Taxonomy & naming
Creagrutus yudja was described by André L. Netto-Ferreira and Cristiane S. Moreira in 2018, in a paper published in Zootaxa (4375, issue 2). The type locality is the Rio Xingu basin in the Brazilian state of Pará. Eschmeyer's Catalog of Fishes records the valid name as Creagrutus yudja Netto-Ferreira & Moreira, 2018.
The genus Creagrutus (family Characidae) is a diverse and taxonomically challenging group of small Neotropical characids distributed across river systems from Mexico to Argentina. Within the genus, C. yudja is considered the sister taxon to Creagrutus nigrotaeniatus based on molecular and morphological evidence. It is distinguished from its congeners by a combination of characters: the absence of infraorbital 6, a comparatively shallow body depth (13.7–19.2% of standard length), 34–36 perforated lateral-line scales, and 4–6 post-anal scales.
The specific epithet yudja is an ethonym taken from the Yudjá, the indigenous people of the Xingu basin in Pará who self-identify by this name, meaning 'keeper of the river'. The formal common name Turbo Tetra is used on FishBase.
Morphology
Creagrutus yudja is a miniature characid, reaching a maximum recorded standard length of 1 in. The body is notably slender relative to most Creagrutus, with a body depth that falls between 13.7 and 19.2 percent of standard length — shallower than related species — giving the fish an elongated, almost terete profile.
Key meristic features include 34 to 36 perforated lateral-line scales and 4 to 6 post-anal scales. A diagnostically important character is the absence of infraorbital 6, which separates it from several congeners. Like other small Creagrutus, the colouration is subdued — generally silvery with a lateral stripe or band and subtle dorsal pigmentation — though precise details of live colouration were not documented in the founding literature cached here. Sexual dimorphism, if present, has not been described for this species.
Habitat
Creagrutus yudja is known only from tributaries of the Rio Xingu in Pará state, Brazil. Within this basin it occupies clear-water streams and river arms across an elevational range of approximately 82 to 123 metres above sea level. The waters in which it occurs are characterised by moderate conductivity and a near-neutral pH of around 7, with mixed substrates of sand and rock — conditions typical of the clear-water Xingu system.
The species' area of occupancy has been estimated at 154 mi² and its extent of occurrence at approximately 5,145 mi². This restricted geographic footprint, confined to a single river basin within a single Brazilian state, is the defining ecological fact of C. yudja's biology and underlies its conservation vulnerability. The IUCN recognises only one to two threat-based locations for the species.
Feeding
No dedicated feeding studies have been published for Creagrutus yudja, and direct dietary data from the wild remain sparse. Like most small Creagrutus, it is presumed to be an opportunistic invertivore, taking small aquatic invertebrates — insect larvae, microcrustaceans, and similar prey — in benthic and mid-water positions.
In the aquarium, small Creagrutus generally adapt to finely crushed flake food, micro-pellets, and small live or frozen foods such as newly hatched brine shrimp, Daphnia, or micro-worms. Because wild specimens have not entered the hobby trade in any meaningful numbers, keeper experience with C. yudja specifically is essentially absent from published hobbyist literature.
Mating
Reproductive behaviour has not been described for Creagrutus yudja. Across the genus Creagrutus and the broader family Characidae, small characids are typically open-water or plant-associated egg scatterers, releasing adhesive or semi-adhesive eggs among fine-leaved vegetation or over substrate with no subsequent parental care.
In the absence of any specific data, C. yudja is expected to follow this general pattern — brief pairing or group spawning, scattering of small eggs, and immediate departure by the adults. Any observations from aquarium-maintained individuals would represent valuable new information, as none appear to exist in the published or hobbyist literature to date.
Breeding
Creagrutus yudja has not been bred in captivity in any documented case known from the literature or hobby sources. Based on the general biology of small Creagrutus and allied Characidae, eggs would be expected to be small, adhesive or semi-adhesive, deposited among fine-leaved plants or substrate, and to receive no parental attention after spawning. Incubation times and fry requirements are uncharacterised.
The species' Endangered status and its absence from the aquarium trade mean that captive breeding programmes are not presently a conservation tool for this fish. Any future captive maintenance should prioritise recording spawning behaviour and basic developmental data, which are entirely unknown.
In the aquarium
Creagrutus yudja is not established in the aquarium hobby. No commercial or hobbyist supply of captive-bred or wild-caught specimens is documented, and its Endangered status in a restricted Amazonian basin makes significant availability unlikely in the near term. Information on practical maintenance requirements is therefore largely inferential.
By analogy with other small, clear-water Amazonian Creagrutus species, it would be expected to do best in soft to moderately hard, near-neutral water (pH around 6.5–7.5) at temperatures in the range of 75–82 °F, in a well-filtered aquarium with gentle flow and cover in the form of fine-leaved plants or leaf litter. A schooling or shoaling disposition is probable. Any keeper fortunate enough to obtain specimens should document water parameters, behaviour, and — if spawning occurs — reproductive observations, and share findings through peer-reviewed or established hobby channels.
Conservation
Creagrutus yudja is assessed as Endangered (EN) on the IUCN Red List under criterion B2ab(iii), version 3.1, based on an assessment dated 23 November 2020 and published in 2021. The listing reflects an area of occupancy of just 154 mi² combined with ongoing, severe decline in habitat quality, with the population currently confined to one to two threat-based locations.
The principal threats are the Belo Monte hydroelectric dam — the largest infrastructure project on the Xingu River, which has fundamentally altered flow regimes, sediment dynamics, and thermal conditions in the basin — together with rapid deforestation driven by agricultural expansion and water abstraction. No protected areas or conservation sites currently cover the known range of C. yudja. Despite these pressures the IUCN notes that the population trend is currently stable, though habitat quality continues to decline.
The species' alliance with the Yudjá people is more than symbolic: indigenous territorial rights over Xingu headwaters represent, in practice, the most meaningful existing buffer against the forest clearance and river modification that threaten C. yudja and the wider fish assemblage of the upper Xingu.