Gymnotichthys Fernández-Yépez, 1950 Opisthanodus Ahl, 1935 Moenkhausia is a genus of freshwater fish in the family Characidae native to tropical and subtropical South America.

These are medium-sized tetras where the largest species only reach around 12 cm (4.7 in).

[1] The diamond tetra and red-eye tetra, which are commonly kept in aquaria, are members of this genus.

[2][3] There are currently 90 recognized species in this genus: