Silver Dollar (Metynnis argenteus)
Quick Answer
Silver Dollar (Metynnis argenteus) is a deep-bodied characin from the Amazon and Paraguay River basins of South America. It requires a minimum 75 Gallons (284 liters) aquarium with a pH of 5.5 to 7.5 and temperature range of 75°F to 82°F (24°C to 28°C). This dedicated herbivore occupies the middle water zone, requires a school of 6 or more, and makes an excellent addition to large community setups with compatible tank mates.
Quick Facts
| Scientific Name | Metynnis argenteus |
|---|---|
| Common Names | Silver Dollar |
| Family | Serrasalmidae |
| Genus | Metynnis |
| Type | Freshwater |
| Temperament | peaceful |
| Care Difficulty | beginner |
| Lifespan | 10 years |
| Maximum Size | Up to 6 in (15 cm) |
| Diet | Herbivore |
| Temperature | 75–82°F (24–28°C) |
| pH | 5.5–7.5 |
| Hardness | 4–18 dGH |
| Minimum Size | 75 gallons |
Key Takeaways
- Requires a minimum 75-gallon tank with 48-inch length for a school of 6 to 8.
- Dedicated herbivore: 80% plant matter, 15% protein, 5% fat.
- Extremely skittish; remove all sharp decorations to prevent injury.
- Thin scales increase susceptibility to ich and medication sensitivity.
- Breeding triggered by simulating rainy season with cool water changes.
- Will destroy soft-leaved aquarium plants; use Anubias, Java Fern, or silk plants.
Overview
Species Overview
The Silver Dollar (Metynnis argenteus) is one of the most iconic and recognizable freshwater aquarium fish in the hobby. Named for its perfectly round, disc-shaped body and brilliant metallic silver coloration, this species belongs to the family Serrasalmidae, making it a close relative of piranhas and pacus. First described by Ahl in 1923, the Silver Dollar originates from the Amazon and Paraguay River basins of South America, specifically the Tapajos River basin in Brazil.
Physical Characteristics
Adult Silver Dollars reach approximately 6 inches (15 cm) in length with a deep, laterally compressed body that can measure nearly as tall as it is long. The body exhibits a striking metallic silver sheen with subtle iridescent flashes of red, blue, and green under proper lighting. Males display a distinctive red border along the anal fin, while females are generally rounder in body shape, particularly when gravid. The anal fin of males features a characteristic bump approximately three-quarters of the way down, a key sexing characteristic.
Lifespan
With optimal care, Silver Dollars live 8 to 10 years in captivity, with some individuals exceeding 12 years. Their longevity is directly tied to water quality, diet composition, and tank size. Fish kept in undersized tanks or fed improper diets typically succumb to organ failure or chronic stress-related diseases within 3 to 5 years.
Conservation Status
The Silver Dollar is currently listed as Not Evaluated by the IUCN. Wild populations remain stable throughout their native range, and the species is heavily captive-bred for the aquarium trade, reducing pressure on wild stocks.
Care
Housing & Pond Requirements
Minimum Tank Specifications
The absolute minimum tank size for a school of 6 adult Silver Dollars is 75 gallons (284 liters) with dimensions of at least 48x18 inches (120x45 cm). However, a 100 to 125 gallon (378 to 473 liter) tank is strongly recommended for long-term housing. Tank height is less critical than length; these fish need wide swimming lanes, not vertical space. Juveniles under 3 inches can temporarily reside in a 55-gallon tank but will outgrow it within 6 to 8 months.
Filtration Requirements
Silver Dollars are heavy waste producers. You must provide filtration rated at 10x tank turnover per hour minimum. A high-capacity canister filter is mandatory. Supplement with powerheads or circulation pumps to eliminate dead zones. Weekly water changes of 30% are non-negotiable to maintain nitrates below 20 ppm. Ammonia and nitrite must remain at 0 ppm at all times.
Substrate & Decor
Use smooth, rounded gravel or sand substrate. Dark-colored substrates enhance their silver coloration and reduce reflection stress. Remove all sharp decorations as these fish panic-dash when startled and will injure themselves on sharp edges. Provide driftwood for grazing and territorial definition. Use silk plants or robust live plants (Anubias, Java Fern, Hornwort) as they destroy soft-leaved vegetation.
Lighting
Subdued lighting is critical. Bright lights cause chronic stress and hiding behavior. Use floating plants (Water Lettuce, Duckweed, Frogbit) to diffuse overhead lighting. Implement a ramp-up timer that gradually increases light intensity over 30 minutes to prevent panic responses.
Lid & Security
Silver Dollars are powerful jumpers. A tight-fitting lid is absolutely mandatory. Use glass canopies or mesh screens secured with clips. They have been known to launch themselves several feet out of open tanks when startled.
