Taxonomy & naming
Creagrutus tuyuka was described by Richard P. Vari and Flávio C.T. Lima in 2003 in the journal Copeia (volume 2003, issue 3). The type series was collected from Rio Tiquié at the community of Cachoeira Comprida, a beach below a waterfall at approximately 0°15'44"N, 70°01'05"W in the state of Amazonas, Brazil; the holotype is deposited at the Museu de Zoologia da Universidade de São Paulo (MZUSP 65679). Eschmeyer's Catalog of Fishes lists the name as valid under the family Stevardiidae, subfamily Creagrutinae, though the broad umbrella of Characidae remains in common use and is adopted here per the data-submission convention of this atlas.
The genus Creagrutus Günther, 1864 is a large assemblage of small to mid-sized characids distributed across the Amazon, Orinoco, and drainages of Central America, collectively informally grouped as 'river tetras'. C. tuyuka is distinguished from its closest congeners — C. amoenus and C. kunturus — by the absence of a distinct midlateral spot or stripe, and by subtle proportional differences including a relatively shorter snout-to-anal and snout-to-pelvic distance and a shallower caudal peduncle. Meristic counts recorded at description: 10 dorsal soft rays, 14–15 anal soft rays, and 39–41 vertebrae.
Morphology
C. tuyuka is a slender, fusiform characid reaching a maximum standard length of 2.5 in. The body plan is typical of the genus: a pointed snout, a small terminal mouth suited to picking invertebrate prey from hard substrates, and a relatively unremarkable silvery coloration that provides camouflage against the light-coloured sandy beds it frequents. The absence of the midlateral stripe or spot present in related species is one of the primary diagnostic characters separating it from close relatives.
Fin counts are moderate for the group: 10 dorsal soft rays and 14–15 anal soft rays. The vertebral count of 39–41 falls within the typical Creagrutus range. Sexual dimorphism, if present, has not been formally described in the original account.
Habitat
The species is known from the Rio Tiquié, a tributary of the Rio Uaupés within the upper Rio Negro basin, in Amazonas state, Brazil. The Rio Uaupés (Vaupés in Colombia) drains a large area of the Guiana Shield lowlands and is notable for its dark, blackwater character, though the Rio Tiquié and some of its tributaries run as clear water streams with sandy bottoms — the habitat FishBase records for C. tuyuka at its type locality. FishBase notes the species inhabiting the edges of pools below rapids, a microhabitat associated with moderate current and well-oxygenated water.
The broader distribution encompasses the Rio Uaupés basin in Brazil and Colombia. A Rio Negro basin ichthyofauna checklist published in ZooKeys confirms the species' occurrence in the upper Rio Negro drainage, consistent with the type locality data. Water conditions in clear-water tributaries of the upper Negro tend toward warm temperatures, low pH, and very low conductivity, though the precise field parameters at Cachoeira Comprida have not been published in the sources available to this account.
Feeding
FishBase records C. tuyuka as feeding on benthic aquatic insect larvae, consistent with its demersal habit and its occurrence along the edges of pools and below rapids where invertebrate drift and benthic infauna concentrate. The species is classified as a demersal, tropical freshwater fish, suggesting most foraging occurs at or near the substrate.
Behaviourally, FishBase notes that C. tuyuka forms small schools of four to six individuals that swim close to the substrate — a foraging strategy common among small Amazonian characids hunting benthic prey items.
Mating
No published account of courtship behaviour in C. tuyuka has been located for this entry. Based on the biology of the genus and the family Characidae broadly, the species is assumed to practise open egg-scattering with no parental care, with spawning likely triggered by seasonal cues such as rising water levels and temperature shifts associated with Amazonian flood pulses.
In the aquarium hobby C. tuyuka is essentially unknown as a maintained or bred species, and no first-hand spawning reports have been documented in the sources consulted. The egg-scattering mode typical of small characids would suggest spawning among fine-leaved vegetation or over the substrate, with adhesive or semi-adhesive eggs.
Breeding
Detailed breeding data for C. tuyuka in captivity are not available; the species is rarely if ever encountered in the ornamental trade, and no published breeding accounts have been located. By analogy with other small Creagrutus species and Amazonian characids generally, it is expected to scatter small adhesive eggs among vegetation or over fine substrate, with no parental care and a short incubation period at tropical temperatures.
Any keeper working with this species would be advised to follow protocols used for small Amazonian tetra relatives: a dimly lit breeding tank with fine-leaved plants or spawning mops, very soft and slightly acidic water replicating the clear-water streams of the upper Rio Negro, and prompt removal of adults after spawning. Data are too sparse to give reliable clutch sizes or incubation times.
In the aquarium
Creagrutus tuyuka is essentially unknown in the ornamental fish trade and has not been established in hobbyist collections to any documented degree. The species is a scientific collection fish whose biology is known almost entirely from the type series and from its ecological context in the upper Rio Negro drainage.
Should specimens become available, the natural habitat data suggest that soft, slightly acidic, clear water at tropical temperatures (roughly 75–82 °F) would be appropriate, replicating the clear-water stream conditions of the Rio Tiquié. As a small, schooling, substrate-oriented species it would likely fare best in a species tank or with other small, peaceful Amazonian fishes, with a fine sandy substrate, moderate current, and subdued lighting. Diet in captivity would likely be accepted as frozen and live invertebrate foods — bloodworm, Daphnia, Artemia, and similar items — reflecting its insectivorous wild diet.
Conservation
Creagrutus tuyuka is assessed as Least Concern (LC) on the IUCN Red List, with the assessment completed on 4 March 2021. The Least Concern listing reflects no identified major threats to the species and a distribution in the upper Rio Negro basin — a region that, while subject to gradual deforestation pressure, retains large areas of intact habitat relative to other Amazonian drainages.
The upper Rio Negro watershed, including the Rio Uaupés and its tributaries, falls partly within Indigenous territories and protected areas in both Brazil and Colombia, providing some long-term habitat security. No targeted commercial collection of C. tuyuka is known to occur. The species' limited distribution — currently confirmed from the upper Uaupés basin — nonetheless warrants continued monitoring, particularly as infrastructure development and land-use change expand into the upper Negro catchment.