Taxonomy & naming
Creagrutus ouranonastes was described by Richard P. Vari and Adam S. Harold in 2001. The type locality is the Apurimac River drainage at the Río Chalhuanca area in Peru, and the holotype and paratypes are housed in the US National Museum of Natural History (USNM), Smithsonian Institution. The valid name, as recorded in Eschmeyer's Catalog of Fishes, is Creagrutus ouranonastes Vari & Harold, 2001.
Creagrutus is a large genus within the family Characidae with representatives distributed across much of tropical and subtropical South America and parts of Central America. The genus name derives from the Greek kreagreytos, meaning 'to tear or rip up the flesh,' a reference to feeding behaviour attributed to the group. Species of Creagrutus are typically small, somewhat drab stream fishes that are distinguished from one another largely by meristic and morphometric characters; the genus has undergone extensive revision but remains challenging, with many species described only in the past few decades.
The specific epithet ouranonastes has not been widely parsed in accessible literature; the type material and original description by Vari and Harold establish it as a distinct species within the Ucayali basin fauna of Peru.
Morphology
Creagrutus ouranonastes reaches a maximum recorded standard length of 4 in, placing it among the larger members of its genus, though most individuals are likely smaller in practice. FishBase records the maximum size from unsexed or male specimens. Like other Creagrutus, it is a benthopelagic freshwater fish with the typical small-characid body plan: a fusiform to slightly compressed trunk, a terminal or subterminal mouth, and the characteristic adipose fin of the Characidae.
As is common across Creagrutus, coloration is subdued — silvery to dusky with patterning more useful for species-level identification than for field recognition. Detailed morphometric and meristic data, including fin-ray and scale counts, are presented in the original description but are not widely reproduced in hobbyist resources. Sexual dimorphism, if present, has not been prominently documented in the available literature for this species.
Habitat
Creagrutus ouranonastes is endemic to the upper Apurimac River basin, part of the Ucayali drainage system in the Peruvian Andes. The species is known from the Río Chalhuanca area, a tributary of the upper Apurimac in the department of Apurímac, Peru. The Apurimac is one of the major headwater rivers of the Amazon system, draining Andean slopes at elevations that typically produce cool-to-moderate tropical stream conditions.
FishBase characterises the species as a benthopelagic freshwater fish in tropical waters, consistent with the Creagrutus pattern of inhabiting flowing streams and rivers with clear or moderately turbid water. Its narrow geographic range — confined to a single sub-basin in the upper Ucayali — makes it one of many Peruvian endemic characids with restricted distributions in Andean stream systems. Precise habitat parameters such as water temperature, pH, and substrate preferences are not documented in the available literature.
Feeding
No targeted dietary studies are available for Creagrutus ouranonastes specifically. Creagrutus species generally are considered opportunistic feeders in their stream environments, taking small aquatic invertebrates, insect larvae, and organic detritus as available in the benthopelagic zone they occupy.
Given the absence of species-specific feeding data, aquarium-based inferences must be treated cautiously. If kept in captivity, it would almost certainly accept small live and frozen invertebrate foods appropriate to its size, following the dietary pattern of comparable small South American stream characids.
Mating
No direct observations of mating behaviour in Creagrutus ouranonastes have been published in the accessible literature. As a member of the Characidae, egg-scattering open spawning is the expected reproductive mode, with eggs deposited among aquatic vegetation or substrate without subsequent parental care — the typical pattern for small South American characids.
Males may exhibit minor size or morphometric differences from females, but prominent sexual coloration dimorphism has not been described for this species. Data are sparse and the following section on breeding reflects what can reasonably be inferred from family-level biology rather than observed fact for this taxon.
Breeding
Specific breeding observations for Creagrutus ouranonastes in captivity or in the wild are not documented in the available literature. Based on the biology of Characidae generally, the species would be expected to scatter small adhesive or semi-adhesive eggs among fine-leaved plants or substrate, with no parental care following spawning. Eggs would develop independently and hatch within a few days under typical tropical freshwater temperatures.
The species has not achieved a profile in the ornamental fish hobby and is not known to be bred commercially or by hobbyists. Any breeding programme would need to be established from wild-collected material, about which data remain limited. Incubation duration, fry size, and rearing requirements have not been reported.
In the aquarium
Creagrutus ouranonastes is not established in the ornamental fish hobby and is unlikely to be encountered by aquarists outside of scientific collections or rare importations. It has no documented common name and is known primarily from museum specimens and the scientific literature.
If available, it could reasonably be kept in a community arrangement suited to small South American stream characids: a well-filtered aquarium with moderate flow, subdued lighting, and soft to moderately hard tropical freshwater conditions approximating its Andean headwater origin. Its maximum size of 4 in SL warrants adequate tank volume, and the benthopelagic habit suggests it would appreciate lower-water-column cover. Given the lack of husbandry records, keeping this species should be considered entirely experimental.
Conservation
Creagrutus ouranonastes is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 22 April 2014. The LC designation indicates that the species does not meet the quantitative thresholds for a threatened category based on information available at that time, though the assessment reflects conditions more than a decade ago.
The species is a Peruvian endemic with a narrow known range in the upper Apurimac basin. The Apurimac watershed faces ongoing pressures from agriculture, gold and other mining activity, hydropower development, and deforestation in highland catchments — threats common to many Andean river systems. Whether the population of C. ouranonastes has been reassessed since 2014 or whether its range encompasses populations adequate to buffer these pressures is not clear from the literature available. Its restricted distribution and reliance on a single river sub-basin make it potentially vulnerable to future degradation even within an LC designation.