Diet
Diet & Nutrition
Silver Dollars are dedicated herbivores, not omnivores as often misclassified. Their digestive systems are specialized for processing plant matter, and a protein-heavy diet causes severe health complications including fatty liver disease, bloat, and shortened lifespan.
Health
Health & Disease Management
Silver Dollars are generally hardy when kept in appropriate conditions. However, their thin, reflective scales and skittish nature make them susceptible to specific diseases and injuries that heavily-scaled, calmer fish avoid. Preventive care through water quality maintenance and quarantine protocols is far more effective than treatment.
Ich (Ichthyophthirius multifiliis)
The most common parasitic infection in Silver Dollars due to their thin, reflective scales.
- Small white salt-like spots on body and fins, rapid breathing, rubbing against decorations, twitching, darting behavior, clamped fins.
Sudden temperature drops, introduction of infected fish, latent parasites activated by stress, poor water quality.
Quarantine all new fish for 14 days. Maintain stable temperature between 75°F and 82°F. Avoid adding cold water during water changes. Use a hospital tank for treatment.
Skin Flukes (Gyrodactylus / Dactylogyrus)
External parasites that attach to gills and skin, causing irritation and secondary infections.
- Excessive mucus production, rapid gill movement, flashing against substrate, reddened gills, labored breathing.
Introduction via live foods, new plants, or infected tank mates. Poor water quality exacerbates infestation.
Quarantine live foods. Treat new plants with potassium permanganate dip. Maintain pristine water conditions. Praziquantel is the treatment of choice.
Bacterial Fin Rot & Columnaris
Secondary bacterial infections often following injury from panic-dashing or parasite damage.
- Frayed or receding fins, white cotton-like patches on mouth or body, lethargy, loss of appetite, reddening at fin bases.
Poor water quality, injury from sharp decorations, stress from inadequate schooling, untreated parasitic infections.
Remove sharp decorations. Maintain nitrates below 20 ppm. Treat with broad-spectrum antibiotics (Maracyn, Furan-2) and perform daily 25% water changes during treatment.
Bloat & Constipation
Digestive disorders caused by improper diet, overfeeding, or low-fiber intake.
- Swollen abdomen, stringy or absent feces, loss of appetite, floating at surface, lethargy.
Overfeeding, excessive protein, lack of dietary fiber, feeding dry foods without soaking, beef heart or mammalian proteins.
Feed a primarily vegetable-based diet. Soak dry foods before feeding. Offer blanched peas as a natural laxative. Fast for 24 hours if symptoms appear.
Physical Injury from Panic-Dashing
Self-inflicted trauma caused by the fish dashing into tank walls or decorations when startled.
- Scales missing, bruising, torn fins, split lips, cloudy eyes from impact trauma.
Sudden light changes, loud noises, approaching the tank too quickly, inadequate school size, sharp tank decorations.
Remove all sharp objects. Use ramp timers for lighting. Place tank in low-traffic area. Maintain school of 8+. Add Stress Coat to water after any injury event.
Breeding
Breeding Silver Dollars
Breeding Silver Dollars in captivity is challenging but achievable with the right setup and patience. They are egg scatterers that spawn in groups, typically triggered by seasonal cues mimicking the Amazon rainy season. Success requires a large breeding tank, precise water parameters, and careful conditioning.
Compatible Tank Mates
Species Comparison
| Feature | Silver Dollar | Red Hook Silver Dollar | Pacu | Bala Shark |
|---|---|---|---|---|
| Scientific Name | Metynnis argenteus | Myloplus rubripinnis | Colossoma macropomum | Balantiocheilos melanopterus |
| Max Size | 6 inches (15 cm) | 12 inches (30 cm) | 30+ inches (76+ cm) | 14 inches (36 cm) |
| Temperament | Peaceful, skittish | Peaceful, slightly bolder | Peaceful but enormous | Peaceful, very active |
| Minimum Tank Size | 75 gallons (284 L) | 125 gallons (473 L) | 300+ gallons (1135+ L) | 125 gallons (473 L) |
| Diet | Herbivore (80% plants) | Omnivore (60% plants) | Omnivore (nuts, fruit, plants) | Omnivore (flakes, pellets, live) |
| pH Range | 5.5 - 7.5 | 6.0 - 7.5 | 6.0 - 7.5 | 6.5 - 8.0 |
| Schooling Requirement | 6+ individuals | 3+ individuals | Solitary or pairs | 5+ individuals |
| Plant Compatibility | Destroys soft plants | Moderate plant damage | Destroys all plants | Generally safe with plants |