Rainbow shark
A grey-bodied cyprinid with red fins, close relative of the red-tailed black shark and about as territorial, but towards a slightly wider range of tankmates. The albino form is common in shops and behaves identically.
Quick profile
- Scientific name
- Epalzeorhynchos frenatus
- Adult size
- 12–15 cm (4.7–5.9 in)
- Lifespan
- 5–8 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
As hardy as its relative and with the same single requirement: enough floor that the fish's territory is not the whole tank.
Sandy-bottomed rivers and flooded areas, moving between the main channel and the floodplain with the season.
Identity and names
- Common name
- Rainbow shark
- Scientific name
- Epalzeorhynchos frenatus
- Family
- Cyprinidae
- Order
- Cypriniformes
- Class
- Actinopterygii
- Also sold as
- Epalzeorhynchos frenatus, Epalzeorhynchos frenatum, Labeo frenatus, ruby shark, red-finned shark
- Former or synonymous names
- Labeo frenatus, Epalzeorhynchos frenatum
Name ambiguity
Widely written as Epalzeorhynchos frenatum in aquarium literature. GBIF's backbone holds frenatus as the accepted spelling and the catalogue follows it, with the other form searchable.
Varieties and strains
| Variety | What it means in practice |
|---|---|
| Albino rainbow shark | A pigment-reduced line with white body and red fins. Identical in size, diet and temperament, and noticeably more inclined to stay under cover in a brightly lit tank. |
Adult size and growth
12–15 cm (4.7–5.9 in)
Typical lifespan in an aquarium: 5–8 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 territorial bottom fish that pursues along the floor. The length is the escape distance for whatever else lives down there.
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: Mekong and Chao Phraya lowland water. The species moves between channel and floodplain seasonally and experiences a wide range of conditions, which is reflected in a tolerant band.
Where these figures come from
Habitat class
Lowland floodplain
Seasonally inundated flat country — várzea, chaco, swamp margin — where the water body changes size, depth and chemistry through the year.
The habitat's defining feature is change, so a single band describes it badly. Species from here are generally tolerant of a wide range and intolerant of nothing much — which makes them easy to keep and easy to keep wrongly.
- Conductivity
- 40–300 µS/cm
- Flow
- still
- Dissolved oxygen
- low
- 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 | 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 territorial bottom fish that pursues along the floor. The length is the escape distance for whatever else lives down there. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Wood, rock and caves, with a clear route out of each. Sight-line breaks reduce the amount of the tank the fish treats as its own. |
Behaviour
- Works the substrate and the lower surfaces of wood, rasping at biofilm in short passes.
- Rushes at any other bottom-dweller entering its area and breaks off short of contact more often than not, which is why the harassment is chronic rather than injurious.
Telling males from females
Females are broader across the belly when mature. The difference is slight and is not usable in a shop tank.
Feeding
Grazes biofilm and algae and takes small invertebrates. A vegetable component keeps it in better condition than a purely protein diet.
- Diet type
- Omnivore
- Staples
- Sinking pellets, Algae wafers, Frozen bloodworm, Blanched spinach
Breeding
- Strategy
- Not achieved in home aquaria; trade stock is hormone-induced on farms
- 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 | 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.
- The albino form lacks the dark body pigment and is sold alongside the wild type. Its requirements and temperament are the same; its tolerance of bright open tanks is not, and it uses cover more.
- Frequently sold in pairs by shops that stock it in groups. Farmed juveniles tolerate each other; adults in a domestic tank do 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
- The Mekong and Chao Phraya basins — Thailand, Laos and Cambodia
- Habitat
- Sandy-bottomed rivers and flooded areas, moving between the main channel and the floodplain with the season.
What the checklists say
3 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 | 1 | 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 | 2 | 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 frenatus | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | The Mekong and Chao Phraya basins — Thailand, Laos and Cambodia | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 12–15 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 5–8 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. 3 distribution statements held from GBIF checklists — introduced in 1 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 unless the aquarium is genuinely large and heavily broken up. Aggression is directed at its own species first and at other bottom-dwellers second.