Physical restoration of dykes and water gates along the shorelines of the Prey Nup area was done in 1998 to preserve rice field areas from being washed-off during high tides. The four first polders constructed resulted in the recuperation of about 5,500 ha for rice field cultivation. Before the rehabilitation, the area was also a common dwelling place for freshwater, brackish water and marine fish species (43 species). Information regarding effects of seasonal variations on species richness and stock assessment were obtained from capture surveys of native fishermen using 11 different kinds of fishing gears from 1998 to 2001. The influence of rehabilitating the area on the fish community species richness, stock recruitment and dynamics were investigated. Surveys showed that the marine fish species (11) were completely wiped-out from this area leaving only about 31 brackish and freshwater species. These remaining species, coming from the upstream catchment areas, colonized these rice fields especially during the rainy