Metynnis

Metynnis is a genus of serrasalmid fish from tropical and subtropical South America. 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. They generally reach 8–15 cm (3–6 in) in standard length, although a few species may reach up to 18 cm (7 in). The genus contains many of the species known as silver dollars in the aquarium trade.

Though part of the subfamily Serrasalminae, members of this genus are not commonly called piranhas, due to their largely herbivorous diets.