Taxonomy & naming
Creagrutus phasma was described by the American ichthyologist George S. Myers in 1927. The genus Creagrutus is placed within the family Characidae — the largest family of freshwater fishes — and encompasses well over a hundred recognised species distributed from Central America through tropical South America. Eschmeyer's Catalog of Fishes (Catalog of Fishes) governs the valid name; the authority is not parenthesised because the species has remained in its original genus since description.
The genus name Creagrutus traces to the Greek roots for 'to tear or rip up flesh', reflecting the predatory dentition characteristic of the group. Within Characidae, Creagrutus species are small, elongate or moderately deep-bodied characids that tend toward invertivory in fast-moving or seasonally variable tropical streams. The genus has undergone considerable revision in recent decades as molecular and morphological studies have clarified species limits across its broad range.
Morphology
Creagrutus phasma is a small characid with a maximum recorded standard length of 2.5 in. The body depth is reported as greater than 3.75 times in standard length, indicating a moderately slender profile rather than a deep-bodied one. Like other Creagrutus, it carries the basic characid bauplan: a single dorsal fin, a small adipose fin behind it, a forked caudal fin, and the toothed jaws typical of Characiformes.
Detailed colour pattern descriptions in life are not extensively documented in accessible literature for this species. Published morphometric data indicate it is a compact fish of modest proportions consistent with a benthopelagic lifestyle in the lower and mid-water column of its riverine habitats.
Habitat
Creagrutus phasma ranges across a geographically broad region of northern South America, from the upper Negro River drainage in the Brazilian state of Amazonas northward into the Orinoco River basin, with confirmed records from Colombia and Venezuela in addition to Brazil. This places it across a substantial span of Amazonian and Orinoco lowland river systems.
FishBase classifies it as benthopelagic and tropical, consistent with other Creagrutus that inhabit the mid and lower water column of freshwater rivers and streams. Research on floodplain habitat affinity in Neotropical systems has recorded the species predominantly during the low-water season in littoral-zone habitats — roughly 67 percent of occurrences in one study came from the low-water period — suggesting a seasonal shift in microhabitat use tied to the flood pulse. Tropical lowland freshwater temperatures across its range typically span the low to mid 20s Celsius up into the upper 20s.
Feeding
Creagrutus phasma is documented as a benthic invertivore, taking invertebrate prey from the substrate and lower water column. This feeding guild is consistent with its benthopelagic habits and with the dietary ecology reported for Creagrutus and allied characids more broadly in Neotropical river systems.
In the littoral zones of floodplain rivers where it has been studied, benthic invertivores like C. phasma exploit aquatic insect larvae, microcrustaceans, and other small invertebrates concentrated in the near-bottom habitat, with prey availability and habitat use shifting seasonally in response to the annual flood pulse.
Mating
Specific mating behaviour of Creagrutus phasma has not been documented in the published or hobbyist literature accessible to this account. As a member of Characiformes, it almost certainly employs the ancestral egg-scattering open-spawning strategy widespread across the order, in which males pursue and court females prior to the simultaneous release of eggs and sperm into the water column or over suitable substrate.
In Neotropical floodplain rivers, characid reproductive activity is commonly cued to the seasonal flood pulse, with spawning often timed to rising water levels and increasing water temperature at the onset of the rainy season. Fine-leaved aquatic plants and submerged vegetation in the littoral zone, where C. phasma shows a preference during low-water periods, are likely spawning sites during the appropriate season, as is typical of small egg-scattering characids.
Breeding
No captive breeding accounts for Creagrutus phasma are recorded in accessible hobbyist or scientific literature. The species is not established in the aquarium trade and is rarely if ever kept by aquarists, so there is no accumulated knowledge base for breeding in captivity.
By analogy with other egg-scattering Characidae, breeding in captivity would be expected to involve soft, warm tropical water — temperatures in the upper 20s Celsius, low to moderate hardness — fine-leaved plants or spawning mops as egg substrate, and removal of adults from the spawning vessel after egg deposition to prevent predation. Eggs and fry care requirements are inferred from the wider clade rather than from any direct observation of this species.
In the aquarium
Creagrutus phasma is essentially unknown in the aquarium hobby. It does not appear in the mainstream ornamental-fish trade, and no established husbandry literature exists for the species. Its natural range across the Negro and Orinoco basins suggests an affinity for warm, soft to moderately mineralised tropical freshwater — temperatures roughly in the 75–82 °F range and neutral to mildly acidic pH — though precise water-chemistry requirements have not been characterised for this species.
At 2.5 in standard length it is a small fish. Its benthopelagic habit and invertivorous diet suggest it would require live or high-quality frozen foods in captivity and would likely do best in a well-filtered, planted aquarium with peaceful tankmates of similar size. Any aquarist who encounters C. phasma in the trade would be working from inference rather than established practice.
Conservation
Creagrutus phasma was assessed as Least Concern (LC) on the IUCN Red List in 2021. The assessment noted the species' broad distribution across the upper Negro River system of Brazil and the Orinoco basin of Colombia and Venezuela, and identified no obvious threats of sufficient severity to elevate the conservation category above Least Concern at the time of assessment.
The species benefits from occurring across a geographically extensive range that spans multiple major river drainages in northern South America — a contrast with range-restricted endemics that face higher inherent extinction risk. Continued monitoring of land-use change, deforestation, and water-quality degradation across Amazonian and Orinoco catchments is relevant to this and the many other small characids that share its broad range.