Taxonomy & naming
Paramyloplus ternetzi was described by the British ichthyologist John Roxborough Norman in 1929. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes. Like most of the silver dollars, it was originally placed in the old, broadly defined genus Myleus; the Catalog of Fishes (Eschmeyer, California Academy of Sciences), the modern authority for valid names, now places it in Myloplus, part of the hard split of the historic Myleus assemblage into several narrower genera (Myloplus, Tometes, Ossubtus and others) as the group's internal relationships were resolved. Older aquarium literature and some trade listings still use the combination Myleus ternetzi; the currently valid name is Paramyloplus ternetzi.
The genus sits within the silver dollar and pacu lineage of Serrasalmidae, distinct from the true piranhas (Pygocentrus, Serrasalmus), which carry a single row of blade-like predatory teeth rather than the flatter, molariform grazing dentition of the silver dollars.
This fish was long listed as Myloplus ternetzi; Eschmeyer's Catalog of Fishes places the species in Paramyloplus, and the current combination Paramyloplus ternetzi is followed here.
Morphology
Paramyloplus ternetzi has the classic silver dollar profile: a strongly laterally compressed, disc-shaped body that is almost circular in outline, giving it the coin-like silhouette that gives the group its common name. The body is bright silver overall, with the sheen that earns aquarium specimens the trade name "neon green silver dollar" showing as an olive-to-greenish cast across the upper flanks under good light, fading to plain silver toward the belly.
FishBase records a maximum size of 9.1 in standard length, making this one of the more modestly sized silver dollars — considerably smaller than the large Amazonian Myloplus and Metynnis species that can approach 11.8 in. Fin shape is typical of the group: a deeply forked caudal fin and a small, fatty adipose fin, both useful for the quick, darting bursts of a schooling, open-water fish. Aquarium stock is usually sold much smaller, at roughly 2–2.4 in as juveniles.
Habitat
Paramyloplus ternetzi is native to the eastern and northeastern rivers of the Guiana Shield in northern South America. FishBase describes it as favouring lentic (still or slow-flowing) waters with steep banks, rather than fast, well-oxygenated channels — a preference shared with several of its silver dollar relatives, which tend to concentrate in calmer river margins, backwaters and flooded-forest habitat where overhanging vegetation provides both cover and food.
Water across its native range is tropical and comparatively mild: FishBase cites a temperature range of roughly 68–77 °F and a pH of about 6.0–7.2, placing it in soft-to-moderately-hard, mildly acidic to near-neutral water typical of Guiana Shield blackwater and clearwater tributaries, without the extreme acidity sometimes assumed for South American characins.
Feeding
Paramyloplus ternetzi is herbivorous, and FishBase specifically records it feeding on the leaves of river plants, with fruit and seeds from the flooded forest canopy taken seasonally when available. This diet is consistent with the molariform, crushing teeth typical of silver dollars, built for grazing plant material rather than seizing prey.
In the aquarium this translates directly into a plant-shredding herbivore: keepers should offer blanched vegetables (courgette, cucumber, spinach), spirulina-based flake or pellet, and algae wafers as the bulk of the diet, supplemented with a modest amount of protein such as bloodworm or quality pellet food. A vegetable-poor diet in a planted tank does not stop the fish grazing — it simply redirects its appetite onto the aquarium's own plants.
Mating
Detailed courtship behaviour for Paramyloplus ternetzi specifically is not well documented in the available literature. FishBase notes that reproduction in the species is asynchronous and occurs across the year, intensifying during the rainy season — a pattern consistent with many Guiana Shield floodplain fish that time spawning activity to seasonal water-level rises rather than to a single fixed breeding season.
No reliable external sexual dimorphism is documented for this species; keepers in the hobby generally cannot sex silver dollars by colour or fin shape, and successful breeding groups are typically built from a larger shoal conditioned together on a rich, varied diet rather than from a deliberately selected pair.
Breeding
Silver dollars as a group are egg-scatterers, and Paramyloplus ternetzi follows that pattern: it is an egg-scatterer among fine-leaved plants, with no parental care of eggs or fry. Spawning is occasionally achieved in the hobby by conditioning a group on live and vegetable foods and softening and acidifying the water to encourage a spawning response, echoing the rainy-season trigger implied by FishBase's asynchronous, rain-intensified reproduction pattern.
Once eggs are scattered over fine-leaved plants or a spawning mop, the adults show no further investment — eggs and fry are left unguarded and are readily eaten by the adults or tankmates if not separated. This is not a commercially farmed species in the way large-scale pacus are; captive breeding is an occasional hobbyist achievement rather than a routine trade source, and most specimens sold are wild-collected or farmed abroad rather than home-bred.
In the aquarium
Paramyloplus ternetzi is a peaceful, actively schooling fish that should always be kept in a proper group rather than alone or in a pair — a lone or thinly-stocked silver dollar is a nervous, skittish fish prone to bolting at the smallest disturbance. Because it tops out at 9.1 in SL and swims in open water, it needs a large, long aquarium with plenty of horizontal swimming space; robust, well-filtered set-ups with driftwood and rockwork for cover suit it far better than a densely planted aquascape, since it will graze soft-leaved aquatic plants down to bare stems given the chance.
Water should be kept warm — roughly 68–77 °F per FishBase, though trade care sheets for aquarium-line stock cite a slightly broader 75–82 °F — and mildly acidic to near-neutral, around pH 6.0–7.5, with strong filtration and frequent water changes to handle a large, actively feeding shoal. It is a generally serene tankmate for other similarly sized, non-aggressive fish, but its size and grazing habit mean it is not a good match for a delicate community planted tank.
Conservation
Paramyloplus ternetzi is assessed by the IUCN Red List as Least Concern, with a decreasing population trend noted alongside high resilience and low vulnerability to fishing pressure. Its range across the rivers of the eastern and northeastern Guiana Shield is not subject to the intensity of commercial fishing or habitat conversion seen in more heavily developed parts of South America, and the species does not currently face a specific documented threat.
As with many Guiana Shield freshwater fish, the broader long-term pressures on its habitat — small-scale mining, deforestation and associated sedimentation, and future hydropower development — are relevant watch items for the region even though the species itself is not currently classified as threatened.