Oscar and Silver arowana
Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.
Should not be attempted. At least one factor is expected to cause harm.
- Minimum volume
- 9000 L
- Minimum length
- 465 cm
- Factors considered
- 8
Concerns
Silver arowana reaches about 120 cm and takes fish small enough to swallow. At roughly 40 cm, an adult Oscar is inside that range. This is usually discovered as fish quietly disappearing overnight rather than as visible aggression. Silver arowana has a very large — prey approaching its own length and Oscar is deep-bodied, so the size at which Oscar stops being a possible mouthful is HIGHER than the usual third-of-body-length rule — around 60% of Silver arowana's length rather than 40%.
Derived from: traits.predation.smallFish, adultSize on both records, and the stored body form and gape of both
Temperature requirements overlap at 26–29 °C, though the band does not sit centrally for both animals. Aim for the middle of it and keep the heater accurate.
Derived from: environment.temperature on both records
Oscar defends a territory and both animals use the same part of the tank, so give the territory-holder a defensible area away from the main swimming space.
Derived from: traits.territoriality and zone on both records
Oscar becomes markedly more aggressive while spawning. A pairing that has been peaceful for months can change within a day, so plan for where the other animal goes if it does.
Derived from: traits.breedingAggression
Silver arowana becomes markedly more aggressive while spawning. A pairing that has been peaceful for months can change within a day, so plan for where the other animal goes if it does.
Derived from: traits.breedingAggression
Why it can work
- pH requirements overlap at 6–7.2.
- Hardness requirements overlap at 3–10 °dGH.
- The two occupy different levels of the tank, which reduces direct competition for space.
Derived, or documented?
These are different claims and are shown separately. The verdict above is derived from stored traits — arithmetic on AquariumHQ's own records. Whether the pairing is actually reported to work is a separate question, and for most pairs the honest answer is that we hold nothing.
Environmental compatibility
Derived from stored traits
Temperature, pH, hardness, size and behavioural traits compared between the two records. Sound as far as it goes, and it is not evidence that the pairing works.
Behavioural evidence
Widely reported in practice
Reported consistently across aquarium practice without a single citable source. Treated as real but not as measurement.
AquariumHQ's overall position
Conditional, and conditional on a system most people asking about it do not have. Given the space it is one of the more sensible ways to keep an arowana with company; below that space it is two large predators in a box.
What would change it: A system measured in metres rather than centimetres, and feeding the arowana at the surface separately so it does not learn to look downward for food.
Factor by factor
- Zone separationReported
The arowana uses the top few centimetres of water and the oscar the middle and bottom. This is the rare large-predator pairing where the two animals genuinely occupy different space, and it is the whole reason it is attempted.
- Feeding competition and the oscar's speedReported
The oscar takes food fast and from anywhere in the tank. An arowana that has to compete for it feeds at the surface less confidently, which is associated with the eye deformity this species is prone to.
- Tank scaleDerived
Both are large fish and the arowana's requirement is a purpose-built system rather than an aquarium. In anything smaller the zone separation that makes this work disappears.
| Depends on | How much |
|---|---|
| Tank size and dimensions | decisive |
| Life stage | minor |
| The individual animal | significant |
How good is the overlap?
Whether two ranges intersect is a necessary condition, not evidence. What matters is WHERE the shared band sits: an overlap at the top of one animal's range and the bottom of the other's is a forced compromise however wide it looks, and it is the case a simple intersection test cannot see.
| Dimension | Assessment | What that means here |
|---|---|---|
| Temperature | Workable | The shared band 26–29 °C is usable, though it does not sit centrally for both animals. |
| pH | Comfortable for both | The shared band 6–7.2 pH sits centrally in both ranges, with room to drift. |
| Hardness | Workable | The shared band 3–10 °dGH is usable, though it does not sit centrally for both animals. |
Factor by factor
Every factor states what it rests on. Most are derived from the traits stored on both records — sound arithmetic on AquariumHQ's own data, and not a report about how the pairing actually goes. Where a factor says 'not known', the data is missing and saying so matters, because a missing factor and a favourable one look identical once both are absent.
