Taxonomy & naming
Tometes lebaili was described by Michel Jégu, Philippe Keith and Elizabeth Belmont-Jégu in 2002, with the formal species description published in Environmental Biology of Fishes in 2004. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, and to the genus Tometes, one of several phytophagous (plant-eating) lineages that the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises as split out from the old, broadly defined genus Myleus. All species currently placed in Tometes are herbivorous, rheophilic serrasalmids, and T. lebaili is described directly under this genus in the primary literature, with no record of an earlier Myleus combination.
The species epithet honours a collector or collaborator associated with the original Guiana Shield fieldwork (the cache consulted for this article does not preserve the specific etymological dedication, so no further detail is asserted here). T. lebaili is one of the larger-bodied members of its genus, and like its relatives it is easily confused at a glance with other Guiana Shield silver dollars unless fin and body proportions are checked carefully.
Morphology
Tometes lebaili has the deep, laterally compressed, coin-like body plan typical of silver dollars, but it is a substantially larger fish than the name suggests: FishBase records a maximum size of 20 in standard length, with adult specimens commonly around 15.5 in SL and the original holotype measuring 4.5 in SL. This places it well above the familiar Metynnis and Myloplus species kept as small community-tank silver dollars.
Mature males undergo a distinctive breeding transformation: an elongated lobe on the anal fin, a lengthened dorsal fin, and in some individuals a reddened body colour — secondary sexual characters that make ripe males readily distinguishable from females and juveniles. Juveniles and non-breeding adults are more uniformly silver, consistent with their camouflage among sunlit, current-swept rock and vegetation.
Habitat
This species is a strict rheophile, restricted to fast-flowing, well-oxygenated rapids and cataracts rather than the sluggish backwaters and floodplain lakes many of its relatives tolerate. Its documented range covers the eastern Guiana Shield, spanning the Trombetas, Commewijne, Mana, Maroni, Oyapock and Amapá Grande / Araguari river basins across Suriname, French Guiana and adjacent Brazil.
Within rapids, T. lebaili is closely tied to beds of Podostemaceae — specialised aquatic riverweeds that anchor to submerged rock in fast current and can only survive where flow and water clarity remain high. Young fish shelter and feed among the plant leaves in these rapids, picking invertebrates from the vegetation, while adults graze the Podostemaceae itself. This tight habitat dependency makes the species vulnerable to anything that silts up or slows these rapids stretches.
Feeding
Tometes lebaili is an herbivore that feeds almost exclusively on Podostemaceae, the rheophilic riverweeds that grow attached to submerged rock in the rapids it inhabits — an unusually specialised diet even by the standards of a phytophagous serrasalmid. Juveniles supplement this with small invertebrates picked from among the plant leaves before shifting to a diet dominated by plant material as they mature.
In the aquarium this translates directly: feed a vegetable-forward diet of blanched greens (courgette, cucumber, spinach), spirulina-based flake or pellet, and algae wafers, with only modest protein supplementation. A silver dollar of this genus kept in anything but a hardscaped or heavily plant-sacrificial tank will graze living plants down to bare stems within days — this is a grazing fish before it is anything else, and its aquarium diet should mirror that.
Mating
Specific courtship behaviour has not been documented in the sources available for this account, but the pronounced breeding dimorphism recorded in the species — an elongated anal-fin lobe and dorsal fin, and reddened body colour in ripe males — strongly implies visual courtship displays and male-male or male-female signalling typical of seasonally breeding rheophilic characins, timed to rising water and current during the wet season. Data on pairing behaviour, nest-site selection or spawning triggers in this species specifically is sparse and not asserted here beyond what the cache supports.
Breeding
Tometes lebaili has not been recorded as bred in the aquarium hobby, and the sources reviewed for this account contain no description of its reproductive behaviour beyond the male secondary sexual characters noted above. As a rheophilic rapids specialist tied to a very particular current and substrate regime, it is unlikely to spawn successfully in typical home aquaria, and prospective keepers should not expect to breed this species. Silver dollars in general (genera such as Metynnis and Myloplus) are known as egg-scatterers over fine-leaved vegetation with no parental care, and if T. lebaili follows that pattern it would likely do so as well, but this has not been confirmed for the species and is not stated as fact here.
In the aquarium
This is not a fish for a modest community tank: with a documented maximum of over 20 in SL, an adult Tometes lebaili needs a very large aquarium — realistically several hundred litres to over a thousand as it approaches full size — with strong water movement replicating its native rapids habitat. High oxygenation, robust filtration and current-generating powerheads are far more important here than for typical still-water silver dollars.
As a dedicated herbivore, T. lebaili will strip soft aquatic plants efficiently; keepers wanting a planted display should choose only tough, unpalatable species or accept a hardscape-only setup of rock and driftwood instead. Like other silver dollars it is a shoaling fish and should be kept in a group rather than alone, which further raises the realistic space requirement. Because of its size, current needs and grazing habits, it suits large, specialist rheophilic-biotope setups far more than a standard planted community tank, and it is rarely available in the aquarium trade given its specialised rapids habitat and restricted Guiana Shield range.
Conservation
The IUCN Red List assesses Tometes lebaili as Vulnerable (VU), an assessment dated January 2021. The total population is thought to probably exceed 10,000 individuals, but numbers are declining in the main river channels across its range. The primary threats are overfishing and habitat destruction linked to gold mining, which degrades the clear, fast-flowing rapids and the Podostemaceae beds the species depends on for both shelter and food.
Because T. lebaili is a rheophilic specialist restricted to a relatively narrow band of Guiana Shield rivers, its populations have little room to shift to alternative habitat when rapids are silted or altered by mining activity — a pressure that is widespread and ongoing across the Guiana Shield's gold-mining regions. Conservation of this species is therefore closely tied to water-quality and habitat protection in the Trombetas, Commewijne, Mana, Maroni, Oyapock and Amapá Grande / Araguari basins rather than to any direct aquarium-trade pressure, since it is not a significant trade species.