Looking at the round, flat, and shimmering silver dollar, it is easy to see how this fish acquired the name. Although many specimens seen in shops are scarcely larger than the size of a shiny dime, don't be fooled. Adults become much larger than their namesake, growing to nearly a half foot across.
COMMON NAMES: Silver dollar
SCIENTIFIC NAME: Metynnis argenteus
ADULT SIZE: 6 inches (16 cm)
LIFE EXPECTANCY: 10+ years
|Social||Peaceful, suitable for community tanks|
|Tank Level||Mid dweller|
|Minimum Tank Size||20 gallons|
|Diet||Herbivore, eats plants|
|pH||5.0 to 7.0|
|Hardness||Up to 15 dGH|
|Temperature||75 to 82 F (24 to 28 C)|
Origin and Distribution
Metynnis argenteus originates in the Tapajós River Basin in Brazil but is widespread in shallower tributaries and river systems across northern South America. It is only one of a dozen different species known in the aquarium trade as the "silver dollar." Metynnis argenteus, Metynnis hypsauchen, Metynnis lippincottianus, Myleus rubripinnis, and Mylossoma aureum are all species regularly seen for sale in the aquarium industry.
Generally considered the archetypal silver dollar, Metynnis argenteus is often confused with Metynnis hypsauchen which is similar in appearance. Metynnis argenteus can sometimes be distinguished from other species by their small dots on their sides.
Colors and Markings
Metynnis argenteus silver dollars are generally a shiny silver over the entire body, but with a slight green or blue tint in the right light. In healthy habitats, they will have small tinted dots on their sides. Hints of red will also appear, especially on the anal fin of the male, which is edged in red.
Silver dollars are a schooling fish by nature and do best when kept in schools of six or more. A very peaceful shoaling species, they do not do well on their own, but even a large group will be skittish and timid when left without shelter.
They are peaceful enough to be trusted with much smaller fish than themselves, and yet they are robust enough to handle the company of much larger species. Peaceful large catfish such as plecos and doradids would be a good choice, as would many non-aggressive cichlids.
Silver Dollar Habitat and Care
Silver dollars are hardy and easy to care for. Although this fish is fairly durable, the aquarist must maintain a very large tank for them. A school or six or more will require an aquarium of 75 gallons or larger. Silver dollars prefer subdued lighting, dark substrate, plenty of room to move about, as well as many good hiding places.
It’s advisable to use plastic plants or very sturdy live plants because they will eat most live plants. They do best in soft moderately acidic water, although they're not fussy about water conditions. Silver dollars are not overly demanding about water quality, though they do best in clean and clear, well-aerated, and well-filtered moving water.
Silver Dollar Diet and Feeding
Interestingly, silver dollars are in the same family as piranhas, but instead of being carnivores, they are almost exclusively vegetarian. Their favored foods include vegetable flakes such as spirulina, and leafy greens such as lettuce, watercress, and cooked romaine or spinach. They will also eat cooked vegetables such as peas and squash. When feeding any fresh food, take extra care to remove any uneaten portions promptly, as their decay will foul the water.
Even though the silver dollar prefers a vegetarian diet, they will also eat meaty foods as treats. They are especially fond of bloodworms, mosquito larvae (glass worms), and brine shrimp. If the silver dollars are in a community tank, watch them at feeding time to ensure that more active and aggressive fish don’t get the bulk of the food. Some silver dollar individuals can be rather timid in the crowd and can end up underfed as a result. The use of feeding rings will likely mitigate this issue.
Males have a longer anal fin that is tinged with red on its front. During courtship and breeding, the male will also develop two large black spots that are vertically arranged just behind the base of the pectoral fins. The red color on the male fins gets richer and black borders appear. Some male specimens will also display other dark marbling on the body. Females show little, if any, variation in color during courtship and breeding.
Breeding the Silver Dollar
Silver dollars are easy to breed. They will occasionally spawn without assistance in a large well-suited aquarium. To create breeding pairs, start with a half-dozen or more juveniles and raise them to maturity together. They will reach breeding age at about one year of age and about four inches in length. To optimize breeding success, it's best to condition the males and females in separate tanks prior to breeding. For seven to 10 days, feed them a high-quality plant and vegetable diet with some meaty treats.
They are naturally group spawners but they can also be bred in known pairs. Breeding pairs should be removed from their school and transferred into a breeding tank. Although the parents will not consume their own eggs or fry, other fish will, so when spawning, place them in a separate tank.
To facilitate spawning, make sure the water is soft (8 dgH or below) and warm (80 to 82 F). Keep the lighting dim, and provide fine-leafed plants; these will be eaten if they are live rather than plastic plants. When ready to spawn, the males will darken, especially around the anal, caudal, and dorsal fins, and their hints of red will intensify.
Eventually, a pair will spawn and the female will lay up to 2,000 eggs. The eggs will fall to the bottom of the tank where they will hatch in three days; they will not be bothered by their vegetarian parents. After approximately a week, the fry will be free swimming and able to eat fine foods such as commercially prepared fry food, finely crushed spirulina, or freshly hatched brine shrimp.
More Pet Fish Species and Further Research
If silver dollars appeal to you, and you are interested in some compatible fish for your aquarium, read up on:
Check out additional fish breed profiles for more information on other freshwater fish.