Silver Dollar

Although closely related to the piranha, silver dollar fish are generally peaceful. People don’t tend to fish for or consume them, but these freshwater fish are popularly kept in aquariums around the world.

An Incredible Fish: Five Silver Dollar Facts

• Silver dollar fish belong to the same family, Characidae, as piranha fish and pacu fish. Unlike those types of fish, however, they are not aggressive.
• One of the most striking things about the silver dollar fish is its extremely flattened appearance, which is akin to that of a silver dollar coin.
• Although silver dollar fish are omnivores, they feed primarily on plant matter and vegetation. If kept in an aquarium with living plants, they will typically consume all of them.
• There are at least 16 species of these fish across two genera. However, when people talk about silver dollar fish, they are usually referring to one of two species: Metynnis argentus and Metynnis hypsauchen.
• Thanks to their peaceful nature and fondness for schooling together, they are popular additions to freshwater aquariums.

Classification and Scientific Name

These fish belong to the class Actinopterygii, the order Characiformes, the family Characidae, and primarily the genus Metynnis, of which there are 14 described species. Two described species of these fish also belong to the genus Myloplus.

That being said, the most common fish that are considered to be silver dollar fish are Metynnis argentus and Metynnis hypsauchen, which are virtually identical to one another. The primary distinguishing feature between the two is the presence of black patches behind the eyes and on the body of M. hypsauchen.

This fish comes by its name honestly. The name for the most common species, Metynnis argentus, translates as follows: Metynnis means “with plowshare,” which indicates a flattened appearance; argentus means “covered with silver,” which belies the fish’s silvery appearance and coloring.

Species

These fish are members of the family Characidae, which consists of 217 genera and 1,464 species of fish. Within the two primary genera, Metynnis and Myloplus, there are 14 and two described species, respectively. Some notable species of these fish include:

• Silver dollar fish — Species that are called simply this are Metynnis argentus and Metynnis hypsauchen, which are practically identical.
• Red hook silver dollar fish — This species, Myleus rubripinnis, has different coloring and distinctive fin shapes when compared to generic silver dollar fish. In the wild, they can grow to lengths of up to 22 inches.
• Spotted silver dollar fish — Found primarily in French Guyana and Brazil, this fish grows up to 6.5 inches in length and has patterns of black dots.
• Other common types of silver dollar fish include the striped silver dollar fish, or M. fasciatus; the red-spotted silver dollar fish, or M. luna, which is known for its spotted appearance; the speckled silver dollar fish, or M. maculatus; and the black-barred silver dollar fish, or M. otuquensis.
• Tiger silver dollar fish — This fish, Metynnis fasciatus, is striped like a tiger and lives primarily in rivers in the Amazon rainforest.

Appearance

As its common name implies, this fish looks uncannily like a large silver dollar coin. These fish have round, laterally flattened bodies, are very deep-bodied, and grow to an average of 6 inches in length. Their overall coloring is silvery, but slight hints of green and blue tinting can be seen in the right light conditions.

Males and females look largely the same. However, males have fins that are slightly longer and that are tinged red.

As noted previously, some types of these fish vary in appearance and coloring. Some have patches, spots, stripes, or bar-like patterns. Myleus rubripinnis, the red hook silver dollar fish, features a red anal fin and can grow up to 22 inches in length.

Distribution, Population, and Habitat

These fish are not popularly consumed by humans, so they do not face the risk of being overfished. However, official estimates of total population numbers for these fish are not available. In the wild, these fish are endemic to South America; in particular, they are found in Guyana and in the Amazon, east of the Rio Negro to Paraguay. It is believed that they may be endemic to the Tapajos River basin in Brazil as well.

In the wild, these fish prefer rivers that are dark and filled with debris, including peat, gravel, rocks, and driftwood, which make for good hiding places. They prefer moderate water flows, and they thrive best in water with a pH level of between 5 and 7, a hardness of up to 15 dGH, and a temperature of between 24° and 28° Celsius, or 75° to 82° Fahrenheit. As pelagic fish, these fish spend most of their time near the surface of the water.

Predators and Prey

What Eats The Silver Dollar?

The primary predators of these fish are larger fish, reptiles, and birds. Humans do not enjoy fishing for or consuming these fish, so they face no risk there.

What Does The Silver Dollar Eat?

Although these fish are technically omnivores, they skew more toward being herbivores than anything else. When they do consume other animals, they tend to prey on worms and small insects.

Reproduction and Lifespan

These fish reach sexual maturity at about one year of age, or when they reach approximately 4 inches in size. In the wild, they spawn in groups in wooded, heavily vegetated, shallow waters in flooded rivers and tributaries. Males court females by chasing them around before shimmying up alongside them. Females release their eggs, around 2,000 of them, near or in floating plants. Males then fertilize the transparent, slightly yellow-colored eggs, which then fall and float off into the water. The eggs hatch in approximately three days, and the resulting fry can free swim in six to nine days; they reach adult size at about six to eight months of age.

In captivity, these fish live for an average of 10 years.