Red claw crab
The crab most often sold to freshwater keepers, and a brackish mangrove animal. Kept in fresh water it lasts months rather than years, and the decline is slow enough that the water is rarely blamed.
Quick profile
- Scientific name
- Parasesarma bidens
- Adult size
- 4–5 cm (1.6–2 in)
- Lifespan
- 2–3 years
- Temperature
- 24–28 °C (75–82 °F)
- pH
- 7.5–8.5
- Hardness
- 12–30 °dGH
- Minimum tank
- 60 L (16 US gal)
- Minimum length
- 60 cm
- Swimming zone
- Bottom
- Social
- Loose group
- Diet
- Omnivore
- Overall confidence
- moderate confidence
What keeping this species involves
Robust in the right water and steadily failing in the wrong one. Almost every difficulty reported with this species traces back to being sold as freshwater.
Mangrove mud between the tides, in water that is neither fresh nor sea.
Identity and names
- Common name
- Red claw crab
- Scientific name
- Parasesarma bidens
- Family
- Sesarmidae
- Order
- Decapoda
- Class
- Malacostraca
- Also sold as
- Parasesarma bidens, Perisesarma bidens, mini crab, Thai crab
Adult size and growth
4–5 cm (1.6–2 in) — Carapace width, with a leg span around twice that.
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.
Water and tank requirements
Land, water and enough floor for two crabs to avoid each other. Height is wasted.
Why these ranges: The pH and hardness here follow the salinity this animal actually needs — roughly 1.005 to 1.010 specific gravity — rather than being independent targets. Brackish water at the right density arrives at this band on its own.
| Requirement | Value | Notes |
|---|---|---|
| Temperature | 24–28 °C (75–82 °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. |
| Minimum volume | 60 L (16 US gal) | A floor, not a recommendation. |
| Minimum footprint | 60 cm long | Land, water and enough floor for two crabs to avoid each other. Height is wasted. |
| Water flow | low | Match the outflow to this rather than to the filter's rating. |
| Lid required | Yes | This species jumps. |
| Structure | Half land, half brackish water, with sand, driftwood and a secure lid. It climbs and it escapes. |
Behaviour
- Spends much of the day out of the water on wood or rock, returning to wet the gills.
- Waves the red claws in display; the gesture is directed at other crabs rather than at the keeper.
Feeding
Scavenges anything that reaches the bottom and will take slow or sleeping fish. Calcium matters as much as protein.
- Diet type
- Omnivore
- Staples
- Sinking pellets, Frozen bloodworm, Blanched vegetables, Leaf litter, Cuttlebone
Breeding
- Strategy
- Planktonic larvae requiring full sea water
- Difficulty
- rarely achieved
- 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.
| Towards | Risk | What it means |
|---|---|---|
| Small fish | moderate | Anything that fits in the mouth is at risk once this species reaches adult size. |
| Adult dwarf shrimp | high | Cover reduces losses but rarely prevents them where the risk is high. |
| Shrimplets | near-certain | 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.
- Fresh water shortens its life without ever looking like an emergency. This is the single most common welfare failure in the species.
- It will drown if the water is deep and there is no reliable way out.
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
- Mangrove coasts from Japan and China south through South-East Asia
- Habitat
- Mangrove mud between the tides, in water that is neither fresh nor sea.
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 |
|---|---|---|
| Native | 1 | A checklist states the species occurs here naturally. |
Legal status and responsible practice
Restriction note
Traded in very large numbers and recorded outside its native mangrove range in a few places, though it is not a species that features on invasive-species lists AquariumHQ has checked. No jurisdiction's rules on it have been established here. The practical point for a keeper is disposal rather than purchase: brackish tank water carries larvae and should never reach a drain that meets natural water.
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 | Parasesarma bidens | Observed / measured | high confidence | Catalogue of Life; GBIF — Global Biodiversity Information Facility |
| native range | Mangrove coasts from Japan and China south through South-East Asia | Observed / measured | moderate confidence | GBIF — Global Biodiversity Information Facility |
| adult size | 4–5 cm | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| lifespan | 2–3 years | Aquarium-literature consensus | moderate confidence | AquariumHQ husbandry synthesis |
| temperature | 24–28 °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 | ≥ 60 L | AquariumHQ editorial position | moderate confidence | AquariumHQ husbandry synthesis |
| minimum tank length | ≥ 60 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 2026-08-13. 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 — native 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.
Group size and social behaviour
Males fight over shelter. More hiding places than crabs is the difference between coexistence and losing claws.