Taxonomy & naming
Creagrutus molinus was formally described by Richard P. Vari and Achille S. Harold in 2001, in a comprehensive phylogenetic and taxonomic revision of the genus Creagrutus published in Smithsonian Contributions to Zoology (no. 613, pp. 1–239). The type locality is the upper Rio Araguaia basin in the state of Mato Grosso, Brazil, specifically the area around Barra do Garças. The Catalog of Fishes records the valid name as Creagrutus molinus Vari & Harold, 2001.
Creagrutus belongs to the subfamily Stevardiinae within Characidae (the family placement used here follows Catalog of Fishes conventions). The genus is the largest in Stevardiinae, comprising well over a hundred described species distributed primarily along the Andean cordillera and adjacent lowland drainages, with a handful of species — including C. molinus — occupying the ancient crystalline shield drainages of central Brazil. Its position within the upper Araguaia makes it biogeographically notable: the rio Araguaia originates on the Central Brazilian Plateau and is one of the major tributaries of the Tocantins system, itself draining into the Atlantic near Belém.
Morphology
Creagrutus molinus is a small, elongate characid reaching a maximum recorded standard length of 2 in. Like other members of its genus it has the typical characid form: a fusiform, slightly compressed body, a forked tail, an adipose fin, and a complete lateral line. The genus name Creagrutus references flesh-tearing or hooked structures, and the species epithet molinus — from the Latin for 'grinder' — alludes specifically to the notably large teeth present in both the upper and lower jaws, a feature distinguishing it within the genus.
Beyond the dentition and size data recorded at the time of description, detailed published accounts of coloration and soft-tissue characters for C. molinus are sparse in the accessible literature, as is typical of many recently described Creagrutus species known only from type series. The species is presumed to share the genus's general lateral line and fin-formula characters described by Vari and Harold in their revision. Data on live coloration, fin pigmentation, and secondary sexual dimorphism remain undocumented in the hobby literature.
Habitat
Creagrutus molinus is known only from the upper Rio Araguaia basin, Mato Grosso, Brazil. The upper Araguaia is a seasonally flooded savanna-riverine system running through the cerrado biome, a biodiversity hotspot under severe agricultural pressure. The Barra do Garças region, near the type locality, sits on the plateau edge where the river exits the central highlands. The surrounding landscape is dominated by gallery forest along waterways within a broader open cerrado matrix.
Most Creagrutus species inhabit clear, fast-flowing, often shallow streams with sandy or rocky substrates, typically under gallery forest canopy. Water in the upper Araguaia tributaries tends to be soft and acidic to slightly acidic, reflecting the nutrient-poor quartzite and sandstone geology of the Central Brazilian Plateau. No specific physicochemical parameters have been published for the type-locality stream at the time of the species' description, and no further collections have been widely reported. A related congener recorded from other South American drainages (C. beni) is associated with temperatures of 72–79 °F and pH 6.0–7.2, parameters that may approximate conditions in similar cerrado streams, though this extrapolation carries uncertainty.
Feeding
No dietary data specific to Creagrutus molinus have been published. Across the genus, Creagrutus species are generally considered opportunistic micro-predators or insectivores, taking small invertebrates including aquatic insect larvae, microcrustaceans, and terrestrial insects that fall onto the water's surface, a feeding mode common among characids inhabiting forest-shaded streams.
The notably enlarged dentition implied by the epithet molinus suggests a capacity for processing harder prey items or perhaps larger invertebrates than congeners with smaller teeth, though this inference is tentative without published stomach-content studies. In the aquarium, congeners are typically fed small live and frozen invertebrates — Daphnia, newly hatched brine shrimp, bloodworm, and micro-pellets — and accepted observations from the genus provide the only practical guide for this species given the absence of hobby records.
Mating
No observations of reproductive behaviour have been published for Creagrutus molinus, and the species has not been documented in the aquarium trade. Across Characidae generally, and within Creagrutus specifically, the reproductive mode is egg-scattering with no parental care: males pursue females, and eggs are broadcast over substrate or vegetation and left unattended. Fertilised eggs are adhesive in some characids, settling among fine-leaved plants or gravel interstices, though specifics vary by species.
No courtship behaviour, secondary sexual characters, or seasonality data have been described for C. molinus. In cerrado stream environments, breeding in characids often correlates with the onset of the wet season (October–March), when rising water levels and food availability trigger spawning activity, but this remains an inference for this species.
Breeding
Creagrutus molinus has not been bred in captivity, and no spawning observations appear in the available literature. Its small size — under 2.5 in SL — and its membership in a large characid genus of broadly similar biology suggest that, were it to become available in the hobby, it would likely follow the egg-scattering, open-spawning pattern typical of the family: adults scatter adhesive eggs among fine-leaved plants or over substrate, the eggs hatch within a few days at tropical temperatures, and the small fry require very fine first foods.
Until the species is collected, imported, or studied in controlled conditions, no specific guidance on brood size, incubation period, fry rearing, or sex ratios can be offered. Data on this species in captivity are, at present, absent.
In the aquarium
Creagrutus molinus has not been documented in the aquarium hobby. The species is known only from scientific collections in its native Brazilian drainage and has not appeared in the ornamental fish trade in any published record. No husbandry information — tank size, social requirements, diet acceptance, or compatibility — is available.
For aquarists interested in the genus, closely related and occasionally available Creagrutus species (such as C. beni from Bolivia and Peru) provide a proxy: these fish are small, peaceful, and best kept in soft, slightly acidic water at 72–79 °F with subdued lighting and a well-planted or decorated tank. Given the species' Data Deficient IUCN status and restricted range, any collection for the trade would need to be conducted with conservation oversight. At present, C. molinus is a species of scientific interest rather than an aquarium subject.
Conservation
Creagrutus molinus is listed as Data Deficient (DD) on the IUCN Red List, with the assessment conducted on 7 November 2018 by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). The DD listing reflects a genuine lack of population, distribution, and trend data sufficient to assign a threat category — not a determination that the species is unthreatened.
The upper Rio Araguaia basin, the species' only known range, sits within the cerrado biome, which has lost over half of its original cover to cattle ranching, soy cultivation, and infrastructure development, making it one of the most threatened tropical savannas on Earth. Stream and gallery-forest habitats in this region face siltation, deforestation of riparian corridors, and water extraction. A species known only from a single basin in this landscape, with no documented population surveys since its description, carries implicit extinction risk that its Data Deficient status does not capture. Targeted surveys to establish its current distribution and abundance are the most pressing conservation need.