Quick answer: Silver dollar fish are peaceful, disc-shaped South American schooling fish, related to pacu and piranhas but completely gentle. The common silver dollar (Metynnis argenteus) and the spotted silver dollar (Metynnis lippincottianus) grow to about 6 inches (15 cm), while the red hook silver dollar gets much bigger. They live around 10 years, need a group of at least 5, and do best at 75 to 82 F with pH 6.0 to 7.5. Adults need a 75 gallon tank or larger. What most people get wrong is buying them for a planted tank. Silver dollars are herbivores and will eat almost every soft live plant you own.
Silver dollar fish at a glance
| Detail | Silver dollar fish |
|---|---|
| Scientific name | Metynnis argenteus (common silver dollar) and related Metynnis and Myloplus species |
| Family | Serrasalmidae, the same family as pacu and piranhas |
| Origin | Rivers of South America, including the Amazon basin and Guyana |
| Adult size | About 6 in (15 cm), sometimes up to 8 in. Red hooks grow larger |
| Lifespan | Around 10 years |
| Temperature | 75 to 82 F (24 to 28 C) |
| pH | 6.0 to 7.5 |
| Hardness | 4 to 18 dGH |
| Minimum tank | 75 gal (285 L) for adults, about 48 to 60 in long |
| Group size | 5 or more |
| Temperament | Peaceful but skittish |
| Diet | Mostly herbivore |
| Plants | Eat most soft live plants |
| Care level | Moderate, mainly because of size |
Types of silver dollar fish: which one do you have?
| Type | Scientific name | Adult size | Look | Minimum tank |
|---|---|---|---|---|
| Common silver dollar | Metynnis argenteus | About 6 in | Plain shiny silver disc, males have red on the anal fin | 75 gal |
| Spotted silver dollar | Metynnis lippincottianus | About 5 to 6 in | Silver with small dark spots | 75 gal |
| Hard-bellied silver dollar | Metynnis hypsauchen | About 6 in | Silver, often a dark spot behind the gill | 75 gal |
| Red hook silver dollar | Myloplus rubripinnis | About 10 to 12 in in tanks, larger in the wild | Bright red, hooked anal fin on males | 125 gal or more |
| Tiger or striped silver dollar | Metynnis fasciatus | About 6 in | Silver with thin dark vertical stripes | 75 gal |
Here’s the honest part most silver dollar guides leave out. Shops sell them at 1 to 2 inches, and they look perfect for a 20 or 30 gallon tank. Within a year they’re the size of a hand, and they live for a decade. Red hooks are even more of a surprise. If you don’t have room for at least a 75 gallon tank, and a 125 gallon for red hooks, these aren’t the fish for you, however peaceful they are.
How big do silver dollar fish get?
Common, spotted and hard-bellied silver dollars: about 6 inches (15 cm) long and almost as tall, so they look even bigger than they sound. Some reach 8 inches.
Red hook silver dollars: about 10 to 12 inches in large aquariums, and bigger in the wild.
Growth speed: fast. Juveniles can double in size in a few months and reach about 4 inches, breeding size, at around a year old.
How long do silver dollar fish live?
Around 10 years with good water, a varied plant-based diet and enough space. Stunted fish in small tanks usually live much shorter lives.
Silver dollar fish tank size and setup
Tank size. 75 gallons is the minimum for a group of 5 adult Metynnis, and bigger is better. Juveniles can start in a 55 gallon tank, but plan the upgrade. Red hooks need 125 gallons or more. Our 150 gallon fish tank guide covers a size that suits them very well.
Long, not tall. They’re fast, active swimmers, so length matters more than height. Aim for a tank 48 inches long or more.
Lid. They’re nervous and jump when startled. Use a tight lid.
Filter. Strong filtration with moderate flow. A canister filter or two large hang-on-back filters work well, since they eat a lot and make a lot of waste.
Substrate and decor. Sand or smooth gravel, driftwood and rocks. Leave plenty of open swimming space in the middle.
Lighting. Dim to moderate. Floating plants or dim light make them less skittish.
Cycled tank. Their bioload is high, so the tank must be fully cycled first. See our how to cycle a fish tank guide.
Do silver dollar fish eat plants?
