CrayfishfreshwaterUndemanding

Dwarf Mexican crayfish

A 4 cm crayfish, small enough not to threaten most fish and interesting enough to carry a tank on its own. The orange form in trade is a captive-bred colour strain; the wild species is endangered in its only lake.

Quick profile

Scientific name: Cambarellus patzcuarensis
Adult size: 3.5–5 cm (1.4–2 in)
Lifespan: 1.5–3 years
Temperature: 18–25 °C (64–77 °F)
pH: 7–8.5
Hardness: 8–20 °dGH
Minimum tank: 40 L (11 US gal)
Minimum length: 45 cm
Swimming zone: Bottom
Social: Loose group
Diet: Omnivore
Overall confidence: moderate confidence

What keeping this species involves

Hardy in hard alkaline water with adequate calcium for moulting.

Vegetated shallow lake margins.

Identity and names

Common name: Dwarf Mexican crayfish
Scientific name: Cambarellus patzcuarensis
Family: Cambaridae
Order: Decapoda
Class: Malacostraca
Also sold as: CPO, orange dwarf crayfish

Adult size and growth

3.5–5 cm (1.4–2 in)

Typical lifespan in an aquarium: 1.5–3 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.

Water and tank requirements

Floor area and hiding places; each individual needs its own shelter, particularly around moulting.

Requirement	Value	Notes
Temperature	18–25 °C (64–77 °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	8–20 °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	Floor area and hiding places; each individual needs its own shelter, particularly around moulting.
Water flow	low	Match the outflow to this rather than to the filter's rating.
Lid required	Recommended	Reduces evaporation and prevents accidents.
Structure	Many small caves and dense cover. A moulting crayfish is defenceless and must be able to hide.

Behaviour

Moults regularly and is vulnerable for a day or two afterwards.
Will catch a sleeping fish occasionally; slow bottom-dwellers are most at risk.

Feeding

Leave the discarded shell in the tank — the animal eats it to recover calcium.

Diet type: Omnivore
Staples: Sinking pellets, Blanched vegetables, Frozen foods, Leaf litter, Its own moulted shell

Breeding

Strategy: Female carries eggs and juveniles under the tail
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
Towards	Risk	What it means
Small fish	low	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	moderate	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	nibbles	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.

Never release a crayfish. Non-native crayfish are among the most damaging freshwater invaders in Europe and carry crayfish plague, and keeping several species is prohibited in the EU.
Copper-sensitive, like all crustaceans.

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: Lake Pátzcuaro, Michoacán, Mexico — endemic and endangered in the wild
Habitat: Vegetated shallow lake margins.

What the checklists say

4 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	3	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

Several non-native crayfish are listed as invasive alien species of Union concern in the EU, with keeping and sale prohibited. Restrictions differ by species and by country — check before acquiring any crayfish, and never release one.

What AquariumHQ has recorded, by jurisdiction, with the instrument each entry comes from and how far the check went. Ecological risk and legal status are separate: a species can be ecologically risky and legally unrestricted, or restricted where it could never establish.

GB — England and Wales

Permit requiredpossession

Article 2(1) provides that no person shall keep any live crayfish except under the authority of a licence granted by the Minister. The prohibition is drawn at FAMILY level — it covers freshwater decapod crustaceans of the Astacidae, Cambaridae and Parastacidae — with two exceptions: the native white-clawed crayfish Austropotamobius pallipes, and the signal crayfish Pacifastacus leniusculus within the postal districts listed in the Schedule.

Instrument: Prohibition of Keeping of Live Fish (Crayfish) Order 1996, article 2(1)

Cambarellus patzcuarensis is a member of the Cambaridae, so the dwarf Mexican crayfish sold openly for aquariums is inside the prohibition. This surprises a great many aquarists, because the animal is a few centimetres long and the legislation is popularly associated with the signal crayfish. Checked against the instrument itself; the family-level scope is wider than Mega Sprint 2 recorded.

Checked against the instrument · last checked 2026-08-11 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

GB

Prohibitedrelease

Release or escape of any non-native animal is an offence. Crayfish are among the aquarium animals most capable of establishing in temperate fresh water, and several European crayfish populations began exactly this way.

