Thai micro crab

Quick facts

Adult size

1 cm

Lifespan

can live up to 2 years

Tank zone

bottom

Temperament

peaceful

Difficulty

intermediate

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

22–28°C

pH

6.5 to 7.5

Hardness

5 to 15 dGH

Tank requirements

Minimum volume

10 L

Minimum length

25 cm

Flow

low

Lighting

any

Substrate

any

Hiding spots

needed

Feeding

Diet: omnivore, feeds primarily at the bottom.

Filter feeder and biofilm grazer. In mature tanks with established biofilm on plants, moss, and hardscape, they feed themselves by filtering particles from the water and grazing surfaces. Supplemental feeding with powdered food (spirulina powder, crushed flake dust, baby shrimp food) helps in newer or very clean tanks. They use their small chelae to pick particles from surfaces and their maxillipeds to filter the water column. They don't eat standard fish food pellets or wafers; the food needs to be fine enough for their tiny feeding apparatus. Feed every other day if supplementing.

Nocturnal feeder; drop food after lights out so it can eat without competition.

Compatibility

• One of the smallest freshwater crabs available at 1–1.5 cm. Fully aquatic, unlike most freshwater crabs that need land access.
• Extremely delicate and easily eaten. Species-only tanks or shrimp tanks are the safest option. Even small fish like neon tetras may harass or eat them.
• Peaceful and reclusive. They hide among plant roots, moss, and fine-leaved plants during the day. Expect to rarely see them unless you look carefully.
• Best housed with small shrimp (Neocaridina, Caridina) and snails. The crabs ignore shrimp and shrimp ignore the crabs.

Habitat

Native to a single river system in Thailand: the Tha Chin River (also called the Suphan Buri River), a tributary of the Chao Phraya. The species (Limnopilos naiyanetri) was described by Chuang and Ng in 2005. The extremely restricted natural range raises conservation concerns, though the species is not currently IUCN-assessed. The body is translucent gray to brown with fine hair-like setae on the legs and claws that aid in filter feeding. They look like tiny spiders more than traditional crabs. Adult size is 1–1.5 cm across the carapace. Fully aquatic; they never leave the water. Found among root masses and dense aquatic vegetation in their native river. In the aquarium, they cling to moss, plant roots, and sponge filter surfaces. Most specimens in the trade are wild-caught. Captive breeding occurs but is not common commercially. The species became available in the hobby around 2008-2010 and remains a specialty item, not a mainstream pet store offering.

Breeding

Females carry eggs under the abdomen. Larvae are thought to develop directly into miniature crabs without a planktonic larval stage, which means breeding in fresh water is theoretically possible. Reports of successful captive breeding exist but are uncommon. Sexing is difficult at this size; females may have a wider abdominal flap. Clutch sizes are very small (a few eggs). In mature, densely planted tanks, juveniles occasionally appear, suggesting spontaneous breeding. Dedicated breeding has not been widely documented, and most keepers who find baby crabs in their tanks are pleasantly surprised rather than having planned for it.

Common problems

Invisibility is the main frustration. Thai micro crabs are so small and reclusive that keepers forget they're in the tank. They hide in moss, plant roots, and filter sponge, emerging only briefly. In tanks without dense plant cover, they hide in the filter or hardscape and are essentially never seen. Provide thick moss (java moss, weeping moss) for them to inhabit. Starvation in clean tanks without biofilm is a risk; ensure the tank is mature with established surfaces before adding them. Copper sensitivity applies to all crustaceans; avoid copper-based medications. They're fragile during handling and should be transferred by scooping the moss or plant they're sitting on rather than trying to net or pick up the crab directly. Availability is inconsistent and they're more expensive than most common aquarium invertebrates.

Bioload

Bioload coefficient: 0.2 (1 cm crab; essentially zero bioload).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size