Taxonomy & naming
Creagrutus melanzonus was described by Carl H. Eigenmann in 1909, placing it in the genus Creagrutus, where it remains. Creagrutus is a large genus of Neotropical characids in the family Characidae, distributed across lowland and foothill stream systems throughout South America and into Central America. Many species in the genus are morphologically similar and separable only by careful examination of scale counts, fin-ray counts, and pigmentation patterns; Creagrutus is accordingly one of the taxonomically challenging 'incertae sedis' groups within the Characidae.
The valid name as listed in Eschmeyer's Catalog of Fishes is Creagrutus melanzonus Eigenmann, 1909. No synonyms or subsequent taxonomic changes are recorded for this species in the standard literature.
Morphology
Creagrutus melanzonus is a small, slender characid reaching a maximum recorded standard length of 1.5 in. Like other members of the genus it has the typical characid body plan: a compressed, fusiform profile, a small adipose fin between the dorsal and caudal fins, and a moderately forked tail. The body is silvery with a dark lateral stripe running from behind the head to the caudal peduncle, a pigmentation pattern reflected in the species name.
Beyond the basic body form and the lateral band, detailed morphological data — fin-ray counts, scale formula, and head proportions — are not available from the sources in the research cache. Given the small adult size of 1.5 in SL, the species is among the smaller members of the genus.
Habitat
Creagrutus melanzonus inhabits freshwater streams and creeks across a broad coastal lowland range spanning from the Cuyuní River drainage of eastern Venezuela east through Guyana, Suriname, and into the Sinnamary River basin of French Guiana. The species is described as benthopelagic and has been collected over substrates of sand, gravel, and rocks in upstream river areas and upland creeks.
The species is noted as rare in collections, suggesting it either occurs at low densities or frequents microhabitats that are undersampled by standard collection methods. Water chemistry data specific to collection sites for this species are not available; the Guiana Shield streams it inhabits are typically soft, acidic to near-neutral, and clear to slightly tannin-stained.
Feeding
No specific feeding data for Creagrutus melanzonus are recorded in the literature available for this account. Creagrutus species are generally considered opportunistic invertivores in the wild, taking small aquatic invertebrates, insect larvae, and occasionally plant matter from the substrate and water column — a feeding style consistent with their benthopelagic lifestyle in flowing streams.
In the aquarium, congeners and ecologically similar small characids accept fine granular foods, small live and frozen invertebrates such as Daphnia and Artemia nauplii, and quality micro-pellets. Data sparse for this species specifically.
Mating
No spawning observations for Creagrutus melanzonus are documented in the available literature. Small Neotropical stream characids of the Creagrutus type are generally presumed to be egg-scatterers, releasing non-adhesive or slightly adhesive eggs among fine-leaved plants or over the substrate, with no parental care provided by either sex.
The mating behaviour of Creagrutus as a genus is poorly studied, and specific courtship or spawning details for C. melanzonus remain undescribed. Data sparse.
Breeding
Captive breeding of Creagrutus melanzonus has not been documented in the hobby or scientific literature available for this account. If the general biology of small stream characids applies, eggs would likely be scattered over fine substrate or vegetation, hatch within a few days at tropical temperatures, and require very small first foods such as infusoria or rotifers before graduating to newly hatched Artemia nauplii. No parental care would be expected.
Given the species' rarity in collections and virtual absence from the aquarium trade, captive breeding accounts remain undocumented. Data sparse.
In the aquarium
Creagrutus melanzonus is not an established aquarium fish and is essentially absent from the ornamental trade. It is known primarily from museum specimens and scientific collections. Should the species become available, its small size (1.5 in SL) and presumed stream habitat suggest it would suit a small, well-oxygenated aquarium with moderate flow, a sand or fine-gravel substrate, and some cover from driftwood or leaf litter replicating the Guiana Shield creek environment.
Water parameters for the genus Creagrutus beni — a congener for which aquarium data exist — indicate pH 6.0–7.2, temperature 72–79 °F (71.6–78.8°F), and water hardness around 10–20 dH; these may serve as a rough guide for C. melanzonus, though conditions specific to this species' collection localities have not been reported. The species should be considered data-sparse for aquarium husbandry purposes.
Conservation
Creagrutus melanzonus is assessed as Least Concern (LC) on the IUCN Red List, based on the 2020 assessment. The species' range spans multiple river drainages across Venezuela, Guyana, Suriname, and French Guiana — a sufficiently broad extent of occurrence to support a Least Concern rating in the absence of evidence of major population decline or specific threats.
The Guiana Shield region where this species occurs retains large areas of relatively intact forest and associated freshwater habitat, and the lowland creek systems it inhabits are not subject to the intense development pressure seen elsewhere in South America. It is not commercially exploited for the aquarium trade at any significant scale. No species-specific conservation measures are in place or considered necessary at present.