The freshwater prawn Macrobrachium lar requires its chelipeds for defensive behaviors. When chelipeds are autotomized, it is beneficial for prawns to regenerate and then elongate the lost chelipeds as rapidly as possible. These prawns are hypothesized to distend their regenerating chelipeds by hydrostatic inflation immediately following ecdysis. The periods required for limb regeneration and subsequent elongation in adult M. lar were measured to be 18.8 ± 1.6 days for single cheliped replacement and 17.4 ± 1.3 for double cheliped replacement. Control prawns with both chelipeds intact were shown to molt every 19.1 ± 1.7 days. These measured periods for limb regeneration and subsequent elongation in M. lar are faster than those periods reported previously for all other adult decapod crustaceans measured from late intermolt (stage C_3–4). This rapid rate of cheliped replacement allows M. lar to minimize the amount of time they may be threatened with territory loss or predation.