Instrument: Wildlife and Countryside Act 1981, section 14

Instrument recorded, species entry not re-checked · last checked 2026-08-11 · AquariumHQ has recorded the instrument and what it does, but has not re-confirmed this species' entry against the current consolidated text. Listings are amended, so treat this as a pointer to the right law rather than as a confirmation of the current position, and check with the authority before acting.

AU

Prohibitedimport

Australia operates a permitted list: a live specimen may be imported only if it appears on the list. Non-native freshwater crayfish are not generally permitted, so the absence of the species from the list is itself the restriction.

Instrument: Environment Protection and Biodiversity Conservation Act 1999 — List of Specimens taken to be Suitable for Live Import

This is the inverse of how prohibited-list jurisdictions work, and it changes what 'not on the list' means. In the EU, not being listed means not restricted by that instrument. In Australia, not being listed means not importable.

CA

Not verified by AquariumHQpossession

The federal schedule was read in full on 2026-08-11. The only crayfish it lists is the rusty crayfish, Orconectes rusticus, at Part 2 item 89, and that listing applies to Manitoba rather than to Canada as a whole. Cambarellus patzcuarensis does not appear anywhere in it, so no restriction was identified. That is not a finding that keeping this species is lawful in Canada: the provinces legislate separately and have not been checked here, and schedules are amended. Check with the relevant authority before acquiring, selling or moving any animal.

Instrument: Aquatic Invasive Species Regulations (SOR/2015-121), Schedule

ABSENCE FROM A FEDERAL SCHEDULE IS NOT PERMISSION. Canada's provinces legislate on invasive species in their own right, and several maintain lists considerably broader than the federal one. What has been established here is a negative about one instrument, not a positive about Canadian law: this species is not federally scheduled, and AquariumHQ has not checked any provincial regime. The status stays unverified for that reason.

Checked against the instrument · last checked 2026-08-11 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

EU

Not verified by AquariumHQpossession

No restriction was identified in the sources AquariumHQ checked for the EU as of 2026-08-11. That is not a finding that keeping, selling or moving this species is lawful there: sub-national rules, permit regimes and trade-specific requirements exist that these sources do not cover, and lists are amended. Check with the relevant authority before acquiring, selling or moving any animal. Specifically: the crayfish entries on the Union list are named species — Faxonius limosus, Faxonius virilis, Pacifastacus leniusculus, Procambarus clarkii and Procambarus virginalis — and Cambarellus patzcuarensis is not among them. A genus or family the list does not name is not thereby permitted; it is merely not caught by this instrument.

Checked against the annex rather than assumed. The Union list names species individually and does not use genus-level entries for crayfish, which is the opposite of the drafting used in the England and Wales crayfish order.

Checked against the instrument · last checked 2026-08-11 · An editor has read the current text of the named instrument and confirmed this species' entry on the date shown.

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	Cambarellus patzcuarensis	Observed / measured	high confidence	Catalogue of Life; GBIF — Global Biodiversity Information Facility
native range	Lake Pátzcuaro, Michoacán, Mexico — endemic and endangered in the wild	Observed / measured	moderate confidence	GBIF — Global Biodiversity Information Facility
adult size	3.5–5 cm	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
lifespan	1.5–3 years	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
temperature	18–25 °C	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
ph	7–8.5 pH	Aquarium-literature consensus	moderate confidence	AquariumHQ husbandry synthesis
general hardness	8–20 °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 2026-08-11. 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. 4 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 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 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 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 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 would improve this: Go and read a source. This is reachable and has not been reached.

Dwarf Mexican crayfish

Quick profile

What keeping this species involves

Identity and names

Adult size and growth

Water and tank requirements

Group size and social behaviour

Behaviour

Feeding

Breeding

Tankmates and compatibility

Welfare considerations

Problems to watch for

Where it comes from

What the checklists say

Legal status and responsible practice

GB — England and Wales

GB

AU

CA

EU

Evidence

Why we say this