I recently did a report for school on silver dollar fish...well this was it.:
Silver Dollar Fish
Family: Serrasalmidae
Origin: Guyana
Adult Size: 5 inches (14 cm)
Social

eaceful,suitable in community tanks
Lifespan: 10+ years
Tank Level: Mid dweller
Minimum Tank Size: 20 gallons
Diet: Herbivore, eats plants
Breeding: Egglayer
Care: Intermediate
pH: 5.0 - 7.0
The silver dollar is a tropical fish belonging to the Characidae family which is closely related to piranha and. Originating in South America, this somewhat round-shaped silver fish with slight red-tinged anal fin is mostly found in aquariums. It will grow to a maximum length of approximatley 6 inches. I have two and they are still about the size of a quarter or a silver dollar. They have grown quite quickly as just last week they were no larger than a nickel.
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.
Silver Dollars are in the same family as Piranhas, but instead of being carnivores, they are almost exclusively vegetarian. Their favored foods are vegetable flakes such as lettuce, and cooked romaine or spinach. They will also eat cooked vegetables such as peas and squash.
Even though the Silver Dollar prefers a vegetarian diet, they will eat meaty foods as treats. They are especially fond of bloodworms, mosquito larvae and brine shrimp. If the Silver Dollar is in a community tank, watch them at feeding time to ensure that more active and aggressive fish don’t get all the food.
Silver Dollars can be rather timid in a crowd. The two that I own are really shy and jittery. They can swim really fast and are almost impossible to catch without getting really mad. They seem to enjoy hideing in tall weeds or grasses or in rocks,