Siamese fighting fish and Ember tetra
Can these two share a tank? The assessment below is derived from stored behavioural and environmental traits, not from a compatibility chart.
Workable only in unusual circumstances. Not a pairing to plan around.
- Minimum volume
- 65 L
- Minimum length
- 75 cm
- Factors considered
- 8
Concerns
Siamese fighting fish grows to roughly three times the length of Ember tetra. Even without deliberate predation, that size gap makes opportunistic mouthfuls likely as the larger fish matures.
Derived from: adultSize on both records
Siamese fighting fish 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
Siamese fighting fish 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
Why it can work
- Temperature requirements overlap comfortably at 24–28 °C, with room for both animals to sit inside their preferred range.
- pH requirements overlap at 6–7.
- Hardness requirements overlap at 2–8 °dGH.
- Ember tetra needs a group of at least 10. Kept in smaller numbers it is not simply lonely — shoaling species held below their threshold show chronic stress behaviour, colour loss and, in several species, increased aggression towards tankmates.
- The two occupy different levels of the tank, which reduces direct competition for space.
Conditions
Most interesting pairings are conditional on something. These are the things the keeper can actually change.
- At least 10 Ember tetra, counted as one group
- At least 65 L with a footprint of 75 cm or more, before counting anything else in the tank
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
Frequently recommended and the recommendation is reasonable, provided the reader understands that it depends on the individual betta and that the tetras are small enough to eat. A tank plan that has nowhere to put the tetras if it goes wrong is not a plan.
What would change it: Numbers and planting. A group of ten in a well-planted 60 cm tank is a different proposition from six in a bare 45.
Factor by factor
- WaterDerived
Warm, soft, slightly acidic suits both without either being at an edge. Among betta community pairings this is one of very few where the chemistry is not a compromise.
- Size and gapeDerived
An ember tetra is 2 cm and inside a betta's gape. That the pairing usually works reflects betta temperament rather than the arithmetic being favourable.
- Fin interestReported
Ember tetras are not reported as fin-nippers, which is the risk running the other way and the one that actually ends most betta community tanks.
| Depends on | How much |
|---|---|
| Tank size and dimensions | significant |
| Life stage | none |
| The individual animal | decisive |
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 | Comfortable for both | The shared band 24–28 °C sits centrally in both ranges, with room to drift. |
| pH | Workable | The shared band 6–7 pH is usable, though it does not sit centrally for both animals. |
| Hardness | Workable | The shared band 2–8 °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 | Comfortable for both. The shared band 24–28 °C sits centrally in both ranges, with room to drift. |
| pH | Derived from stored traits | Workable. The shared band 6–7 pH is usable, though it does not sit centrally for both animals. |
| Hardness | Derived from stored traits | Workable. The shared band 2–8 °dGH is usable, though it does not sit centrally for both animals. |
| Body size | Derived from stored traits | Siamese fighting fish reaches about 7 cm against 2.2 cm for Ember tetra — a ratio of 3.2. Size disparity drives opportunistic predation independently of temperament. |
| Predation | Derived from stored traits | Highest predation risk in either direction is "low". |
| Territoriality | Derived from stored traits | Strongest territoriality across the pair is "moderate". |
| Breeding aggression | Derived from stored traits | Breeding aggression reaches "strong". A pairing peaceful for months can change within a day of a spawn. |
| Fin-nipping | Evidence-backed | No nipper-and-target combination between these two. Reported: Ember tetras are not reported as fin-nippers, which is the risk running the other way and the one that actually ends most betta community tanks. |
| 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 | Ember tetra needs at least 10. A shoaling species held below its threshold shows chronic stress and, in several species, increased aggression towards tankmates. |
| Group-size dependency | Derived from stored traits | The outcome depends on group size as much as on the pairing: under-grouped shoalers nip more and hide more. |
| 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 | Different feeding strategies, so direct competition is limited. |
| Risk to shrimp and snails | Derived from stored traits | Highest risk either animal poses to dwarf shrimp or snails is "high". |
| Effect on plants | Derived from stored traits | Neither animal damages planting. |
| Tank dimensions | Derived from stored traits | The more demanding of the two needs at least 45 L and 45 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: none. See the documented record. |
| Individual variation | Evidence-backed | Individual variation: decisive. |
Environmental overlap
| Parameter | Shared range | Reading |
|---|---|---|
| Temperature | 24–28 °C | Aim for the middle of the shared band. |
| pH | 6–7 | Stability matters more than the exact figure. |
| Hardness | 2–8 °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 Siamese fighting fish or Ember tetra.
- 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.
These two animals come from different kinds of water, and that is where the arithmetic below comes from rather than from anything about their temperaments.
Siamese fighting fish
Rice paddy, ditch and drain
central Thai floodplain and paddy
80–500 µS/cm · still flow · low oxygen
Ember tetra
Soft forest stream
20–120 µS/cm · low flow · moderate oxygen
- TemperatureSiamese fighting fish 24–28°CEmber tetra 23–29°C
Both inside their range from 24–28°C — 100% 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.
- pHSiamese fighting fish 6–7.5Ember tetra 5–7
Both inside their range from 6–7 — 67% 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 hardnessSiamese fighting fish 2–15 dGHEmber tetra 1–8 dGH
Both inside their range from 2–8 dGH — 86% 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.