The African Knife Fish Xenomystus nigri is a most intriguing fish for many Aquarists. This is one of the most popular species of knife fish available. Most species of knifefish are very shy and rarely seen during daylight hours. But the African Knife is a member of the Notopteridae family which contains some of the more outgoing species.

Some of the members of the Notopteridae family, such as the Clown Knifefish, can grow to huge proportions. The African Knifefish can grow pretty big too in the wild, as large as 12 inches. But a maximum size of around 8 inches is more realistic for a tank raised specimen.

The African Knife Fish has a flat body with an arched back. It is often confused with the Bronze FeatherbackNotopterus notopterus but can readily be distinguished because it lacks a dorsal fin. Its body color is a uniform blackish gray brown. Its anal fin and caudal fin (tail fin) are joined, giving it a long continuous fin along the underside. This fin undulates, allowing it to move either forwards or back wards, making it a very graceful swimmer. It has a number of common names it can be found by including African Brown Knife Fish, Brown Knife Fish, and Black Knifefish, along with combinations of these terms like Brown African Knifefish, African Black Knifefish, and Black African Knife Fish.

This is one of the easiest species of knifefish to care for. The African Knifefish is hardy and generally more outgoing than other species of knifefish. This knifefish makes a good candidate for a community aquarium containing medium to large sized fish. An interesting characteristic of this fish is its ability to emit a bell-like or barking sound, produced by ejecting air from its swim bladder. Since they are wild caught, they may seem shy at first, but given time they will come out of their shell. Yet being nocturnal they will tend to be most active at night.

African Knife Fish

Scientific Classification


African Knife Fish – Quick Aquarium Care

Aquarist Experience Level:Intermediate
Aquarium Hardiness:Moderately hardy
Minimum Tank Size:55 gal (208 L)
Size of fish – inches11.8 inches (30.00 cm)
Temperature:72.0 to 82.0° F (22.2 to 27.8&deg C)

Habitat: Distribution / Background

The African Knife Fish Xenomystus nigri was described by Günther in 1868. They are found in many of the coastal rivers of Africa including the Congo, Nile, Niger, Ogooue, and Chad River basins. Most of the specimens that make it into the aquarium hobby are exported from Nigeria.

The species is listed on the IUCN Red List as Least Concern (LC). But it has a wide distribution with no known major threats. Other common names they are known by are African Brown Knife Fish, Black Knife Fish, Brown Knife Fish, Brown African Knifefish, African Black Knifefish, and Black African Knife Fish.

African Knife Fish are normally found in quiet waters overgrown with vegetation. These fish are mostly nocturnal and hunt at night for snails, crustaceans, insects, worms, and smaller fish.

  • Scientific Name: Xenomystus nigri
  • Social Grouping: Solitary
  • IUCN Red List: LC – Least Concern


The African Knife Fish can reach up to 12 inches (30 cm) in the wild, but aquarium raised specimens are usually smaller, reaching around 8 inches (20 cm). The uniform blackish gray brown body of the African Knifefish is flat and elongated with an arched back. It has a continuous fin along the underside formed by a joining of the caudal and anal fin. It is a graceful swimmer and this fin allows it to move both forwards and backwards. These fish have no dorsal fins.

It has a large mouth and two short barbels used for hunting. When not hiding it will normally be seen swimming with its head down and barbels close to substrate hunting for food. The barbels help to locate food. Like other knifefishes, it is a nocturnal predator that also uses electrical fields to navigate and find prey.

Its scales are very small giving them an almost scaleless appearance with the only break being the lateral line. The lateral line is this fishes most important sensory apparatus, It has nerve filled pits throughout which gives it the ability to swim in lightless waters by emitting electrical pulses. An interesting characteristic is its ability to emit a bell-like or barking sound, produced by ejecting air from its swim bladder.

  • Size of fish – inches: 11.8 inches (30.00 cm) – In the wild, the African Knifefish can grow as large as 12″ (30 cm), but a maximum size of around 8″ (20 cm) is more realistic for a tank raised specimen.
  • Lifespan: 10 years – Their average life expectancy runs between 3 – 7 years, with an occasional lifespan of 10 years.

Fish Keeping Difficulty

These knifefish are very hardy after the first 30 days in a new environment. These fish are mainly wild caught and can be very timid and hard to fed at first. So there is a high mortality rate during this acclimation time. Once you get past the first 30 days they are very easy to take care of. Making sure they are getting their share of the food is the hardest part. They are not only shy but also normally only eat at night unless trained to eat during the day, which can be done.

  • Aquarium Hardiness: Moderately hardy
  • Aquarist Experience Level: Intermediate

Foods and Feeding

The African Knifefish are carnivores. In the wild they begin to eat when the sun sets and continue throughout the night, feeding on worms, crustaceans, insects and snails. A tank of around 55 gallons is large enough to keep an adult in good condition for all of its life. They are one of the few species of knife fish that will eat dried foods such as flakes and sinking pellets. A varied diet is important so be sure to also feed some fresh or frozen foods such as brine shrimp or bloodworms. They will eat small fish but this is more of a warning that small tank mates may disappear, not a suggestion for feeding.

