The silver dollar is one of the most popular freshwater schooling fish. The name comes from their silver, scale-less sides that resemble a silver dollar. Silver dollars are actually closely related to tetras, and have the same easygoing temperament as larger tetras such as the Buenos Aires Tetra. Despite being hardy and relatively well-mannered, silver dollars do require some extensive research before you go out and buy your own. This article applies to most of several different species of silver dollar, but the various recommendations in this article are targeted specifically for Metynnis argenteus, which is the species of silver dollar most commonly sold in pet stores.
The primary challenge with silver dollar fish relates to their size; regardless of their relatively non-aggressive demeanor, they will still eat anything that fits in their mouths just like any other fish. In other words, by the time the silver dollar reaches adulthood, it may very well be able to snack on its compatibly-tempered tank mates. The other challenge -- which is primarily size-related -- is that these are a very shy schooling fish that prefer to be in groups of five or more. Simply the fact that they’re large schooling fish brings in another serious consideration – they prefer to life in groups of at least five, and with a fish that easily reaches 8” in diameter they do have some pretty demanding space requirements.
Silver Dollar Housing
Generally, silver dollars are sold young and measuring between approximately an inch to an inch and a half in diameter. Don’t be fooled – healthy silver dollars achieve their full size very quickly and must have plenty of extra swim space. A standard 55G aquarium is the minimum size for a school of five silver dollars, and that’s assuming that they’re the only fish in there.
You’ll want to find a good filter for the aquarium that turns over at least six times the total water volume in the tank every hour. In other words, a 55G tank will require a filter rated for no less than 330G turnover per hour. Silver dollars are not strong swimmers, and prefer only gentle currents in the aquarium. Most HOB (hang-on-back) work very well for a silver dollar tank.
Silver dollars are avid vegetarians that will readily eat live aquarium plants. Hardy, broad-leafed plants may be safe in the tank provided the fish have a well-balanced diet with vegetable supplements, but stick to low-cost plants that won’t leave you devastated if they eat them.
With healthy water and sufficient space a silver dollar should not jump above the water line very often, but bear in mind that they can. Just in case, make sure to invest in a tight-fitting lid that completely covers the top of the aquarium in order to avoid the risk of having a fish jump out.
Nitrate levels need to be kept under 40ppm with partial water changes, but under 20ppm is generally appreciated by the aquarium inhabitants. Vacuuming your gravel regularly will ensure that waste and uneaten food are removed regularly, and this will help keep nitrate levels under control. Be aware that a properly-cycled tank should not have any ammonia or nitrite in the water whatsoever, and if your tank is testing with it then either the aquarium is not properly cycled, or too many new fish were added in at once. This will cause an ammonia spike, which will have to be controlled with very frequent partial water changes until it balances back out.
Proper Feeding of Silver Dollars
Silver dollars must have a variety of different food to really thrive, just as with any other type of fish. No species of creature can get all their nutritional needs met through a single food source, and the same is true for silver dollar fish – they can live, but not thrive off of only a single flake or pellet food off the pet store shelves.
As mentioned previously, a silver dollar’s diet must include a vegetable of some kind such as algae wafers, spinach, wilted greens (i.e. mustard greens, dandelion greens, or turnip greens) or romaine lettuce (it’s harder for them to eat fresh greens that have not wilted), or cooked vegetable such as peas, squash, or green beans.
Small amounts of meaty food are required. Consider live or frozen baby brine shrimp, grindel worms, micro-worms, or similar easy-to-obtain food. If all else fails, freeze-dried blood worms, krill, or shrimp pellets will work, though these are not ideal.
Off-the-shelf flakes and pellets can be added into the feeding rotation as some lower-cost filler, as fish do not require very rich food for every feeding. There is some nutritional value in these foods, but very little in average store brands, so it is definitely recommended not to use them alone.
Good Silver Dollar Tank Mates
The relatively docile and somewhat shy silver dollars need tank mates with similar temperaments, which generally includes medium to large tetras (i.e. Buenos Aires, serpaes, phantoms, black skirts, etc.). If there is enough space, they can also be housed with giant danios, and occasionally smaller pearl or zebra danios.
Corydoras, botia loaches, bristlenose plecostamus, and other bottom dwellers that range from medium to large often do well in a silver dollar tank. Bear in mind that the plecostamus most often sold in pet stores, the common plecostamus, may not do well with silver dollars; they are notorious “slime suckers” and may injure the larger fish by eating their slime coat. Silver dollars do well with the aforementioned fish because they stay primarily around the middle level of the tank, so larger fish that prefer the bottom and the top get along quite well with them.
Every species of fish has unique needs, so be sure to always thoroughly research prospective new additions to the tank before you buy. Remember that you are buying fish and planning their housing based on their average adult size; nearly all fish sold in pet stores are juveniles and will grow quite a bit from where they are at the point of purchase. Never add more than a couple of fish at a time to any given aquarium, giving the beneficial bacteria a chance to adapt to the greater ammonia load to prevent potentially fatal ammonia spikes. Silver dollars are generally very hardy and easy to care for, but their basic needs do need to be understood and fulfilled in order for them to live a healthy, long life.