Taxonomy & naming
Mylesinus paraschomburgkii was described in 1989 by Michel Jégu, Geraldo Mendes dos Santos and Efrem Jorge Gondim Ferreira, in a paper (published in French) that separated it from its only congener, Mylesinus schomburgkii, on the basis of specimens collected in the Trombetas and Uatumã river basins of Brazilian Amazonia. The genus Mylesinus sits in the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, alongside the true piranhas (Pygocentrus, Serrasalmus) and the other silver-dollar genera such as Myloplus, Metynnis and Tometes.
Serrasalmidae taxonomy has been reworked substantially since the 1990s, with several silver-dollar species moved out of the old, broad genus Myleus into Myloplus, Tometes and Ossubtus, and the pacus split out of a once-inclusive Colossoma. Mylesinus itself has remained a small, stable genus of two recognised species and is not affected by that reshuffling; the Catalog of Fishes (Eschmeyer, California Academy of Sciences) continues to list Mylesinus paraschomburgkii as the valid combination. The specific epithet references its close resemblance to, and description alongside, M. schomburgkii — "para-" signalling "beside" or "near" that species.
Morphology
Mylesinus paraschomburgkii has the classic silver-dollar profile: a deep, strongly laterally compressed, disc-shaped body with a mirror-bright silver flank, built for maneuvering through open water in a tight school rather than for ambush or ramming speed. FishBase records a maximum length of 14 in standard length for the species, a genuinely large size for a silver dollar and one that keepers routinely underestimate when buying juveniles.
As in other serrasalmids adapted for grazing plant matter, the jaw carries closely packed, multicuspid teeth suited to clipping leaves and fruit rather than the single row of blade-like, flesh-shearing teeth found in true piranhas. Colouration is unremarkable and typical of the genus — an overall silvery sheen without the strong red or orange markings seen in some other serrasalmids — consistent with a fish that relies on shoaling and speed for protection rather than camouflage or display.
Habitat
The species is known from the lower Amazon's left-bank tributaries, principally the Trombetas and Uatumã river basins (part of the wider Rio Negro tributary system) and the Araguari River, in Amazonas and Amapá states, Brazil — a comparatively narrow native range for a serrasalmid. It is a benthopelagic freshwater fish, occupying the water column over sand, submerged wood and rocky substrate in river channels rather than deep floodplain forest, and occurrence records cluster tightly around these named basins rather than spreading across the wider Amazon.
Water across this range follows the broader pattern for Serrasalmidae in Amazon/Guiana blackwater-influenced tributaries: warm (roughly 75–86 °F, commonly cited around 79–82 °F for the family) and acidic to near-neutral (pH roughly 5.5–7.5), often with low dissolved oxygen and tannin-stained water in the more blackwater-influenced reaches. Specific published water-chemistry data for M. paraschomburgkii itself is sparse; the figures above reflect Serrasalmidae family norms for this region rather than a species-specific study.
Feeding
Mylesinus paraschomburgkii is fundamentally herbivorous. Diet studies on Amazonian pacus and silver dollars from the Araguari River system — based on artisanal fishermen's knowledge as well as direct observation — document a diet built around fruits and seeds that fall from the flooded forest canopy, plant fragments, and periphyton (the algal film on submerged wood and stone), with insects taken opportunistically, particularly in the wet season. Seasonal shift is notable: fruit and seed consumption dominates in low water, while periphyton and insect intake rises as the flood pulse brings more of that food into reach.
In the aquarium the species is described in hobbyist accounts as a large eater that "will eat anything" placed in the tank — a trait that is convenient for feeding but a serious liability for any live plant. A varied vegetable-forward diet works best: blanched vegetables (courgette, cucumber, spinach), spirulina-based flake or pellet, algae wafers and occasional fruit, supplemented with a modest amount of protein such as quality pellets or the occasional insect-based food. Feeding it primarily meaty or fish-based foods does not match its natural diet and is not recommended.
Mating
No detailed courtship account for Mylesinus paraschomburgkii is documented in the available literature or hobby sources, and no external sexual dimorphism has been reported — sexes are not reliably distinguishable by colour or body shape. What is known follows the pattern for silver dollars generally: fish condition up as a settled shoal, and spawning behaviour, where it has been observed in related species, is associated with softer, more acidic water rather than a distinct pairing ritual like that of substrate-nesting piranhas. Data on this species specifically is sparse, and this account does not extend beyond what the sources support.
Breeding
As with other silver dollars, Mylesinus paraschomburgkii is presumed to be an egg-scatterer: adults release eggs over fine-leaved plants or vegetation with no nest built and no parental care given, unlike the substrate-guarding true piranhas in the same family. It is occasionally bred in the hobby under soft, acidic water conditions, though documented captive-breeding reports specific to this species are scarce — most silver-dollar breeding accounts in the literature concern the more commonly kept Metynnis and Myloplus species rather than Mylesinus.
Eggs and fry receive no parental protection once scattered, so a densely planted breeding setup (fine-leaved species tolerant of being picked at) and removal of the adults after spawning are standard practice for silver dollars generally. Given the sparse species-specific record, keepers attempting to breed this fish should expect to draw on general silver-dollar protocol rather than a proven M. paraschomburgkii-specific method.
In the aquarium
Mylesinus paraschomburgkii is a schooling fish that needs a real group and a large footprint of open swimming space — hobbyist accounts describe it as an active, not-too-aggressive shoaler that settles poorly if kept alone or crowded. At a documented maximum of 14 in standard length, it is a substantial adult fish that outgrows small and mid-sized community tanks; prospective keepers should plan for a large aquarium from the outset rather than upgrading later.
The single most important care point is that this is a committed plant-shredder: it will strip a planted aquarium of soft-leaved vegetation, and forum accounts specifically recommend a robust, hard-scaped tank — driftwood, rock, sand — over an aquascape. Given it belongs to the same family as the true piranhas, some jurisdictions may regulate serrasalmids broadly, so keepers should check local law before acquiring one, though M. paraschomburgkii itself carries none of the bite-risk reputation of Pygocentrus or Serrasalmus. Strong filtration is warranted for a large-bodied, heavy-eating schooling fish.
Conservation
The IUCN Red List assesses Mylesinus paraschomburgkii as Least Concern, with the assessment dated November 2018. No specific threats have been identified, and the population within its native Trombetas–Uatumã–Araguari range is considered stable. Its restricted native distribution — a handful of named river basins in the northern Brazilian Amazon rather than the whole basin — means it is inherently more exposure-limited than a wide-ranging serrasalmid like the pacu or red-bellied piranha, but no basin-specific pressure (damming, deforestation, fishing) has been documented as a current concern for this species specifically.
The species does not appear to be a significant target of the aquarium trade at commercial scale, and specimens reaching hobbyists are presumed to be wild-collected given the absence of any farmed or captive-bred supply chain in the sources reviewed.