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Encyclopedia / Oddballs & Predators / Black ghost knifefish
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Variations

1 kinds · tap one for a closer look

Black ghost knifefish

Apteronotus albifrons · Bgk, Ghost knife

Shy, nocturnal; eats very small fish.

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50 cmAdult size ✓
24–28 °CTemperature ✓
6–8pH ✓
648 LSmallest tank ✓
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Tank mates
Check your own mix →
Not recommended
  • Black ghost knifefish eats animals up to about 4 cm. Neon tetra only grows to 2.5 cm.
  • Only a narrow temperature range suits both: 24–25 °C.
Not recommended
  • Black ghost knifefish eats animals up to about 4 cm. Cardinal tetra only grows to 3 cm.
Not recommended
  • Black ghost knifefish eats animals up to about 4 cm. Black neon tetra only grows to 3.2 cm.
With conditions
  • Only a narrow temperature range suits both: exactly 24 °C.
With conditions
  • Only a narrow temperature range suits both: 24–25 °C.
Compatible
Compatible
Compatible
Compatible
Compatible

337 species in our list are a good match.

Facts checked against sources on 16 Oct 2026. ✓ means a source backs it; ? means no reliable source yet. See sources

Care and water

Hardness ✓5–10 dGH
Group size ✓Can live alone
Temperament ✓Peaceful
Swims at ?Bottom
Care level ✓Moderate
Diet Carnivore
Lifespan ?Unknown
Size in shops 6–10 cm
Growth Medium

Behavior

Shy, nocturnal; eats very small fish.

Food

Frozen bloodworms, worms.

Tap a food to see what it is.

Male or female

MaleLarger, longer snout
FemaleSmaller
TipHard
How hard to tellHard

Health

Common problems. Tap one to see the signs. This is a guide, not a diagnosis.

Breeding

Rarely bred in captivity ·

Not bred in home aquariums; it is bred commercially in large outdoor ponds in Indonesia.

Pairing

Buy several juveniles and grow them out. Visible sex differences are small, so you may need many fish to get a pair.

Setup

A large, dim tank (400+ L) with PVC tubes, caves and fine plants. Soft, slightly acidic water.

What starts it

Rainy-season-style changes: cooler water changes, plenty of live food and dim light.

Eggs

Reported fecundity is about 1 to 105 eggs per spawn; no reliable hatch time found.

Raising the fry

Fry eat newly hatched brine shrimp and microworms. They are delicate in the first weeks.

Common mistakes
  • Using bright light
  • Adding salt or harsh medicine
  • Housing with aggressive tank mates
Full breeding guide, day-by-day plan and simulator →

Where it lives in the wild

RegionAmazon and Orinoco basins
Rivers and lakesAmazon, Orinoco and Paraná-Paraguay systems
HabitatFast, sandy rivers
Native rangeAbout 2,000 km across
See it on the world map

The story of the black ghost knifefish

It has a weak electric organ and senses its surroundings by electrolocation, its main sense since its eyesight is very poor. Native South Americans are reported to regard it with superstition.

Linnaeus described the black ghost knifefish in 1766, originally as Gymnotus albifrons. It produces a weak electric field to sense objects and other fish in dark water. Mostly active at night, it is kept for its graceful, ribbon-fin swimming.

First described by Carl Linnaeus in 1766.

  • It senses its surroundings with a weak electric field.
  • A long rippling fin under its body lets it swim backwards as easily as forwards.
  • It is most active at night and hides in tubes or caves by day.

Sources

14 facts checked with sources