Black ghost knifefish
A velvet-black fish that swims by undulating a single long anal fin and navigates by generating and reading a weak electric field. It reaches fifty centimetres, is entirely nocturnal, and is sold at eight centimetres as a novelty.
Quick profile
- Scientific name
- Apteronotus albifrons
- Adult size
- 40–50 cm (15.7–19.7 in)
- Lifespan
- 10–15 years
- Temperature
- 24–28 °C (75–82 °F)
- pH
- 6–7.5
- Hardness
- 2–12 °dGH
- Minimum tank
- 500 L (132 US gal)
- Minimum length
- 180 cm
- Swimming zone
- Bottom
- Social
- Solitary
- Diet
- Carnivore
- Overall confidence
- moderate confidence
What keeping this species involves
A large nocturnal fish with an unusual sensory system, a strict live-and-frozen diet and a real sensitivity to water quality. Sold as an oddity to keepers who meet all of that afterwards.
Sandy-bottomed river channels with submerged wood, in warm soft water with moderate current.
Identity and names
- Common name
- Black ghost knifefish
- Scientific name
- Apteronotus albifrons
- Family
- Apteronotidae
- Order
- Gymnotiformes
- Class
- Actinopterygii
- Also sold as
- Apteronotus albifrons, black ghost, ghost knifefish, black knifefish
Adult size and growth
40–50 cm (15.7–19.7 in)
Typical lifespan in an aquarium: 10–15 years. Almost every animal sold in a shop is a juvenile, so the tank has to suit the size in the first line rather than the size in the bag.
Shape, which is what the compatibility engine reads instead of length alone: elongate with a moderate. A knife: long, blade-thin and much narrower than a 45 cm fish sounds.
Water and tank requirements
A fifty-centimetre fish that swims forwards and backwards along the floor and needs the length to do it. Its electrical sense also means it needs distance from other electroreceptive fish.
Temperature (°C)
Scale: 0 to 36 °C.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Why these ranges: Amazonian river channels, warm and soft. The species is sensitive to accumulated nitrate and to poor water quality in a way that its hardiness in other respects disguises.
Where these figures come from
Habitat class
Clearwater lowland river
Transparent, mineral-poor rivers draining ancient shield geology — the Tapajós and Xingu type — with low sediment and good light penetration.
Soft water with more movement and more oxygen than a forest stream. Species from here generally want current and open swimming room as much as they want the chemistry.
- Conductivity
- 20–100 µS/cm
- Flow
- moderate
- Dissolved oxygen
- near saturation
- Seasonality
- strong
These are figures for the KIND of water body, not measurements of this species. They are AquariumHQ’s summary of the general limnology and are given wide because the water is.
- TemperatureReasoned on this record
- This record states its own reason for this band. See the water section.
- pHReasoned on this record
- This record states its own reason for this band. See the water section.
- General hardnessReasoned on this record
- This record states its own reason for this band. See the water section.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 24–28 °C (75–82 °F) | Stability matters more than hitting an exact figure. |
| pH | 6–7.5 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 2–12 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 500 L (132 US gal) | A floor, not a recommendation. |
| Minimum footprint | 180 cm long × 60 cm deep | A fifty-centimetre fish that swims forwards and backwards along the floor and needs the length to do it. Its electrical sense also means it needs distance from other electroreceptive fish. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Soft sand, wood and tubes or caves large enough for an adult. It rests inside a tight space through the day and the space has to grow with the fish. |
Behaviour
- Swims backwards as readily as forwards by reversing the wave along its anal fin, which is how it navigates inside a tube.
- Generates a continuous weak electric field and reads distortions in it, which is how it hunts and how it recognises other individuals of its kind.
Telling males from females
No reliable external difference.
Feeding
Hunts invertebrates by electrolocation after dark. Dry food is usually refused and feeding has to happen when the fish is active.
- Diet type
- Carnivore
- Staples
- Live blackworm, Frozen bloodworm, Earthworm, Frozen mysis, Prawn
- Avoid
- Dry flake
Breeding
- Strategy
- Not reliably achieved in aquaria; commercial stock is farmed by induction
- Difficulty
- rarely achieved
- Parental care
- none
Tankmates and compatibility
Assessments are derived from stored traits by the compatibility engine, with the reasoning shown. A verdict is a statement about probability, not a guarantee — individual temperament can override it.
| Towards | Risk | What it means |
|---|---|---|
| Small fish | near-certain | Anything that fits in the mouth is at risk once this species reaches adult size. |
| Adult dwarf shrimp | near-certain | Cover reduces losses but rarely prevents them where the risk is high. |
| Shrimplets | near-certain | Determines whether a shrimp colony can grow rather than merely persist. |
| Snails | moderate | Applies to snails you wanted as well as snails you did not. |
| Long or trailing fins | none | Fin damage is an entry point for secondary infection. |
| Plants | none | Tough species such as Anubias and Java fern survive most grazers. |
Assessed pairings
Any pair in the catalogue can be assessed with the compatibility checker.