  • Diet Type: Carnivore
  • Flake Food: Occasionally
  • Tablet / Pellet: Yes
  • Live foods (fishes, shrimps, worms): Most of Diet
  • Meaty Food: All of Diet
  • Feeding Frequency: Daily

Aquarium Care

This species of knifefish needs clear and pristine water to survive. High quality filters are necesary and there needs to be away that the filters do not create to much of a current. Weekly 30 – 50% water changes should be done, depending on the bio load. These fish are very sensitive to water changes and the water should be tested often to assure that you will have a healthy fish.

  • Water Changes: Weekly – Do a 30 – 50% water change weekly.

Aquarium Setup

The African Knife fish will spend most of its time near the bottom, although they will occasionally swim to the surface to grab a gulp of air. A tank of around 55 gallons is large enough to keep an adult in good condition for all of its life. The African Knife fish does best in a well planted tank with hiding places amoung rocks and drift wood and some open area for swimming. These fish do need a good amount of unobstructed swimming room as well. Plants are best especially along the back and sides to leave some open area for swimming.

Plants with long twisted roots are best and offers hiding places for your Knife Fish. These are nocturnal fish and appreciate floating plants to break up and help subdue any light. Clay flower pots make great caves for these fish so they have a safe place to take refuge. Soft sand is the best choice for substrate. To get the most enjoyment out of this fish add some Moonlight LED lights to make viewing this fish easier as they will tend to hide when normal tank lights are on.

  • Minimum Tank Size: 55 gal (208 L)
  • Suitable for Nano Tank: No
  • Substrate Type: Any
  • Lighting Needs: Low – subdued lighting – Prefers low lighting but can be comfortable in aquariums with moderate to high lighting if there are places to hide. Add Moonlighting LED lights to get a good viewing of your knife.
  • Temperature: 72.0 to 82.0° F (22.2 to 27.8&deg C)
  • Range ph: 6.0-8.0
  • Hardness Range: 5 – 15 dGH
  • Brackish: No
  • Water Movement: Weak
  • Water Region: Bottom – This species of knifefish will spend most of its time near the bottom, although they will occasionally swim to the surface to grab a gulp of air.

Social Behaviors

They are peaceful towards other species but adults will sometimes turn aggressive towards others of their own kind. Younger fish like to be in groups, but as they mature they become solitary fish. Knife fish can co-habitat if that are given about 55 Gallons per knife. They do have a relatively large mouth so smaller tank mates may disappear. Some of the Mormyridae fishes, such as the Elephantnose and the Baby Whale make good tank mates as do Synodontis catfish.

  • Venomous: No
  • Temperament: Semi-aggressive
  • Compatible with:
    • Same species – conspecifics: Sometimes – Get along when young, and adults can co-habitat if that are given about 55 Gallons per knife.
    • Peaceful fish (): Monitor – The African Knifefish is a carnivore and it will eat smaller fish.
    • Semi-Aggressive (): Threat
    • Aggressive (): Threat
    • Large Semi-Aggressive (): Threat
    • Large Aggressive, Predatory (): Threat
    • Monitor – They are peaceful with larger tank mates that are big enough to not be considered food.
    • Shrimps, Crabs, Snails: Threat – is aggressive – In the wild, this fish hunts at night for worms, crustaceans, insects and snails.
    • Plants: Safe

Sexual differences

Sexual differences are unknown. During spawning the female will become rounder and more colorful then the male.

Breeding / Reproduction

This fish has been bred in an aquarium but is extremely difficult. When spawning, these fish prefer quiet water with lots of vegetation for hiding. The male knife will start the courtship by making a barking sound to attract the female. During spawning is the easiest time to tell the difference between the male and female. the female Knife will be rounder in shape and more colorful around this time. She will the lay around 200 eggs and guard them until they hatch.

  • Ease of Breeding: Difficult

Fish Diseases

These are very shy fish initially. It sometimes takes time to get them to eat and break their shyness. Most African Knife Fish have the hardest time in the first 30 days of change and the mortality rate is the highest during that time. Overall these fish are hardy and disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease.

Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. Because these fish eat live food, disease can be passed to them from their foods. Make sure to quarantine live food before feeding.

A good thing about the African Knife is that due to their resilience, an outbreak of disease can often be limited to just one or a few fishes if you deal with it at an early stage. When keeping more sensitive types of fish, it is common for all fishes to be infected even before the first warning signs can be noticed. The best way to proactively prevent disease is to give your fish the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish is more likely to acquire disease.

As with most fish the African Knife are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.


The African Knifefish is commonly available.



 Xenomystus nigri (Image Credit: Haplochromis, Wikimedia Commons CC BY-SA 3.0 Unported)