Found in mostly Brazil’s Rio Negro, this fish has a distinguishing dark “fifth” stripe and has both red and blue varieties. It’s named after ichthyologist Johann Jacob Heckel and is the most difficult discus to keep, because it likes somewhat softer (and lower pH) and warmer water than the other species. It has two subspecies, the Blue Head Symphysodon Discus Discus – which has a blue head (obviously), and the Symphysodon Discus Willischwartzi.