Oscar
A 35 cm cichlid with genuine individual character and an appetite to match. Sold at 5 cm into tanks that will be inadequate within a year, and one of the most commonly rehomed fish in the hobby.
Quick profile
- Scientific name
- Astronotus ocellatus
- Adult size
- 30–40 cm (11.8–15.7 in)
- Lifespan
- 10–15 years
- Temperature
- 24–29 °C (75–84 °F)
- pH
- 6–7.8
- Hardness
- 3–18 °dGH
- Minimum tank
- 450 L (119 US gal)
- Minimum length
- 150 cm
- Swimming zone
- All levels
- Social
- Solitary
- Diet
- Carnivore
- Overall confidence
- high confidence
What keeping this species involves
The waste output of a 35 cm carnivore requires filtration and water changes on a different scale from a community tank.
Slow, warm, structured river margins and floodplain lakes.
Identity and names
- Common name
- Oscar
- Scientific name
- Astronotus ocellatus
- Family
- Cichlidae
- Order
- Cichliformes
- Class
- Actinopterygii
- Also sold as
- tiger oscar, velvet cichlid
Adult size and growth
30–40 cm (11.8–15.7 in) — Grows fast — 20 cm within the first year is normal.
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.
Water and tank requirements
A 35 cm fish needs a tank in which it can turn round and accelerate. 150 cm × 60 cm is the practical minimum for one adult and there is no version of this species that fits a 200 L tank.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 24–29 °C (75–84 °F) | Stability matters more than hitting an exact figure. |
| pH | 6–7.8 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 3–18 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 450 L (119 US gal) | A floor, not a recommendation. |
| Minimum footprint | 150 cm long × 60 cm deep | A 35 cm fish needs a tank in which it can turn round and accelerate. 150 cm × 60 cm is the practical minimum for one adult and there is no version of this species that fits a 200 L tank. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Yes | This species jumps. |
| Structure | Heavy, stable hardscape. Anything movable gets moved. |
Behaviour
- Rearranges substrate and decor deliberately.
- Recognises and responds to individual people — one of the reasons it is so often bought and so often outgrown.
Feeding
- Diet type
- Carnivore
- Staples
- Large cichlid pellets, Frozen prawn and mussel, Earthworms
- Avoid
- Feeder fish — a disease vector with no nutritional advantage, Mammalian meat such as beef heart as a staple
Breeding
- Strategy
- Substrate spawner; both parents guard
- Difficulty
- challenging
- Parental care
- guarding
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 | high | 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 | uproots | 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.
- 'Hole-in-the-head' erosion is common in oscars and is associated with poor water quality and inadequate diet rather than being an inevitable disease.
- Feeder fish are a significant disease and nutrition risk. Do not use them.
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
- Amazon and Orinoco basins
- Habitat
- Slow, warm, structured river margins and floodplain lakes.
What the checklists say
28 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 | 4 | A checklist states the species occurs here naturally. |
| Introduced | 14 | 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 | 10 | 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 | Astronotus ocellatus | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Amazon and Orinoco basins | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 30–40 cm | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| lifespan | 10–15 years | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| temperature | 24–29 °C | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| ph | 6–7.8 pH | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| general hardness | 3–18 °dGH | Aquarium-literature consensus | high confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 450 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 150 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 2026-08-11. 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 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. 28 distribution statements held from GBIF checklists — native in 4, introduced in 14 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 sizeOne sourceBased on a verified authoritative source.1 citation, 1 independent origin
A single source: fishbase.
- 45.7 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.
- 22–25 °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 24–29 °C; FishBase records 22–25 °C. This is the largest excursion in the catalogue against a range that is NOT a source default, so it cannot be dismissed. But it also cannot be settled here. FishBase's figure is startlingly cool for a fish native to the Amazon basin, where water is warm year-round, and a 22–25 °C environmental range for such a species has the shape of a collection artefact — a few records taken at particular sites and seasons — rather than a description of the species' thermal world. That is a hypothesis about the source, not evidence, and AquariumHQ holds no second source for oscar temperature. The advice is left standing because changing it on one contested reading would be the same error in the opposite direction.
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.
- 6–8 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. No usable species-specific observation is held for this parameter. The only figure the source publishes is one it repeats across unrelated families, which the lineage detector grades a default rather than a measurement of this fish. The advised band is therefore AquariumHQ's own position from general husbandry practice for this kind of animal, and is presented as that rather than as a sourced 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.
- 5–19 °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. No usable species-specific observation is held for this parameter. The only figure the source publishes is one it repeats across unrelated families, which the lineage detector grades a default rather than a measurement of this fish. The advised band is therefore AquariumHQ's own position from general husbandry practice for this kind of animal, and is presented as that rather than as a sourced range.
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.
Group size and social behaviour
Kept singly or as an established pair. Two unpaired adults in one tank is a fight.