Thai dwarf rock crab
Siamthelphusa sp.
Also known as Siamthelphusa ranongensis, Thai micro rock crab, Mekong crab, Thai rock crab, Thai creek crab, Mekong freshwater crab
FreshwaterCrab
Care at a glance
- Temperature
- 72–82°F
- 22–28°C
- pH
- 6.8–7.8
- Adult size
- 1.2 in
- 3 cm
- Minimum tank
- 11 gal
- 40 L
- Temperament
- Mostly peaceful
- Social behavior
- Social
- Tankmates
- With caution
- Swim level
- Bottom
- Diet
- Omnivore
- Difficulty
- Easy
- Breeding
- No record
- Rarity
- Rare
- Family
- Gecarcinucidae
- Origin
- Thailand
Overview
The Thai dwarf rock crab is a small, fully aquatic bottom dweller that needs no land section. It is easy to keep.
Did you know
The name most keepers use for the Thai dwarf rock crab, Siamthelphusa ranongensis, does not exist in science. No paper has ever published it, and it looks like a made-up label after Ranong province. Ranong sits on Thailand's Andaman coast, a long way from the Mekong that the crab's other trade name points to.
Caring for the Thai dwarf rock crab
Keep the Thai dwarf rock crab in a normal aquarium of 11 gal (40 L) or more. Give it a sand bed, stacked rock and driftwood to cling to, mosses and gentle flow. Fit a tight lid, because it climbs airline and heater cables.
Use mineral-rich water with some hardness, at 72 to 82°F (22 to 28°C) and a pH of 6.8 to 7.8. Soft water makes molting go wrong, and cuttlebone or another calcium source helps with molts. Keep copper medications out of the tank.
It spends the day grazing biofilm and algae off rock and wood and picking over the substrate. Offer sinking pellets, algae wafers, blanched vegetables and the odd frozen bloodworm.
The Thai dwarf rock crab is mostly peaceful and lives well in a small group. It gets along with snails, larger shrimp and fish too quick to catch, but it can take slow or tiny fish and shrimplets. Most stock is wild caught, so quarantine new arrivals.
Good to know
It belongs to the Gecarcinucidae, the big family of Asian freshwater crabs that skip the sea entirely and hatch fully formed young. Bott set up the genus Siamthelphusa in 1968, and it holds nine described species from Thailand and Malaysia. Ng and Naiyanetr added five of them in a 1997 revision. The trade animal has never been firmly matched to one of them, so it is sold as Siamthelphusa sp. One shop lists it as S. retimanus. Shops quote about 6 to 7 cm across the legs, which puts the carapace near 3 cm. The true adult size of the trade form is not on record.
In the wild
The Thai dwarf rock crab is imported from Thailand, where Siamthelphusa crabs live in slow, plant-lined streams and flooded rice country.
Common questions
What size tank does a Thai dwarf rock crab need?
A Thai dwarf rock crab needs at least 11 gal (40 L). It spends most of its time in the bottom.
What temperature and pH does a Thai dwarf rock crab need?
A Thai dwarf rock crab is comfortable at 72–82°F (22–28°C) with a pH of 6.8–7.8.
What does a Thai dwarf rock crab eat?
A Thai dwarf rock crab grazes biofilm and algae off rock and wood and picks over the substrate. Offer it sinking pellets, algae wafers, blanched vegetables and the odd frozen bloodworm.
How big does a Thai dwarf rock crab get?
An adult Thai dwarf rock crab reaches about 1.2 in (3 cm).
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