Red-tailed black shark
A matt-black cyprinid with a scarlet tail, sold everywhere as a community fish and reliably territorial towards anything of similar shape. Every fish in the trade is commercially bred; the wild population is assessed as extinct.
Quick profile
- Scientific name
- Epalzeorhynchos bicolor
- Adult size
- 12–15 cm (4.7–5.9 in)
- Lifespan
- 6–10 years
- Temperature
- 22–27 °C (72–81 °F)
- pH
- 6.5–7.8
- Hardness
- 5–15 °dGH
- Minimum tank
- 180 L (48 US gal)
- Minimum length
- 120 cm
- Swimming zone
- Bottom
- Social
- Solitary and territorial
- Diet
- Omnivore
- Overall confidence
- moderate confidence
What keeping this species involves
Hardy, adaptable and easy to feed. The whole difficulty is territorial: it needs a tank long enough that its claimed area is not the entire floor.
Clear flowing streams and river margins over sand and gravel, with wood and rock providing defensible cover.
Identity and names
- Common name
- Red-tailed black shark
- Scientific name
- Epalzeorhynchos bicolor
- Family
- Cyprinidae
- Order
- Cypriniformes
- Class
- Actinopterygii
- Also sold as
- Epalzeorhynchos bicolor, Labeo bicolor, redtail shark, red-tailed labeo, fire tail
- Former or synonymous names
- Labeo bicolor
Adult size and growth
12–15 cm (4.7–5.9 in)
Typical lifespan in an aquarium: 6–10 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: fusiform — the ordinary torpedo with a small terminal mouth. Assigned from what is typical of Cyprinidae, not examined for this species.
Water and tank requirements
A single fish claims a section of floor and drives others out of it. The length is what allows a bottom-dwelling tankmate to be somewhere the shark is not.
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: Chao Phraya lowland streams, which are moderately soft and near-neutral. The band is wide because the species is genuinely tolerant, not because the habitat is poorly described.
Where these figures come from
Habitat class
Hill stream and rapids
Fast, cool, oxygen-saturated running water over rock and gravel, typically at altitude or on a steep gradient.
Oxygen and flow are the requirement, not the chemistry. A hill-stream species in still water at the right pH is being kept badly, and the failure is slow enough that the keeper usually blames something else.
- Conductivity
- 50–300 µS/cm
- Flow
- high
- Dissolved oxygen
- near saturation
- Seasonality
- moderate
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 | 22–27 °C (72–81 °F) | Stability matters more than hitting an exact figure. |
| pH | 6.5–7.8 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 5–15 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 180 L (48 US gal) | A floor, not a recommendation. |
| Minimum footprint | 120 cm long × 40 cm deep | A single fish claims a section of floor and drives others out of it. The length is what allows a bottom-dwelling tankmate to be somewhere the shark is not. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Caves, wood and rock, each with a way out. The fish adopts one shelter as a base and returns to it after every excursion. |
Behaviour
- Patrols a fixed route between shelters and chases anything it meets on the bottom along the way.
- Loses the black body colour and goes grey when stressed, which is a quick and reliable read on whether it is settled.
Telling males from females
Females are usually deeper-bodied. There is no reliable colour or fin difference and sexing is not practical at shop size.
Feeding
Grazes algae and biofilm and takes small invertebrates and detritus. It is not an algae-eating specialist and will not keep a tank clean on its own.
- Diet type
- Omnivore
- Staples
- Sinking pellets, Algae wafers, Frozen bloodworm, Blanched courgette
Breeding
- Strategy
- Not achieved in home aquaria; commercial stock is produced by hormone induction
- Difficulty
- rarely achieved
- Parental care
- none
Every fish in the trade comes from induced spawning on commercial farms. There is no reliable account of an unassisted aquarium spawning.
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 | none | Anything that fits in the mouth is at risk once this species reaches adult size. |
| Adult dwarf shrimp | moderate | Cover reduces losses but rarely prevents them where the risk is high. |
| Shrimplets | high | Determines whether a shrimp colony can grow rather than merely persist. |
| Snails | none | Applies to snails you wanted as well as snails you did not. |
| Long or trailing fins | occasional | Fin damage is an entry point for secondary infection. |
| Plants | grazes-algae | 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.
- Assessed as extinct in the wild while being one of the most widely traded aquarium fish in existence. The trade is entirely supported by farmed production.
- Sold at four centimetres as a community fish. The territoriality appears as it matures rather than immediately, so the tank works for months before it does not.
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
- Thailand — the Chao Phraya basin, where it is now considered extinct in the wild
- Habitat
- Clear flowing streams and river margins over sand and gravel, with wood and rock providing defensible cover.
What the checklists say
6 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 |
|---|---|---|
| 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 | 3 | The source records the species as present and does not say whether it is native or introduced. AquariumHQ does not fill that in. |
No checklist AquariumHQ holds positively calls this species native anywhere, so the native range above rests on AquariumHQ’s own reading of the literature rather than on a cited checklist.
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 | Epalzeorhynchos bicolor | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Thailand — the Chao Phraya basin, where it is now considered extinct in the wild | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 12–15 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 6–10 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 22–27 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 6.5–7.8 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 5–15 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 180 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 120 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. 6 distribution statements held from GBIF checklists — introduced in 3 country. 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.
- Territorial behaviourIt defends ground, and the shape of what it defends decides the tank more than the volume does.
- Scientific and trade namesThis species has been published under more than one accepted name.
- Wild conditions and aquarium recommendationsThe water band on this page is an AquariumHQ position with a stated reason, not a measurement of a river.
- How to read a compatibility verdictThis animal is recorded as nipping fins, which is one of the few compatibility factors with real reports behind it.
Group size and social behaviour
One per tank. Two of these in anything short of a very large aquarium is a sustained conflict, and the loser is harassed continuously rather than fought once.