Yes, almost all of them. In the wild they graze on plants and fruit, and in an aquarium they’ll strip soft stem plants, swords and carpeting plants within days.
| Plant | Will silver dollars eat it? |
|---|---|
| Anubias | Usually left alone, tough and bitter leaves |
| Java fern | Usually left alone |
| Bolbitis | Usually left alone |
| Hornwort | Sometimes eaten, but grows fast enough to keep up |
| Java moss | Often nibbled |
| Amazon swords, crypts and stem plants | Eaten |
| Duckweed and floating plants | Eaten, sometimes used as cheap food |
Best approach: use tough plants like anubias and java fern tied to wood, or good quality artificial plants and hardscape. Our fish tank decorations guide has ideas.
What do silver dollar fish eat?
- Staple: spirulina flakes or a good herbivore pellet
- Vegetables: blanched zucchini, cucumber, peas, spinach and lettuce, several times a week
- Fruit, occasionally: small pieces of banana or melon
- Protein treats: frozen brine shrimp or bloodworms once or twice a week
Feed once or twice a day, only what they eat in a few minutes. Remove leftover vegetables after a few hours.
Temperament and tank mates
Silver dollars are peaceful schooling fish. They don’t bite their tank mates, but they’re very skittish. A small group, a bare tank or loud surroundings make them dart around and crash into the glass. A group of 5 or more makes them calmer and more confident.
| Good tank mates | Avoid |
|---|---|
| Larger peaceful cichlids like severums and geophagus | Aggressive cichlids such as the green terror |
| Plecos, including the bristlenose pleco | Tiny fish like neon tetras, which can be outcompeted or eaten |
| Rainbowfish and giant danios | Shrimp and small snails |
| Larger catfish like Raphael catfish | Slow, long-finned fish that can’t compete for food |
| Rope fish and other large, calm fish | Very large predators that could eat young silver dollars |
Male vs female silver dollar fish
- Males: have a longer, more curved anal fin, often with red or dark edging, and sometimes more color during spawning.
- Females: have a straighter, shorter anal fin and a rounder belly when carrying eggs.
Sexing is easiest in adults over about 4 inches.
Silver dollar fish breeding
Silver dollars breed in aquariums, but the size of the tank makes it a project for experienced keepers.
- Tank. A large, shallow tank with floating plants and dim light.
- Water. Soft and slightly acidic, about pH 6.0 to 6.5 and GH 4 to 8, at 79 to 82 F (26 to 28 C).
- Spawning. Females scatter up to about 2,000 eggs, which sink to the bottom or land among plants.
- Remove the adults after spawning to protect the eggs.
- Hatching. Eggs hatch in about 3 days, and fry swim freely after about 6 to 9 days.
- Feed the fry infusoria or vinegar eels at first, then baby brine shrimp and crushed spirulina flakes.
Common silver dollar fish problems
Fish darting and crashing into the glass. Too few fish, too small a tank, or too much light. Add more silver dollars, cover the back with a background and add floating plants.
All your plants disappeared. They ate them. Switch to anubias, java fern or artificial plants, and feed more vegetables.
Fish jumping out. No lid or a gap in the lid. Cover the tank completely.
Cloudy water and high nitrates. High bioload and leftover vegetables. Upgrade filtration and change water more often. See our cloudy fish tank water guide.
White spots. Usually ich, often after stress or a temperature drop. Raise the temperature slowly and treat.
Stunted, rounded growth. The tank is too small. Upgrade to 75 gallons or more.
FAQ
How big do silver dollar fish get?
Common and spotted silver dollars grow to about 6 inches (15 cm), sometimes up to 8. Red hook silver dollars reach about 10 to 12 inches in aquariums.
How long do silver dollar fish live?
Around 10 years with good care and a large enough tank.
What size tank do silver dollar fish need?
At least 75 gallons for a group of 5 adults. Red hook silver dollars need 125 gallons or more.
What do silver dollar fish eat?
Mostly plant foods like spirulina flakes, herbivore pellets and blanched vegetables, with occasional brine shrimp or bloodworms.
Do silver dollar fish eat plants?
Yes. They eat most soft live plants. Anubias and java fern are usually left alone.
Are silver dollar fish aggressive?
No. They’re peaceful but skittish. Keep them in groups of 5 or more with other large, calm fish.
How many silver dollar fish should be kept together?
At least 5. Bigger groups are calmer and show more natural schooling.
Are silver dollar fish related to piranhas?
Yes, they’re in the same family, Serrasalmidae, but silver dollars are plant eaters and are completely peaceful.
