Assassin snail
A predatory snail that hunts other snails, burrowing through sand to find them. Effective against a pest-snail population and slow enough that it never becomes a plague itself.
Quick profile
- Scientific name
- Anentome helena
- Adult size
- 1.5–2.5 cm (0.6–1 in)
- Lifespan
- 2–3 years
- Temperature
- 22–28 °C (72–82 °F)
- pH
- 7–8
- Hardness
- 6–20 °dGH
- Minimum tank
- 20 L (5 US gal)
- Minimum length
- 30 cm
- Swimming zone
- Bottom
- Social
- Loose group
- Diet
- Carnivore
- Overall confidence
- moderate confidence
What keeping this species involves
Hardy in hard water; the only real requirement is sand and a food supply.
Sandy-bottomed streams and lakes.
Identity and names
- Common name
- Assassin snail
- Scientific name
- Anentome helena
- Family
- Nassariidae
- Order
- Neogastropoda
- Class
- Gastropoda
- Former or synonymous names
- Clea helena
Adult size and growth
1.5–2.5 cm (0.6–1 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: globose with a moderate. The one snail in the catalogue that hunts. It takes other snails, which the engine's own snail-predation trait carries.
Water and tank requirements
Needs sand to burrow through and enough floor area to hunt across.
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
Lowland floodplain
Seasonally inundated flat country — várzea, chaco, swamp margin — where the water body changes size, depth and chemistry through the year.
The habitat's defining feature is change, so a single band describes it badly. Species from here are generally tolerant of a wide range and intolerant of nothing much — which makes them easy to keep and easy to keep wrongly.
- Conductivity
- 40–300 µS/cm
- Flow
- still
- Dissolved oxygen
- low
- 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 — lowland floodplain. Lowland floodplain generally runs 22–32°C, and the advised band of 22–28°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 — lowland floodplain. Lowland floodplain generally runs 6–7.5, and the advised band of 7–8 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: 20.5 to 33.5 °C.
Scale: 5.7 to 8.3 pH.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 22–28 °C (72–82 °F) | Stability matters more than hitting an exact figure. |
| pH | 7–8 | 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 | 20 L (5 US gal) | A floor, not a recommendation. |
| Minimum footprint | 30 cm long | Needs sand to burrow through and enough floor area to hunt across. |
| Water flow | low | Match the outflow to this rather than to the filter's rating. |
| Lid required | Recommended | Reduces evaporation and prevents accidents. |
| Structure | Sand substrate is required for normal hunting behaviour. |
Behaviour
- Buries itself and ambushes passing snails.
Feeding
Once the pest snails are gone it needs feeding directly, or it starves.
- Diet type
- Carnivore
- Staples
- Other snails, Frozen bloodworm, Sinking protein foods
Breeding
- Strategy
- Lays single eggs in tough capsules on hard surfaces
- Difficulty
- straightforward
- Parental care
- none
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 | moderate | Determines whether a shrimp colony can grow rather than merely persist. |
| Snails | near-certain | 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.
- Will take shrimplets and weakened adult shrimp, so it is not a safe addition to a breeding shrimp tank.
- Eats nerite and mystery snails as readily as pest snails.
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
- South-east Asia — Thailand, Malaysia, Indonesia
- Habitat
- Sandy-bottomed streams and lakes.
What the checklists say
1 distribution statement 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. |
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 | Anentome helena | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | South-east Asia — Thailand, Malaysia, Indonesia | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 1.5–2.5 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 2–3 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 22–28 °C | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| ph | 7–8 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 | ≥ 20 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 30 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 2026-08-11. 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. 1 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.
- Schooling and shoalingThis species is recorded as loose group, and the number it is kept in decides how it behaves.
- Scientific and trade namesThis species has been published under more than one accepted name.
- The kinds of water aquarium fish come fromThis record's water bands follow lowland floodplain, which is the kind of water this animal is recorded from.
Group size and social behaviour
Separate sexes; several are needed for breeding, which is slow.