Taxonomy & naming
Creagrutus beni was described by Carl H. Eigenmann in 1911, based on material from the Beni drainage of Bolivia — the river system that gives the species its epithet. It belongs to the large neotropical characid genus Creagrutus, which spans lowland and foothill streams across much of South America and embraces well over a hundred species. The genus sits within the tribe Stevardiinae or allied groupings depending on the classification followed, and the family Characidae in the broad sense remains the accepted placement. Eschmeyer's Catalog of Fishes recognises the valid name as Creagrutus beni Eigenmann, 1911.
The genus name Creagrutus derives from Greek roots alluding to the shape of the fish's body. The specific epithet beni is a toponym, referring directly to the Río Beni of Bolivia, the type locality region. With over a hundred congeners, many only recently described, Creagrutus is one of the larger and less well-known genera in Characidae — its species are small, superficially similar in pattern, and largely passed over by hobbyists in favour of more flamboyant tetras.
Morphology
Creagrutus beni is a slender, moderately compressed characin, reaching a reported maximum of 3 in standard length. The body is elongate relative to many tetras and built for active swimming near the bottom and mid-water. Coloration follows the genus's typical understated scheme: a pale silvery to yellowish body overlaid by a dark or golden lateral stripe running from behind the head to the base of the caudal fin — the 'goldstripe' of its common name — with a darker dorsal field and a pale belly.
The fins are clear to lightly pigmented, and there is no pronounced sexual colour difference, though females are typically deeper-bodied when in spawning condition. As with most small characins, Creagrutus beni bears the family's characteristic adipose fin between the dorsal and caudal. The dentition includes the inner and outer tooth rows present throughout the family. Data on detailed meristics for C. beni specifically are sparse in the hobbyist literature, and serious taxonomic comparisons rely on the original description and subsequent revisions of the genus.
Habitat
Creagrutus beni is native to the upper Madeira River basin, principally recorded from the northeastern Bolivian portion of that drainage — the Beni system and associated tributaries. There are also records from Argentina, suggesting a broader range within the upper Madeira catchment than Bolivia alone. The species occupies freshwater streams and river margins at low to moderate elevation, classified as benthopelagic, meaning it spends time near the substrate as well as in open water.
Typical habitat consists of clear to lightly stained tropical freshwater, probably with overhanging vegetation and submerged leaf litter. FishBase records a temperature of approximately 72 °F and pH near 6 for the species, indicating soft, slightly acidic, cool-to-warm conditions characteristic of many Andean foothill and piedmont drainages. The soft-water, mildly acid conditions of the upper Madeira system contrast with the harder lowland waters of the Amazon main stem.
Feeding
Creagrutus beni is an omnivore in the broad sense, feeding opportunistically on small invertebrates, organic matter, and whatever food items present themselves near the substrate and mid-water. The natural diet of Creagrutus species generally includes aquatic insects and their larvae, small crustaceans, plant material, and detritus, with precise diet composition varying by stream and season.
In the aquarium it accepts a wide range of standard foods without difficulty: quality flake, small pellets, and frozen or live foods such as brine shrimp and Daphnia. As a bottom-associated species it benefits from sinking foods that reach the lower water column, though it will also take food at the surface. Variety in the diet supports overall condition and helps maintain the lateral stripe's coloration.
Mating
Creagrutus beni has not been the subject of detailed reproductive studies in the wild, and specific breeding observations in captivity are not well documented in the available literature. As a member of Characidae, it is presumed to be an egg-scattering open spawner typical of the family, with no parental care. Males likely display to receptive females with fin erection and lateral posturing, as seen in related small characins.
Congener research on Creagrutus guanes and related species in tropical mountain rivers suggests that reproductive seasonality in the genus may be influenced by diet quality and seasonal environmental cues such as temperature shifts or water level changes associated with wet and dry seasons. If C. beni follows this pattern, spawning readiness in nature may peak in warmer periods or at the onset of seasonal flooding.
Breeding
No detailed captive breeding accounts are recorded in the accessible literature for Creagrutus beni. Extrapolating from the biology of comparable small characins, breeding would likely follow the standard characid model: egg-scattering over fine-leaved plants or substrate, with adhesive or semi-adhesive eggs deposited in small numbers, no parental care, and a tendency for adults to consume eggs if not separated.
For any serious breeding attempt, conditioning on live or frozen foods, a separate, well-planted spawning tank with soft, slightly acid water around 72–75 °F, and prompt removal of adults after spawning would be the recommended approach. Fry would require very fine foods initially — infusoria or commercial liquid fry food — before graduating to newly hatched brine shrimp. Given the sparse captive breeding record, successful reproduction with this species would be a noteworthy hobbyist achievement.
In the aquarium
Creagrutus beni is described as a peaceful shoaling species that does best kept in groups of six or more individuals. It is suited to a modestly sized aquarium — a minimum of around 20 US gal is suggested — with soft, slightly acidic water in the range of 72–79 °F and pH 6.0–7.2, hardness up to around 10–20°dH. These parameters mirror its native Bolivian piedmont streams and should be maintained with gentle filtration to avoid strong currents.
A planted tank with subdued lighting, some open swimming space, and a dark substrate shows the fish to best advantage and reduces stress in a species that is naturally associated with shaded, vegetated streams. Its peaceful disposition makes it compatible with other small, non-aggressive species from similar water conditions. It will accept pellets, flake, and live or frozen foods such as brine shrimp and Daphnia without difficulty. Creagrutus beni is an uncommon species in the trade and one of interest mainly to hobbyists who enjoy less mainstream characins; its undemanding nature and calm temperament make it a good community fish once the soft-water requirements are met.
Conservation
Creagrutus beni does not appear to have a dedicated IUCN Red List assessment at this time. FishBase records the species as Least Concern, reflecting that it occupies a reasonably broad range within the upper Madeira basin of Bolivia and into Argentina, and faces no known acute threats that would elevate its risk category. The upper Madeira system supports diverse fish communities, and while deforestation and habitat degradation affect many Bolivian drainages, no population-level concern specific to this species has been formally assessed.
As with many small, obscure characins, the primary data gap is simply scientific attention: Creagrutus beni is rarely collected for the aquarium trade, seldom the subject of population surveys, and known mainly from museum material and sporadic records. A formal IUCN assessment would require renewed survey effort across its range to evaluate population trends. In the meantime, the species' tolerance of a moderate range of water conditions and its presence across more than one drainage system suggest a currently stable, if data-limited, status.