Thai micro crab

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

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.

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.

Origin and habitat

Endemic to a single river: the Tha Chin River in Nakhon Pathom Province, Thailand; no confirmed population has been found anywhere outside this river basin. First scientifically described in 1991 by Christina Chuang and Peter Ng. The species name honors Professor Phaibul Naiyanetr of Chulalongkorn University. The genus name Limnopilos loosely translates to "freshwater hairy," referencing the bristle-covered body. A member of the family Hymenosomatidae (false spider crabs). Wild individuals were found clinging to the roots of floating water hyacinths (Eichhornia crassipes) in slow-moving, plant-dense water. The extremely restricted natural range raises conservation concerns, though no IUCN assessment exists. Carapace reaches only about 1 cm in width at maturity; leg span may reach 2.5 cm. Semi-translucent, ranging from grey to light brown; the carapace and chelipeds are covered in soft setae (hairs) that collect detritus and may provide food or serve as camouflage. Fully aquatic; never leaves the water. A filter feeder and scavenger that extends feathery appendages into the water column to collect suspended particles and biofilm. First introduced to the aquarium hobby in 2008 through a German importer. Remains a specialty item. Lifespan roughly 1-1.5 years.

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 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

Further reading

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