Black ghost knife fish guide

Black ghost knife fish (Apteronotus albifrons) is one of the most unusual freshwater fishes that you may encounter in amateur aquariums. The fish has nocturnal habits. During the day time it is rather timid and quite often stays in a shelter on a tank bottom.

Habitat in the wild

In the wild black ghost knife fish originates in upper basin of Amazon river over the territory of Bolivia, Peru, Brazil and Colombia. The fish prefers slow black waters (water with large amount of tanning agents produced by fallen leaves).

The black ghost knifefish has nocturnal habits and it tends to hide in some shelter during a day (under snags or in shore holes). The fish tries to stick to a certain area, which it guards from the species of its kind. Apteronotus feeds on larvae of various insects and juveniles.

In Amazon river habitat has rather low lighting and the fish has quite poor eyesight due to this. To compensate shortness of vision the black ghost knifefish generates low electric field around itself due to which it senses any movements and defines objects.

This electric field helps the fish to hunt and navigate; except this it helps Apteronotus to communicate with the species of its kind and to find females.

Scientific NameApteronotus albifrons
Common NamesBlack ghost knife fish; black ghost fish
Range and habitatSouth America
Size50 cm (20 in)
Lifespan10 years
Ease of keepingDifficult
Minimum tank size105 US gallons (400 L)
Temperature75-82 °F (24-28 °C)
Water hardness5-20 dGH


Black ghost knife fish body is elongated and has no scales, it gradually narrows towards the tale. Its abdomen is quite flat, the head is large and the mouth is pointed. The black ghost knifefish doesn’t have abdominal and dorsal fins, though its anal fin is rather well developed and it stretches from the head to its tail. Due to waving motion of the anal fin Apteronotus can move in any direction.

The tail fin is relatively small. The body is black with a white line on its back and two yellow-white transverse stripes on its tail stalk.

The black ghost knifefish is one of those using bioelectrogenesis and around its tail stalk it has an organ that irradiates low electrical pulses, due to which the fish navigates in dark water. In the wild black ghost knife fish can grow up to 50 cm (20 in) long, in a tank it is up to 40 cm (16 in). The lifespan is 10 and more years.

Difficulties in keeping

The black ghost knifefish is recommend for experienced aquarists to keep. Since the fish has no scales it is very sensitive to diseases and chemicals in tank water. It is recommend to have an external filter with UV sterilizer, which decreases chances of any diseases development. The fish is also sensitive to tank water parameters and their abrupt change.

Like many similar fishes Apteronotus is timid and hesitant, especially when put in a new tank. Another problem is that it is a nocturnal predator and it should be fed at night or in the evening.

Keeping in a tank

Tank size

An adult black ghost knife fish is a large fish and it needs a large tank. It’s better to keep it in tanks from 105 US gallons (400 L) capacity and more.


A powerful external filter with UV sterilizer is a must for such a tank. The fish produces lots of waste, since it eats protein food and it is sensitive to tank water quality. Using such a filter will help you to solve lots of problems if the fish gets ill. Infectious diseases are much more dangerous for this fish, then for any other tank dweller because it has no scales on its body.

Required tank water parameters: temperature 75-82 °F (24-28 °C), pH 6.0-8.0.

Tank decor

The black ghost knife fish is a nocturnal predator. Most of the time it spends close to the tank bottom. During the day it likes hiding in shelters and leaves them only to feed or at night.

It is better to keep black ghost knife fish alone in a tank, since adult males quite often fight to guard their territory. If you have more than one species in your tank, it is desirable to provide them with large number of shelters (snags, stones, caves etc.) Some aquarists use transparent tubes where the fish feels safe, but at the same time you can see it.

It is desirable to have some floating plants in a tank to create half-light and to create average water flow there.


Is a carnivorous one and in the wild it mainly feeds on insects larvae, juveniles and small fish. In a home tank nothing changes greatly – the black ghost knife fish eagerly eats both live and frozen food: bloodworm, tubifex as well as chopped prawns and calamari.

Very seldom the fish eats dry food. It is recommend to feed once a day before switching on the tank lighting or after the lights are off. When looking for food the fish relies on how electromagnetic fields change. It detects these changes by means of special receptors located along the whole length of the body.

Tank mates

The black ghost knife fish is compatible with any non-aggressive species except small fishes like neon tetra or guppy, which it will treat as food.

Gender differences: male vs female

The black ghost knife fish doesn’t have rather strong gender dimorphism. In the wild male and female find each other due to electrical pulses they irradiate, which are of different frequency for the male and female.


For black ghost knife fish breeding you’ll need a thickly planted tank with snags and shelters. The fish should have a balanced diet that includes live food (bloodworm, worms) – all these contributes to the fish getting reproductive.

As a rule the breeding stock appears within the group of 6-10 species. You can stimulate breeding by flooding and draining the tank, i.e. simulating rain and drought periods in the wild.

The clutch is usually between some snags or in a cave. Yellow eggs are 2 mm in diameter. Three days later the larvae appears.