Welfare considerations
Points where the way this species is commonly sold or kept differs from what it actually needs.
- Scaleless and notably sensitive to medication, particularly copper and full-dose whitespot treatments.
- Two of these in one tank interfere with each other's electrical fields continuously, which is a form of stress with no visible symptom until the subordinate fish stops feeding.
Problems to watch for
Most problems in a tank containing this species are general rather than species-specific. Start with the troubleshooting index and work from the observation rather than from a guess at the cause.
What AquariumHQ does not yet hold
Species-level disease susceptibility is modelled in the graph and is not yet populated. Health pages will not be published until each condition has veterinary sourcing, because health content written without evidence is the most harmful thing this product could publish. The gap is recorded in the coverage report.
Where it comes from
- Native range
- The Amazon and Paraná basins of South America
- Habitat
- Sandy-bottomed river channels with submerged wood, in warm soft water with moderate current.
What the checklists say
18 distribution statements retrieved from GBIF checklists. Establishment means is reproduced from the source where it states one, and left unstated where it does not — a record of presence is not a record of origin.
| Status | Places | What this means |
|---|---|---|
| Native | 8 | A checklist states the species occurs here naturally. |
| Introduced | 3 | A checklist states the species arrived here with human help. That is not a statement that it is established, harmful or illegal. |
| Recorded as present, establishment means not stated | 7 | The source records the species as present and does not say whether it is native or introduced. AquariumHQ does not fill that in. |
Evidence
Every stored value with the kind of support behind it and where to check it. Evidence type and confidence are separate axes: an editorial position held confidently and a measurement held tentatively are different things.
| Claim | Value | Evidence type | Confidence | Source |
|---|---|---|---|---|
| scientific name | Apteronotus albifrons | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | The Amazon and Paraná basins of South America | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 40–50 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 10–15 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 24–28 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 6–7.5 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 2–12 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 500 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 180 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
Last reviewed 2026-08-10. Values labelled as an aquarium-literature consensus are AquariumHQ editorial positions rather than measurements — see how evidence is handled.
Why we say this
What each figure on this page rests on, and how far that is from being independently established.
Every figure on this page has a provenance. Open any claim to see what AquariumHQ holds for it, which sources say what, and what a claim of that kind actually needs. Different claims need different evidence: an accepted scientific name is settled by one authority, while a legal restriction needs a current primary instrument. A single source is often the right answer rather than a thin one.
scientific nameAquariumHQ's own position, externally checkableBased on a verified authoritative source.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: accepted scientific name and classification — 1 authoritative source in an appropriate context. Checked against gbif on 2026-08-29. One authoritative backbone is what this class requires.
What would improve this: Go and read a source. This is reachable and has not been reached.
native rangeAquariumHQ's own position, externally checkableBased on a verified authoritative source.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: where the species occurs — 1 authoritative source in an appropriate context. 18 distribution statements held from GBIF checklists — native in 8, introduced in 3 countries. Establishment means is reproduced from the source, never inferred from occurrence.
What would improve this: Go and read a source. This is reachable and has not been reached.
adult sizeAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
lifespanAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
temperatureAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
phAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
general hardnessAquariumHQ's own position, externally checkableAquariumHQ's own position, derived from evidenced inputs.
AquariumHQ's own position on a claim an external source could support.
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. No external source is required for this class. AquariumHQ's position stands on its stated reasoning.
What would improve this: Go and read a source. This is reachable and has not been reached.
minimum tank volumeAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: minimum tank size — no external source is required, provided AquariumHQ shows its reasoning. No authority publishes this. AquariumHQ derives it, and the derivation is recorded with its inputs and assumptions.
What would improve this: Keep the rationale current. There is no source to find.
minimum tank lengthAquariumHQ's judgement — no authority publishes thisAquariumHQ's own position, derived from evidenced inputs.
No external authority publishes this. The rationale carries the reasoning.
What this kind of claim needs: minimum tank size — no external source is required, provided AquariumHQ shows its reasoning. No authority publishes this. AquariumHQ derives it, and the derivation is recorded with its inputs and assumptions.
What would improve this: Keep the rationale current. There is no source to find.
Guides relevant to this species
Chosen from this record's own traits rather than listed on every page.
- Predator and prey sizeIt takes fish that fit in its mouth, and its mouth grows with it.
- Territorial behaviourIt defends ground, and the shape of what it defends decides the tank more than the volume does.
- Wild conditions and aquarium recommendationsThe water band on this page is an AquariumHQ position with a stated reason, not a measurement of a river.
- Rehoming an animal you can no longer keepThis animal reaches 50 cm. Most of the difficult rehoming cases are fish sold small that were always going to become impossible.
Group size and social behaviour
Territorial with its own kind and with other electric fish, because their fields interfere. One per tank is the workable arrangement in almost every domestic aquarium.