Synonyms: Metynnis anisurus, M. dungerni, M. eigenmanni, M. heinrothi, Myletes argenteus
Physical description: A tall, laterally compressed fish that is shaped like a disk or plate. It has small eyes and a back. The base body color is silver and the fins are transparent. The belly is slightly reddish silver. A line extends through the iris. The pectoral fins are red. A string of spots extends across the body.
Size/Length: To 8" (20 cm)
Similar species: Other Metynnis species, and fish of the genera Myletes, Mylossoma, and Serrasalmus.
Habitat: South America; shallow areas of rivers with heavy vegetation in Guyana
Aquarium: 48" (122 cm) or 55 gallons (210 L) is adequate for smaller fish. Adult fish should be moved to a tank measuring at least 56" (142 cm) with a capacity of at least 75 gallons (285 L). The tank should be large and roomy with lots of open swimming areas. Provide hiding places with solid rock structures and driftwood. The lighting should be dimmed and use a dark gravel bottom. Live plants will usually be consumed, so use plastic plants as an alternative. Some robust, sturdy plants may not be bothered if the fish are fed sufficiently. Silver Dollars prefer shallow tanks.
Water chemistry: pH 6-7.5 (6.8), 4-18 dH (12), 75-82°F (24-28°C)
Social behavior: Keep with fish of relative size, as smaller fish may be eaten. The Silver Dollar does best when kept in a school of six or more fish.
Suggested companions: Other "Silver Dollars" (see "Remarks"), Loricarids, Pimelodids, South and Central American cichlids, Pacus, Arawana, Anostomus.
FOOD: Pellets; vegetables; lettuce, peas, spinach; plants; large vegetable flakes; live foods are usually accepted.
SEX: Male has a longer anal fin and has a red marking and front of belly.
Breeding techniques: Only possible in a large, shallow tank. Silver Dollars often spawn in schools. Recommend water with the following values: a pH 6.0-6.5, a water hardness of 4-8 dH, and a water temperature of 79-82°F (27-28°C). Have floating plants and slightly dimmed light. About 2000 eggs are produced by each female. The eggs fall to the bottom. Remove the adult fish after the spawning. The fry hatch in 3 days, and are free swimming after 6-9 days. They first eat plankton, but later, will take vegetable flakes.
Breeding potential: 9. Breeding is difficult because of the volume of water needed for a group of fish to spawn.
Remarks: Over 20 species of Metynnis are available, with most species reaching about 8" (20 cm) in size. "Silver Dollars" sometimes include other genera including Mylossoma and Myleus. These genera are difficult to distinguish, although differences are usually apparent in the adipose fin. Metynnis have a long-based adipose fin, while Mylossoma and Myleus have a short-based, rounded adipose. An important food fish in South America.
Difficulty of care: 5. The Silver Dollar is a hardy fish that, because of its size, must be kept in a large tank.