Should I buy it?
Black ghost knifefish
Apteronotus albifrons
Also known as: black ghost, bgk
A nocturnal predator at 45 cm that uses weak electric fields to navigate. Needs a large tank with caves and is highly sensitive to fin-nipping neighbours.
Black ghost knifefish tank mates · 300L tank size hub
semi-aggressive · advanced care
Sources & confidencemedium · partially verified · beginner: not recommended
Typical care sources — real tanks still vary. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Specialist dedicated tanks 500L or more with low lighting, sand, and carefully selected large peaceful companions.
Avoid if: Standard community setups, tanks under 300L, or any fish that might compete for caves or nip fins.
Common mistakeHousing a black ghost with barbs or small tetras is how keepers invent shredded anal fins and chronic stress within days. The long fin is a nipping target, and small fish may also become night prey as the knife grows. Plan robust companions in 500L-class volume — or a species-focused setup.
Top things that go wrong
- Grows large or needs a very big footprint. Black ghost knifefish is often sold at sizes that hide adult length (~45cm) and a published minimum near **500L**. Shop tanks are not adult housing.
- Fin-nipping risk in typical community layouts. Will nip long fins or slow fish when the school is too small, bored, or kept in a short tank.
- Mouth gap vs tiny tank mates. May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
More issue cards below, after species context.
Additional planning warnings
Specialist husbandry
Black ghost knifefish is fine singly or as a researched pair — check behaviour before doubling up.
Shrimp & snails
Not shrimp-safe — adults, fry, or both get eaten.
What most shops don't tell you
- 1.Myth: black ghost knifefish are shy nano oddballs for a 40L community with tetras. Reality: adults need hundreds of litres, dim cover, night feeding, and no fin-nippers — the juvenile ‘ghost’ in a small display is a schedule toward a large specialist fish.
- 2.Predation risk scales with gape, night feeding, and crowding. 'they grew up together' is a schedule, not a law.
- 3.Sold as a 12 cm 'ghost' for a 40 L showpiece, then growing past 40 cm in the same flat with no plan for an upgrade.
- 4.Lit bright all day. The fish stays hidden, eats poorly, and gets labelled shy when it is just wrong-lit.
- 5.Buy a tank for the adult, not the 12 cm shop juvenile. Provide a long pipe to hide in by day, dim ambient light, and no bite-sized dither in the same volume.
- 6.Advanced species — research stable parameters before buying.
About this species
Black ghost knifefish are weakly electric South American predators that hunt by electrolocation in the dark. Adults reach 40 to 50 cm, closer to a stingray-class fish than a community oddball. They need a 500 L or larger tank with caves, dim lighting, and no fish small enough to swallow.
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No close matches listed.
No reverse lookups listed yet.
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease6
- Peacefulness0
- Community fit0
- Small-tank fit30
- Hardiness36
- Energy54
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Avoid “one of everything” baskets — Black ghost knifefish belongs in a plan built around territory, line-of-sight breaks, and matched water chemistry.
Compatibility
Tank mates for Black ghost knifefish
No unconditional “safe” tank mates are listed for Black ghost knifefish — this shortlist has CAUTION pairings that need specific conditions and RISKY pairings to avoid. Conditional (CAUTION — read the pair page before buying): Bala / silver shark, Boesemani Rainbowfish, Congo Tetra, Dwarf Gourami, Giant danio. Avoid (RISKY): Chili Rasbora, Corydoras Catfish, Ember Tetra, Guppy, Neon Tetra. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
None listed. Use the pair checker before mixing.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
No safe-mate list on this record yet. Use the fish index to find species with similar care, then run a pair check before you buy.
Behaviour and temperament
Black ghost knifefish are semi-aggressive specialists by size and night predation risk, not community dither. They stay calmer alone or with robust similarly sized fish in a long dim tank. Stress shows as hiding all day and fin damage when barbs or bright chaos share the glass.
What sets them off
- Small groups or boredom
- Long-finned or slow tank mates
- Bare tanks without structure
Fin nipping: Will nip long fins or slow fish when the school is too small, bored, or kept in a short tank.
Predation: May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
Territory: Holds a patch (cave, corner, or surface). Break sight lines so neighbours can pass.
Planted tanks: good — easy plant ideas
In the glass: typical and warning signs
- A knife patrols at night along wood and caves in a long dim tank.
