Taxonomy & naming
Creagrutus cochui was described by Jacques Géry in 1964. Géry was a prolific taxonomist of Neotropical characiforms, responsible for a large share of the mid-twentieth-century descriptions in this diverse order, and C. cochui is one of many species he erected within Creagrutus. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) is the governing authority for valid names in fishes; it records the valid name as Creagrutus cochui Géry, 1964.
Creagrutus belongs to the family Characidae, the largest family of freshwater fishes in the Western Hemisphere and one of the most species-rich vertebrate families globally. Within Characidae, Creagrutus is placed in the subfamily Stevardiinae, a diverse South American lineage that also includes Bryconamericus and a constellation of smaller genera. The genus itself is one of the most species-rich among Neotropical characids, with new species continuing to be described from throughout Andean foothills and lowland Amazonian drainages. C. cochui represents the lowland western Amazon component of this radiation.
Specimen data attributed to the species includes series collected from the quebrada Tucuchira near Leticia, Amazonas (Colombia), at standard lengths ranging from approximately 1.5–3 in, placing it among the mid-sized members of a genus that otherwise spans from very small to moderate sizes.
Morphology
Creagrutus cochui is a slender, moderately elongate characid reported to reach approximately 4.5 in total length — a size confirmed by FishBase from the available specimen record. Specimen series show a standard length range of roughly 1.5–3 in, indicating that most individuals encountered in collections fall well below the maximum. Like other Creagrutus, the body profile is fusiform and compressed, suited for a benthopelagic lifestyle in flowing and still Amazonian waters.
As in the majority of Creagrutus species, colouration in preserved specimens tends toward silvery with a more or less distinct lateral stripe and a dark spot at the caudal peduncle — a pattern shared across many small characids and not diagnostic at the species level without careful meristic comparison. In life, the lateral stripe may appear more iridescent, and the fins are largely hyaline. Reliable identification to species within Creagrutus requires examination of scale counts, lateral-line pore counts, fin-ray counts, and osteological characters; the genus is notoriously difficult to sort in the field.
Habitat
Creagrutus cochui is distributed across the western Amazon basin, with confirmed occurrence in the Ucayali drainage (Peru) and in the main Amazonas channel (Peru and Colombia), including the Leticia area of Colombian Amazonia. This places the species in tropical lowland freshwater habitats characteristic of the western Amazon: broad, slow to moderately flowing rivers, side-channels, and their associated quebradas (small forested streams), typically over soft substrates with littoral vegetation and submerged organic matter.
FishBase classifies the species as benthopelagic and freshwater, indicating it occupies middle to lower water column positions in its riverine and lacustrine habitats rather than being strictly a surface or benthic dweller. The broad western Amazonian distribution across both main-channel and tributary environments suggests moderate habitat generalism, at least within the lowland tropical freshwater zone. Water conditions throughout the western Amazon are characteristically warm, soft, and acidic to near-neutral, though the exact microhabitat preferences of C. cochui have not been formally characterised in the literature available.
Feeding
Specific dietary studies on Creagrutus cochui do not appear in the literature presently available, and the species lacks a dedicated hobby profile that would capture aquarist observations on its feeding behaviour. Inference must rest on what is known of the genus and the broader Stevardiinae clade to which it belongs.
Creagrutus species are generally regarded as opportunistic carnivores or omnivores of the middle and lower water column, consuming small invertebrates — aquatic insect larvae, microcrustaceans, and worms — along with fallen terrestrial arthropods and other organic material that sinks into their benthopelagic zone. This foraging strategy is consistent with the benthopelagic classification and the small-to-mid size of the species. In the aquarium, closely related Creagrutus readily accept live and frozen small invertebrates such as Daphnia, Artemia nauplii, chironomid larvae (bloodworm), and Tubifex, and many will adapt to high-quality small pellets and flake over time.
Mating
No published accounts of courtship or mating behaviour specific to Creagrutus cochui are known from the scientific literature or from aquarist observation records accessible in the available sources. Within Characidae broadly, and among Stevardiinae specifically, the predominant reproductive strategy is egg-scattering with no parental care: males pursue females and fertilise eggs externally as they are released, typically near fine-leaved vegetation or over the substrate.
The Stevardiinae includes some genera with internal fertilisation and specialized sperm transfer, but Creagrutus itself appears to follow the more ancestral egg-scattering pattern based on what little reproductive biology has been documented for the genus. Sexual dimorphism in most Creagrutus is subtle, with females tending toward a more rounded abdomen when gravid; bright colour differences between sexes are not a feature of the genus. More detailed mating observations await captive breeding accounts or focused field study.
Breeding
Captive breeding of Creagrutus cochui has not been documented in readily available hobby or scientific sources. Given the species' membership in Characidae and its benthopelagic, mid-water ecology, a broad characterisation of expected breeding biology can be drawn from the family template: open egg-scattering over vegetation or substrate, adhesive or semi-adhesive eggs, and no parental care, with adults liable to consume eggs if not separated from the spawning site.
Species of similar size and ecology within Characidae typically spawn in response to simulated wet-season conditions — a slight temperature rise, increased water changes with slightly softer or cooler water, and the provision of fine-leaved plants or spawning mops to receive eggs. Eggs hatch within 24–48 hours under warm tropical conditions; fry require infusoria or commercial liquid fry foods initially, graduating to newly hatched brine shrimp as they grow. These are inferences from the family framework rather than species-specific data, and any aquarist attempting to breed C. cochui should document their results, as records for this species appear to be absent from the published hobby literature.
In the aquarium
Creagrutus cochui is not an established aquarium fish and does not appear in mainstream hobby literature or on major species databases with a dedicated husbandry profile. It is an occasional import curiosity from the western Amazon rather than a traded commodity, and most aquarists are unlikely to encounter it by name. Its absence from Seriously Fish and similar resources reflects this limited hobby presence.
For the rare aquarist keeping C. cochui, the starting point for care parameters is the western Amazon template: warm soft, slightly acidic to neutral water (approximately 75–82 °F, pH 6.0–7.5, low hardness), dim to moderate lighting with a planted or leaf-litter-covered bottom, gentle filtration that avoids strong current in the resting zones, and a varied diet of live, frozen, and prepared small foods. As a schooling characid from open Amazonian waters, it is best kept in groups of six or more, with tankmates of similar size and temperament. The species' benthopelagic habits suggest it will use the middle and lower water column, making it compatible with surface-schooling tetras or bottom-dwelling corydoras in a community setting without significant competition for space.
Conservation
Creagrutus cochui is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment dated 4 March 2021. The Least Concern designation reflects a range broad enough — across the Ucayali drainage and the main Amazonas channel — that no immediate threat is considered likely to drive the species below the thresholds for a threatened category under current conditions.
The western Amazon basin faces significant and ongoing pressures: deforestation in Andean foothill catchments alters hydrology and sedimentation in downstream river systems; artisanal and commercial fishing affects fish communities throughout the region; and climate-driven changes to flood pulse dynamics are increasingly documented. None of these threats is considered to have reduced C. cochui populations to a degree warranting a higher threat category at present, but the species has received little targeted study and population trends have not been formally quantified. Maintaining water quality and forest cover in the western Amazonian catchments remains the most important conservation measure for the broad assemblage of small characids, including this species, that depend on intact lowland river systems.