Silver dollars are a common schooling fish found in many mid-to-large aquariums. Like all fish, there are a few simple tricks that can help you keep them in optimal health and a couple of pitfalls you’ll want to avoid. It’s easy enough, you just need to know!
Let’s dive right in with some tips and tricks for silver dollar fish care, helping you make sure that your school stays in top form.
Silver Dollar Quick Care Sheet
- Common Name: Silver Dollar
- Alternate Common Name(s): n/a
- Latin Name: Metynnis argenteus or Metynnis hypsauchen
- Care Level: Intermediate
- Tank Size: 55+ Gallons
- Size: 6”
- Diet: Primarily Herbivorous
- Behavior: Semi-Aggressive
- Lifespan: 10+ years
- Reproduction Type: Egg Scatterers
- Water Temperature: 75–82 °F (24–28 °C)
- pH: 6.5-7.5
- Water Hardness: 4-18dGH
Origins of the Silver Dollar
The Silver Dollar is a close relative of piranha and pacu that often finds its way into aquariums. They’re natives of the waterways of South America, with several species spread throughout the region. The main one of concern for aquarium keepers is Metynnis argenteus, which is the most common species seen in the pet trade.
There are a few look-alikes but care is mostly the same. We’ll touch on these in a moment, but you’re unlike to run into anything but Metynnis argenteus and Metynnis hypsauchen without knowing.
These are schooling fish, and since they reach a decent size at 6 “, so you’ll want to make sure you have a large enough tank for them. A 55-gallon long is a bare minimum for a group of Silver Dollars but a 75-gallon tank is much better. They should be kept in groups of at least six to maintain their natural schooling behavior.
Silver Dollars are almost as tall as they are long, with a very thin profile seen from the front or back. The strange shape is just enhanced by the glittering scales that give them their name. The Silver Dollar is a common fish, usually sold at 2-3” in length
These fish have been kept in captivity for a long time, and they started out as a hardier species than most. They breed at a rapid rate, and almost all of these fish are captive-bred rather than being caught from the wild.
The Silver Dollar is a hardy, adaptable fish. They’re able to live through most aquarium conditions without complaint, aren’t prone to disease, and are easy to feed. They’re close to an ideal fish for aquariums because of this trait.
Silver Dollars are best considered semi-aggressive. While they get along fine with most fish they will bully some smaller fish and don’t back down from encounters with other schooling fish. It’s a far cry from the aggression of piranha but it’s something to note when you’re choosing tank mates out for them.
There’s one big caveat to their care: you can’t keep Silver Dollars in a planted tank.
Not because it’s detrimental to the fish. It’s quite the opposite. Silver Dollars will constantly graze on live plants and just a few of them can destroy the aquascape in a large planted tank in a few days. I’ve managed to keep Anubias sp. in the same tank but they seem driven to shred and eat any plant they can find.
Silver Dollars are medium-sized fish endemic to South America. They’re known to be hardy, adaptable, and voracious herbivores. These traits have made them a favorite of many keepers, particularly those who like to keep South American biotopes.
Silver Dollar Species
There are quite a few species described as Silver Dollars, but only two are usually sold without further description.
These are Metynnis argenteus and Metynnis hypsauchen. These can be easily distinguished from each other. M. hypsauchen has black blotches near the eyes. They’re the same size and act the same, which means you shouldn’t have a problem with either.
Some species of note:
- Red Hook Silver Dollar (Myloplus rubripinnis)- These beautiful specimens have red spots and get a little bigger on average than standard Silver Dollars. They’re reported to reach 15”+ so a much larger tank is needed.
- Tiger Silver Dollar- An Amazonian variety with striping that resembles a tiger.
- Spotted Silver Dollar- A spotted variety of Silver Dollar. Often a bit smaller than other species.
Most of the variant species have different spots, patterns, or bars than the standard Silver Dollar. They’ll usually be within an inch of each other in size.
The exact species is primarily a problem for breeders. These fish are very similar in size, identical in care, and school together.
If you’re not breeding them it will be a non-issue but it’s still nice to know the exact species in your tank. That said, introducing a Myloplus rubripinnis to a tank that’s sized for normal Silver Dollars is going to cause some issues.
Ideal Tank Setup
The ideal tank for keeping a small community of Silver Dollars is easy to put together. You’ll just need to go through the usual motions and make sure that they have enough space.
I recommend the largest tank you can afford up to about 125 gallons if you want to keep a school of Silver Dollars. Larger tanks also open up more stocking options.
