Sao Francisco basin

The white piranha, Serrasalmus brandtii, may be restricted to the rio São Francisco watershed in eastern Brazil. Also known as 'green piranha' or 'Brandt's pirambeba', it appears infrequently in the trade, and its name is sometimes misapplied to the distantly related Pygopristis denticulata. Adults are uniformly golden-bronze with dark fin margins and a concave head profile above the eye. It is best kept alone as a single specimen.

The saddle cichlid, Aequidens tetramerus, is a cichlid found across much of northern South America, from the Amazon and Orinoco basins to the Guianas. The type species of its genus, it occurs in several colour forms, and fish from Ecuador and Peru are sought after for the red or orange colouration on the lower head and belly. As currently recognised it is likely to represent a group of related fishes, some of which may be described as distinct species.