- Daytime hiding under cover is normal ownership, not instant illness alone.
- Shredded anal fin after barbs arrive means the mix failed immediately.
- Refusal to feed in bright bare tanks usually means lighting and cover first.
- Night predation risk rises as gape grows — small tetras are not lifelong companions.
- They rarely ‘play nice’ in short bright communities marketed as oddball kits.
- Remove nippers the same day fin damage starts.
- Do not buy the juvenile unless the adult footprint already exists.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
soft
Diet
carnivore
Black ghost knifefish are nocturnal carnivores that need meaty foods after lights dim — frozen foods, appropriate predator diets, not a daytime community flake pinch. Feed when the fish patrols, confirm intake, and match filtration to a large messy carnivore. A shy day-hider that never sees food at night is an ownership failure, not a picky strain.
Shrimp & snails
Not shrimp-safe — adults, fry, or both get eaten.
Black ghost knifefish is fine singly or as a researched pair — check behaviour before doubling up.
- Hold 24 to 28 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 6 to 7.2 and a hardness you can re-test in two weeks. A one-time strip in the shop car park is not a water test.
- Footprint: short wide tanks and tall narrow tanks fish differently for the same volume. Match the tank shape to the swim pattern, not just the litre count.
- Tank volume meets or exceeds 500L published minimum for adults.
- Heater can hold 24–28°C without cooking cooler-water tank mates.
- No known fin-nippers paired with long-finned fish unless you accept documented risk.
- No tank mates small enough to fit the adult mouth gap for this species.
- Filter maturity / stable parameters before adding sensitive stock.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 500L minimum tank needs a filter rated for at least 2000L/hr turnover and a heater to hold 24–28°C reliably.
Plant suggestions
Black ghost knifefish does well in planted tanks. Plants compatible with 24–28°C and pH 6–7.2:
Research: partially verified · Confidence: medium · 2 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- LiveAquaria. Black ghost knifefish (Apteronotus albifrons care sheet)
Primary: large-aquarium retailer care profile: very large tank, dim lighting, hiding, carnivore diet, and size expectations. Cross-check the stated minimum with your own footprint and filtration; Fishori uses a stricter home-aquarium minimum than a catalog line.
- FishBase. Apteronotus albifrons
Secondary: natural history and max length; weakly electric foraging in the dark. Translate into tank length and nocturnal feeding, not a neon-tetra list.
Evidence notes
- A Seriously Fish apteronotus-albifrons profile URL was not found (search returned the site 404). LiveAquaria is the best stable, aquarium-specific primary available without resorting to wiki mirrors; FishBase is kept for size and range context. Expect debate between hobby sources on true adult length and 'minimum tank' gallons.
- All compatibility text reflects typical hobby experience and the Fishori model. Individual fish, shop stress, and the order tank mates are added in can still defy a single-paragraph label.
Common questions about Black ghost knifefish
- How big do Black ghost knifefish get?
- Black ghost knifefish adults run about 40–50 cm. In home tanks they usually land near 45 cm — plan space and filtration for that, not the juvenile in the shop bag.
- What size tank does Black ghost knifefish need?
- 500L is the planning floor for adult swimming space and bioload. A 600L+ tank is the more comfortable long-term footprint. Length and depth matter as much as raw litres for active or territorial fish.
- Are Black ghost knifefish aggressive?
- Black ghost knifefish are semi-aggressive specialists by size and night predation risk, not community dither. They stay calmer alone or with robust similarly sized fish in a long dim tank. Stress shows as hiding all day and fin damage when barbs or bright chaos share the glass.
- What is the most common mistake with Black ghost knifefish?
- Housing a black ghost with barbs or small tetras is how keepers invent shredded anal fins and chronic stress within days. The long fin is a nipping target, and small fish may also become night prey as the knife grows. Plan robust companions in 500L-class volume — or a species-focused setup.
- What fish can live with Black ghost knifefish?
- This profile currently has no curated unconditional safe-mates shortlist for Black ghost knifefish. Other species may still return GOOD in the pair checker, so check the exact pair rather than treating this shortlist as exhaustive. Bala / silver shark, Boesemani Rainbowfish, Congo Tetra, Dwarf Gourami are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid Chili Rasbora, Corydoras Catfish, Ember Tetra, Guppy (RISKY). Run the pair checker for your exact water and tank size before stocking.