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CrayfishfreshwaterUndemanding

Signal crayfish

A North American crayfish introduced to Europe for aquaculture in the 1960s, which carries the crayfish plague without dying of it and has driven native European crayfish towards extinction across much of the continent. Keeping it is prohibited across the European Union.

Quick profile

Scientific name
Pacifastacus leniusculus
Adult size
12–18 cm (4.7–7.1 in)
Lifespan
6–10 years
Temperature
4–24 °C (39–75 °F)
pH
7–8.5
Hardness
10–25 °dGH
Minimum tank
100 L (26 US gal)
Minimum length
80 cm
Swimming zone
Bottom
Social
Loose group — at least 1
Diet
Omnivore
Overall confidence
moderate confidence

What keeping this species involves

Physically robust and legally prohibited across a large part of the world. The reason not to keep it is not a husbandry one.

Rivers, streams and lakes with banks it can burrow into, in cool temperate water.

Identity and names

Common name
Signal crayfish
Scientific name
Pacifastacus leniusculus
Family
Astacidae
Order
Decapoda
Class
Malacostraca
Also sold as
Pacifastacus leniusculus, Pacific crayfish, signal crawfish

Adult size and growth

12–18 cm (4.7–7.1 in)

Typical lifespan in an aquarium: 6–10 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: depressed — flattened top to bottom with a moderate. Assigned from what is typical of Astacidae, not examined for this species.

Water and tank requirements

Recorded for completeness. Keeping this species is prohibited across the European Union and restricted elsewhere, so the tank question does not arise in most of the jurisdictions this catalogue serves.

Temperature (°C)

Signal crayfish
4–24

Scale: 0 to 36 °C.

pH (pH)

Signal crayfish
7–8.5

Scale: 4 to 9.5 pH.

Hardness (°dGH)

Signal crayfish
10–25

Scale: 0 to 30 °dGH.

The bands AquariumHQ publishes for the signal crayfish, each drawn against the full range this catalogue uses for that parameter. A narrow band on a wide scale is a specialist; a wide one is a genuinely tolerant animal. Source: AquariumHQ husbandry position for this record — an editorial range, not a measurement

Why these ranges: A cool temperate species from Pacific north-west rivers, tolerant of winter cold. The figures document the species rather than recommending a way to keep it.

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.

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 hardnessSet by a requirement of the animal
Hardness here is set by moulting rather than by habitat. A crayfish rebuilds its entire exoskeleton several times a year and draws the calcium for it from the water and from its own gastroliths; in soft water the moult is where the animal dies. The band is a provision for that, and it is deliberately firmer than some of these species' recorded habitat.
RequirementValueNotes
Temperature4–24 °C (39–75 °F)Stability matters more than hitting an exact figure.
pH7–8.5A stable pH outside the ideal band is usually better than an unstable one inside it.
General hardness10–25 °dGHCheck your supplier's published figure before choosing species.
Minimum volume100 L (26 US gal)A floor, not a recommendation.
Minimum footprint80 cm long × 45 cm deepRecorded for completeness. Keeping this species is prohibited across the European Union and restricted elsewhere, so the tank question does not arise in most of the jurisdictions this catalogue serves.
Water flowmoderateMatch the outflow to this rather than to the filter's rating.
Lid requiredRecommendedReduces evaporation and prevents accidents.
StructureRock, gravel and bank material it can burrow into, with a fully covered tank.

Group size and social behaviour

Aggressive and dominant over native European crayfish, which it displaces from shelter as well as infecting.

Structure
Loose group
Minimum group
1

Behaviour

  • Burrows extensively into river banks, which causes measurable erosion in invaded rivers.
  • Carries Aphanomyces astaci, the crayfish plague organism, as a chronic infection without symptoms, and transmits it to European crayfish for which it is almost invariably fatal.

Telling males from females

Males have larger claws. Both sexes show the white or turquoise patch at the claw hinge that gives the species its name.

Feeding

Eats plants, invertebrates, fish eggs and carrion. Burrowing into banks is a significant secondary impact, causing erosion and collapse.

Diet type
Omnivore
Staples
Sinking pellets, Blanched vegetables, Frozen fish

Breeding

Strategy
Eggs carried beneath the female's abdomen through the winter
Difficulty
straightforward
Parental care
carries eggs

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.

Risk this species poses to common tankmates
TowardsRiskWhat it means
Small fishhighAnything that fits in the mouth is at risk once this species reaches adult size.
Adult dwarf shrimpnear-certainCover reduces losses but rarely prevents them where the risk is high.
Shrimpletsnear-certainDetermines whether a shrimp colony can grow rather than merely persist.
Snailsnear-certainApplies to snails you wanted as well as snails you did not.
Long or trailing finsnoneFin damage is an entry point for secondary infection.
PlantsconsumesTough 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.

  • The plague it carries can be transmitted on wet equipment, boots and nets as well as by the animal itself. Check, clean and dry is the standard biosecurity practice in affected regions.
  • Introduced deliberately for aquaculture and now the subject of expensive and largely unsuccessful control programmes across Europe.

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
Native to the Pacific north-west of North America; introduced and invasive across Europe and parts of Asia
Habitat
Rivers, streams and lakes with banks it can burrow into, in cool temperate water.

What the checklists say

43 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.

StatusPlacesWhat this means
Introduced34A checklist states the species arrived here with human help. That is not a statement that it is established, harmful or illegal.
Recorded as invasive1A checklist states the species is invasive here. AquariumHQ reproduces that assessment; it does not make one.
Recorded as present, establishment means not stated8The 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.

ClaimValueEvidence typeConfidenceSource
scientific namePacifastacus leniusculusObserved / measuredhigh confidenceCatalogue of Life; GBIF — Global Biodiversity Information Facility
native rangeNative to the Pacific north-west of North America; introduced and invasive across Europe and parts of AsiaObserved / measuredmoderate confidenceGBIF — Global Biodiversity Information Facility
adult size12–18 cmAquarium-literature consensusmoderate confidenceAquariumHQ husbandry synthesis
lifespan6–10 yearsAquarium-literature consensusmoderate confidenceAquariumHQ husbandry synthesis
temperature4–24 °CAquarium-literature consensusmoderate confidenceAquariumHQ husbandry synthesis
ph7–8.5 pHAquarium-literature consensusmoderate confidenceAquariumHQ husbandry synthesis
general hardness10–25 °dGHAquarium-literature consensusmoderate confidenceAquariumHQ husbandry synthesis
minimum tank volume≥ 100 LAquariumHQ editorial positionmoderate confidenceAquariumHQ husbandry synthesis
minimum tank length≥ 80 cmAquariumHQ editorial positionmoderate confidenceAquariumHQ husbandry synthesis
minimum group size≥ 1AquariumHQ editorial positionmoderate confidenceAquariumHQ 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 2026-08-29. 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. 43 distribution statements held from GBIF checklists — introduced in 34, recorded invasive in 1 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.

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.