Metynnis is a genus of serrasalmid fish from tropical and subtropical South America.

[1] They are herbivorous or omnivorous, and inhabit a wide range of freshwater habitats, ranging from rivers and streams (both fast- and slow-flowing), to floodplains, flooded forests, lakes, pools and reservoirs.

[2] They generally reach 8–15 cm (3–6 in) in standard length,[2] although a few species may reach up to 18 cm (7 in).

[1] The genus contains many of the species known as silver dollars in the aquarium trade.

There are currently 15 recognized species in this genus:[1] C. G. E. Ahl, 1923 C. G. E. Ahl, 1923 Pavanelli, Ota & Petry, 2009 C. G. E. Ahl, 1931 C. H. Eigenmann, 1915 (J. P. Müller & Troschel, 1844) (Cope, 1870) Zarske & Géry, 2008 Cope, 1878 (Kner, 1858) Ota, Rapp Py-Daniel & Jégu, 2016[3] C. H. Eigenmann & C. H. Kennedy, 1903 (Steindachner, 1908) C. G. E. Ahl, 1923 Zarske & Géry, 2008