Taxonomy & naming
Moenkhausia uirapuru was described by Willian Massaharu Ohara and Flávio Alicino Bockmann Lima in 2015, with the original description published in Ichthyological Exploration of Freshwaters (volume 26, number 2, page 160). The type locality is a tributary of the rio Galero, upstream of the cascata Uirapuru, in the upper rio Guaporé drainage, rio Madeira basin, on the Chapada dos Parecis plateau, Mato Grosso, Brazil. The holotype is deposited at the Museu de Zoologia da Universidade de São Paulo (MZUSP 115988). Eschmeyer's Catalog of Fishes (CAS) records the valid name as Moenkhausia uirapuru Ohara & Lima, 2015.
The species belongs to Moenkhausia, one of the most speciose genera in the family Characidae, with well over 80 valid species distributed across tropical South America. Within the genus it is placed provisionally among species sharing an incomplete lateral line, which is a common but not unambiguous diagnostic character in this diverse group. No subspecies are recognised, and the species has not been subject to molecular phylogenetic revision to date.
Morphology
Moenkhausia uirapuru is a small characid reaching a maximum recorded length of 2.5 in standard length (SL). The body is moderately compressed laterally, as is typical for the genus. Key diagnostic features noted in the original description include conspicuous red pigmentation on the lips, green-blue iridescent eye colouration, and a transparent or semi-transparent opercle through which the pinkish-red gill filaments are visible — a combination rarely encountered in Moenkhausia.
The meristics are reported as 11 dorsal-fin rays and 19–22 anal-fin rays, with a vertebral count of 30–31. The lateral line is incomplete, a character shared with several other Moenkhausia species. Beyond these data, the original description provides the full morphometric and meristic details; extended colour notes in life from field observation are limited to the pigmentation characters mentioned above, which are considered to fade in preservation.
Habitat
The known range of Moenkhausia uirapuru is confined to two headwater tributaries of the upper rio Guaporé, in Mato Grosso State, Brazil — both within the rio Madeira basin on the Chapada dos Parecis, a high sandstone plateau in central-western Brazil. FishBase characterises the species as a freshwater, benthopelagic fish of tropical headwater streams. The Chapada dos Parecis is the source of several major river systems and supports a mosaic of cerrado (savanna) and gallery forest; its headwater streams tend to be clear, shallow, and oxygenated, with sandy or rocky substrates.
No detailed in-situ water chemistry data for the specific type-locality streams are available in the cache. Based on the regional setting — upland plateau streams draining through sedimentary formations — water is likely soft to moderately soft and acidic to near-neutral, consistent with typical upper Guaporé tributaries, though this should not be taken as a confirmed figure without site-specific measurement.
Feeding
No specific dietary studies have been published for Moenkhausia uirapuru. As a member of Moenkhausia from a productive tropical headwater system, it is expected to be an opportunistic omnivore in the manner of most small characids: taking small invertebrates including aquatic insect larvae and microcrustaceans, terrestrial insects that fall onto the water surface, and potentially algal or plant material.
In the aquarium, small Moenkhausia species generally accept good-quality flake and micro-pellet foods supplemented with frozen or live small invertebrates such as Daphnia, brine shrimp nauplii, and bloodworm. Because this species is essentially absent from the hobby trade, there is no accumulated husbandry literature on its feeding preferences specifically.
Mating
No observations of reproductive behaviour in the wild or in captivity have been published for Moenkhausia uirapuru. Based on the biology of the genus and the broader family Characidae, the species is presumed to be an egg-scattering open spawner. Small Moenkhausia typically broadcast adhesive or semi-adhesive eggs among fine-leaved aquatic plants or submerged vegetation, with no parental care, as is the norm across the subfamily.
Sexual dimorphism, if present, has not been formally described; females of most small Moenkhausia tend to be rounder in the abdomen when gravid, while males may be slightly more slender, but no specific information is available for this species.
Breeding
Moenkhausia uirapuru has not been bred in captivity under controlled conditions in any documented account available at the time of writing. By analogy with congeners of similar size, breeding in captivity would likely follow the standard Moenkhausia pattern: a well-conditioned pair or small group spawning over fine-leaved plants or spawning mops, with adhesive eggs that the adults will eat if not removed. Hatching times for small characids under tropical aquarium temperatures typically range from 24 to 48 hours, with free-swimming fry requiring infusoria or commercial liquid fry food initially before graduating to newly hatched brine shrimp.
Given the species' extremely limited known range and apparent rarity in collections, it is unlikely to be encountered or bred by hobbyists unless dedicated collecting expeditions revisit the Chapada dos Parecis drainage specifically.
In the aquarium
Moenkhausia uirapuru is not established in the aquarium trade as of 2026 and is unlikely to be available commercially. The species has not received a dedicated profile in major hobbyist references, and its rarity in collections means that almost no practical husbandry experience has been recorded. A care approach modelled on other small, upland-stream Moenkhausia species would be reasonable: a well-filtered aquarium with soft to moderately soft, acidic to near-neutral water at tropical temperatures (approximately 75–82 °F), a dark substrate, dim or diffuse lighting, and fine-leaved planting or floating vegetation to replicate the shaded gallery-forest streams of its native habitat.
Should specimens ever become available, the species' small adult size (2.5 in SL) and presumed peaceful disposition suggest it would suit a community of small, compatible characids and other non-aggressive fishes. Its striking lip colouration and the translucent opercle revealing the gill filaments would make it a genuinely unusual and appealing aquarium subject.
Conservation
Moenkhausia uirapuru has not been formally assessed by the IUCN Red List; its status is Not Evaluated (NE) as of 2026. The known range is limited to two headwater tributaries of the upper rio Guaporé on the Chapada dos Parecis, Mato Grosso, Brazil — a restricted natural range that warrants attention even in the absence of a formal assessment. The Chapada dos Parecis faces ongoing pressures from agricultural expansion, particularly soy cultivation and associated deforestation of native cerrado and gallery forest, which can degrade the clear upland streams that small endemic fishes depend upon.
The species' apparent endemism to a small area of headwater streams, combined with the sensitivity of such habitats to land-use change, suggests that a precautionary conservation assessment would be valuable. No targeted population surveys or monitoring programmes are known. Collection for the ornamental trade is not currently a pressure given the species' absence from the hobby market.