Using constructed wetlands (CWs) for purification of aquaculture water is a quite new technique in the Mekong Delta, Vietnam, where aquaculture wastewater is commonly discharged without treatment into the adjacent water bodies. This practice creates environmental problems in the rivers as well as spreading of diseases between aquaculture farmers who use the polluted river water as a water supply in their ponds (Thien et al., 2007; Nhan et al., 2008). Recirculating aquaculture systems are recognized as appropriate systems with minimal ef?uent discharge, ef?cient water reuse and optimal water conservation compared to conventional intensive ?sh ponds (Losordo et al., 1998). The aim of the present study was to assess the suitability of using CWs as a tool to treat ?shpond water in recirculating aquaculture systems, and to compare the performance of CWs with vertical (VF) and horizontal subsurface ?ow (HF) for nitrogen removal.