River Swimming Crab

Varuna litterata, the River Swimming Crab or Estuary Swimming Crab, is a varunid crab distributed across river systems of South and Southeast Asia, typically found in the lower freshwater to brackish reaches of rivers where current is moderate. Its most distinctive feature is its flattened rear pair of legs, which are modified into paddle-like swimming appendages similar to those of marine swimming crabs, allowing it to swim actively through open water.

In the aquarium, V. litterata is a dynamic and entertaining inhabitant that spends time both walking across the substrate and actively swimming in the water column. It is more fully aquatic than Geosesarma and Perisesarma crabs but still benefits from access to above-water resting areas such as emergent rocks or cork bark. Brackish tolerance is noted but it can adapt to freshwater with gradual acclimatisation.

This species is omnivorous and predatory, feeding on fish, invertebrates, detritus, and plant matter in the wild. In the aquarium it should not be kept with small fish or shrimp. A species tank or paludarium with robust, fast tankmates is most appropriate.

Water: 22–28°C, pH 7.0–8.0, GH 5–15, KH 2–10; tolerates brackish; good filtration and flow. Tank: minimum 60 L, smooth substrate, rocks and cork bark above waterline for resting. Feeding: omnivore — frozen shrimp, sinking pellets, vegetables, occasional live invertebrates. Breeding: larvae likely require brackish or marine conditions; full captive cycle not documented. Compatibility: predatory — keep with large robust fish only; not safe with shrimp or small fish.