Taxonomy & naming
Metynnis lippincottianus was described by the American palaeontologist and naturalist Edward Drinker Cope in 1870, based on material from the Amazon basin. It sits in the family Serrasalmidae — piranhas, pacus and silver dollars — within the order Characiformes, and in the genus Metynnis, one of several genera of deep-bodied, herbivorous "silver dollars" that were carved out of the old wastebasket genus Myleus as the family's taxonomy was revised; Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the current authority for the valid combination.
The species has accumulated a tangle of synonyms in the literature and trade, including Metynnis goeldii and Metynnis roosevelti, both now generally treated as the same species; this synonymy, along with the genus's overall similarity across species, is part of why silver dollars are notoriously difficult to identify to species level from photographs alone, and older aquarium literature should be read with that caveat. The common name "silver dollar" describes the coin-like outline and mirrored flanks shared by the whole group; "spotted silver dollar" is used for this species specifically, referencing the faint dark speckling some individuals carry on the body.
Morphology
Metynnis lippincottianus has the strongly laterally compressed, disc-shaped body typical of its genus — a body plan that trades length for a broad, flattened profile, giving the fish its coin-like silhouette and its common name. FishBase records a maximum size of 6.5 in standard length, with aquarium literature more commonly citing adults in the 5–6 in total length range; either way, this is a mid-sized characin that needs real swimming room, not a nano-tank fish.
The body is a bright, mirrored silver overall, sometimes with scattered dark spots or speckling across the flanks (hence "spotted silver dollar"), and the fins are largely clear to lightly dusky. Sexual dimorphism is modest but real: mature males develop a visibly elongated anal fin, often edged or washed with red, which distinguishes them from the shorter-finned females and is the most reliable way to sex a group by eye.
Habitat
The species is native to the Brazilian Amazon basin and river systems of French Guiana, where it inhabits the main river channels, tributaries and seasonally flooded forest of lowland Neotropical drainages. Like many Amazonian characins it tracks the flood pulse, moving into inundated vegetation during high water to feed on submerged leaves, fruit and algae before retreating to river channels and floodplain lakes as the water recedes.
Water across its range is warm and on the soft, mildly acidic-to-neutral side: aquarium and FishBase sources give a temperature range of roughly 73–81 °F and a pH around 6.0–7.0, with hardness tolerated up to about 10 °H. This is consistent with much of the Amazon basin rather than the extreme blackwater conditions of some tributaries, and it should be treated as a general guide rather than a single precise reading, since the cache does not specify a single collection locality.
Feeding
Metynnis lippincottianus is an avid herbivore, and this is the single most important fact for anyone considering it for a planted tank: in the wild it grazes on submerged and flooded vegetation, algae, and fallen fruit and seeds from the forest canopy, and in the aquarium it treats live plants the same way. Soft-leaved species are typically stripped to the stems within days.
In captivity the diet should lean heavily vegetable: blanched courgette, cucumber, peas and spring greens, along with algae wafers and spirulina-based foods, offered regularly rather than as an occasional treat. Some protein — occasional bloodworm or brine shrimp — rounds out the diet, but the bulk of feeding should mirror the wild grazing habit. Keepers who want both silver dollars and a planted tank generally compromise with tough, unpalatable or plastic plants rather than a true aquascape.
Mating
Detailed courtship behaviour for Metynnis lippincottianus is not well documented in the available sources, and no confirmed, repeatable account of captive spawning triggers has been recorded for this species specifically. What is known from the genus and from occasional hobby reports is that ripe adults in a conditioned group may pair off loosely ahead of spawning, with males displaying the elongated, often red-tinged anal fin described above.
External sexing rests on that same fin difference — males show a longer, more colourful anal fin than the shorter-finned females — but there is no other reliable dimorphism to guide pairing, and data on courtship sequence, timing or specific water triggers is sparse enough that it should not be stated with confidence beyond what is given here.
Breeding
Metynnis lippincottianus is an egg-scatterer, not a mouthbrooder, bubble-nester or substrate guarder. Spawning, where it has been observed, involves adults releasing eggs freely over fine-leaved plants or plant-like structure in soft, acidic water, with the eggs left unguarded and no parental care of eggs or fry — a pattern consistent with the wider silver-dollar group (Metynnis, Myloplus).
Confirmed, repeatable captive breeding of this species is uncommon in the hobby; most silver dollars sold in the trade are wild-caught or farmed in outdoor ponds rather than bred in home aquaria. Keepers attempting it should expect to condition a well-fed group in soft, slightly acidic water and provide a mass of fine, feathery plants (or an artificial substitute, given the fish's own appetite for the real thing) as an egg-scattering site, then remove the adults promptly since neither the eggs nor the fry receive any protection from the parents.
In the aquarium
Metynnis lippincottianus is a peaceful, genuinely undemanding schooling fish that does best in a group of five or more — a lone silver dollar is a nervous, skittish fish, while a settled shoal is calm and outgoing. SeriouslyFish recommends a tank of at least 150×37.5×15 in for a full-grown group, reflecting both the fish's adult size and its need for open swimming space; this is not a fish for a small or shallow tank.
The defining care consideration is the diet described above: this species will shred a planted aquascape, so tanks should be hardscaped with wood and rock, robust or artificial plants, and a secure, tight-fitting lid, since silver dollars are strong jumpers and can be skittish enough to injure themselves against the glass if startled without cover to retreat to. Water should be kept warm (73–81 °F) and on the soft, mildly acidic-to-neutral side (pH 6.0–7.0). Tankmates should be chosen with the fish's own modest size and peaceful nature in mind — it can be kept with a range of similarly sized community fish, though very small fish may occasionally be seen as food.
Conservation
The IUCN Red List assesses Metynnis lippincottianus as Least Concern, based on an assessment dated December 2020, reflecting its wide distribution across the Brazilian Amazon and French Guiana and the absence of known major threats to the species as a whole.
The aquarium trade draws on both wild-collected and farmed stock for this and related silver dollar species, and because Metynnis species are broadly similar in appearance and frequently confused or mislabelled at the point of sale, trade data for this species specifically is not fine-grained. No population-specific conservation concerns are noted in the available sources beyond the general pressures — habitat change, deforestation-linked sedimentation — that affect Amazonian freshwater systems broadly.