Symphysodon (discus) is the most demanding mainstream freshwater fish. Three recognized species: S. aequifasciatus (Blue/Brown), S. discus (Heckel), and S. tarzoo (Green/Tefe). Wild type discus from each species commands premium pricing; the captive-bred designer lines (Marlboro Red, Pigeon Blood, Blue Diamond, Snow White) are far easier to keep.
Discus demands soft acidic water (pH 5.5-7.0, GH 1-8 depending on lineage), warm temperatures (82-86°F), and large groups (6+ specimens) to disperse aggression. Wild-caught Heckel needs the most demanding setup - black water tanks at pH 4.5-6.0 with extensive Indian almond leaf and driftwood tannins.