Siamese fighting fish Betta splendens are a well-known and popular aquarium fish kept in captivity around the world. The species is native to central Thailand being a member of a diverse species complex of labyrinth fishes occurring in south-east Asia. Labyrinth fishes typically occur in shallow well vegetated wetlands and forest swamps, tolerating a wide range of environmental conditions including anoxia through their capability to breathe air using an auxiliary sponge-like breathing chamber. Recently an invasion of Siamese fighting fish was uncovered on the Adelaide River floodplain, near Darwin in Northern Australia. This represents the first serious alien fish species incursion in the Northern Territory, with reports previously limited to livebearers (Poeciliidae) and cichlids in isolated habitats, many of which have been controlled by specific actions. This talk discusses the history of establishment and biological notes of Siamese fighting fish on the Adelaide River floodplain, where a very large and extensive population is now known to occur. It also canvasses areas for research on likely spread, possible impacts and potential control.