Crimson-spotted rainbowfish
The most southerly rainbowfish and the one that copes best with a genuine winter. Males develop rows of red spangles over blue-green and display to each other at first light, which is the behaviour the species is kept for.
Quick profile
- Scientific name
- Melanotaenia duboulayi
- Adult size
- 8–11 cm (3.1–4.3 in)
- Lifespan
- 4–6 years
- Temperature
- 14–26 °C (57–79 °F)
- pH
- 6.5–8
- Hardness
- 5–18 °dGH
- Minimum tank
- 120 L (32 US gal)
- Minimum length
- 100 cm
- Swimming zone
- Midwater
- Social
- Schooling — at least 6
- Diet
- Omnivore
- Overall confidence
- moderate confidence
What keeping this species involves
Hardy, adaptable and tolerant of a very wide temperature range. The requirement is length and numbers rather than anything chemical.
Clear coastal streams, river pools and vegetated billabongs, in a subtropical range with cool winters.
Identity and names
- Common name
- Crimson-spotted rainbowfish
- Scientific name
- Melanotaenia duboulayi
- Family
- Melanotaeniidae
- Order
- Atheriniformes
- Class
- Actinopterygii
- Also sold as
- Melanotaenia duboulayi, Duboulay's rainbowfish, duboulayi, crimson spotted rainbow
Adult size and growth
8–11 cm (3.1–4.3 in)
Typical lifespan in an aquarium: 4–6 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: deep-bodied with a small terminal mouth. Assigned from what is typical of Melanotaeniidae, not examined for this species.
Water and tank requirements
A fast active shoaler that displays along a length of open water. This is a horizontal-run species and a short tank suppresses the whole behaviour.
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: Subtropical eastern Australian coastal streams with a real winter — this fish experiences water in the mid-teens for months of the year. The band is wide because the range is seasonal, and its lower end is the reason this species can be kept in an unheated tank in a temperate house.
Where these figures come from
Habitat class
Subtropical stream
Running water at the margins of the tropics — a mild winter, a warm summer and no ice.
Species from here are usually sold as tropical and usually kept several degrees too warm all year. A cooler winter is not neglect; it is the season they evolved in.
- Conductivity
- 100–500 µS/cm
- Flow
- moderate
- Dissolved oxygen
- near saturation
- 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 | 14–26 °C (57–79 °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 | 5–18 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 120 L (32 US gal) | A floor, not a recommendation. |
| Minimum footprint | 100 cm long | A fast active shoaler that displays along a length of open water. This is a horizontal-run species and a short tank suppresses the whole behaviour. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Yes | This species jumps. |
| Structure | Open swimming length, dense planting at the ends, and moderate flow. |
Behaviour
- Colours intensify dramatically during dawn display and fade during the day, so a fish judged in a shop at midday looks nothing like the same fish at 7 a.m.
- Jumps, particularly when startled.
Telling males from females
Males deeper-bodied with more intense colour and a taller first dorsal fin. Females slimmer and plainer.
Feeding
- Diet type
- Omnivore
- Staples
- Flake and small pellets, Frozen daphnia and bloodworm, Live insects, Some algae
Breeding
- Strategy
- Continuous egg scattering into fine-leaved plants or spawning mops
- Difficulty
- straightforward
- Parental care
- none
Spawns readily and daily in warm conditions. Eggs are large and adhesive and hatch in around a week.
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 | 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 | none | Fin damage is an entry point for secondary infection. |
| Plants | none | Tough species such as Anubias and Java fern survive most grazers. |
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.
- Sold as a tropical fish and kept at 26 °C all year. It comes from water in the mid-teens for a third of the year and does better with a cooler season.
- Takes months to colour up. Juveniles in a shop tank are grey and are consistently passed over for that reason.
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
- Coastal drainages of eastern Australia — from south-eastern Queensland to northern New South Wales
- Habitat
- Clear coastal streams, river pools and vegetated billabongs, in a subtropical range with cool winters.
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 | Melanotaenia duboulayi | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Coastal drainages of eastern Australia — from south-eastern Queensland to northern New South Wales | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 8–11 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 4–6 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 14–26 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 6.5–8 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 5–18 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 120 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 100 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum group size | ≥ 6 | 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 2026-08-30. 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. No checklist distribution statement is held for this species. The range on the page is editorial until one is.
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.
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.
Guides relevant to this species
Chosen from this record's own traits rather than listed on every page.
- Schooling and shoalingThis species is recorded as school, and the number it is kept in decides how it behaves.
- Wild conditions and aquarium recommendationsThe water band on this page is an AquariumHQ position with a stated reason, not a measurement of a river.
Group size and social behaviour
Males display at each other continuously, most intensely in the first hour of light. A group with a single male shows almost none of it.