American flagfish
A North American pupfish bought almost exclusively as an algae eater, which it genuinely is — it grazes hair algae most fish will not touch. It is also a substrate-spawning cichlid-tempered fish that harasses long-finned tankmates, and the two facts are rarely sold together.
Quick profile
- Scientific name
- Jordanella floridae
- Adult size
- 5–6 cm (2–2.4 in)
- Lifespan
- 2–3 years
- Temperature
- 18–26 °C (64–79 °F)
- pH
- 6.5–8.5
- Hardness
- 6–20 °dGH
- Minimum tank
- 60 L (16 US gal)
- Minimum length
- 60 cm
- Swimming zone
- All levels
- Social
- Harem
- Diet
- Herbivore
- Overall confidence
- moderate confidence
What keeping this species involves
Tolerates a wide temperature range including unheated rooms, and eats what is in front of it. The difficulty is temperament rather than husbandry.
Warm, still, densely vegetated ponds, ditches and marshes.
Identity and names
- Common name
- American flagfish
- Scientific name
- Jordanella floridae
- Family
- Cyprinodontidae
- Order
- Cyprinodontiformes
- Class
- Actinopterygii
- Also sold as
- Florida flagfish, flagfish, Jordanella floridae
Adult size and growth
5–6 cm (2–2.4 in)
Typical lifespan in an aquarium: 2–3 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. A stocky deep-bodied cyprinodont.
Water and tank requirements
A male holds a floor territory during spawning; the footprint has to contain that territory plus somewhere for a female to be that is not in it.
Temperature (°C)
Scale: 0 to 36 °C.
pH (pH)
Scale: 4 to 9.5 pH.
Hardness (°dGH)
Scale: 0 to 30 °dGH.
Where these figures come from
Habitat class
Temperate still water
Ponds, lakes, canals and slow rivers outside the tropics, with a genuine winter.
The temperature range is the point. These animals experience a seasonal cycle, and keeping them at a constant tropical temperature shortens their lives without ever looking like the cause.
- Conductivity
- 150–800 µS/cm
- Flow
- still
- Dissolved oxygen
- variable
- 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.
- TemperatureFollows the habitat this animal comes from
- Follows the water this animal is recorded from — temperate still water. Temperate still water generally runs 2–28°C, and the advised band of 18–26°C is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
- pHFollows the habitat this animal comes from
- Follows the water this animal is recorded from — temperate still water. Temperate still water generally runs 6.5–8.2, and the advised band of 6.5–8.5 is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
- General hardnessFollows the habitat this animal comes from
- Follows the water this animal is recorded from — temperate still water. Temperate still water generally runs 4–20 dGH, and the advised band of 6–20 dGH is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
Scale: -1.9 to 31.9 °C.
Scale: 6.2 to 8.8 pH.
Scale: 1.6 to 22.4 dGH.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 18–26 °C (64–79 °F) | Stability matters more than hitting an exact figure. |
| pH | 6.5–8.5 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 6–20 °dGH | Check your supplier's published figure before choosing species. |
| Minimum volume | 60 L (16 US gal) | A floor, not a recommendation. |
| Minimum footprint | 60 cm long | A male holds a floor territory during spawning; the footprint has to contain that territory plus somewhere for a female to be that is not in it. |
| Water flow | still | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Dense planting and a broken floor. Java moss and thickets give females somewhere to sit out a spawning male. |
Behaviour
- Grazes surfaces continuously through the day rather than feeding in bouts.
- Males clear and defend a patch of substrate when in breeding condition.
Telling males from females
Males carry the red and iridescent bars that give the fish its name; females are duller with a dark spot on the dorsal fin.
Feeding
Grazes hair algae and blackbeard algae in a way few fish do. A tank with no algae needs vegetable food supplied or the fish starts on plants.
- Diet type
- Herbivore
- Staples
- Algae, Blanched courgette and spinach, Vegetable-based dry foods
- Supplements
- Frozen daphnia and bloodworm
Breeding
- Strategy
- Substrate spawning in a male-guarded depression or moss clump
- Difficulty
- straightforward
- Parental care
- guarding
The male guards and fans the eggs, which is unusual outside the cichlids and is the behaviour worth watching for.
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 | moderate | 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 | occasional | Fin damage is an entry point for secondary infection. |
| Plants | nibbles | 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.
- Nips trailing fins. A tank with guppies, angelfish or a betta in it is the wrong tank for this fish.
- Bought to solve an algae problem and then kept in a tank with no algae. Feed vegetables or it grazes the planting 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
- Florida peninsula and southern Georgia, United States
- Habitat
- Warm, still, densely vegetated ponds, ditches and marshes.
What the checklists say
5 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 |
|---|---|---|
| Introduced | 1 | 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 | 4 | 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 | Jordanella floridae | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Florida peninsula and southern Georgia, United States | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 5–6 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 2–3 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 18–26 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 6.5–8.5 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 6–20 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 60 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 60 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 2026-08-12. 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. 5 distribution statements held from GBIF checklists — introduced in 1 country. 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 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.
Guides relevant to this species
Chosen from this record's own traits rather than listed on every page.
- Territorial behaviourIt defends ground, and the shape of what it defends decides the tank more than the volume does.
- The kinds of water aquarium fish come fromThis record's water bands follow temperate still water, which is the kind of water this animal is recorded from.
- How to read a compatibility verdictThis animal is recorded as nipping fins, which is one of the few compatibility factors with real reports behind it.
Group size and social behaviour
Not a shoaling fish. Keeps loosely, with males holding ground against each other during breeding.