Taxonomy & naming
Creagrutus cracentis was described by Richard P. Vari and Arthur S. Harold in 2001 as part of their comprehensive phylogenetic revision of the Neotropical fish genera Creagrutus Günther and Piabina Reinhardt, published as Smithsonian Contributions to Zoology 613. That monograph revised all cis-Andean species of both genera and placed Creagrutus cracentis within the large and diverse genus Creagrutus, with the type description appearing at page 93. Eschmeyer's Catalog of Fishes is the governing authority for the valid name, recorded as Creagrutus cracentis Vari & Harold, 2001.
Creagrutus belongs to the subfamily Stevardiinae within Characidae, a speciose group of small New World characins distributed widely across river systems from Mexico to Argentina. FishBase notes that this family assignment has been treated variously in recent literature; the genus name derives from the Greek kreagreytos, meaning to tear or rip the flesh, a reference to the sharp teeth characteristic of the group. No common name has been established for this species in the trade or literature.
Morphology
Creagrutus cracentis is a small, elongate characin with a maximum recorded total length of 2.5 in and a maximum published weight of approximately 2.44 g. Like other members of the genus it has the compact, fusiform body plan typical of Creagrutus, with relatively large eyes, a terminal to slightly superior mouth bearing well-developed teeth, and the usual complement of characin features including a small adipose fin.
The trophic level is estimated at approximately 2.5 — the low end of the scale, consistent with a diet dominated by invertebrates rather than fish — based on closest relatives. Detailed morphological characters distinguishing C. cracentis from allied species are presented in the Vari and Harold (2001) revision, which provides the taxonomic standard for the group. Field-collected specimens from the Tapajós basin show the typical coloration of the genus: a pale silvery ground with a darker lateral stripe and unpatterned fins, though pigmentation can vary with preservation and condition.
Habitat
The known range of Creagrutus cracentis is the lower Tapajós River basin in Pará state, Brazil. The Tapajós is one of the Amazon system's major clearwater tributaries — fed by ancient Precambrian shield geology that leaches few minerals, producing water that is notably transparent, tea-coloured to gin-clear, softly acidic, and very low in conductivity and dissolved solids.
Water parameters measured in the Tapajós system reflect this clearwater chemistry: temperatures around 79 °F are typical, and pH values as low as 4.7 have been recorded in the tributary microhabitats where small characins occur. The river experiences pronounced seasonal inundation, with water levels fluctuating by four to five metres between dry and wet seasons, inundating adjacent floodplain forest and profoundly restructuring available microhabitat. Creagrutus species in general occupy benthic to benthopelagic niches in these environments, sheltering among submerged root systems, leaf litter, and woody debris at the margins of main-channel and floodplain habitats.
Feeding
Creagrutus cracentis is an invertivore. Its estimated trophic level of 2.5 (±0.1) places it among small predators feeding primarily on aquatic and terrestrial invertebrates — insect larvae, small crustaceans, worms, and similar benthic prey — gleaned from the substrate or seized from the water column. The dentition of the genus, reflected in the etymological meaning of the name, is adapted for capturing and processing small prey items rather than plant material.
In aquarium conditions, Creagrutus species generally accept live and frozen foods such as Daphnia, bloodworm, and brine shrimp with little difficulty, though their requirements in captivity are poorly documented given their rarity in the hobby. Feeding small, protein-rich invertebrate foods multiple times daily is appropriate for small characins of this trophic guild.
Mating
No specific observations of mating behaviour in Creagrutus cracentis have been published. By analogy with the broader characin clade, the genus is expected to be an egg-scattering open spawner with no parental care — the modal reproductive strategy across Characidae. Males and females are presumed to congregate in shallow, vegetated, or debris-rich microhabitats during spawning events tied to seasonal hydrological cues, particularly the onset of rising water levels in the Tapajós floodplain.
Sexual dimorphism in Creagrutus has not been characterised for this species specifically; in related genera, ripe females tend to be slightly more robust-bodied than males, a common condition in small characins. Courtship behaviour in the group has not been documented in the literature.
Breeding
No captive breeding records for Creagrutus cracentis are known. Based on the biology of comparable small Amazonian characins, breeding would involve egg-scattering over fine-leaved vegetation, submerged roots, or substrate, with adhesive or semi-adhesive eggs and no parental care; adults would likely consume eggs given the opportunity. Incubation and fry development under Tapajós-appropriate conditions — warm, very soft, acidic water — are uncharacterised.
The species' absence from the aquarium trade means that captive breeding protocols have not been developed. Any hobbyist working with wild-caught material would need to replicate the soft, acidic, warm conditions of the Tapajós clearwater system and observe spawning behaviour directly, as published husbandry guidance does not exist for this species.
In the aquarium
Creagrutus cracentis is not established in the aquarium trade and is essentially unknown to hobbyists. Should wild-caught specimens become available, the core requirement would be faithful replication of Tapajós clearwater conditions: very soft, ion-poor water with pH in the range of 4.5–6.5, temperature around 75–82 °F, low conductivity, and good filtration producing clean but gentle flow. Tannin-stained water achieved with botanicals such as dried leaves or alder cones would approximate the natural environment and reduce stress.
As a small, presumably peaceful and shoaling species, it would be best kept in a group of six or more with tankmates of similar size and compatible water requirements — other small Amazonian characins, dwarf cichlids, or small loricariid catfish. A well-planted or densely decorated tank with ample cover would suit the species' likely preference for structured microhabitat. The genus is one of the richest in the Neotropical ichthyofauna but has attracted almost no hobbyist attention compared to better-known characins of the Amazon basin.
Conservation
Creagrutus cracentis is assessed as Least Concern (LC) on the IUCN Red List, with the assessment carried out by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and the status last confirmed under IUCN version 2022-1. The Least Concern rating reflects an absence of evidence for population-level threats severe enough to approach the threshold for a threatened category, though data on abundance and population trends for this species specifically are limited.
The lower Tapajós basin, while broadly intact compared to many Amazonian sub-basins, is not without pressures: deforestation in the upper catchment affects water quality and seasonal hydrology, and large-scale infrastructure developments in the broader Amazon region pose background threats to riverine ichthyofaunas across the basin. The species' restricted known range — confined to the lower Tapajós — means that any significant degradation of that system could affect it disproportionately. It is not targeted by fisheries and has no documented collection for the ornamental trade.