Taxonomy & naming
Creagrutus occidaneus was formally described by Richard P. Vari and Andrew S. Harold in their 2001 monograph on the Neotropical fish genera Creagrutus and Piabucina, a landmark phylogenetic study that restructured understanding of this highly diverse characid lineage. Syntypes were deposited in the Naturhistorisches Museum Wien (NMW), with specimens drawn from localities in Peru including the Madre de Dios and San Martín regions. The type locality is in the Manu River basin of eastern Peru. Eschmeyer's Catalog of Fishes, the authority for valid nomenclature, records the name as Creagrutus occidaneus Vari & Harold, 2001.
The genus Creagrutus belongs to the family Characidae. It is a large and taxonomically complex assemblage of small, slender characids distributed across Central and South America, with most species found in Andean foothill streams and western Amazonian lowlands. The group presents persistent challenges for identification: species are superficially similar, differentiated mainly by subtle meristic and morphometric characters, and new species continue to be described. Creagrutus occidaneus sits within the western Amazonian radiation of the genus.
Morphology
Creagrutus occidaneus is a small, slender fish, reaching a maximum recorded standard length of 2.5 in. Like other members of the genus it has the typical characid body plan: a compressed, moderately elongate form with a complete lateral line, a small adipose fin, and the characteristic toothless gap between the premaxilla and dentary that gives the family its name in some classifications. Coloration in Creagrutus is generally cryptic — silvery to pale tan with a diffuse lateral stripe or series of spots — and detailed descriptions of live coloration are not available for this species specifically.
Distinguishing C. occidaneus from congeners requires examination of meristic characters including scale counts, fin-ray counts, and the number and arrangement of teeth, as set out in Vari and Harold's 2001 revision. In the field and in preservation, members of the genus look broadly similar; accurate identification depends on the original description.
Habitat
Creagrutus occidaneus occurs in the foothills and lowlands of eastern Peru and adjacent Brazil: the Manu River basin and Madre de Dios drainage in Peru, the upper Purus River basin in the Brazilian states of Acre and Amazonas, and the Ucayali drainage of Peru. This places the species in the western Amazon basin at low to moderate elevations, in the transition zone between Andean foothills and the Amazonian lowland plain.
Species of Creagrutus in this region typically occupy clear to slightly turbid streams and small rivers with moderate to swift current, often with sandy or gravelly substrates and good riparian cover. They are associated with oxygenated, warm waters that reflect the Amazonian tropical climate. Detailed water-parameter data for C. occidaneus at its specific collection localities have not been published separately from the original description.
Feeding
Specific dietary data for Creagrutus occidaneus in the wild have not been reported in the sources available. Members of the genus Creagrutus are generally regarded as opportunistic micropredators and omnivores typical of small characids in Amazonian streams: the diet likely includes small aquatic and terrestrial invertebrates, insect larvae, microcrustaceans, and organic detritus taken from the water column and substrate.
In an aquarium context, fish of this size and family background accept fine-grained prepared foods such as micro-pellets and crushed flake, along with small live and frozen invertebrates — Daphnia, baby brine shrimp, and similar items. Specific aquarium feeding records for this species are sparse.
Mating
No published observations of mating behaviour specific to Creagrutus occidaneus are available. Across Creagrutus and allied small characids of the western Amazon, the typical reproductive strategy is egg-scattering: sexually ripe adults broadcast adhesive eggs over fine-leaved aquatic vegetation, submerged leaf litter, or gravel, with no subsequent parental care. Males are generally slimmer than gravid females, but detailed secondary sexual character data for this species have not been reported.
In the aquarium, mating behaviour of small Creagrutus is not well documented in the hobby literature. Conditioning with live and frozen foods would likely promote spawning readiness, as with most small characids.
Breeding
Breeding records for Creagrutus occidaneus in captivity are absent from the available literature. By analogy with other small Neotropical characids, spawning would be expected to follow the egg-scattering pattern: adhesive eggs deposited among fine-leaved plants or over a substrate, hatching within one to three days at tropical temperatures, with no parental investment beyond the spawning act.
The adults would typically consume eggs given the opportunity, so separation of eggs or adults after spawning would be advisable in a controlled breeding attempt. Fry would require very fine first foods such as infusoria or commercial liquid fry diets before graduating to newly hatched brine shrimp. These are inferences from the genus and family; no hobbyist or research breeding accounts have been located for this species specifically.
In the aquarium
Creagrutus occidaneus is rarely encountered in the ornamental fish trade and is not an established hobby species. Its aquarium requirements can be approximated from knowledge of the genus and its western Amazonian habitat: soft to moderately hard, warm water in the 75–82 °F range, good filtration and oxygenation to simulate the well-oxygenated Andean foothill streams it inhabits, and a planted or decorated aquarium with hiding spots among driftwood and fine-leaved plants.
Being a small, active schooling characid, it would be best kept in groups rather than as individuals. Tankmates should be similarly sized and non-aggressive. Because it is not an established aquarium species, husbandry guidance is largely inferential; hobbyists encountering it as a bycatch in wild-caught shipments from Peru should treat it with the same care as other delicate small characids from Amazonian foothill streams.
Conservation
Creagrutus occidaneus is assessed as Least Concern on the IUCN Red List, with the most recent assessment recorded in March 2021 (IUCN Version 2025-2, referenced via FishBase). The species' relatively broad distribution across eastern Peru and the adjacent Brazilian states of Acre and Amazonas — spanning the Manu, Madre de Dios, Ucayali, and upper Purus drainages — supports a non-threatened status, as the range encompasses multiple river basins with substantial intact habitat.
The Amazon foothill and lowland streams this species occupies face ongoing pressures from deforestation, agricultural runoff, and hydroelectric development throughout the region. The Madre de Dios drainage in particular is subject to artisanal gold mining, which degrades water quality and alters stream structure. While none of these threats currently appear to push the species toward a threatened category, continued monitoring of stream-dwelling small characids in this region is important given rapid land-use change across western Amazonia.