Taxonomy & naming
Creagrutus pila was described by Richard P. Vari and Andrew S. Harold in 2001, as part of a systematic revision of the genus Creagrutus within the family Characidae. The type locality is associated with small rivers of the Aguaytía River drainage in the Ucayali department of Peru. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the authority for the valid name Creagrutus pila Vari & Harold, 2001.
Creagrutus is a large and taxonomically complex genus of New World characins distributed across lowland and foothill drainages of Central and South America. The genus belongs to the subfamily Stevardiinae (or is placed within Characidae sensu lato depending on the classification followed), and many of its roughly 70 recognized species are morphologically similar, differing in subtle meristic counts, body proportions, and pigmentation patterns that require close examination to separate. Creagrutus pila has been confirmed from the Ucayali drainage system of Peru, including in regional ichthyofauna inventories of the Aguaytía basin and checklists from Loreto department.
No established common name exists for this species in either the scientific or aquarium literature. It is listed by FishBase under the genus Creagrutus and carries no trade or vernacular name.
Morphology
Creagrutus pila reaches a maximum recorded standard length of 3 in (approximately 2.8 in). Like other members of the genus it is a slender to moderately deep-bodied characid with the typical Creagrutus silhouette: a slightly compressed body, a relatively large eye positioned well forward on the head, a terminal to slightly subterminal mouth, and a complete lateral line. The caudal fin is forked, and the adipose fin — characteristic of most characids — is present.
Pigmentation in Creagrutus species is often a key diagnostic character. In C. pila the body shows the basic Creagrutus pattern of a darker dorsal field shading to a pale or silvery ventral region, with a lateral stripe or band of variable intensity. Precise details of scale counts, fin-ray numbers, and pigmentation pattern as described by Vari and Harold distinguish this species from its congeners, but these characters require specimen examination for reliable identification.
Data on live coloration are sparse for this species, as it is rarely maintained in aquaria and most observations derive from preserved museum material, which loses or alters colour. In life the fish is likely similar to other small Creagrutus: a subtly marked, silver-bodied stream characin without the vivid coloration of the more familiar hobby tetras.
Habitat
Creagrutus pila is endemic to Peru, known from smaller river channels draining into the Aguaytía River, a left-bank tributary of the Ucayali River in the upper Amazon basin. The Aguaytía drains the eastern slopes of the Andes and the adjacent lowland Ucayali department, and is a mid-elevation to lowland system with clear to turbid tributaries depending on season and proximity to the Andean foothills.
FishBase classifies the species as benthopelagic and freshwater, occurring in a tropical climate zone. Creagrutus species in similar upper Amazonian drainages typically inhabit clear, relatively fast-moving streams with gravel or sandy substrates, overhanging riparian vegetation, and abundant leaf litter. Water temperatures in Ucayali department streams at mid-elevation typically range from the mid-20s down to the low 20s Celsius. Specific water chemistry data for the type locality are not available in the current literature, but streams of the Aguaytía basin are generally soft to moderately soft and near-neutral to slightly acidic, reflecting the mixed geology of the region.
A comprehensive ichthyofauna survey of the Aguaytía basin (Quezada García et al. 2017) recorded 211 species from 9,917 specimens and confirmed C. pila as a component of that fish assemblage, alongside a rich diversity of other characins, catfishes, and cichlids.
Feeding
No published dietary analysis exists specifically for Creagrutus pila. Based on the biology of the genus and its benthopelagic lifestyle, it is presumed to be a carnivore or omnivore that feeds primarily on small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial insects that fall onto the water surface — along with detritus and small amounts of plant material.
Creagrutus species in general are active mid-water and near-bottom foragers in stream environments, taking whatever small prey items are available. In the aquarium, members of the genus typically accept a range of small live and frozen invertebrate foods including bloodworm, Daphnia, and brine shrimp, as well as small pellet or granule foods, though published husbandry observations for C. pila specifically are lacking.
Mating
No specific observations of mating behaviour in Creagrutus pila have been published. By analogy with the broader genus and with other small stream-dwelling characins, the species is expected to be an egg-scatterer with no parental care. Males and females likely aggregate near fine-leaved aquatic vegetation or submerged structure during spawning, releasing adhesive or semi-adhesive eggs that settle on vegetation or substrate.
Many small South American stream characids spawn in response to seasonal cues — particularly rain-season temperature drops and increased current — and Creagrutus species in the field are likely seasonal breeders tied to the Ucayali basin's rainfall cycle. Sexual dimorphism in the genus is subtle, with females typically deeper-bodied when gravid; reliable sexing outside the breeding season requires close examination.
Breeding
Creagrutus pila has not been bred in captivity in any documented account available in the scientific or hobby literature. The general reproductive biology of the genus follows the pattern typical of small stream characids: egg-scattering over fine-leaved plants or gravel substrate, adhesive eggs with no parental care, and fry that are free-swimming within a few days of hatching.
For any keeper who does attempt to breed this species, the approach used for similar small South American characins is the most logical starting point: a well-planted breeding tank with soft, slightly acidic water, a temperature drop of a few degrees to simulate rain-season conditions, vigorous water movement, and conditioning on live or frozen foods. Eggs and fry should be separated from adults as soon as possible given the absence of parental care in the genus. First foods for fry of comparable-sized Creagrutus would be infusoria, rotifers, or commercial liquid fry food, followed by newly hatched brine shrimp.
In the aquarium
Creagrutus pila is essentially unknown in the ornamental fish trade and is not commercially available. It has not been the subject of any aquarium keeping accounts in the hobby literature. Any specimens kept would have originated from scientific collecting expeditions or from specialised importations of Peruvian stream fishes, and their husbandry would follow the general framework for small Creagrutus and stream characids from the upper Amazon.
For reference, related Creagrutus species kept by specialists are maintained in aquaria of moderate size — 23.5–35.5 in in length — with clear, well-oxygenated water, a current, a substrate of sand and gravel, and a planted perimeter with open swimming space. Water conditions reflecting the soft, near-neutral chemistry of Andean-foothill tributaries would be appropriate: temperatures in the low-to-mid 20s Celsius, pH around 6.5 to 7.2, and low conductivity. The species is not a candidate for the typical community tank and is only of interest to collectors of Neotropical stream fishes or researchers.
Conservation
Creagrutus pila is assessed as Least Concern (LC) on the IUCN Red List. The LC listing reflects a distribution within the Ucayali River system — a large, hydrologically complex basin — and the absence of identified major threats specific to this species. Multiple regional checklists and ichthyofaunal surveys of the Aguaytía basin and Loreto department confirm its continued presence within its range.
The Ucayali basin faces broad pressures common to Amazonian drainages: deforestation and agricultural expansion in the piedmont zone, stream sedimentation, and artisanal gold mining in upper tributaries. None of these threats has yet triggered a reassessment of C. pila above the LC threshold, but habitat degradation in the smaller tributaries that constitute its core range is a concern for the long-term. The species has no commercial value in the aquarium trade and no subsistence value as a food fish given its small size, so collection pressure is not a factor in its conservation status.