Taxonomy & naming
Creagrutus manu was formally described by Richard P. Vari and Arlen N. Harold in 2001, in a comprehensive revision of the genus Creagrutus (Characiformes: Characidae). The type locality is Quebrada Agua Clara, the first major quebrada on the trail leading from the biological station at Pakitza inside Parque Nacional Manu, at approximately 11°57'S, 71°17'W, in Provincia Manu, Madre de Dios, Peru. Eschmeyer's Catalog of Fishes lists the valid name as Creagrutus manu Vari & Harold, 2001 and places the species within the family Characidae (order Characiformes); some ichthyological classifications assign the broader subfamily Stevardiinae, but the top-level family assignment follows the Catalog.
Creagrutus is a large Neotropical genus of small, often stream-dwelling characids distributed from Central America south through much of Amazonia and the Pacific drainages of South America. The genus name derives from Greek roots meaning 'to tear' or 'flesh-ripper' — a reference to the dentition typical of the group. The species epithet manu refers directly to the Manu River basin, the drainage within which all known specimens were collected. The species was described at page 140 of the Vari & Harold (2001) revision, which substantially reorganised generic limits and described numerous new species simultaneously.
Morphology
Creagrutus manu is a small, slender characid reaching a maximum recorded size of approximately 1.5 in standard length (SL) based on FishBase data for males and unsexed specimens. Like other members of Creagrutus it has the typically compressed, elongate body plan common to stream-adapted small characids, suited to life in current-washed quebrada habitat.
Detailed meristic and morphometric data for this species appear in the original Vari & Harold (2001) revision; the available cache data do not preserve those specifics, so a comprehensive meristic account is not reproduced here. Creagrutus species in general are distinguished from one another by combinations of fin-ray counts, scale counts, body proportions, and the form of the premaxillary and dentary teeth — characters that require preserved specimens and a compound microscope to evaluate reliably. No information is available from the consulted sources on sexual dimorphism beyond what is typical for small Neotropical characids, where females may develop a fuller abdomen when gravid.
Habitat
All known material of Creagrutus manu originates from the upper Manu River basin within Parque Nacional Manu, a UNESCO World Heritage site in the Madre de Dios department of southeastern Peru. The type locality is a quebrada — a small tributary stream — flowing through the lowland Amazonian forest around the Pakitza station, at an elevation characteristic of the foothill and lowland transition zone in this part of the Andes-to-Amazon gradient.
FishBase classifies the species as freshwater benthopelagic, indicating that it occupies the lower and mid-water zones of the stream rather than being exclusively surface-associated. The Manu drainage is noted for its exceptional biodiversity; its headwaters lie within the Andes and descend through cloud forest into lowland Amazonian rainforest, creating a mosaic of habitats that supports a high diversity of stream fishes. Specific water chemistry parameters (temperature, pH, conductivity) for the type locality are not documented in the sources consulted; the broader Manu basin is characterised by soft, slightly acidic to near-neutral water typical of Amazonian headwater systems, though local variation exists.
Feeding
No specific dietary data for Creagrutus manu appear in the sources consulted for this article. Diet is listed as unknown in the FishBase summary for this species.
Based on what is known of the genus Creagrutus more broadly, members are generally regarded as opportunistic carnivores or omnivores of small stream invertebrates, including aquatic insect larvae, microcrustaceans, and terrestrial invertebrates that fall onto the water surface — a feeding strategy typical of small characids occupying shaded, leaf-littered quebrada environments in Amazonia. Whether C. manu conforms exactly to this pattern awaits dedicated dietary study.
Mating
No specific information on the mating behaviour of Creagrutus manu has been documented in the scientific literature or in the sources consulted here. The species has not been maintained or bred in the aquarium hobby to any documented degree, so observational accounts are likewise unavailable.
By analogy with closely related small Neotropical characids, egg-scattering open spawning with no parental care is the expected reproductive mode — adults releasing adhesive or semi-adhesive eggs among fine-leaved vegetation or over the substrate, after which the eggs are abandoned. Whether C. manu shows any particular spawning seasonality linked to Amazonian rainfall cycles is unknown.
Breeding
Breeding in captivity has not been documented for Creagrutus manu in any source consulted for this article. The species is not established in the aquarium hobby, and no captive-breeding accounts are available.
As with mating biology, the reproductive biology of C. manu can only be inferred from the broader pattern seen in Creagrutus and allied small characids: egg-scattering, non-guarding spawners whose adhesive eggs hatch within a few days at ambient temperatures, yielding small, initially planktonic larvae that depend on fine particulate food. Without field or aquarium documentation specific to this species, more precise statements about clutch size, incubation period, or larval development would be speculative.
In the aquarium
Creagrutus manu is not established in the ornamental fish trade and is effectively unknown in the aquarium hobby. No care accounts, husbandry notes, or captive-maintenance records appear in the sources consulted. It has not been exported commercially to any documented degree.
Hobbyists interested in Creagrutus as a group will find a handful of congeners occasionally available through specialist importers, but C. manu itself — a species from within a protected national park — is unlikely to enter the trade in meaningful numbers. Its closest hobbyist relevance is as an example of the extraordinary underdocumented diversity of small Amazonian stream fishes; for those interested in Neotropical biotope aquariums recreating Manu-drainage habitats, it serves as a reminder of how much of that fauna remains known only from museum specimens.
Conservation
Creagrutus manu was assessed as Least Concern (LC) on the IUCN Red List in April 2014, an evaluation conducted by Ericka Correa and Junior Chuctaya of the Universidad Nacional Mayor de San Marcos (UNMSM-MHN). The assessment notes that the population is presumed to be stable and that a large portion of the species' known range falls within Parque Nacional Manu, one of South America's most rigorously protected areas.
The presence of the type locality — and apparently the bulk of known specimens — within a national park affords the species a meaningful degree of habitat protection. Parque Nacional Manu encompasses a vast, largely intact landscape from Andean grasslands to Amazonian lowlands, and its Amazonian sector around Pakitza is among the least-disturbed lowland forest tracts on the continent. The principal conservation uncertainty is the narrowness of the known distribution: the species is documented only from a single quebrada system, meaning that local events within even a protected area could represent a significant portion of the global population. Broadening the survey coverage of stream fish diversity in the Manu basin would help clarify whether C. manu is genuinely rare or merely undercollected.