Systematics of the cichlid genus Symphysodon has been investigated and three species are recognised: S. discus
Heckel, 1840 (synonym: S. discus willischwartzi Burgess, 1981); S. aequifasciatus Pellegrin, 1904 (synonyms: S. discus var. aequifasciata Pellegrin, 1904; S. aequifasciata aequifasciata sensu Schultz, 1960; S. Discus Tarzoo – sic –Lyons, 1960); and S. haraldi, Schultz, 1960 (synonyms: S. aequifasciata haraldi Schultz, 1960; S. aequifasciata axelrodi Schultz, 1960). The present revision is based on DNA sequences of partial  mitochondrial control regions of 48 specimens of Symphysodon from 20  different locations in the central and lower Amazon basin, which revealed three genetically distinct clades of Symphysodon. One of these genetic clusters is composed of specimens that  morphologically are S. discus, but also of S. haraldi and natural hybrids of S. discus x S. haraldi. This indicates that either the “discus” clade is composed, at least partially, of hybrids or, alternatively, that a “haraldi” phenotype evolved (or was retained)  independently in this clade. The other two clades consist of S. aequifasciatus and S. haraldi