Silver Dollar
Metynnis argenteus
Min Tank Size
284L
Adult Size
15.2 cm
Lifespan
10 years
School Size
5+
About
Native to the river basins of South America, particularly the Amazon and its tributaries, silver dollars are striking fish that look almost exactly as their name suggests: flat, round, and gleaming like a freshly minted coin. They're closely related to piranhas, which surprises most people when they learn it, but these guys couldn't be more different in temperament. Completely herbivorous and genuinely peaceful, they're more interested in your java fern than your other fish. Adults reach around 15 cm, so the "6 inch fish" description you'll see thrown around is accurate but easy to underestimate when you're looking at a juvenile in a pet store.
5, giving you reasonable flexibility. They do appreciate soft to moderately hard water, reflecting their South American origins.
Diet is where most people slip up: these fish need a heavy vegetable component. Blanched zucchini, spinach, spirulina-based foods, and fresh lettuce are all taken eagerly. Without enough plant matter they'll resort to eating literally everything green in your tank, which they'll do anyway given the chance. Any live plants in their tank are on borrowed time regardless of how well you feed them.
Despite the plant destruction they're genuinely calm fish that coexist well with many species. See how other hobbyists have worked around the plant problem by browsing tank builds featuring silver dollars.
Water Parameters
Temperature
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Flow Preference
Keeping multiple Silver Dollar together
Silver Dollar are shoaling fish and need company of their own kind. Keep a group of at least 5. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
Silver dollars work well with other large, robust South American fish. Oscars, severums, and large plecos are classic tankmates, partly because those fish are tough enough to handle any accidental collisions and partly because the water parameters overlap well. Large peaceful cichlids can coexist fine as long as the tank is big enough that nobody feels crowded. Avoid small fish entirely, not because silver dollars will hunt them, but because a school of spooked silver dollars can easily injure or kill something like a neon tetra through sheer collision. Shrimp won't survive. Any live plant you care about won't survive either. The tank size needs to be generous, a group of five really wants 300 liters or more for comfortable long-term keeping.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The most common mistake is planting the tank before adding silver dollars. They will eat everything, and they'll do it fast. Artificial plants or extremely robust species like anubias on wood are your only realistic options, and even anubias sometimes gets nibbled. The second mistake is underfiltering. A school of large herbivores processing that much vegetable matter produces serious waste, and ammonia spikes follow quickly in undersized setups. Aim for a filter rated well above your tank volume. Finally, don't skip the lid. Silver dollars are genuinely strong jumpers and a gap in the hood during water changes or feeding is enough opportunity for a fatality.
Behavior & Aggression
Silver dollars are not aggressive fish in any meaningful sense. They don't nip fins, they don't defend territories, and they won't bother other species intentionally. The closest thing to aggression you'll see is minor chasing within the group, which is normal social behavior and rarely causes harm. Where they do cause problems is through sheer panic. They spook easily and a frightened school bolting around a tank can injure slower or more delicate tankmates, and they can also jump clean out of an open top when startled. Keeping the tank calm with consistent lighting and hiding spots reduces stress and erratic behavior.
Things to Know
- Will destroy live plants completely. Use artificial or very robust plants only.
- Needs a tight-fitting lid, they are strong jumpers when startled.
- Adults reach 15+ cm, beginners often underestimate final size.
- Keep in groups of 5 or more or they become skittish and stressed.
- Large school produces significant waste, strong filtration is essential.
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