Why is my Black Ghost Knifefish hiding all the time?

They are naturally nocturnal and photophobic (sensitive to bright light). It is completely normal for them to hide in a dark cave or tube during the day and only become active at night or under dim lighting.

Can I keep two Black Ghost Knifefish together?

It is strongly discouraged. They are highly territorial towards their own kind and will usually fight to the death. Even in very large tanks, their electrical fields interfere with one another, causing severe stress.

Will a Black Ghost Knifefish eat my smaller fish?

Yes. While they are peaceful towards larger fish, they are skilled nocturnal predators. Any fish small enough to fit in their surprisingly large mouths, such as Neon Tetras or Guppies, will eventually be eaten.

How do I treat Ich on a scaleless fish like the Black Ghost Knifefish?

Avoid copper-based medications entirely. Treat parasites by slowly raising the water temperature to 29-30°C over a few days and using aquarium salt, or use a scaleless-safe medication at half the recommended dose.

How do they navigate in the dark?

They possess an electric organ near their tail that emits a continuous, weak electrical field. Electroreceptors across their body detect disturbances in this field, allowing them to map their surroundings and locate prey.

AI-generated illustration for OneShoal

FreshwaterTropicalIntermediate

Black Ghost Knifefish

Apteronotus albifrons

The Black Ghost Knifefish is a captivating, nocturnal oddball from South America known for its sleek, velvety black body, highly intelligent nature, and remarkable ability to swim backwards.

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Ideal Conditions

Temperature: 23 – 28 °C
pH range: 6 – 8
Hardness: 5 – 19 dGH
Adult size: 40 – 50 cm
Adult minimum: 400 litres+
Lifespan: 10 – 15 years
Diet: Carnivore
Water flow: moderate
Preferred setup: Dim lighting, sandy substrate, and ample hiding places such as PVC pipes, driftwood, or smooth caves.

About the Black Ghost Knifefish

With its unique ribbon-like anal fin and lack of a dorsal fin, the Black Ghost Knifefish navigates its environment with extraordinary grace. As a nocturnal species with poor eyesight, it relies on a weak electric organ located near its tail to generate a field that helps it detect objects, prey, and other fish in the dark. These highly intelligent fish can live for over a decade and are known to form bonds with their keepers, eventually learning to accept food directly from their owner's fingers.

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Is it right for your tank?

Check Black Ghost Knifefish against a habitat you already keep. We compare water type, temperature, pH, adult size, group needs and everything living there.

Where Black Ghost Knifefish comes from

Native range

Amazon Basin, Paraná River Basin, Orinoco River Basin

Countries / regions

Brazil, Colombia, Ecuador, Paraguay, Peru, Venezuela

Habitat

Fast-flowing, sandy-bottomed creeks and deep, dark flooded forests.

Widely distributed across tropical South America in deeply shaded or turbid river habitats.

Similar species

Brown Ghost Knifefish
Apteronotus leptorhynchus
Clown Knifefish
Chitala ornata
Elephant Nose Fish
Gnathonemus petersii

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Severum
Heros severus
Large enough not to be eaten, and generally peaceful enough not to harass the knifefish.
Great
Bristlenose Pleco
Ancistrus spp.
Peaceful, armoured bottom-dwellers that will mind their own business and ignore the knifefish.
Great
Silver Dollar
Metynnis argenteus
Fast-moving, upper-water column schooling fish that are much too large for the knifefish to consume.
Great
Oscar
Astronotus ocellatus
While often kept together, highly aggressive Oscars may relentlessly harass the more reclusive knifefish.
Compatible with caution
Neon Tetra
Paracheirodon innesi
Will easily fit into an adult Black Ghost Knifefish's mouth and will be eaten overnight.
Not recommended
Other Black Ghost Knifefish
Apteronotus albifrons
Highly intolerant of conspecifics; their electrical fields interfere with one another, causing severe stress and violent territorial battles.
Not recommended

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