Siamese algae eater
The only widely available fish that reliably eats black brush algae, which is why it is bought. It also reaches 15 cm, becomes territorial with age and largely stops eating algae once well fed.
Quick profile
- Scientific name
- Crossocheilus oblongus
- Adult size
- 12–16 cm (4.7–6.3 in)
- Lifespan
- 7–10 years
- Temperature
- 23–28 °C (73–82 °F)
- pH
- 6.5–8
- Hardness
- 4–18 °dGH
- Minimum tank
- 180 L (48 US gal)
- Minimum length
- 120 cm
- Swimming zone
- Bottom
- Social
- Loose group — at least 4
- Diet
- Algae grazer
- Overall confidence
- moderate confidence
What keeping this species involves
Hardy and adaptable; the problems are adult size, jumping and increasing territoriality.
Fast, clear streams over rock and gravel.
Identity and names
- Common name
- Siamese algae eater
- Scientific name
- Crossocheilus oblongus
- Family
- Cyprinidae
- Order
- Cypriniformes
- Class
- Actinopterygii
- Also sold as
- SAE, crossocheilus
Name ambiguity
Several similar Crossocheilus and Garra species are sold as 'Siamese algae eater', and the flying fox (Epalzeorhynchos kalopterus) is frequently mislabelled as one. The true SAE has a black stripe running into the tail fin itself and lacks a second dark line above it.
Adult size and growth
12–16 cm (4.7–6.3 in)
Typical lifespan in an aquarium: 7–10 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.
Water and tank requirements
A 15 cm fast-swimming fish kept in a small group; nothing shorter than 120 cm suits adults.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 23–28 °C (73–82 °F) | Stability matters more than hitting an exact figure. |
| pH | 6.5–8 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 4–18 °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 | A 15 cm fast-swimming fish kept in a small group; nothing shorter than 120 cm suits adults. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Yes | This species jumps. |
Behaviour
- Jumps; keep the tank covered.
- Becomes territorial towards other bottom-dwellers as it matures.
Feeding
Eats less algae as it grows and as it is fed more. A well-fed adult is not an algae solution.
- Diet type
- Algae grazer
- Staples
- Black brush and thread algae, Algae wafers, Blanched vegetables, Sinking foods
Breeding
- Strategy
- Not established in aquaria
- 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 | none | Cover reduces losses but rarely prevents them where the risk is high. |
| Shrimplets | moderate | 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 | none | 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.
- Frequently mis-sold. Check the stripe runs into the tail fin before buying.
- Bought for a job it stops doing, and then outgrows the tank. Consider whether the algae problem has a cause worth fixing instead.
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
- Mainland South-east Asia — Thailand, Malaysia, Indonesia
- Habitat
- Fast, clear streams over rock and gravel.
What the checklists say
2 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 |
|---|---|---|
| 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 | Crossocheilus oblongus | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Mainland South-east Asia — Thailand, Malaysia, Indonesia | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 12–16 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 7–10 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 23–28 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 6.5–8 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 4–18 °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 |
| minimum group size | ≥ 4 | 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 fishbase on 2026-08-11. 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 checkableLimited evidence — treat with caution.
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. 2 distribution statements held, and not one of them states an establishment means. Presence without native-or-introduced is not a native-range claim, so this stays below requirement rather than being read as one.
What would improve this: Go and read a source. This is reachable and has not been reached.
adult sizeOne sourceBased on a verified authoritative source.1 citation, 1 independent origin
A single source: fishbase.
- 16 cm — FishBase · Maximum recorded · The range the species is recorded from · checked 2026-08-11
What this kind of claim needs: size a well-kept specimen reaches — no external source is required, provided AquariumHQ shows its reasoning. One authoritative source, which is what this kind of claim requires. Independent replication would be welcome and is not the standard.
What would improve this: Corroborate against a second, independent source.
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.
temperatureOne sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin
A single source: fishbase.
- 24–26 °C — FishBase · Tolerated range · The range the species is recorded from · checked 2026-08-11
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. Derived from the observed range rather than copied from it. AquariumHQ advises 23–28 °C; FishBase records 24–26 °C. As with the kribensis, a two-degree record for a widely distributed South-East Asian stream fish is a locality reading. The excursion reflects the record's narrowness, not the advice's breadth.
What would improve this: Corroborate against a second, independent source.
phOne sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin
A single source: fishbase.
- 6.5–8 pH — FishBase · Tolerated range · The range the species is recorded from · checked 2026-08-11
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. Derived from the observed range rather than copied from it. The advised band matches the observed envelope exactly, so no narrowing was applied and none is claimed. It is recorded as AquariumHQ's working position rather than as a derivation — the observation supports where this species is found, and nothing in the repository establishes a separate keeping range.
What would improve this: Corroborate against a second, independent source.
general hardnessOne sourceAquariumHQ's own position, derived from evidenced inputs.1 citation, 1 independent origin
A single source: fishbase.
- 5–20 °dGH — FishBase · Tolerated range · The range the species is recorded from · checked 2026-08-11
What this kind of claim needs: what aquariumhq advises for keeping — no external source is required, provided AquariumHQ shows its reasoning. Derived from the observed range rather than copied from it. The advised band reaches past the observed envelope and carries no individual review. Commercially bred stock is generally more tolerant than wild records suggest, which is the usual explanation, and it has not been established for this species.
What would improve this: Corroborate against a second, independent source.
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.
minimum group sizeAquariumHQ'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: group size — 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: Keep the rationale current. There is no source to find.
Group size and social behaviour
Kept singly or in a group of four or more. Two or three tend to produce one dominant fish bullying the rest.