Taxonomy & naming
Creagrutus yanatili was formally described by Alison M. Harold and Salcedo in a paper published in Ichthyological Exploration of Freshwaters (volume 20, issue 4, pages 377–383). The type locality is the Río Urubamba drainage of the Ucayali basin in the Andes of southeastern Peru, with the holotype and paratypes collected from the Río Yanatili itself. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & van der Laan) is the authority for the valid name Creagrutus yanatili Harold & Salcedo, 2010.
Creagrutus is a large and taxonomically complex genus of small characids distributed across Central America and South America west of the Andes and in the trans-Andean Amazonian lowlands. Species in the genus have historically been difficult to separate on external characters alone, and several have been described only in recent decades as more thorough collections and morphological studies have been undertaken in Andean river drainages. C. yanatili is among the more morphologically distinctive members of its genus owing to its unusually dark pigmentation and the presence of prominent contact organs in males.
Morphology
Creagrutus yanatili reaches a maximum recorded total length of approximately 4 in. The species is characterised by a very dark — almost black — coloration on the operculum (gill covers), body flanks, and fins, which distinguishes it at a glance from the more typically silvery or lightly patterned members of the genus.
The most diagnostically notable feature is the development of hook-like and needle-like contact organs on the anterior branched rays of the anal fin and pelvic fins of males. Such bony hooks and contact organs on fin rays occur in various characid groups and are presumed to play a role in close-contact spawning behaviour, though their precise function in Creagrutus remains unstudied. No detailed meristic data beyond those in the original description are available in the secondary literature.
Habitat
The type locality of Creagrutus yanatili is described as a wide, shallow river with a substrate of sand, pebbles, and smooth stones — the kind of clear, fast-to-moderate Andean foothill stream characteristic of the upper Urubamba drainage in Cusco and adjacent departments of southeastern Peru. The Río Urubamba is a major Amazonian headwater, flowing through the Andean cloud-forest zone before descending into the lowland Amazon basin.
Benthopelagic in habit (per FishBase), the species likely occupies the mid-water and bottom zones of clear, well-oxygenated, moderately cool Andean streams. Detailed water-chemistry data for the collection locality are not available in the published record, but upper Urubamba tributaries at the elevations where C. yanatili occurs are typically cool, fast-flowing, and moderately hard, reflecting the calcium-rich geology of the Andean uplifts. Distribution is restricted to the Ucayali basin, southeastern Peru.
Feeding
No published diet data exist for Creagrutus yanatili in the wild. Creagrutus species as a group are small, opportunistic omnivores typical of Andean characid faunas, and by analogy with congeners and the broader genus would be expected to take small invertebrates — aquatic insect larvae, microcrustaceans — as well as organic debris and possibly fine algal or plant material along the substrate and in the water column.
Given its benthopelagic habit and the sand-and-pebble substrate of the type locality, invertebrates drifting with or living among the substrate are the most probable natural prey items. Data are too sparse to characterise the diet with precision.
Mating
Creagrutus yanatili has not been studied behaviourally in the wild or bred in captivity in any published account. The prominent hook-like and needle-like contact organs on the anterior branched anal and pelvic rays of males are presumed — as in other characids where such structures occur — to facilitate close-contact mating, possibly allowing a male to grasp or stabilise a female during spawning in flowing water.
By analogy with the broader Creagrutus genus and the Characidae in general, the species is expected to be an egg-scattering open spawner without pair bonding or parental care. The adhesive or semi-adhesive eggs would be scattered among fine substrates or vegetation and left to develop unattended. These inferences are tentative; reproductive behaviour has not been documented.
Breeding
No captive breeding records for Creagrutus yanatili have been published, and the species is not known in the aquarium trade. As a small Andean characid, its breeding biology is presumed to follow the general characid pattern: egg-scattering over substrate or fine-leaved vegetation, with adhesive or slightly adhesive eggs and no parental care.
The cool, well-oxygenated Andean stream conditions of the type locality suggest that captive reproduction, if attempted, would likely require cooler water temperatures than typical tropical aquarium setups. Data are too sparse to provide meaningful guidance on clutch size, incubation period, or fry requirements.
In the aquarium
Creagrutus yanatili is not established in the aquarium hobby and has not appeared in the trade in any documented form. No husbandry information is available in the hobby literature.
Its small size (to 4 in TL), Andean origin, and benthopelagic habits suggest it would require a cool, well-oxygenated, spacious aquarium with a sandy or fine-gravel substrate and moderate to strong water flow — conditions approximating a clear Andean foothill stream. In the absence of direct husbandry experience, keeping this species would be experimental territory.
Conservation
Creagrutus yanatili is assessed as Data Deficient (DD) on the IUCN Red List. The designation reflects the limited information available on its population size, range, and the threats it faces — not a determination that it is not at risk. Like many narrowly distributed Andean stream fishes known from only a handful of collection localities, it may be genuinely rare or may simply be undersampled due to the difficulty of accessing steep Andean foothill drainages.
The Río Urubamba drainage in southeastern Peru faces pressure from agricultural expansion, deforestation in the Andean cloud-forest zone, gold mining in some tributaries, and hydroelectric development. Whether any of these pressures directly affect the Río Yanatili system where C. yanatili occurs is unknown. Further fieldwork to establish its actual range, population status, and ecological requirements would be needed before a more informative threat assessment could be made.