Thai dwarf rock crab

Care at a glance

Overview

A mostly peaceful bottom dweller that spends the day grazing biofilm and algae off rock and wood and picking over the substrate. It lives well in a small group and gets along with snails, larger shrimp, and fish too quick to catch, but slow or tiny fish and shrimplets can be taken. Keep the water at 22 to 28 C with a pH of 6.8 to 7.8 and some hardness, keep copper medications out, and offer sinking pellets, algae wafers, blanched vegetables, and the odd frozen bloodworm. Cuttlebone or another calcium source helps with molts. Most stock is wild caught, so quarantine new arrivals.

In the wild

The Thai dwarf rock crab is a small, fully aquatic freshwater crab imported from Thailand, where Siamthelphusa crabs live in slow, plant-lined streams and flooded rice country. It does not need a land section, so keep it in a normal aquarium of 40 liters or more with a sand bed, stacked rock and driftwood to cling to, mosses, and gentle flow. Use mineral-rich water in the 22 to 28 C range with a pH of about 6.8 to 7.8, since soft water makes molting go wrong. Fit a tight lid, because it climbs airline and heater cables.

Good to know

This crab belongs to the Gecarcinucidae, the big family of Asian freshwater crabs that skip the sea entirely and hatch fully formed young. The genus Siamthelphusa was set up by Bott in 1968 and holds nine described species from Thailand and Malaysia, five of them added in a 1997 revision by Ng and Naiyanetr; the trade animal has never been firmly matched to one of them, so it is sold as Siamthelphusa sp., although one shop lists it as S. retimanus. The name Siamthelphusa ranongensis that circulates in the hobby is not a described species; no paper has ever published it, and it looks like a made-up label after Ranong province. Shops quote about 6 to 7 cm across the legs, which puts the carapace near 3 cm, and the true adult size of the trade form is not on record.

Common questions

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