Blue Swimmer Crab

The blue swimmer crab is a species of swimming crab native to the coastal waters of the Indo-Pacific, ranging from the Persian Gulf and eastern Africa through South and Southeast Asia to Australia and Japan. Its rearmost pair of legs is flattened into broad paddles, which the crab uses to swim through open water rather than only walk along the bottom. Males carry a bright blue tint across the claws and carapace, while females show a duller, mottled brown and olive coloring, a difference used to tell the sexes apart at a glance. The species spends daylight hours buried in sand or mud on estuary floors and shallow coastal flats, emerging at night to forage as an active predator and scavenger. It supports one of the largest crab fisheries in the Indo-Pacific region, caught and farmed across countries from India to Australia. Despite the shared common name, it is a separate genus from the Atlantic blue crab and belongs to its own lineage native to a different ocean basin entirely.