Two new species of darter tetra have been described from eastern Brazil by Brazilian scientists Weferson da Graça, Carla Pavanelli, and Paulo Buckup in the latest issue of the journal Copeia. The two new species are named Characidium nupelia and Characidium xavante. Characidium is the most speciose genus of the family Crenuchidae, including 50 valid species, distributed in most freshwater drainages in tropical and subtropical areas of the Neotropical Region located between eastern Panama and La Plata, Argentina.

Characidium nupelia

This species is distinguished from other members of the genus in having a combination of: 12–18 dark vertical bars on the body, with each bar having the width of a scale, 12 scales around the caudal peduncle, interorbital distance 20.5–28.6% head length, caudal peduncle depth 46.2–57.8% head length, the absence of an adipose fin, incomplete lateral line, and a dark blotch on the caudal peduncle. Characidium nupelia was collected in the region affected by the construction of the Manso Hydroelectric Reservoir in the upper Rio Paraguay basin. It is named in recognition of the role of the Nupélia (Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura) in the survey and ecological research of the fish fauna from the Manso Reservoir region, which led to the discovery of this new species.

Characidium xavante

Characidium xavante is distinguished from other members of the genus in having a combination of: 12–18 dark vertical bars on the body, with each bar having the width of a scale, 10 scales around the caudal peduncle, interorbital distance 30.1–38.0% head length, caudal peduncle depth 35.4–44.9% head length, the absence of an adipose fin, incomplete lateral line, and a dark blotch on the caudal peduncle. Characidium xavante was collected from two small tributaries of the upper Rio Xingu basin and is named after its type locality (Xavante is a name of an indigenous Brazilian ethnic group, inhabiting the region where the type locality is found, with the stream at the type locality being named after the ethnic group).