Taxonomy & naming
Creagrutus machadoi was described by Richard P. Vari and A.S. Harold in 2001. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Creagrutus machadoi Vari & Harold, 2001, with the type locality given as the Rio Autana, a tributary of the Orinoco River system in Venezuela. No subsequent taxonomic revision has moved it out of Creagrutus or treated the species as a junior synonym; it remains a valid, monotypic taxon.
The genus Creagrutus belongs to the family Characidae and is one of the most species-rich genera in the broader characin radiation across lowland South America. Creagrutus species are predominantly small, fusiform stream fish — sometimes called 'wimple piranhas' informally in the older literature, though the resemblance is superficial. Some modern phylogenetic treatments and databases place Creagrutus within a reclassified family Stevardiidae, reflecting ongoing revisions to characid higher taxonomy; however, the family field here follows the Catalog of Fishes designation of Characidae as the accepted family for this species.
The specific epithet machadoi is a patronym, though documentation of whom it honours is not available from the sources consulted.
Morphology
Creagrutus machadoi is a small, slender characin reaching approximately 2 in standard length in the male or unsexed specimens recorded by FishBase. Like other Creagrutus, it is presumed to have a fusiform to slightly laterally compressed body, a small terminal mouth, and the small adipose fin characteristic of characids. Beyond the size datum and general body plan inferred from genus membership, detailed morphological data from the original description are not reproduced in the sources consulted here.
Creagrutus species as a group tend to be cryptically coloured — silvery to pale brown with a dark lateral stripe or midlateral spots — blending into the leaf litter and gravel of the stream beds they inhabit. The sexual dimorphism of C. machadoi has not been characterised in available sources.
Habitat
The type locality of Creagrutus machadoi is the Rio Autana, a blackwater or clearwater tributary draining into the upper Orinoco River basin in Venezuela. The Orinoco system spans Venezuela and Colombia, and FishBase lists the distribution as the Caura River basin within that broader basin — the Caura being a major southern tributary of the Orinoco in Bolívar State, Venezuela. Whether the species occurs in Colombia as well as Venezuela is recorded in some database entries but is not confirmed from voucher specimens in the sources reviewed.
Like most Creagrutus, C. machadoi likely occupies shallow, flowing stream habitats over sand, gravel, or leaf-litter substrate, often in shaded reaches beneath gallery forest. Specific water-chemistry data for its natural habitat are not documented in the sources available; conditions across the Orinoco tributaries vary considerably between the acid, tea-coloured blackwaters of rivers such as the Caura and clearer upland streams draining the Guiana Highlands.
Feeding
No dietary studies specific to Creagrutus machadoi are available in the sources consulted. Genus-level inference from other Creagrutus and from small benthic characids in comparable Orinoco tributaries suggests a diet of small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial invertebrates that fall to the stream surface.
In the aquarium, small characids of this body plan typically accept fine-grade dried foods such as crushed flake or micro-pellets alongside frozen or live foods including Artemia nauplii, Daphnia, and micro-worm. Specific feeding observations for C. machadoi in captivity are not recorded.
Mating
Reproductive behaviour has not been documented for Creagrutus machadoi in published literature available to this review. Extrapolating from the reproductive strategies of closely related Neotropical characins, the species is presumed to be an egg-scattering open spawner without parental care, depositing adhesive or semi-adhesive eggs among fine-leaved aquatic plants or substrate debris.
Seasonal spawning cues in Orinoco basin streams are typically tied to rainfall and river level. Rising waters trigger many characins to spawn over flooded marginal vegetation. No specific account of C. machadoi courtship or pairing behaviour exists in the sources consulted.
Breeding
Creagrutus machadoi has not been bred in captivity to the knowledge available in the sources consulted, and no aquarium breeding accounts are on record. The species is essentially unknown in the ornamental fish trade, and captive populations do not appear to exist outside of occasional scientific collections.
For hobbyists who might obtain specimens, typical small-characid breeding protocol — a dimly lit, soft to moderately hard water aquarium with fine-leaved plants or spawning mops, slight current, and a temperature in the low to mid 20s Celsius — would represent a reasonable starting point, as these conditions approximate upland Orinoco tributary environments. Eggs should be separated from adults to prevent predation, and newly hatched fry would require infusoria-grade first foods.
In the aquarium
Creagrutus machadoi is not an established aquarium fish. It does not appear in the ornamental trade, and hobbyist accounts of keeping the species are absent from the sources reviewed. Any specimens in captivity are likely to have originated from scientific collection rather than commercial import.
For the purposes of completeness: small Creagrutus are peaceful, active stream fish that would logically suit a species aquarium or a community of similarly sized, non-aggressive South American fish. A tank with gentle flow, subdued lighting, and leaf litter or fine-substrate bottom decor replicating Orinoco tributary conditions would be appropriate. Given the Data Deficient status and very limited collection record, wild-caught specimens should not be removed from the wild for ornamental purposes.
Conservation
Creagrutus machadoi is assessed as Data Deficient (DD) on the IUCN Red List. The Data Deficient designation does not imply the species is secure; it reflects that insufficient information exists to make a reliable assessment of extinction risk. With only a limited number of known collection localities in the Rio Autana and Caura tributaries of the Orinoco basin, population size and trend are unknown.
The broader Orinoco basin faces pressures including mining activity, deforestation in riparian zones, and hydroelectric development, all of which affect stream habitats of the kind C. machadoi occupies. Taxonomic obscurity means the species receives no targeted conservation attention. Improved survey coverage across its putative range and clarification of its geographic limits would be the most immediate contributions towards a meaningful assessment.