The giant freshwater prawn (Macrobrachium rosenbergii) is one of the most important crustacean species produced in inland aquaculture in many tropical and subtropical countries worldwide. The aim of the current study was to evaluate the growth performance of three strains of giant freshwater prawn that originated from geographically separated locations in a complete (3×3) diallel cross as a starting point for a stock improvement program for the industry in Vietnam. Crosses were established over two generations using two wild Vietnamese river populations (Dong Nai and Mekong) domesticated for the study and an introduced Hawaiian strain that had been in culture for many generations. Juveniles from nine strain combinations were produced using single-pair matings. Results after 15 weeks of grow-out in hapas showed that growth performance of the Hawaiian strain was best among the purebred strains and that certain cross combinations grew significantly faster than purebred strains. Mean body weights of specific cross combinations with Dong Nai or Mekong as dams and the introduced strain (Hawaiian) as sires were significantly heavier than those of purebred Dong Nai or Mekong strains. While males reached heavier mean weights than females, male variation among the strains was obscured by social factors that produced different frequencies of male morphotypes (blue claw, orange claw and small males). Results suggest presence of potentially valuable heterosis and possible impact of the direction of cross. From a practical viewpoint this could be exploited upon by either, including different forms of crossbreeding, or alternatively, by creating a composite population for future selection. Potential problems and challenges encountered during the trials are discussed.