Taxonomy & naming
Creagrutus melasma was described in 1994 by Richard P. Vari, Andrea S. Harold, and Donald C. Taphorn. It belongs to the genus Creagrutus, a large and taxonomically complex assemblage of small characins distributed across tropical South America and Central America. Within the broader family Characidae, Creagrutus is sometimes placed in the subfamily Stevardiinae (or recognised in the family Stevardidae by some authors), though the exact higher-level arrangement has shifted across revisions; the top-level family field for this species follows Characidae as the encompassing group.
The Catalog of Fishes (Eschmeyer, CAS) treats Creagrutus melasma Vari, Harold & Taphorn, 1994 as the valid name. Because the species was described directly into Creagrutus and remains there, the authority is written without parentheses. The genus name Creagrutus derives from the Greek for "to tear" or "to rip up flesh," a reference to the small, sharp teeth characteristic of members of this group. The specific epithet melasma comes from the Greek for "dark spot" or "dark mark," alluding to a pigmentation feature used to distinguish this species from its congeners.
Morphology
Creagrutus melasma is a small, slender-bodied characin reaching a maximum recorded standard length of approximately 2 in. Like other members of the genus it is laterally compressed, with a relatively small head, a terminal to slightly inferior mouth bearing small, pointed teeth, and a body shape suited to life near the substrate in flowing water.
Diagnostic features within the genus Creagrutus typically involve subtle meristic and pigmentation characters — scale counts, fin-ray counts, and the pattern of dark markings along the flanks and caudal peduncle. The specific epithet melasma points to a distinguishing dark marking. As with many small, drab-colored characins of this clade, the species is not strikingly colored and is unlikely to be distinguished from congeners in the field without close examination.
Habitat
Creagrutus melasma is distributed across two distinct drainages in Venezuela: the Orinoco River basin and the Tuy and Neveri rivers, which drain to the Caribbean Sea rather than the Atlantic via the Orinoco. This trans-divide distribution across the Venezuelan cordillera is notable for a small stream fish and suggests either historical connectivity between drainages or active dispersal across watershed boundaries.
FishBase classifies the species as benthopelagic and freshwater, consistent with the typical ecology of Creagrutus — small, fast-flowing streams and rivers of the tropical lowlands and foothills, where fish forage near the bottom and in the water column among rocky or sandy substrates. Precise habitat data for this species specifically are sparse in the published literature.
Feeding
FishBase assigns Creagrutus melasma a trophic level of approximately 2.5, indicative of a primary consumer or low-level omnivore. The genus Creagrutus as a whole tends toward opportunistic feeding on small invertebrates, plant material, and organic detritus encountered near the substrate — a feeding strategy common among small characins of similar body form and habitat.
Specific dietary studies for this species are not available in the accessible literature. Based on trophic-level assignment and comparisons with congeners, the diet likely includes small aquatic invertebrates such as midge larvae and microcrustaceans, supplemented by algae and detrital matter.
Mating
No specific mating behaviour has been documented for Creagrutus melasma in the scientific literature. Members of the broader Creagrutus group are presumed to follow the egg-scattering open-spawning pattern typical of the majority of small South American characins, with adhesive or semi-adhesive eggs deposited among fine-leaved aquatic plants, submerged roots, or gravel, and no parental care by either parent.
Sexual dimorphism in Creagrutus species is generally subtle; females of most congeners become noticeably fuller in the belly when gravid, which may be the most reliable visual cue for distinguishing the sexes in this genus. Specific seasonal or environmental triggers for spawning in this species are unknown.
Breeding
Creagrutus melasma has not been bred in captivity under documented conditions reported in the accessible hobby or scientific literature, and detailed breeding data for the genus as a whole are limited. By analogy with other small characins of similar ecology, spawning is expected to be an egg-scattering event over fine-leaved vegetation or substrate, with adhesive eggs receiving no parental attention and both adults liable to consume eggs given the opportunity.
Incubation periods and fry development for this species are unknown. Given its small adult size, fry would presumably be tiny at hatching and require infusoria-sized first foods before graduating to newly hatched brine shrimp nauplii. Data are too sparse to estimate clutch size or developmental timing with confidence.
In the aquarium
Creagrutus melasma is essentially unknown in the ornamental fish trade and is not a species ordinarily available to aquarists. The genus Creagrutus is very rarely exported from South America, and most hobbyists will not encounter this species except as an occasional bycatch in wild-caught shipments of Venezuelan characins.
For aquarists who do obtain specimens, the small size (to 2 in SL) and presumed preference for clear, well-oxygenated stream water suggest a small to medium aquarium with gentle to moderate flow, a soft substrate, and some plant cover or leaf litter. Water parameters consistent with the Venezuelan piedmont — soft to moderately hard, neutral to slightly acidic, tropical temperatures — would be a reasonable starting point, though no specific captive-care records have been published.
Conservation
Creagrutus melasma was assessed as Least Concern (LC) on the IUCN Red List, with the assessment completed on 27 October 2020. The LC listing reflects the absence of evidence for population-level decline sufficient to trigger a threatened category, and the species' occurrence across two separate Venezuelan river systems provides some distributional buffer relative to strictly single-drainage endemics.
Venezuelan freshwater fish communities broadly face pressures from habitat degradation, agricultural runoff, and deforestation across the Llanos and piedmont regions, but no species-specific threat data are reported for C. melasma in the IUCN assessment. As a small, non-commercial species it is not subject to targeted collection pressure, and its status is expected to remain stable unless watershed-scale habitat changes affect the Orinoco basin or the Caribbean-versant rivers where it occurs.