Mesonauta festivus, the flag cichlid, is a species of cichlid native to the Paraná, Paraguay, Madre de Dios, Guaporé, Mamoré, Jamari and Tapajós river basins in Brazil, Peru, Paraguay and Bolivia. It can reach a standard length of 12.1cm (04.8inches) and is sometimes kept in aquariums.
It was generally recognized as the only valid species in the genus Mesonauta until 1991 when a taxonomic review found that five species should be recognized (a sixth was described in 1998).[1] As a consequence aquarium specimens have generally been labelled M. festivus, but this species is seen far less often than some of its relatives, especially M. guyanae, M. insignis and M. mirificus.[2] The other species in the genus have a more northernly range than M. festivus.[1]