Taxonomy & naming
Tometes ancylorhynchus was described in 2016 by Marcelo Andrade, Márcio Jégu and Tommaso Giarrizzo, alongside its sister species T. kranponhah, in a paper documenting the first two Tometes species known from the Brazilian Shield drainages rather than the Guiana Shield rivers where the genus was first characterised. It belongs to Serrasalmidae — the piranha, pacu and silver-dollar family within Characiformes — and specifically to the phytophagous (plant-eating) lineage that modern taxonomy has split out of the old, broadly defined genus Myleus into several narrower genera, including Tometes, Myloplus and Ossubtus. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Tometes as the valid genus for this species; it should not be confused with older, now-superseded generic placements sometimes still seen in aquarium-trade literature.
The species epithet ancylorhynchus derives from Greek roots meaning "curved" and "snout" or "beak," describing the fish's relatively short, downturned mouth, which the describing authors likened to a curved parrot beak — an adaptation, like the teeth described below, for grazing rather than biting prey. No English common name is in wide use; it is referred to in the small existing literature simply as a Tometes or, informally, by its scientific name.
Morphology
Tometes ancylorhynchus shares the classic serrasalmid silver-dollar profile: a deep, laterally compressed, roughly disc-shaped body built for stable swimming in current rather than for pursuit predation. FishBase records a maximum published size of 15.5 in total length, making it a mid-sized member of its genus — considerably larger than the small aquarium-trade silver dollars (Metynnis) but well short of the large pacus. The mouth is short and curved, set with the multicuspid, closely packed teeth typical of phytophagous serrasalmids — an arrangement built for scraping and shearing plant material and algae from submerged rock rather than for cutting flesh, in clear contrast to the single row of blade-like, tricuspid teeth carried by true predatory piranhas such as Pygocentrus and Serrasalmus.
As a species described only in 2016 from a handful of specimens, detailed accounts of colouration and fin proportions are limited in the available literature; specific data on adult colour pattern beyond the general silver-dollar body form is sparse in the sources consulted for this profile.
Habitat
The species is known from the Xingu and Tocantins-Araguaia river basins in the Brazilian Shield of central-eastern Brazil, part of a broader pattern in which several Tometes species turn out to be restricted to fast-flowing, rock-bottomed reaches of specific river systems rather than being widespread Amazon-basin generalists. Fish in this genus are strongly associated with rapids and rocky substrates, where the current keeps rock surfaces clear for the growth of the algae and aquatic plants — including riverweed of the family Podostemaceae — that make up their diet.
Detailed water-chemistry data specific to T. ancylorhynchus was not found in the sources consulted; broadly, the Xingu and Tocantins-Araguaia systems are warm, tropical, clearwater-to-slightly-stained rivers, and rapids-dwelling serrasalmids of this type are typically found in well-oxygenated, flowing water rather than still floodplain lagoons. Specific pH and temperature figures for this species are data sparse and are not asserted here.
Feeding
Tometes ancylorhynchus is phytophagous — a plant-and-algae grazer, not a predator. FishBase specifically notes that it feeds on Podostemaceae, the riverweed family of aquatic flowering plants that carpets rapids and rock faces in fast-flowing Amazonian and Brazilian Shield rivers, an ecological niche shared with several of its Tometes relatives. Its curved, beak-like mouth and closely packed teeth are adaptations for rasping this tough, rock-anchored vegetation and algae from stone rather than for biting prey or carrion.
In an aquarium setting, a diet built around this natural biology means vegetable-forward feeding: blanched vegetables, spirulina-based foods and algae wafers should form the bulk of the diet, supplemented with a modest amount of protein. Given the species' extreme scarcity in the trade, there is essentially no accumulated hobbyist feeding record to draw on beyond what its wild diet and its silver-dollar relatives imply.
Mating
No courtship or pairing behaviour has been documented for Tometes ancylorhynchus in the sources consulted for this profile; the species was described from a limited number of museum specimens collected in the wild, and it is not established in aquaculture or the aquarium hobby to a degree that would have generated breeding observations. Data on this stage of its life history is sparse, and nothing here should be inferred rather than sourced.
Breeding
There is no documented aquarium or hatchery breeding record for Tometes ancylorhynchus. Based on what is known of its phytophagous serrasalmid relatives — the silver dollars of Myloplus and Metynnis — species in this feeding guild are typically egg-scatterers that release eggs over fine-leaved plants or vegetation with no parental care, but this pattern has not been confirmed for T. ancylorhynchus specifically, and it should be read as an inference from its relatives rather than an observed fact. Given how recently the species was described and how rarely it has been recorded at all, captive breeding data is effectively absent.
In the aquarium
Tometes ancylorhynchus is essentially unknown in the aquarium trade — the sources consulted describe it as having few or no aquarium records, consistent with a species described only in 2016 from a restricted range of fast-flowing Brazilian Shield rivers. Anyone who does encounter it should plan around its real adult size of up to 15.5 in total length, which calls for a large, robust tank with strong water flow approximating its rapids habitat, not a small community setup.
As with other phytophagous serrasalmids, the most important husbandry warning is that this is a plant-shredder: any live vegetation in the tank should be considered food, so keepers wanting a planted display should look elsewhere, or accept that the fish will strip it. A hardscaped tank with driftwood, smooth rock and strong current, alongside a vegetable-heavy diet, better matches its natural ecology than a soft aquascape. Given its rarity, provenance matters — any specimen in the trade is likely to be wild-collected from a narrow native range rather than farmed.
Conservation
Tometes ancylorhynchus has not been formally evaluated by the IUCN Red List; its status is Not Evaluated. This is unsurprising for a species described as recently as 2016 from a geographically restricted range within the Xingu and Tocantins-Araguaia basins — both systems that have faced significant hydrological pressure from large dam projects (including the Belo Monte complex on the Xingu), deforestation-linked sedimentation and mining activity in the wider Brazilian Shield region. A rapids-and-rock specialist that depends on flowing water and attached riverweed for its food supply is inherently more exposed to damming and flow alteration than a floodplain generalist, though no species-specific population or threat assessment currently exists to confirm or quantify that risk.