Taxonomy & naming
Prodontocharax melanotus was described by Norman E. Pearson in 1924, with the type locality recorded as Tumupasa, approximately 30 miles northwest of Rurrenabaque in Bolivia at roughly 1,000 feet elevation. Eschmeyer's Catalog of Fishes (CAS) lists the name as valid with no synonyms. The species belongs to the subfamily Cheirodontinae, a group of small, often schooling characids distributed widely across South America.
The genus Prodontocharax is small, containing only two recognised species. Its placement within Cheirodontinae links it to a diverse assemblage of miniature characins, many of which are similarly overlooked in the hobby despite being ecologically important as mid-water schooling fish and prey items in their native drainages. The specific epithet melanotus refers to a dark marking on the body — from the Greek melanos (black) and otos or related form (ear or back), likely describing a dark spot or stripe visible in preserved specimens.
Morphology
Prodontocharax melanotus reaches approximately 2 in standard length, making it a small characid even by the standards of the subfamily. Like other cheirodontines, it has the typical compressed, elongate-to-moderate body form of a schooling mid-water fish. Published morphological data for this species in the primary literature are sparse, but the genus is characterised by features that help place it among the tooth-bearing small characins of Cheirodontinae.
The specific epithet melanotus suggests a distinctive dark pigmentation feature — likely a spot or stripe in the caudal peduncle or flank region — visible in fresh or preserved material. Precise coloration details and meristic data are not well documented in accessible sources, and the species has not entered the aquarium hobby in any numbers that would generate detailed hobbyist morphology notes. Females are presumed to develop a fuller body profile when in spawning condition, as is typical across small characids.
Habitat
The species is distributed across the Beni, Itenez (Guaporé), and upper Madre de Dios River basins in western South America, spanning parts of Bolivia, Brazil, and Peru. These are predominantly lowland to sub-Andean drainages descending from the Bolivian foothills toward the Amazon basin proper, characterised by clear to lightly turbid waters flowing through gallery forest and seasonal floodplain environments.
The type locality at Tumupasa, Bolivia lies in transitional foothills terrain at moderate elevation, suggesting the species tolerates a range of conditions from foothill streams to lowland river channels. No detailed water-chemistry data — temperature, pH, or hardness — are documented in the available sources for this species. Benthopelagic habits are noted by FishBase, suggesting it occupies both the water column and areas close to substrate, as is common in small cheirodontine schools foraging through leaf litter margins and open water.
Feeding
Prodontocharax melanotus is presumed to be an omnivore in the manner typical of Cheirodontinae, feeding on small invertebrates, microcrustaceans, insect larvae, algae, and organic detritus. Cheirodontines as a group occupy a generalist position in riverine food webs, often taking zooplankton and aufwuchs as well as small prey items near the surface and mid-water.
No specific dietary studies have been published for this species. In the aquarium, similarly sized cheirodontine characids adapt readily to dry foods and frozen invertebrates such as Daphnia, Cyclops, and brine shrimp, and there is no reason to expect Prodontocharax melanotus to differ significantly from that pattern, though it remains essentially untested in captivity.
Mating
No specific observations of courtship behaviour in Prodontocharax melanotus have been published. Based on its systematic placement in Cheirodontinae, the species almost certainly practises egg-scattering open-water or vegetation-associated spawning without parental care, the reproductive mode that prevails across the subfamily and indeed across the majority of small characids.
In related cheirodontines, males typically initiate pursuit of females when in breeding condition, with spawning occurring in bursts over fine-leaved plants or root tangles. Eggs are adhesive in many species of the group, attaching briefly to vegetation before the adults disperse. Sexual dimorphism is probably limited to a slightly fuller abdomen in ripe females.
Breeding
Captive breeding of Prodontocharax melanotus has not been documented in the available literature, and the species is not established in the ornamental trade. By analogy with other small Cheirodontinae, it would be expected to scatter small, adhesive eggs among fine-leaved plants or spawning mops, with no parental care and a short incubation period at warm temperatures.
Any attempt to breed this species in captivity would likely follow the general protocal used for small Amazonian tetras: a species tank or breeding pair isolated into a well-planted aquarium with soft, slightly acidic to neutral water, conditioning on live and frozen foods, and removal of adults after spawning to prevent egg predation. Fry at hatching would need very fine first foods such as infusoria or commercial liquid fry food before graduating to newly hatched brine shrimp. These details remain speculative in the absence of documented breeding records.
In the aquarium
Prodontocharax melanotus is not established in the ornamental fish hobby and is not commercially available through normal trade channels. No dedicated husbandry notes exist in hobbyist literature. Its small size (under 2 in SL), schooling habit inferred from its systematic position, and probable tolerance of a range of soft to moderately hard water conditions would make it suitable for a quiet community aquarium of small South American fishes if it were to become available.
Any keeper working with this species would be advised to maintain it in a school of six or more individuals, provide a planted aquarium with subdued lighting and open swimming space, and offer a varied diet of small live, frozen, and prepared foods. Water parameters consistent with its western Amazonian provenance — warm (72–82 °F), soft to moderately hard, near-neutral to slightly acidic pH — would be a reasonable starting point in the absence of species-specific data.
Conservation
Prodontocharax melanotus is assessed as Least Concern (LC) on the IUCN Red List, with the assessment published in October 2020. Its distribution across three South American countries (Bolivia, Brazil, and Peru) in multiple river basins — the Beni, Itenez, and upper Madre de Dios — provides a degree of geographic security that justifies the current assessment, as no single localised threat is likely to imperil the species across its entire range.
The species is not subject to commercial collection pressure, having never entered the ornamental fish trade in significant numbers. Broader threats facing Amazonian freshwater fish — deforestation-driven sedimentation, agricultural runoff, and hydrological changes from large infrastructure — apply to its range but are not documented as causing specific population declines for this species. No dedicated conservation programmes target it, and its small size and obscurity mean it is likely to remain understudied relative to more charismatic Amazonian fishes.