In order to evaluate the status of aquatic resources and its vulnerability to overexploitation and global climate change in different ecosystems in the Mekong Delta, Vietnam, some studies on these aspects have been conducted. A study on fish biodiversity in Hau River, the largest branch of Mekong River running through Vietnam in the Mekong Delta, was implemented to investigate the water quality, fish diversity, plankton and benthic community. Other study was conducted in Phu Quoc Island where seahorses (Hippocampus spp.) have been considered vulnerable to overfishing to investigate their composition and abundance to serve as base for protection, management and conservation of the resource. Another study was implemented in the mangrove ecosystem in Ca Mau, the cape of Vietnam to investigate the water quality and diversity of shellfish. Details will be illustrated in the full paper with results of number of fish, phytoplankton, zooplankton and benthos species in the Hau River. Similarly, number species of seahorse and their abundance throughout the year will also be presented. The composition of shellfish including crustacean and mollusk will also be given in details. In addition to biodiversity status, water quality in different ecosystem will also be discussed in detail with variation among ecosystems and seasons.