Taxonomy & naming
Myloplus tumukumak was formally described in 2018 by Marcelo Andrade, Michel Jégu and Cárlison Gama, based on a type series collected in the Camopi River, part of the Oyapock drainage that forms the border between Brazil and French Guiana. It sits in the family Serrasalmidae — the piranhas, pacus and silver dollars — a lineage that has been repeatedly re-split by modern taxonomists; the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises Myloplus as one of several genera carved out of the old, broadly defined "Myleus", alongside relatives such as Tometes and Ossubtus. M. tumukumak is described as closely resembling M. rubripinnis in overall body shape and colour pattern, distinguished on details of scale counts (59–70 perforated lateral-line scales) and fin-ray counts (23–25 branched dorsal-fin rays, 35–38 branched anal-fin rays).
The species epithet references the Tumucumaque Mountain Range (also rendered Tumucumaque or, in the original description, tumukumak), the sandstone plateau straddling the Brazil–French Guiana border that gives the species its known range. As a 2018 description with a very small, geographically narrow type series, M. tumukumak has not been assessed by the IUCN and is essentially absent from the aquarium hobby literature; nothing in the available record suggests it has an established common name.
Morphology
The type specimen — a paratype held at the Royal Belgian Institute of Natural Sciences (IRSNB 20.223) — measured 2 in standard length, a juvenile-to-subadult size typical of a freshly described type series rather than a mature adult. Like its close relative M. rubripinnis, M. tumukumak has the classic silver dollar build: a strongly laterally compressed, rounded-to-diamond-shaped body designed for holding station and manoeuvring in open water rather than hugging cover. The original description notes comparatively large scales on the flanks relative to related species, a useful field character alongside the lateral-line and fin-ray counts used to separate it from M. rubripinnis.
Adult size has not been documented for this species; the type series does not include large adults, and no aquarium or field reports of full-grown individuals appear in the available record. Based on the size range of its close relatives in the genus, which commonly reach roughly 6–8 in total length, an adult M. tumukumak of comparable size would not be surprising, but that figure should be read as an inference from relatives, not a confirmed measurement for this species.
Habitat
Myloplus tumukumak is known only from the Tumucumaque Mountain Range region straddling northeastern Brazil and French Guiana, with type and paratype material collected from the Camopi River (Oyapock drainage) and additional records from the Araguari river drainage. These are clear-to-blackwater rivers draining ancient sandstone uplands in the Guiana Shield, a region with comparatively little human disturbance and few detailed water-chemistry surveys published for this exact watershed.
No site-specific temperature or pH readings accompany the description, so water parameters here follow the pattern documented for related Myloplus species in similar Guiana Shield and Amazonian drainages: warm, soft-to-neutral and mildly acidic water, broadly in the range of pH 5.0–7.0 and roughly 75–82 °F. That should be treated as a genus-level approximation for this specific, poorly surveyed river system rather than a measurement taken from the type locality itself.
Feeding
No stomach-content or dietary study has been published specifically for Myloplus tumukumak. The genus Myloplus, however, is well documented as omnivorous with a strong herbivorous lean: related species graze algae, aquatic plants, fallen fruit and seeds, supplementing this plant-heavy diet with some insects and other small invertebrates. Their dentition — multicuspid, molar-like teeth suited to shearing and crushing plant material — supports this pattern across the genus and the wider silver-dollar group.
In the absence of species-specific data, a keeper should assume M. tumukumak follows this genus-wide pattern: a diet built around vegetable matter (blanched greens, spirulina-based foods, algae wafers) with occasional protein, rather than a carnivorous or predatory diet. This has direct consequences for tank planning, covered under "In the aquarium".
Mating
No courtship or spawning behaviour has been documented for Myloplus tumukumak, either in the wild or in captivity — unsurprising for a species known from a handful of type specimens and essentially unseen in the aquarium trade. External sexual dimorphism has not been described for this species and is not well documented across the genus generally; related silver dollars show no strong, reliable external sex differences, and gravid females are typically identified by a fuller body rather than by colour or fin shape.
Given the complete absence of species-specific reproductive data, nothing here should be read beyond what related Myloplus species suggest: a schooling fish in which conditioned, well-fed groups are the precondition for any spawning behaviour, rather than a species with documented pair-bonding or courtship display.
Breeding
Myloplus tumukumak has no documented breeding record, in the wild or in the aquarium — it is data sparse to the point of essentially unknown. Silver dollars in this genus, where breeding has been observed at all, are egg-scatterers: eggs are released over fine-leaved plants or vegetation with no nest built and no parental care given, and only a minority of hobbyists have managed to breed related species like M. rubripinnis or M. schomburgkii, generally by conditioning a group in soft, acidic water and allowing them to scatter eggs among dense fine-leaved plantings.
There is no reason from the available record to expect M. tumukumak to differ from this genus-wide pattern, but given that the species has barely, if ever, been kept in the hobby, that expectation should be read as inference rather than observation. Practically speaking, this is not a species anyone should expect to source captive-bred stock of.
In the aquarium
Myloplus tumukumak is not an established aquarium fish — it has no meaningful presence in the hobby trade, likely owing to its very recent description, narrow known range, and the practical difficulty of collecting from a remote Guiana Shield headwater system. Any specimen offered for sale under this name should be treated with real skepticism and, where possible, verified against the original description's meristic characters, since it is easily confused with the much more commonly traded M. rubripinnis.
Were a keeper to obtain confirmed stock, the sound approach is to follow genus-level care for Myloplus silver dollars: a large, long aquarium with substantial open swimming space, kept in a proper school rather than alone or in pairs, since these are schooling fish that become skittish and stressed in isolation. Because the genus grazes plants readily, this is a fish for a robust, hardscape-driven tank with tough or artificial plants, not a delicate aquascape — soft-leaved plantings will be shredded. Warm, soft-to-neutral, mildly acidic water and strong filtration for a bioload-heavy grazer round out reasonable care, but all of this is extrapolated from relatives rather than confirmed for this specific species.
Conservation
Myloplus tumukumak has not been assessed by the IUCN Red List; its status is Not Evaluated. This is typical for a species described as recently as 2018 from a small type series and narrow known range — formal assessment simply has not caught up with the description.
Its known range in the Tumucumaque Mountain Range straddling Brazil and French Guiana includes areas with comparatively low human population density and, in parts, formal protection (the Brazilian side overlaps protected areas within the wider Tumucumaque conservation mosaic), which is a favourable backdrop, but no population-level data exists to support any specific conservation status. Given how little is known — no confirmed adult size, no documented diet or breeding biology beyond genus-level inference, and no aquarium presence — the most honest statement is that this species is conservation-data-deficient in practice, whatever its formal IUCN designation eventually becomes.