The silver dollar (Metynnis argenteus) is a tropical fish belonging to the Characidae family which is closely related to pirahna and pacú. Originating in the Tapajós River basin in South America, this somewhat round-shaped silver fish with slight red-tinged anal fin is mostly found in tanks kept by fish-keeping hobbyists. It will grow to a maximum length of 14 centimeters (5.5 inches). The silver dollar is a peaceful schooling species that spends most of its time in the mid- to upper-level of the water. Its maximum lifespan is more than 10 years. An egg-layer, the adult fish will spawn around 2,000 eggs. This breeding occurs in soft, warm water in low light. Silver dollars natively live in a tropical climate in the sides of weedy rivers. They prefer water with a pH of 5–7, a water hardness of up to 15 dGH, and an ideal temperature range of 24–28 °C (75–82 °F). Their diet is almost exclusively vegetarian and in captivity they will often eat all the plants in a tank. They will also eat worms and small insects.

Taken from WikipediA