Taxonomy & naming
Creagrutus britskii was described by Richard P. Vari and Arnold S. Harold in 2001 in their landmark monograph on the Neotropical fish genera Creagrutus Günther and Piabina Reinhardt, published as Smithsonian Contributions to Zoology 613. That work constitutes the definitive genus-level phylogenetic study and species-level revision for the cis-Andean Creagrutus, and C. britskii is one of several new species erected in it. Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS) recognises the valid name as Creagrutus britskii Vari & Harold, 2001.
The genus Creagrutus belongs to the family Characidae — the largest family of freshwater fishes in South America — and is placed within the order Characiformes. Creagrutus species are small, largely benthic characids distributed across South and Central America, often occupying foothill and highland streams. The specific epithet honours the Brazilian ichthyologist Heraldo A. Britski of the Museu de Zoologia da Universidade de São Paulo, who made major contributions to South American ichthyology and from whose material several new taxa have been described.
Morphology
Creagrutus britskii is a slender, moderately elongate characid reaching a maximum recorded standard length of approximately 2 in. Like other members of the genus it is a benthopelagic fish with a body form suited to life close to the riverbed: the ventral profile is relatively flat and the head somewhat depressed, facilitating foraging on substrates. The fin complement is typical of Characidae, including an adipose fin.
Detailed meristic and morphometric data are provided in the Vari and Harold (2001) monograph, which supplies the diagnostic characters separating C. britskii from its congeners within the cis-Andean species group. In life the coloration of Creagrutus species is generally cryptic — silvery to brownish, often with a lateral stripe or mid-lateral band — suited to small, clear highland streams. Data on live coloration for this species specifically are sparse in the available sources.
Habitat
Creagrutus britskii is endemic to the upper Tocantins River basin in central Brazil, with confirmed records from the states of Goiás, Maranhão, Pará, and Tocantins. It occupies moderate-sized highland tributaries with widths roughly in the range of 20–82 ft, over rocky, gravel, or gravel-mud bottoms and with variable current ranging from slow to fast. The IUCN assessment describes it as a benthopelagic species of freshwater wetland rivers and permanent streams.
The upper Tocantins basin sits on the Brazilian Cerrado plateau, where streams are generally clear to moderately turbid and subject to seasonal rainfall variation. The species appears to favour smaller tributary systems rather than the main channel, a habitat preference that has buffered it somewhat from the large-scale dam construction that has affected the main Tocantins stem. It occurs within the boundaries of the Estação Ecológica Serra Geral do Tocantins, a protected area that provides some formal safeguard for part of its range.
Feeding
Creagrutus britskii feeds primarily on benthic aquatic insects, consistent with its bottom-swimming habit and the trophic position recorded on FishBase (trophic level 2.5). In the moderate-sized gravel-bottomed streams it inhabits, the benthos is typically rich in chironomid larvae, mayfly nymphs, and other invertebrates on which small rheophilic characids depend.
No detailed dietary studies specific to C. britskii are available in the current literature. The genus Creagrutus more broadly has been characterised as insectivorous to omnivorous, with the balance depending on stream productivity and prey availability. In an aquarium context Creagrutus species can be expected to accept small live and frozen invertebrate foods and eventually prepared foods, though the species is rarely if ever encountered in the hobby.
Mating
No specific observations of mating behaviour in Creagrutus britskii have been published. Based on broader knowledge of the family Characidae, Creagrutus species are presumed to be egg-scattering open spawners in which males pursue females and spawning occurs without preparation of a nest site. The adhesive or semi-adhesive eggs are likely scattered among fine-leaved aquatic plants or deposited over gravel substrates, with no parental care from either sex.
Seasonal spawning cued by rainfall and the associated changes in water temperature and conductivity is typical of many Cerrado stream fishes, which experience marked wet and dry seasons. Any mating aggregation or display behaviour specific to C. britskii remains undocumented.
Breeding
Creagrutus britskii has not been documented in captive breeding programmes, and no aquarium breeding records appear in the accessible literature. By analogy with other small characids of the region, it would be expected to spawn over fine-leaved vegetation or spawning substrate, with eggs hatching within a few days at tropical temperatures and the fry requiring small foods such as infusoria or rotifers before graduating to newly hatched brine shrimp.
The species is not available in the aquarium trade. Any captive study would require material collected under appropriate permits from Brazil, where export of native freshwater fishes is tightly regulated. For hobbyists interested in the genus, a few other Creagrutus species occasionally appear in specialist shipments from South America, though the group as a whole remains poorly represented in the hobby.
In the aquarium
Creagrutus britskii is essentially unknown in the aquarium hobby and is not in commercial trade. The few individuals that might reach specialist aquarists would have been collected as incidental catch during scientific sampling. As a small, bottom-oriented insectivore from clear highland tributaries, it would logically be housed in a well-oxygenated aquarium with a sandy or fine-gravel substrate, moderate current, and a diet of small live or frozen invertebrates.
Water parameters reflecting the upper Tocantins basin — tropical temperatures likely in the 72–82 °F range, near-neutral to slightly acidic or neutral pH — would be appropriate, though no published aquarium data exist for the species. Given its obscurity and restricted wild range, conservation and scientific study take precedence over the hobby for this fish.
Conservation
Creagrutus britskii is assessed as Least Concern (LC) on the IUCN Red List, based on an assessment conducted on 7 November 2018 by Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). The species has an estimated extent of occurrence of approximately 113,564 mi² across four Brazilian states, and its population trend is considered stable.
The principal identified threat is dam construction along the Tocantins River, most notably the Serra da Mesa reservoir, which has inundated habitat in part of the species' range. However, the IUCN assessment concludes that C. britskii's small size, benthopelagic habit, and preference for smaller tributary streams rather than the main river channel mean it is not considered at imminent extinction risk. Its occurrence within the Estação Ecológica Serra Geral do Tocantins provides a degree of habitat protection. Continued monitoring is warranted given ongoing hydroelectric development pressure in the Tocantins basin.