Taxonomy & naming
Creagrutus holmi was described by Richard P. Vari and Andréa S. Harold in 2001, in a comprehensive revision of the genus Creagrutus. The type locality is the Marañón River basin above the Pongo de Manseriche, the dramatic canyon where the Marañón River cuts through the Andes before entering the Amazonian lowlands of northeastern Peru. Eschmeyer's Catalog of Fishes recognises the valid name as Creagrutus holmi Vari & Harold, 2001.
Creagrutus is one of the largest and most complex genera within the family Characidae, with dozens of species distributed across northern and western South America. Members are small, silvery characids that superficially resemble one another and are distinguished primarily by counts of lateral-line scales, fin-ray numbers, and subtle body proportions — the kind of meristic detail that makes the group challenging to identify without a voucher specimen and reference keys. Erling Holm (b. 1950), Curator of Ichthyology at the Royal Ontario Museum in Toronto, collected material used in the type series; the specific epithet holmi is a Latin genitive patronym honouring him.
Morphology
Creagrutus holmi is a small, slender characid reaching a maximum recorded standard length of 3.5 in, though most individuals in collections are smaller. The body form is typical of the genus: moderately compressed laterally, with a somewhat pointed snout, a small terminal mouth, and the characteristic double-lobed adipose fin of the Characidae.
Colouration is subdued — silvery on the flanks with a darker dorsal surface, often showing a faint lateral stripe and a small caudal spot, consistent with the general pattern seen across closely related species of the upper-Amazon drainage. Specific meristic characters (lateral-line scale counts, fin-ray formulae) distinguish it from congeners but are not easily assessed in live or aquarium specimens. Sexual dimorphism within the genus is typically slight, with females tending to be deeper-bodied when gravid.
Habitat
The species is recorded from the Marañón River basin above the Pongo de Manseriche in northeastern Peru — an area that falls within the upper Amazon drainage system and encompasses foothill and Andean submontane streams at moderate elevations. FishBase characterises it as a benthopelagic freshwater species, consistent with the foraging habits typical of small Creagrutus, which tend to occupy the lower and mid water column of clear to lightly turbid streams.
The Marañón above Pongo de Manseriche drains a geologically and ecologically distinct zone isolated from the main lowland Amazonian basin by the gorge itself. Waters in this region are typically fast-flowing, well-oxygenated, and moderately cool by tropical standards, with a rocky or sandy substrate and riparian forest cover. Precise water chemistry records for this locality are sparse in the available literature.
Feeding
Creagrutus species are opportunistic micro-predators and omnivores. In nature they are reported to consume small invertebrates — insect larvae, microcrustaceans, and terrestrial insects that fall to the water surface — as well as small amounts of plant material and detritus. The genus name itself alludes to strong anterior teeth adapted for seizing prey.
Detailed dietary data for Creagrutus holmi specifically are not available in the accessible literature; the above reflects the well-documented feeding ecology of the genus across its range. In captivity, comparable Creagrutus species accept small live and frozen invertebrate foods readily, and can be maintained on a varied diet of micro-pellets, frozen Daphnia, and brine shrimp nauplii.
Mating
No published observations of spawning behaviour specific to Creagrutus holmi are available. The genus belongs to the broader characid clade characterised by open egg-scattering spawning with no parental care, and this is the pattern assumed for C. holmi in the absence of contrary evidence.
In related small characids of Andean foothill streams, courtship is brief and involves the male pursuing the female through vegetation or over the substrate. Spawning likely coincides with seasonal rainfall that raises water levels and triggers reproductive activity, a pattern common across small Neotropical characids from riverine environments. Adhesive or semi-adhesive eggs are deposited among fine-leaved aquatic plants or over substrate, after which the adults disperse.
Breeding
Creagrutus holmi has not been reported as established in the ornamental trade, and no captive breeding accounts are on record in the accessible hobby or scientific literature. What can be stated with reasonable confidence, based on the biology of the genus and family, is that it is almost certainly an egg-scatterer with no parental investment: eggs are released among fine-leaved vegetation or over substrate, hatch after a few days, and the adults take no further role.
Should captive specimens become available, a set-up mimicking Andean foothill stream conditions — cool, well-oxygenated, moderately soft to moderately hard water — with spawning mops or fine-leaved plants, and the removal of adults post-spawning, would be the logical starting approach. Fry of small characids typically require infusoria or rotifers as first foods before graduating to nauplii.
In the aquarium
Creagrutus holmi is not a species currently available in the mainstream ornamental trade. Specimens reach hobbyists only occasionally through scientific collectors or specialist importers dealing in rare Neotropical species, and virtually no husbandry literature exists for this fish specifically.
Based on the ecology of the genus and its Andean foothill origins, C. holmi would be expected to do best in a moderately cool, well-oxygenated aquarium with gentle to moderate current, a dark substrate, and some plant cover. As a small characid it would be suitable for a species tank or a community of similarly sized, non-aggressive fishes. Given the data-sparse nature of this species in the hobby, keepers acquiring specimens should document their observations and consider sharing records with the broader community.
Conservation
Creagrutus holmi is assessed as Least Concern (LC) on the IUCN Red List, reflecting that no major range-wide threats have been identified and that it is not considered to approach the thresholds for a more elevated category. The Marañón basin above Pongo de Manseriche supports a diverse ichthyofauna, and the broader upper-Amazon foothill zone, while subject to ongoing pressures from agriculture, mining, and deforestation, retains extensive intact habitat.
The species is not traded at scale, so commercial collection is not a pressure. As with many small Andean characids, the primary long-term risks are habitat alteration from land-use change and, in the longer term, climate-driven shifts in Andean hydrology. Continued survey work in the upper Marañón drainage would help refine understanding of the species' range and population status.