Japanese trapdoor snail
A livebearing coldwater snail with an operculum it seals itself behind, kept mostly in ponds and mostly for the same reason as in aquaria: it eats detritus and does not eat plants. It is also established across large parts of North America, which is the more important fact about it.
Quick profile
- Scientific name
- Cipangopaludina japonica
- Adult size
- 4–6 cm (1.6–2.4 in)
- Lifespan
- 3–5 years
- Temperature
- 10–26 °C (50–79 °F)
- pH
- 7–8.5
- Hardness
- 8–25 °dGH
- Minimum tank
- 40 L (11 US gal)
- Minimum length
- 45 cm
- Swimming zone
- Bottom
- Social
- Tolerant of any grouping
- Diet
- Detritivore
- Overall confidence
- moderate confidence
What keeping this species involves
Asks only for hard water and something to eat, and is unbothered by cold — it overwinters under ice in outdoor ponds, which is a survival tolerance rather than a range to aim for.
Still and slow water with soft beds, including ponds, lakes and canals.
Identity and names
- Common name
- Japanese trapdoor snail
- Scientific name
- Cipangopaludina japonica
- Family
- Viviparidae
- Order
- Architaenioglossa
- Class
- Gastropoda
- Also sold as
- Chinese mystery snail, black trapdoor snail, Cipangopaludina japonica
Name ambiguity
Sold interchangeably with Cipangopaludina chinensis, and the trade names 'Japanese trapdoor' and 'Chinese mystery snail' are applied to both. Neither is a Pomacea, despite 'mystery snail' being the usual name for one.
Adult size and growth
4–6 cm (1.6–2.4 in)
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.
Shape, which is what the compatibility engine reads instead of length alone: globose with a grazing or sucking mouth. Assigned from what is typical of Viviparidae, not examined for this species.
Water and tank requirements
A large grazer that works across the substrate; floor area and bioload dilution set the requirement.
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 10–26°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 7–8.5 is consistent with it. This is AquariumHQ's reasoning from the habitat, not a measurement of the species.
- General hardnessSet by a requirement of the animal
- Hardness here is a shell requirement, not a habitat statement. A snail or mussel builds and repairs aragonite continuously, and in water without dissolved calcium the shell erodes faster than the animal can replace it — visibly, at the apex first. The band is therefore set by what the animal has to take out of the water rather than by what its river happens to contain, and several of these species are recorded from water considerably softer than the band advises.
Scale: -1.9 to 31.9 °C.
Scale: 6.2 to 8.8 pH.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 10–26 °C (50–79 °F) | Stability matters more than hitting an exact figure. |
| pH | 7–8.5 | A stable pH outside the ideal band is usually better than an unstable one inside it. |
| General hardness | 8–25 °dGH | Check your supplier's published figure before choosing species. |
| Carbonate hardness | 4–15 °dKH | Buffering capacity — what stops the pH moving. |
| Minimum volume | 40 L (11 US gal) | A floor, not a recommendation. |
| Minimum footprint | 45 cm long | A large grazer that works across the substrate; floor area and bioload dilution set the requirement. |
| Water flow | low | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Soft substrate to burrow into and hard alkaline water to maintain the shell. |
Behaviour
- Seals itself behind a hinged operculum when disturbed or when conditions deteriorate.
- Burrows into soft substrate and can be absent from view for days.
Feeding
Leaves healthy plants alone, which distinguishes it from the apple snails it is confused with.
- Diet type
- Detritivore
- Staples
- Detritus, Algae films, Blanched vegetables, Sinking wafers
Breeding
- Strategy
- Ovoviviparous — females release fully formed juveniles
- Difficulty
- straightforward
- Parental care
- bearer
Separate sexes, so a single individual cannot found a population — unlike the hermaphroditic pest snails.
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 | none | 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.
- A coldwater animal kept at tropical temperature has a shorter life; it is better suited to an unheated tank or a pond. Pond keepers should note that survival under ice is documented for this species and is not the same as a range to keep it in.
- Shell erodes in soft acidic water and the erosion does not reverse.
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
- East Asia — Japan and neighbouring regions; introduced widely in North America
- Habitat
- Still and slow water with soft beds, including ponds, lakes and canals.
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 | 3 | 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 | 2 | 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.
Legal status and responsible practice
Restriction note
Established across much of North America and treated as an invasive species there, with keeping and transport restricted in some states and provinces. AquariumHQ has not established the position in any specific jurisdiction; check with the relevant wildlife authority before acquiring, selling or moving these snails, and never release them or their water into natural systems.
Never release aquarium life into the wild
Aquarium animals, plants, and aquarium water must never be released into ponds, rivers, canals, drains or the sea — not even in a country where the species is sold freely. Released fish and invertebrates establish populations that displace native species, and released plants and water carry pathogens, parasites and fragments capable of spreading without any animal at all. If you can no longer keep an animal, rehome it through an aquarium society, a retailer that accepts returns, or another keeper.
- Rehome through a local aquarium society, a specialist retailer or another keeper.
- Unwanted plants go in household waste or a hot compost heap, never in a watercourse or a garden pond.
- Never empty a bucket of tank water into a drain that discharges to open water.
- If an animal is beyond rehoming, ask an aquatic veterinarian about humane euthanasia rather than releasing it.
Legal status is recorded from the sources named and was correct on the verification date shown. Rules change, and sub-national rules often differ from national ones. Check the current position with the relevant authority before acquiring, selling or moving any animal or plant.
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 | Cipangopaludina japonica | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | East Asia — Japan and neighbouring regions; introduced widely in North America | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 4–6 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 3–5 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 10–26 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 7–8.5 pH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| general hardness | 8–25 °dGH | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank volume | ≥ 40 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 45 cm | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| carbonate hardness | 4–15 °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. 5 distribution statements held from GBIF checklists — introduced in 2 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.
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.
Guides relevant to this species
Chosen from this record's own traits rather than listed on every page.
- Native, introduced and invasiveThis record carries an invasive or legal note, and those are five separate claims that are easy to read as one.
- 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.
Group size and social behaviour
Indifferent to its own kind. Separate sexes, unlike most aquarium snails.