55 gallons is a minimum. I would recommend running double the rated filters on a 55-gallon tank that contains a school of Silver Dollars. You’ll also want to avoid adding any other fish to the tank.
75 gallons is a comfortable size for a Silver Dollar school and allows you more options. You can fit a good six or seven of these fish in one and possibly a few more depending on how your test readings look once the tank is cycled.
Equipment and Decorations
Standard equipment is sufficient for a group of Silver Dollars. Just go down the usual tropical fish checklist:
- HOB or Canister Filter- In-tank filters are usually too small for these fish, use something with a bit more power to ensure they’re healthy.
- Heater- Appropriate size for the tank. Check out our calculations if you’re not sure.
- Substrate- Anything works, including a bare bottom. If you have bottom feeders use their preferred particle size, whether chunky gravel or soft sand.
- Decorations- You’ll want some driftwood or rocks to fill in the tank a bit and provide cover for your other fish. Silver Dollars are primarily open water swimmers, but a bit of shade can still provide security.
Plants are a no-go with Silver Dollars. They will be devoured quickly. Silk plants are fine if you still want the planted look.
I’ve heard from various sources that this plant or that plant remains uneaten. My experience was that they’d destroy everything but Anubias sp. and the various Java Ferns. Java Moss may be safe as well, but I’d just sidestep the issue entirely by using some silk plants.
The Dietary Issue
Silver Dollars are primarily herbivores but not strictly. They’ll still eat flakes and even meaty frozen foods like bloodworms. Alternating algae tablets and flake has worked very well for me in the past.
These fish have two dietary issues of concern to the aquarist:
- Silver Dollars will eat your plants. All of them. Adding Silver Dollars to a planted tank is a bit like dropping a piranha into a tank full of guppies.
- These fish will eat smaller invertebrates. Larger snails are fine but small crayfish, crabs, and shrimp will end up as dinner in no time.
The first can be a serious problem.
My first school was dropped into a tank with well-established Cryptocoryne and Vallisneria species. They undid 6 months of hard work that night. It was a lesson I’ve never forgotten.
Please note that Silver Dollars will eat algae but not enough for them to be considered cleaners.
The invertebrate issue varies a lot more. They eat them more opportunistically, so it will be slow attrition over time. They don’t eat enough snails to be viable as a natural control for them, but they will eat smaller ones when they come across them.
The occasional serving of blanched vegetables is a great idea, but not required to maintain their optimal health.
The bottom line is just to keep invertebrates and plants out of their tank. Feeding should consist of varied foods with an emphasis on plant matter.
Cycling the Tank
Silver Dollars can survive a fish-in cycle if you’re willing to put in the serious work required to make it a safe environment. I recommend adding them to a tank that already has the bacteria in place to avoid issues.
If you’ve never cycled a tank, it’s a simple process:
- Set up the tank as normal, including equipment, but don’t add any fish yet.
- Add a small amount of flake in the morning and evening, testing for ammonia at each addition after the first “feeding.”
- Test for ammonia daily after finding it. Keep testing until it no longer registers on your test.
- Begin testing for nitrite daily until it reaches undetectable levels.
- Begin testing for nitrate twice daily. Once it’s at an acceptable level (<15ppm in most cases) you can begin adding fish gradually.
- Add a few fish at a time and continue testing nitrates, only adding more once the nitrates have returned to a decent level.
Silver Dollars produce a considerable bioload once they hit over 2 ½” or so, adding them over time is a better idea than dropping the whole school in at once.
Doing this with the fish in is trickier. You’ll need to make sure that you change out at least 25% of the water each time you detect ammonia or nitrites. This isn’t optional. It’s a lot of work and I recommend doing a fishless cycle in all cases.
There are dozens of animals suitable to be kept alongside a school of Silver Dollars. You’ll find they get along well with the vast majority of fish that have a similar size.
You’ll want to avoid anything too small. Fish under 3” or so will tend to suffer the brunt of their aggression. I can’t recall seeing a group ever bully a fish to death but I’ve seen them tear up fins and confine small schooling fish to a small area.
This problem is minimized with bottom dwellers. I wouldn’t keep them in a tank with Otocinclus catfish, but I’ve kept groups alongside large schools of Corydoras sp. without any problems. I’d still rely on something like a Bristlenose Plecostomus for cleanup, or just a common Pleco in tanks bigger than 75 gallons.
Some have also kept them with smaller loaches with success. Kuhli and Yoyo Loaches are both good choices for active bottom dwellers in a tank that features Silver Dollars.
