Apareiodon affinis, the darter characine, is a species of fresh water ray-finned fish native to the Río de la Plata Basin in southern Brazil, Paraguay and northern Argentina.

[2] The darter characine is a small, fusiform fish growing to a maximum length of 14.3 cm (5.6 in).

There are no dentary teeth and the pectoral fins have a single, unbranched fin-ray which the fish uses to prop itself up on the substrate.

In the Upper Paraná basin, the sexes have distinct diploid numbers, the males showing 2n = 54 and the females 2n = 55.

[6] This is a non-migratory species and its reproductive strategy involves external fertilisation and a lack of parental care of eggs or young.