In an attempt to investigate the feasibility of stock enhancement of the predominant mud crab species, Scylla paramamosain in the Mekong Delta, Vietnam, a number of investigations were undertaken including collection of background fishery information, abundance, recruitment, population dynamics, growth, effects of tagging on growth and survival of crabs, and fitness of hatchery-reared and wild crabs. Results from the investigation of seasonal abundance and recruitment of S. paramamosain in a selected estuarine mangrove area revealed that they are persistent throughout the year, despite the freshwater period during the monsoon season. However, the peak in abundance coincided with the dry season when salinity is higher ( l 5-20ppt). Salinity tolerances/preferences in juveniles under laboratory conditions indicated that crabs are not able to survive in 0ppt for more than one week and the most preferable salinities are 15-20ppt. This range of salinity is consistent with the peak abundance of crabs in the wild but the mechanism for survival of wild crabs in freshwater is not known. Application of microwire tagging in S. paramamosain showed no significant effects on growth and survival of crabs. Juvenile crabs as small as 20 mm CW can be tagged successfully. Using this tagging method in a mark-recapture study has, for the first time, enabled determination of growth rate in S. paramamosain under natural conditions. The growth rate was similar to that obtained in pond conditions and indicates that crabs may attain an adult size 3-4 months after release. This is encouraging for future potential stock enhancement. However, abundance estimates for S. paramamosain from the mark-recapture study showed that monthly recruitment in the selected study area over a twelve month sampling period in 2000 was fairly high, with a sharp peak in March of 1,269,809 month^-1 falling to 114,512 month^-1 in November. This indicates that a restocking program in this area may be unworkable as a huge number of hatchery-reared juveniles would need to be produced to make a significant difference to the already substantial natural influx of recruits. Fitness of hatchery-reared crabs was found to be affected by several factors including nutrition and rearing techniques and still needs to be improved, although they were found to exhibit superior growth than their wild conspecifics in one experiment. Production of hatchery-reared juveniles through the nursery phase may be successful, with application of bricks as shelters and shrimp as diet. However, further investigations of suitable stocking densities, use of shelters/substrates and diets to support economical effectiveness are required.