Schooling fish that will fight back, like Black Skirt Tetra and Tiger Barbs, also do well with these fish. The size disparity is made up for by the smaller fish’s aggression. This is also the case with Rams and other dwarf cichlids, who are solitary but won’t take any crap from a school of Silver Dollars.
They do well alongside some showcase fish as well, particularly Angelfish and Discus.
When it comes to cichlids I’m hesitant to recommend them. Most beginners won’t have a suitable place to transfer something with the bioload of a school of Silver Dollars if it doesn’t work out. I’ve kept them with Oscar, Jack Dempsey, and Green Terror without any issues but it won’t work out in every case. Keeping any fish with the more aggressive cichlid species is a bit of a gamble due to their varied personalities and temperaments.
The following list of qualities should be considered when you’re considering a fish:
- Size- Size is less of a consideration with Silver Dollars than many others but nothing should be big enough to eat them or small enough to easily fit in a Silver Dollar’s mouth.
- Temperament- Silver Dollars can hold their own with aggressive fish but often leave peaceful fish alone. They can sometimes be placed with aggressive fish if their size is considered carefully beforehand.
- Swimming Level- Silver Dollars will swim in the top and middle level of the tank and rarely venture into the bottom. Avoid overcrowding these regions.
- Speed- Silver Dollars aren’t particularly fast, and they won’t be able to catch
- Fins- Long fins are a bad idea with Silver Dollars. They slow fish down and provide an exciting target to chew on. While not overly aggressive, fin nipping can occur with these fish.
The perfect example of a fish unsuitable for housing with Silver Dollars is Betta splendens. Their long and flowing fins, slow movement, and relative lack of aggression (with non-Betta species) would make them vulnerable to Silver Dollars.
Some good fish to start with are:
- Black Skirt Tetra
- Tiger Barbs
- Dwarf Cichlid (Rams)
- Zebra Danio
But there are many more than these that are suitable. Like every other fish, you may need to sit down and examine the viability of your combination from all angles, but Silver Dollars are rarely the fish that throws off the balance of a tank.
Use of Silver Dollars in Cichlid Tanks
Silver Dollars are a great option for cichlid tanks that have room, but you need to have a good handle on the cichlid’s care before you introduce them.
The main use of Silver Dollars in these tanks is as a dither fish. Dither fish are used to make other fish feel safe and to help spread out aggression by sparring with their more unruly neighbors.
They’re a bit different from a target fish, which is a tough fish used to take “hits” from more aggressive fish.
With Silver Dollars used in this way, it’s important to have a large enough school to spread the aggression out. A determined cichlid attacking one or two Silver Dollars can do a lot of damage. Attacking six will spread things out and the school will keep the fish from getting harassed constantly.
Silver Dollars are among my favorite dithers, the only fish in the same class are Tinfoil Barbs. The latter are much bigger and their use as a schooling dither fish requires a huge tank, Silver Dollars can fit fine in a cichlid-inhabited 125 gallon.
Silver Dollars make fine dither fish for small to middling cichlids.
Breeding Silver Dollars
Silver Dollars are remarkably easy to breed, they’re just terrible parents.
Silver Dollars breed constantly when kept in good health and both sexes are present. They’re egg-scatterers, meaning they spread eggs over a large area after breeding.
Females tend to be shorter but rounder than males. Once you have a pair you want to breed you should remove them to another cycled tank. A tinge of red is also in the anal fin of most males. They don’t have any clearer signs of sexual dimorphism.
The two fish will spawn once a day or so when they’ve begun breeding. The female will drop a few thousand eggs. These hatch in 3-4 days, at which point you may want to remove the parents.
This isn’t due to the fry getting devoured. Silver Dollars aren’t cannibals for the most part, but the adults will out-compete the fry for food. The fry can be fed small portions of finely ground flake or your preferred fry diet.
They only take about 9 months to become full size. You should have plans to rehome them, sell them, or whatever you plan on doing with the fry before you encourage breeding. You’re going to end up with a few hundred 6” fish and they all need to be in a healthy environment.
Silver Dollar fry will sometimes manage to live in a community tank despite other fish predating upon them. The parents will be laying eggs often after the initial coupling, so putting them back in the main tank may not stop the flow of babies.
That said, it’s very rare that fry of any species makes it to adulthood in a community tank. They’re simply too attractive as a food source.
More Than Pocket Change
The Silver Dollar is a great fish for beginners and advanced aquarists alike. Their shining skin, peaceful swimming, and tight schooling have made them a favorite for many tanks across the world. While they usually play a smaller part than their size indicates, these fish definitely have their own allure. Just keep them away from your plants!
So, do you think Silver Dollars are the right choice for your tank?