Care guide · Freshwater · fish
Silver dollar
Metynnis argenteus
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Metynnis argenteus is a South American silver dollar in the family Serrasalmidae. Its deep, silvery body belongs to a relative of piranhas, but its feeding habits are very different and largely plant-oriented. The trade name ‘silver dollar’ is used for several Metynnis species, and M. hypsauchen is very similar. Confirm the fish’s identity with the seller; a common name alone is not enough. Its main care needs are substantial swimming space, a group, and stable water quality. Ask about the fish’s adult identification and buy only specimens that are visibly feeding well.
Plan your aquarium →At a glance
- Temperature
- 24–28 °C
- pH
- 6.0–7.0
- GH
- 0–10 °dGH
- Aquarium length
- At least 180 cm
- Minimum aquarium volume
- At least 260 L
- Adult size
- At least 15 cm
- Group size
- At least 5 individuals
- Temperament
- Peaceful
About this species
Seriously Fish reports 150 mm standard length, while a US government screening summary cites 140 mm. Standard length ends at the base of the tail and excludes the caudal fin. Plan for roughly 14–15 cm body length as an adult. A small fish in a shop is not a guide to its eventual space needs. The species is deep-bodied and actively uses the middle and upper parts of the aquarium.Natural habitat
Specialist aquarium literature describes the species as probably endemic to Brazil’s Rio Tapajós drainage. A US risk-screening report records broader distribution reports and stresses that identification and knowledge of Metynnis are not always certain. Avoid building a precise biotope recipe from one distribution map. What is clear for aquarium care is that this is a tropical freshwater fish.Aquarium and layout
For a group of adults, Seriously Fish recommends a minimum footprint of 180 × 38 cm and about 260 litres at the stated tank height. Length and width matter more than extra height. Keep at least five together and use a secure cover. They readily eat plants, so choose robust furnishings, consider artificial plants, and provide some subdued areas. Smaller tanks may suit juveniles temporarily, but should not be presented as adult housing.Water conditions
The specialist aquarium profile gives 24–28°C, pH 6.0–7.0 and GH 0–10 dGH. Other databases report broader environmental values, but these are not necessarily better aquarium targets. Keep temperature and chemistry stable and prevent waste from accumulating. Test water regularly and maintain a consistent change schedule. Do not make abrupt adjustments just to chase a single reading; stable, suitable conditions matter more.Behaviour and group size
Silver dollars are shoaling fish and are generally described as peaceful with larger, calm species. Much smaller fish may be eaten. Choose companions by adult size, swimming behaviour and available space, not just similar pH or temperature. These fish mainly occupy middle and upper water. Live plants are often consumed, so a densely planted layout can be difficult to maintain. Observe the group after introduction and watch for persistent chasing or food competition.Feeding
This species eats a strongly plant-based diet, while accepting a varied omnivorous menu. Regularly offer suitable vegetables such as courgette, cucumber, peas or leafy greens, alongside complete vegetable, spirulina or algae foods. Small animal foods may be used occasionally as supplements rather than the staple. Feed portions the group can consume promptly and remove leftovers; uneaten food can degrade water quality.Breeding
The specialist source describes group spawning in a large breeding aquarium. Conditioning and softer, more acidic water near the warm end of the stated range are mentioned; eggs fall to the bottom and are reported to hatch in about three days. Once the yolk sac is absorbed, fry need very fine food such as infusoria. These are reported observations, not a guaranteed recipe. Consider the required space and the work of raising potentially many fry.Sources & review
This care guide draws on several specialist sources and was last checked on .
View the sources
- Seriously Fish — Metynnis argenteus — specialist aquarium profile, size, setup, water, diet and reproduction
- National Center for Biotechnology Information — NCBI Taxonomy — accepted name and lineage to Serrasalmidae
- U.S. Fish and Wildlife Service — Ecological Risk Screening Summary — reported size, feeding ecology, distribution caveats and taxonomic uncertainty