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.