Taxonomy & naming
Myloplus zorroi was described in 2016 by Marcelo Andrade, Michel Jégu and Tommaso Giarrizzo in ZooKeys, based on material from the Rio Madeira basin in Brazilian Amazonia. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, and to the genus Myloplus, one of several silver-dollar genera (alongside Tometes and Ossubtus) that taxonomists split out of the old, broadly defined genus Myleus as the family's classification was revised through molecular and morphological work in the 2000s and 2010s. Any older literature or trade reference using "Myleus" for this species lineage reflects that superseded classification, not the currently valid combination.
FishBase notes that M. zorroi is distinguished from other Myloplus species by a count of 13–19 low prepelvic spines along the ventral keel, a character used alongside body proportions and dentition to separate the genus's many superficially similar species. As with several recently described Amazonian serrasalmids, the species has no established common name in English; Brazilian sources place it among the fishes generically called "pacu" in the region.
Morphology
Myloplus zorroi has the classic silver-dollar body plan: a deep, laterally compressed, disc-shaped body that trades the elongated profile of a typical characin for a rounder, more piranha-like silhouette, though without the predatory dentition of its carnivorous relatives. Sources report a maximum size of 18.5 in as an adult total length, with FishBase separately recording 13 in standard length — a substantial fish either way, and considerably larger than the small silver dollars (Metynnis species, for instance) most commonly seen in the aquarium trade.
The original description emphasises the low prepelvic spine count (13–19) along the belly as a key diagnostic feature separating M. zorroi from congeners, together with dentition specialised for crushing hard-shelled seeds and fruit rather than shearing flesh. Detailed colouration has not been documented in the sources available for this account; readers should not assume it matches any particular commercially traded Myloplus species.
Habitat
Myloplus zorroi is known from the Rio Madeira basin in Brazilian Amazonia, where the type description places it in moderately to rapidly flowing, clear rivers over rocky and sandy bottoms at depths of roughly 2–8 metres — a notably different habitat from the sluggish, tannin-stained floodplain waters often associated with Amazonian characins. This is a tropical, benthopelagic river fish rather than a still-water or heavily vegetated-habitat specialist.
No direct water-chemistry measurements for the species were found in the available sources. Given the genus and the clear, flowing character of its known habitat, water is inferred to run warm and likely neutral to slightly acidic, but this account deliberately avoids asserting extreme blackwater conditions that the cache does not support — treat the figures given in Facts as a genus-level approximation, not a measured value for this species.
Feeding
Myloplus zorroi is frugivorous, with specialised crushing dentition adapted to hard-shelled seeds and fruit that fall into the river from the surrounding forest canopy — a foraging strategy shared with pacus generally, which play an important ecological role dispersing seeds through Amazonian floodplain and riverine forests. Like other Myloplus species it should also be expected to browse aquatic vegetation and soft plant matter opportunistically.
In the aquarium, related Myloplus species are kept on a diet centred on vegetable matter — blanched greens, spirulina-based foods and algae wafers — supplemented with some protein; there is no documented aquarium feeding record specific to M. zorroi itself, so this guidance is extrapolated from the genus rather than drawn from direct observation of the species.
Mating
No courtship or spawning behaviour has been documented for Myloplus zorroi in the sources available for this account. Silver dollars in the genus Myloplus are not known for elaborate pair-bonding or nest-building; where breeding has been observed in related genus members it typically follows a rise in temperature and softening of water, triggering group spawning activity rather than a distinct courtship display. Nothing specific to this species can be stated with confidence beyond that genus-level pattern.
Breeding
Myloplus zorroi has no documented aquarium breeding record. Based on the broader pattern seen in the silver-dollar genera (Metynnis, Myloplus), the species is presumed to be an egg-scatterer that releases eggs over fine-leaved plants or similar cover, with no parental care of eggs or fry — but this is inferred from genus-level biology, not confirmed for M. zorroi specifically, and readers should treat it as a reasonable expectation rather than an established fact.
Given the species' large adult size, remote Amazonian range and total absence from the aquarium trade, there is essentially no prospect of home breeding at present; any future captive-breeding record would need very large, mature specimens and river-scale swimming space that few hobbyist setups can provide.
In the aquarium
Myloplus zorroi is not established in the aquarium hobby, and the handful of sources describing it are taxonomic and scientific rather than aquaristic. That said, its documented adult size of 18.5 in is the single most important fact for anyone who might encounter it in the trade: this is a large-river fish that will outgrow any conventional home aquarium and needs public-aquarium-scale swimming space and filtration to keep long-term, not a specimen to buy as a juvenile without a plan for its adult size.
As a herbivore-leaning pacu relative, it should be expected to browse and shred soft or fine-leaved aquatic plants given the opportunity, so a heavily planted aquascape is not a realistic setting for it even where space allows. Related Myloplus species tolerate a warm tropical range of roughly 72–81 °F. Given the complete absence of a hobby track record, prospective keepers should treat any specific care claims for this species with real caution and default to the conservative, large-tank, vegetable-forward approach used for its better-known genus relatives.
Conservation
Myloplus zorroi has not been assessed by the IUCN Red List and currently carries a status of Not Evaluated. This is unsurprising for a species described only in 2016 from a single Amazonian river basin, and it reflects a lack of formal assessment rather than any known conservation concern.
The species is known only from the Rio Madeira basin, a river system that has seen substantial hydroelectric dam construction and associated habitat change in recent decades. No population trend or threat data specific to M. zorroi were found in the available sources, so this account does not assert a conservation status beyond what the Red List itself records; the Rio Madeira's broader dam-driven habitat pressures are noted here as context, not as a documented threat to this particular species.