| Factor | Basis | Finding |
|---|---|---|
| Temperature | Derived from stored traits | Workable. The shared band 26–29 °C is usable, though it does not sit centrally for both animals. |
| pH | Derived from stored traits | Comfortable for both. The shared band 6–7.2 pH sits centrally in both ranges, with room to drift. |
| Hardness | Derived from stored traits | Workable. The shared band 3–10 °dGH is usable, though it does not sit centrally for both animals. |
| Body size | Derived from stored traits | Silver arowana reaches about 120 cm against 40 cm for Oscar — a ratio of 3.0. Size disparity drives opportunistic predation independently of temperament. |
| Predation | Derived from stored traits | Highest predation risk in either direction is "near-certain". |
| Territoriality | Derived from stored traits | Strongest territoriality across the pair is "strong". |
| Breeding aggression | Derived from stored traits | Breeding aggression reaches "moderate". A pairing peaceful for months can change within a day of a spawn. |
| Fin-nipping | Derived from stored traits | No nipper-and-target combination between these two. |
| Aggression | Derived from stored traits | Strongest intraspecific aggression across the pair is "strong". It bears on the pairing because a fish under pressure from its own kind redirects. |
| Social requirements | Derived from stored traits | Neither animal requires a group. |
| Group-size dependency | Derived from stored traits | The outcome does not depend on group size for either animal. |
| Tank zone | Derived from stored traits | The two use different levels of the tank, which reduces direct competition for space. |
| Activity level | Derived from stored traits | Activity levels are compatible. |
| Food competition | Derived from stored traits | Both are carnivores. |
| Risk to shrimp and snails | Derived from stored traits | Highest risk either animal poses to dwarf shrimp or snails is "near-certain". |
| Effect on plants | Derived from stored traits | Oscar uproots plants, which constrains the aquascape rather than the pairing. |
| Tank dimensions | Derived from stored traits | The more demanding of the two needs at least 6000 L and 420 cm of length before anything else is in the tank. Volume alone does not describe a home for a fish that swims in straight lines. |
| Life stage | Evidence-backed | Life-stage dependency: minor. See the documented record. |
| Individual variation | Evidence-backed | Individual variation: significant. |
Environmental overlap
| Parameter | Shared range | Reading |
|---|---|---|
| Temperature | 26–29 °C | Aim for the middle of the shared band. |
| pH | 6–7.2 | Stability matters more than the exact figure. |
| Hardness | 3–10 °dGH | Check your source water before committing. |
What this assessment cannot tell you
- Individual temperament varies, particularly in cichlids and in bettas, and can override a favourable verdict for Oscar or Silver arowana.
- The assessment is for the pair in isolation. A third species can change the outcome in either direction.
- Both animals are assessed at adult size, not at the size they are sold.
- A verdict is a statement about probability, not a guarantee.
Where the two water bands meet
Derived from the ranges AquariumHQ publishes for each species. The compatibility engine reads the same numbers; this is what they look like drawn on one axis.
Temperature (°C)
Scale: 0 to 36 °C.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Why the bands sit where they do
The overlap above is arithmetic. This is where the two numbers came from — the kind of water each animal is recorded from, and how much room that leaves.
Both animals come from lowland floodplain, which is why the bands below sit where they do.
Oscar
Lowland floodplain
40–300 µS/cm · still flow · low oxygen
Silver arowana
Lowland floodplain
40–300 µS/cm · still flow · low oxygen
- TemperatureOscar 24–29°CSilver arowana 26–30°C
Both inside their range from 26–29°C — 75% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
- pHOscar 6–7.8Silver arowana 5.5–7.2
Both inside their range from 6–7.2 — 71% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
- General hardnessOscar 3–18 dGHSilver arowana 1–10 dGH
Both inside their range from 3–10 dGH — 78% of the narrower animal’s range.
A wide window. Both animals are inside their own range across most of it, and the tank can be run without either sitting at an edge.
Computed from the ranges AquariumHQ publishes for each species, each of which records what it rests on — a source value, a habitat inference, a physiological requirement or a trade convention. Most are habitat inferences, and the species pages say which.