fish would require a very large tank. However, if this is an option, this may result in a higher chance of success.

When multiple males are present, they will compete against each other. The males will act aggressively and try to drive the other males away from the female. The female will select a single male to spawn at night. According to a study published in the Indonesian Aquaculture Journal, a spawning ratio of two males and three females may achieve better reproductive performance. However, further research may be required before concluding on the best spawning ratio.

In order to induce spawning, maintaining good water quality is important. Daily water changes of up to 60% may help induce spawning behavior. Some aquaculture farms may administer hormones to help induce spawning as well.

After a spawn, the adults may eat the eggs. Therefore, covering the ground with large gravel may help. The eggs would fall between the gravel, preventing them from getting eaten. After a spawn, the eggs can be collected manually as well. The eggs should hatch within 3 days to a week.

Similar to the adults, the fry are also carnivorous. Feed them protein-rich foods such as small worms and pellets. Since they may be reluctant to eat during the day, it is best to feed them after dark.

Male or Female

Distinguishing between male and female Black Ghost Knife Fish can be challenging since they have very few differences. The few differences they have are rather subtle, but here are some of their differences:

  • Males tend to have eyes positioned more toward the top of their heads than females.
  • Females tend to have eyes positioned more towards the front of their heads than males.
  • Males tend to be skinnier, and females have a fuller body.
  • Females produce higher electric organ discharge (EOD) at a higher frequency than males.


Black Ghost Knife Fish are susceptible to diseases such as fin rot, ich, fungal infections, bacterial infections, and parasites.

Many of the diseases that the Black Ghost Knife Fish are susceptible to aren’t rare. In fact, many of them are diseases that would impact many other freshwater fish.

However, do keep in mind that Black Ghost Knife Fish do not have scales. Therefore, they may be more susceptible to these diseases than other fish that are protected by their scales.

Due to their lack of scales, they are significantly more susceptible to injury from sharp objects. Therefore, it is important to handle them with care and avoid keeping sharp objects in the tank.


Are Black Ghost Knife Fish Blind?

Black Ghost Knife Fish have poor eyesight but are not completely blind. Even though they don’t have strong eyesight, this is rarely a problem since they use their electric organ and receptors to sense their surroundings. Since they are most active during the night and often forage in murky waters, their electrolocation abilities are more useful than their eyesight.

Do Black Ghost Knife Fish produce electric shock?

Black Ghost Knife Fish does have the ability to produce and sense electric impulses. However, it is not strong enough to shock or stun other fish. The electric impulses are mainly used for electrolocation and communication.

Their electric discharge organs (EODs) are useful while they hunt for insect larvae. However, once again, the electric impulses are not used to shock or stun their prey. It is used to locate them.

They possess electromotor and electrosensory organs but are considered only weakly electric fish. In fact, the electric impulses are often undetectable by other fish.

How do Black Ghost Knife Fish sleep?

Black ghost knifefish sleep during the day, often nestled in crevices of rocks, driftwood, or dense vegetation. Aquatic plants with large leaves, such as Java Fern and Amazon Sword will provide plenty of cover for the fish, giving them a sense of security while they sleep. Keep in mind that these fish can be timid, so the cover will be beneficial to them.

In an aquarium environment, if you provide them a hiding tube, they will most likely sleep in there during the day.

Do Black Ghost Knife Fish have teeth?

Black Ghost Knife Fish do not have teeth, but they do have a beak-like structure.

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