Taxonomy & naming
Creagrutus nigrostigmatus was described by Dahl in 1960 from material collected in the lowland drainage of northern Colombia. The valid name is listed in Eschmeyer's Catalog of Fishes under the authority Dahl, 1960. The genus Creagrutus belongs to the family Characidae within the order Characiformes and encompasses a large number of small, benthopelagic characids distributed across northern South America and Central America.
A systematic revision of the trans-Andean species of Creagrutus by Harold and Vari (1994), published as Smithsonian Contributions to Zoology, provided detailed redescriptions of the trans-Andean members of the genus and placed species relationships on a firmer footing. Creagrutus nigrostigmatus is one of the Colombian lowland representatives of this diverse, often morphologically similar group. The specific epithet nigrostigmatus derives from Latin niger (black) and stigmatus (marked or spotted), referring to a dark pigment mark that helps characterise the species.
The Checklist of Freshwater Fishes of Colombia (Álvarez-León et al., 2013) records common names in Colombian Spanish as sardina and chispa-tota, and notes that the species is native (Na) and assigned to both the Magdalena (Mg) and Cauca (Ca) drainage codes, with a freshwater-estuarine (DE) habitat designation.
Morphology
Creagrutus nigrostigmatus is an exceptionally small characid, reaching a maximum recorded standard length of 1 in. At this size it is among the smallest members of the genus. The body form is typical of Creagrutus — moderately elongate and laterally compressed, with a relatively pointed snout and the general facies of a miniature, unspecialised characin.
FishBase records the species as benthopelagic, consistent with a life spent near the substrate in slow or still water. Specific pigmentation details, meristic counts, and fin configurations are documented in the Harold and Vari (1994) revision; reliable description of live colouration in the field or in captivity is not available in the sources consulted for this article.
Habitat
The species is known from Caño Pechilín and Caño Zaragocilla, two small watercourses within the lower Magdalena basin of northern Colombia. The IUCN assessment describes the habitat as temporary coastal streams with sandy-clay bottoms and turbid waters. FishBase records the species as occurring in quiet parts of stream with abundant detritus — consistent with a slow-flow, detritus-accumulating microhabitat rather than open channel or riffle conditions.
The extent of occurrence has been estimated by the IUCN at approximately 261 mi², and the species is known from only one location in the assessment's sense, meaning a single coherent area subject to a single threatening process. The surrounding landscape is heavily used for cattle ranching, which degrades riparian vegetation and stream structure. This combination of a naturally narrow range and ongoing habitat pressure defines the conservation situation of the species.
Feeding
FishBase records the diet of Creagrutus nigrostigmatus as detritus, positioning it as a detritivore that sifts organic material from the substrate or water column in the quiet, detritus-rich stream reaches it inhabits. This feeding mode is ecologically consistent with its benthopelagic habit and the turbid, sediment-laden character of its habitat.
Beyond this broad dietary assignment, detailed information on feeding behaviour, gut contents, or prey selectivity is not available in the sources consulted. Its minute size limits prey to very small particles, and it almost certainly supplements detritus feeding with small invertebrates, biofilm, or algae as opportunity allows — a typical generalist strategy in small characids of this guild.
Mating
No specific observations of mating behaviour have been documented in the literature reviewed for this article. As a small, unspecialised characid in the family Characidae, Creagrutus nigrostigmatus would be expected to follow the egg-scattering open-spawning strategy typical of the group: males and females broadcast adhesive eggs among fine-leaved vegetation or substrates, with no pair bond formed and no parental care provided.
The rarity of the species and the remoteness and degraded state of its habitat mean that field observations of reproductive behaviour are essentially absent from the record. If seasonal flooding of the temporary coastal streams it inhabits drives reproductive timing, spawning may be linked to water-level fluctuations, as in many lowland Neotropical characids — but this remains inference rather than documented fact.
Breeding
Creagrutus nigrostigmatus has not been bred in captivity in any documented account accessible through the sources consulted. Its minute adult size, specialised detritus-feeding ecology, and extreme rarity in the trade mean that captive husbandry and breeding data are essentially unavailable.
By analogy with related small characids, eggs would be expected to be adhesive, scattered among fine-leaved plants or deposited on the substrate, and to receive no parental care. Adults would be expected to consume their own eggs if given the opportunity. These are inferences from the genus- and family-level patterns rather than species-specific observations, and are noted here only to provide orientation for any future captive study.
In the aquarium
Creagrutus nigrostigmatus is not established in the aquarium hobby. Its tiny maximum size of 1 in SL, detritivore diet, and endemic status in degraded Colombian lowland streams make it an unlikely candidate for routine availability. The species has no recorded trade history and appears in no mainstream hobbyist literature.
For any specialist keeping very small, undemanding Neotropical characids, the ecological requirements suggested by the wild record — quiet or still water, turbid conditions, abundant detritus, tropical temperatures — would translate to a densely planted species tank with a fine or sandy substrate, minimal flow, and careful attention to water quality. Given its Endangered status and the absence of captive-bred stock, the acquisition of wild specimens would raise serious ethical concerns; it is better considered a conservation subject than a hobby fish.
Conservation
Creagrutus nigrostigmatus is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), with the assessment dated 08 October 2014 and published in the 2016-1 update. The criterion reflects a small estimated extent of occurrence (approximately 261 mi²), a single known location, and continuing decline in habitat quality driven primarily by cattle ranching in the catchment.
The species' entire known range is confined to two small watercourses — Caño Pechilín and Caño Zaragocilla — in the lower Magdalena basin of northern Colombia. Habitat degradation from livestock grazing causes sedimentation, vegetation loss, and altered hydrological regimes that directly compromise the quiet, detritus-rich stream conditions the species depends on. With no buffer population elsewhere and no known captive population, the species' survival is entirely contingent on conditions in a tiny, threatened lowland area. Effective conservation would require protection or restoration of riparian vegetation along its two known stream localities and surveys to determine whether additional populations exist.