Tebicuary

The tail-spot pygmy cory, Gastrodermus hastatus, long known as Corydoras hastatus, is a tiny armoured catfish with a wide range across the Amazon and Río Paraguay basins. It is known from Brazil, Bolivia, Paraguay and northeastern Argentina. Unlike most congeners it swims in midwater, forming mixed schools with similarly patterned small characids such as Serrapinnus kriegi. It is frequently confused with G. pygmaeus, but has a dark, roughly diamond-shaped spot on the caudal peduncle where G. pygmaeus has a dark lateral stripe.

The Buenos Aires tetra, Hyphessobrycon anisitsi, is a characid from the Paraná and Uruguay river systems in Brazil, Paraguay, Argentina and Uruguay. A popular and hardy aquarium fish, it is also available as a line-bred albino strain, sometimes traded as 'golden'. It has a reputation for fin-nipping, though mostly when too few are kept or space is limited, and a group of at least 8-10 is the minimum.

Corydoras aurofrenatus is an armoured catfish from the Río Paraguay-Paraná system in Paraguay, also recorded in Argentina and Bolivia. It has been traded as C. sp. 'Corrientes' and CW005. Each flank carries two dark blotches, one behind the head and one below the adipose fin, and the caudal-fin lobes are long with the upper more extended. C. ellisae has been treated as a junior synonym, although this appears not to have achieved wide acceptance.