Sailfin molly
A coastal fish sold as a freshwater community animal, and the one most likely to be quietly failing in soft acidic water. Males carry a dorsal fin they raise like a sail, and grow it only in a tank long enough to display in.
Quick profile
- Scientific name
- Poecilia latipinna
- Adult size
- 10–15 cm (3.9–5.9 in)
- Lifespan
- 3–5 years
- Temperature
- 22–28 °C (72–82 °F)
- pH
- 7.5–8.5
- Hardness
- 12–30 °dGH
- Minimum tank
- 120 L (32 US gal)
- Minimum length
- 90 cm
- Swimming zone
- All levels
- Social
- Harem
- Diet
- Herbivore
- Overall confidence
- moderate confidence
What keeping this species involves
Hard alkaline water and vegetable food. Given both it is robust; given neither it declines slowly in a way usually blamed on the fish.
Coastal fresh and brackish water — marshes, ditches and lagoons — often at salinities well above fresh.
Identity and names
- Common name
- Sailfin molly
- Scientific name
- Poecilia latipinna
- Family
- Poeciliidae
- Order
- Cyprinodontiformes
- Class
- Actinopterygii
- Also sold as
- Poecilia latipinna, giant sailfin molly
Adult size and growth
10–15 cm (3.9–5.9 in) — Females larger than males. Sold at 3–4 cm.
Typical lifespan in an aquarium: 3–5 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
Males display broadside along a line and need the run to do it; a shoal of 12 cm livebearers also produces a bioload that needs the volume.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 22–28 °C (72–82 °F) | Stability matters more than hitting an exact figure. |
| pH | 7.5–8.5 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 12–30 °dGH | Check your supplier's published figure before choosing species. |
| Carbonate hardness | 8–20 °dKH | Buffering capacity — what stops the pH moving. |
| Minimum volume | 120 L (32 US gal) | A floor, not a recommendation. |
| Minimum footprint | 90 cm long | Males display broadside along a line and need the run to do it; a shoal of 12 cm livebearers also produces a bioload that needs the volume. |
| Water flow | moderate | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Open swimming water, hard alkaline chemistry and algae to graze. |
Behaviour
- Grazes surfaces continuously through the day.
- Males raise the dorsal fully and turn broadside to display.
Telling males from females
Males have the enlarged dorsal and a gonopodium; females are larger, deeper-bodied and plain-finned.
Feeding
A grazer with a long gut. A protein-heavy diet is associated with the digestive problems that give mollies their reputation for being delicate.
- Diet type
- Herbivore
- Staples
- Vegetable-based dry foods, Algae, Blanched vegetables
- Supplements
- Frozen brine shrimp and daphnia
Breeding
- Strategy
- Livebearing, with broods every four to six weeks
- Difficulty
- incidental
- Parental care
- bearer
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 | low | 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 | grazes-algae | 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.
- Kept in the soft acidic water that suits tetras it does poorly, and the decline takes months rather than days.
- Reaches 12 cm or more. The tank it is sold into is very rarely the tank it needs.
- Tolerates brackish water and does not require it. Adding salt to a community tank on this species' account harms everything else in it.
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
- Atlantic and Gulf coastal plain of the United States and north-eastern Mexico, widely introduced elsewhere
- Habitat
- Coastal fresh and brackish water — marshes, ditches and lagoons — often at salinities well above fresh.
What the checklists say
32 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 | 1 | A checklist states the species occurs here naturally. |
| Introduced | 19 | 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 | 12 | 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 | Poecilia latipinna | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Atlantic and Gulf coastal plain of the United States and north-eastern Mexico, widely introduced elsewhere | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 10–15 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 3–5 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 22–28 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 7.5–8.5 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 12–30 °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 | ≥ 90 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| carbonate hardness | 8–20 °dKH | Aquarium-literature consensus | 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. 32 distribution statements held from GBIF checklists — native in 1, introduced in 18 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 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.
carbonate 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.
Group size and social behaviour
Males display at each other and at females continuously. Numbers of females are what keeps that from becoming pursuit of one animal.