Metynnis hypsauchen

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The Silver Dollar, or Metynnis hypsauchen, is a South American characid with a deep, laterally compressed body and a remarkably bright silver color. Its appearance resembles a small shining coin as it moves through the middle level of the aquarium in a group. Despite its miniature-piranha appearance, this fish is mainly peaceful and schooling, with a strong preference for plant-based foods. It is best kept in a spacious, well-filtered aquarium with open swimming areas. The specimens offered here are wild collected. With a rarity rating of 2 out of 3, the species remains reasonably available, although stock can vary between shipments.

General species description

Metynnis hypsauchen belongs to the Serrasalmidae family, a group that also includes piranhas and several related herbivorous fishes. It is recognized by its disc-shaped body, reflective flanks and schooling behavior. In an aquarium, a group of at least five or six individuals is recommended to reduce stress and encourage natural activity. It is an active swimmer that mainly uses the middle level and appreciates good water circulation. An aquarium of at least 400 liters is preferable for an adult group because of its size, deep body and constant activity. Its generally calm temperament with similarly sized fish makes it suitable for a large community aquarium. However, it may nibble soft-leaved plants, especially when sufficient vegetable food is not provided.

Geographic origin and biotope

Reference country: Brazil, with a distribution associated with the Amazon basin and tributaries of the upper Madeira basin. Wild populations inhabit tropical waterways where temperatures remain stable and riverbank vegetation provides shade. Habitats may include calm channels, backwaters, flooded areas and sections containing submerged wood. The water is usually soft to moderately acidic, with a bottom made of sand, mud and plant debris. Water levels change seasonally, allowing the fish to use temporarily flooded habitats. A setup with slightly brown or amber water, roots and subdued lighting is well suited to the species. Filtration should be effective without creating an excessively strong current, since the fish prefers a moderate flow and open swimming space.

Precise location and local name

The type locality is associated with the Rio Guaporé in Brazil, within the upper Madeira drainage. In the aquarium trade and in Brazil, the name pacu-prata is used for silver-colored fish of this type. The name Silver Dollar is primarily used in English-speaking aquarium circles and refers to the round shape and metallic shine of the body. Commercial names may sometimes group several Metynnis species or related genera, so identification should be based on morphology and the scientific name. In an aquarium, it is preferable to keep several individuals of the same species rather than mixing Silver Dollars of uncertain identification. This makes schooling behavior easier to observe and reduces differences in size or dietary needs.

Appearance and physical characteristics

The body of Metynnis hypsauchen is tall, strongly compressed from side to side and covered with reflective scales that create an almost uniform silver coloration. The fins may show grayish or slightly reddish tones, while the eye and scales reflect aquarium lighting strongly. Its overall shape is adapted for quick swimming among plants and submerged branches. The species reaches approximately 15 cm in total length as an adult, sometimes more under favorable aquarium conditions. Juveniles are more slender and gradually become deeper-bodied as they grow. The mouth is suited to grazing on plant material, and the teeth allow the fish to cut pieces from leaves. Mature males may develop longer and more colorful anal and dorsal fins, although these differences are less obvious in young fish. Its most distinctive visual feature remains its metallic shine when schooling.

General diet

Metynnis hypsauchen is primarily herbivorous, although its natural diet may include small organisms associated with plants and organic debris. In the aquarium, the staple diet should consist of wafers, pellets or flakes containing a high proportion of plant matter, supplemented with fresh foods. Blanched vegetables such as zucchini, spinach, romaine lettuce and cucumber are usually accepted readily. Frozen foods may be offered occasionally, but they should not replace the vegetable portion. A varied diet supports coloration, growth and overall condition. Feed small portions because the group can be very enthusiastic at feeding time. To reduce damage to aquarium plants, use hardy plants or quality artificial plants. The priority is a diet rich in fiber and vegetables, offered regularly and without excess that could compromise water quality.

Essential data

• River of origin: Rio Guaporé
• Local name used: Pacu-prata
• Origin of the scientific name: Metynnis is a genus name of Greek origin; hypsauchen is formed from Greek roots.
• Etymology of the full name: Metynnis is the genus name; hypsauchen approximately means high-necked.
• Common/vernacular names: Silver Dollar, pacu-prata, silver dollar fish
• Family: Serrasalmidae
• Subfamily: No subfamily commonly retained for this species
• Name pronunciation: met-IN-iss hip-SAW-ken
• Discovery: Johannes Müller and Franz Hermann Troschel, 1844
• Maximum adult size: About 15 cm
• Water temperature and pH: 24 to 28 °C; pH 5.5 to 7.5
• Waterway appearance and surrounding vegetation: Tropical calm to moderately flowing water, riverbank vegetation, submerged wood and flooded areas
• Typical tankmates: Geophagus proximus, Pterophyllum scalare, Brochis splendens
• Temperament and behavior: Peaceful, highly social, active and sometimes nervous when kept in too small a group
• Water depth: Midwater sections of rivers and flooded habitats
• Sexual dimorphism: Adult males may be more colorful, with more developed anal and dorsal fins
• Bottom structure and flow: Sand, mud and plant debris; low to moderate flow

In your aquarium

To keep Metynnis hypsauchen successfully, provide a large aquarium, a stable group and a daily plant-based diet. Warm, clean and well-oxygenated water, combined with roots and open swimming space, will encourage natural behavior. Monitor soft-leaved plants and offer vegetables to reduce grazing on the décor. Since these fish are wild collected, gradual acclimation is especially important. Patience during introduction, consistent water quality and peaceful tankmates of similar size are the keys to maintaining an active, healthy and long-lived group.