Taxonomy & naming
Creagrutus nigrotaeniatus was described by Fernando Cesar Paes Dagosta and Manoela Maria Ferreira Pastana in 2014, in a paper published in Zootaxa (volume 3765, number 6, pages 571–582). The type locality is the rio Juruena in Mato Grosso state, Brazil, part of the Tapajós basin of the Amazon drainage. Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS) is the governing authority for the valid name, which carries no parenthetical wrapper because the species was placed directly in Creagrutus at description.
Creagrutus is a large, widely distributed genus of small characids (family Characidae) found across the Amazon, Orinoco, and Pacific-slope river systems of South America. The genus is diagnosed by a suite of characters including tooth number and arrangement on the dentary and premaxilla, scale counts, and post-anal scale number. C. nigrotaeniatus is set apart within this complex by 8–10 dentary teeth, 4–5 post-anal scales, and 36–37 vertebrae — meristic data recorded in the original description. No common name has been established in major hobbyist literature, and the species is virtually unknown in the ornamental fish trade.
Morphology
Creagrutus nigrotaeniatus is a small, slender-bodied characid reaching approximately 1.5 in in standard length (SL) based on specimens recorded in FishBase. The body plan is typical for the genus: moderately elongate, laterally compressed, with a pointed snout and a small terminal mouth bearing 8–10 teeth on the dentary.
The most distinctive external feature, and the source of the specific name, is the bold dark mid-lateral stripe that extends from the orbit posteriorly to the base of the caudal fin. The dorsal fin carries 10 soft rays; the anal fin 11–13 soft rays. Vertebral count is 36–37. These meristic values, in combination with the post-anal scale count of 4–5, distinguish this species from close relatives. As with many small-bodied Creagrutus, sexual dimorphism has not been described in detail in the available literature, and data on colour differences between males and females are sparse.
Habitat
Creagrutus nigrotaeniatus is known from the upper rio Juruena, a major tributary of the rio Tapajós in Mato Grosso state, Brazil. The Tapajós basin drains a large portion of the Brazilian Shield and the southern Amazon, and its upper reaches include clear-to-blackwater streams and rivers running over sandy and rocky substrates in cerrado-to-forest transition zones.
FishBase classifies the species as benthopelagic and tropical freshwater. Specific habitat details — vegetation type, current speed, substrate preference, or micro-habitat use within the river — are not documented in the available literature, and the species' habitat requirements must be inferred broadly from genus-level ecology. Creagrutus as a group tends to occupy small-to-medium rivers and streams, often in areas of gentle to moderate current, where members forage near the bottom or in the water column among leaf litter and submerged structure.
Feeding
FishBase assigns Creagrutus nigrotaeniatus a trophic level of 2.6, placing it in the omnivore-to-insectivore range characteristic of small characids. Species at this trophic level typically take a mix of small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial insects — together with some plant or detrital material depending on seasonal food availability.
No detailed gut-content analyses for this species appear in the available literature. Its feeding ecology is therefore best inferred from the genus, whose members are generally opportunistic feeders in soft-bottomed and mixed-substrate stream environments. In captivity, small characids of similar size and ecology adapt readily to prepared foods supplemented with frozen or live invertebrates.
Mating
No species-specific mating observations have been recorded for Creagrutus nigrotaeniatus in the scientific or hobbyist literature. As a member of the family Characidae, the species is presumed to follow the open egg-scattering reproductive strategy typical of the group: non-adhesive or weakly adhesive eggs scattered among fine-leaved vegetation or over substrate, with no parental care by either sex.
This spawning mode is consistent with the general biology of small characids of similar ecology and body size. The absence of documented sexual dimorphism makes identification of reproductive pairs difficult without close observation, and the species' obscurity in the hobby means captive breeding notes do not appear in available sources.
Breeding
Breeding has not been documented for Creagrutus nigrotaeniatus in either the scientific or hobbyist literature. Based on the reproductive biology of related small characids, spawning would be expected to involve the scattering of small, adhesive or semi-adhesive eggs among fine-leaved aquatic plants or over open substrate, with no parental investment after egg deposition. Eggs and larvae would be left to develop unguarded.
Incubation period and larval development data are not available for this species. For aquarists wishing to attempt breeding, the approach used for other small stream-dwelling characids would be a logical starting point: a well-conditioned group in soft, slightly acidic water, a temperature in the low-to-mid 20s Celsius, and fine-leaved plants or spawning mops as egg-deposition sites. Any eggs produced should be removed to a separate rearing vessel to protect them from the adults.
In the aquarium
Creagrutus nigrotaeniatus is essentially absent from the aquarium trade and there are no established husbandry records for the species. Its small adult size — under 2 in SL — and its membership in a genus of peaceful, schooling characids suggest it would be manageable in a modestly sized aquarium if wild-caught specimens became available through specialist importers.
By analogy with other small Creagrutus and similar Amazonian stream characids, a 23.5–31.5 in aquarium with gentle filtration, a dark substrate, dim lighting or floating plants, and soft to moderately soft, slightly acidic water around 72–79 °F would approximate its likely habitat preferences. A group of six or more individuals would be appropriate, given the schooling tendency of the genus. The species is not available commercially as of the date of this article, and any specimens in trade would almost certainly be wild-collected from the Tapajós basin.
Conservation
Creagrutus nigrotaeniatus is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment conducted on 7 November 2018. The DD listing reflects the limited ecological and population data available at the time — not a determination that the species is secure, but rather that insufficient information exists to assign a threat category under IUCN criteria.
The species is known from the upper rio Juruena in Mato Grosso, a state subject to significant and ongoing deforestation, agricultural expansion, and river modification associated with soybean production and hydroelectric development in the southern Amazon. These pressures affect water quality, flow regimes, and riparian habitat throughout the Tapajós basin. While no specific population assessments exist for this species, the broader threat context for endemic stream fishes of the Cerrado-Amazon transition is one of increasing concern. Further survey work in the Juruena drainage would be needed to establish the species' range limits and abundance before a more precise conservation status can be determined.