Taxonomy & naming
Monotocheirodon pearsoni was described by Carl H. Eigenmann in 1924, based on material from the Rio Beni drainage of Bolivia. The genus Monotocheirodon is monotypic — M. pearsoni is its only member — and is placed within the family Characidae, the largest family of freshwater fishes. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Monotocheirodon pearsoni Eigenmann, 1924.
The specific epithet pearsoni is a patronym, almost certainly honouring a collector or naturalist associated with the original collecting expedition, though detailed documentation of the dedication is not widely available in secondary literature. The combination of a monotypic genus and an obscure type locality in the Bolivian Amazon has meant this species receives limited treatment in ichthyological reviews compared to species from more heavily sampled drainages.
Morphology
Monotocheirodon pearsoni is a small characid, with FishBase recording a maximum standard length of 1.5 in. Like many small members of Characidae it is a laterally compressed, fusiform fish adapted to life in the water column of lowland tropical streams and rivers. The genus name encodes a morphological character: Monotocheirodon combines roots referring to a single feature of the jaw or dentition that distinguishes it from related genera.
Detailed colour descriptions from wild-caught specimens are sparse in the accessible literature. Absent published aquarium or photographic records for this species, a precise characterisation of live colouration and fin morphology cannot be given here. Its benthopelagic habitat assignment from FishBase suggests it occupies the lower and mid-water zones rather than the surface.
Habitat
Monotocheirodon pearsoni is recorded from the Rio Beni basin of Bolivia — a major south-western Amazonian tributary that drains the eastern slopes of the Andes and the Bolivian lowlands before joining the Madeira River system. The Rio Beni system encompasses a wide range of habitat types, from Andean foothills streams to lowland várzea and terra firme forest waters.
FishBase categorises the species as benthopelagic and tropical freshwater, consistent with a small characid that occupies the mid-to-lower water column in slow to moderately flowing lowland streams or rivers. Specific water-chemistry data (temperature, pH, conductivity) are not documented for this species in the available literature. The broader Rio Beni basin is characterised by soft, mildly acidic to near-neutral waters typical of western Amazonian lowland drainages, though values vary widely across the system.
Feeding
No specific dietary studies have been published for Monotocheirodon pearsoni. As a small benthopelagic characid from Amazonian lowland waters, it likely feeds on small invertebrates — insect larvae, microcrustaceans, and similar zooplankton — together with any organic material available in the water column and at the substrate surface, a foraging strategy typical of small characids in comparable habitats.
In the absence of published stomach-content analyses or aquarium feeding observations for this species, a more detailed dietary account cannot be provided without risk of fabrication.
Mating
No published observations of mating behaviour in Monotocheirodon pearsoni are available. Small characids in this part of the Characidae radiation are characteristically egg-scattering open-water or plant-associated spawners, releasing adhesive or semi-adhesive eggs among fine-leaved vegetation or over the substrate, with no parental care given to eggs or larvae.
It is reasonable to expect M. pearsoni to follow the same basic pattern, but specific details of courtship behaviour, spawning stimulus, or reproductive season in the wild have not been documented in the accessible literature.
Breeding
Monotocheirodon pearsoni has not been reported in the aquarium trade and there are no published accounts of its captive breeding. By analogy with closely related small Amazonian characids, spawning would be expected to involve egg scattering over fine-leaved plants or substrate, with adhesive eggs developing without any parental attention and adults liable to consume eggs if not separated.
Incubation periods, fry size, and larval feeding requirements are undocumented for this species. Data sparse.
In the aquarium
Monotocheirodon pearsoni does not appear to be available in the ornamental fish trade and there are no known records of it being kept in aquaria. Its small size — under 2 in standard length — and Amazonian origins suggest it would be compatible in principle with a soft, warm, low-current biotope setup suited to small characids from the Rio Beni drainage.
Given the complete absence of husbandry records, no responsible care guidance beyond these generalities can be offered. Any future aquarium observation of this species would be a genuine contribution to knowledge.
Conservation
Monotocheirodon pearsoni is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment referenced in FishBase dating to April 2014. The Least Concern listing reflects the absence of evidence for significant population decline or range restriction at the time of assessment, rather than an affirmative finding of abundance.
The Rio Beni basin faces ongoing pressures from deforestation, agricultural conversion in the Bolivian lowlands, and historical hydropower proposals. How these pressures affect M. pearsoni specifically is not documented. As a monotypic genus, it represents a unique evolutionary lineage; its obscurity in research and the trade means its population status has received little dedicated monitoring.