Taxonomy & naming
Creagrutus magdalenae was described by the American ichthyologist Carl H. Eigenmann in 1913 from material collected in the Río Magdalena basin of Colombia. The valid name is confirmed by the Catalog of Fishes (California Academy of Sciences), where it is listed under species ID 33082 with Eigenmann, 1913 as the authority. The genus Creagrutus currently encompasses approximately 74 described species distributed across the trans-Andean river systems of northern and western South America as well as the Orinoco and Amazon drainages to the east.
Creagrutus belongs to the family Characidae in the broad sense and has historically been placed within various subfamilial arrangements as the systematics of the Stevardiidae clade have been revised. The trans-Andean species — those occurring west of the Andes in Pacific-slope and Caribbean-slope drainages — are treated as a morphologically coherent assemblage, and C. magdalenae falls within this trans-Andean group by virtue of its Magdalena basin distribution. A closely related species, C. guanes, also occurs in the Magdalena system and has been studied for its spawning behavior in highland tributaries.
Morphology
Creagrutus magdalenae is a small characid reaching a maximum recorded length of 2 in standard length (SL). Like other members of the genus it has a slender, fusiform body typical of rheophilic or benthopelagic small characids: a rounded snout, terminal to slightly subterminal mouth, and the characteristic adipose fin of the family. The body is generally silvery with the lateral-line region often slightly countershaded.
Within Creagrutus, species identification relies heavily on detailed meristic counts (scale rows, fin-ray counts, lateral-line scales) and morphometric proportions rather than on easily visible external features, which overlap substantially among congeners. Sexual dimorphism in the genus is generally subtle; females may be slightly deeper-bodied when gravid, as is typical for egg-carrying characids of similar size.
Habitat
Creagrutus magdalenae is restricted to the Río Magdalena basin in Colombia, one of the most significant river systems draining the inter-Andean valleys of the country. The Magdalena flows northward between the Central and Western Cordilleras before emptying into the Caribbean Sea. The species occupies freshwater environments and is recorded as benthopelagic — associated with the lower portion of the water column and substrate zones — in tropical conditions.
The Magdalena basin spans a wide range of elevations and habitat types, from fast-flowing highland tributaries descending from the Andes to slower lowland stretches. Trans-Andean Creagrutus species in this drainage are typically found in clear to moderately turbid stream and river environments. Related species from the same drainage, such as C. guanes, have been documented using montane stream habitats where seasonal dry periods concentrate fish and influence breeding behavior.
Feeding
FishBase records a trophic level of 2.4 for Creagrutus magdalenae, consistent with a diet based primarily on small invertebrates and organic matter taken near the substrate. The benthopelagic habit suggests it forages through the lower water column and along the bottom, picking off insect larvae, microcrustaceans, and similar small prey items characteristic of the guild of small Neotropical stream characids.
In common with most small characids of similar size and ecology, C. magdalenae is unlikely to be a dietary specialist; opportunistic consumption of whatever invertebrates are locally available — aquatic insect larvae, small crustaceans, and possibly algal or plant material — is the expected feeding mode. No aquarium feeding observations are available for this species, which is not regularly kept in captivity.
Mating
No direct mating observations have been published for Creagrutus magdalenae. The genus belongs to Characidae, where the overwhelming majority of species are egg-scattering open-water or substrate spawners with no parental care. Males in related Creagrutus species are generally smaller and more slender than females, and spawning is typically triggered by seasonal cues — particularly the onset of the rainy season or temperature drops associated with dry-season conditions in some montane habitats.
The related Magdalena drainage species C. guanes has been noted to exhibit breeding behavior tied to dry-season conditions in mountain streams, suggesting that seasonality may influence reproductive timing in the genus within this drainage. In the absence of species-specific data, C. magdalenae is assumed to share the typical characid mating pattern: no pair bond, no territory, and brief egg-scattering in open water or among fine substrate.
Breeding
Breeding biology for Creagrutus magdalenae has not been documented in the scientific literature, and the species is not bred in captivity. Based on the biology of Characidae broadly and the genus Creagrutus in particular, the reproductive mode is almost certainly egg-scattering with adhesive or semi-adhesive eggs deposited among fine-leaved aquatic plants or over substrate, with no parental care from either parent after spawning. Eggs are vulnerable to predation and would be abandoned immediately upon release.
The closely related C. guanes from the same Magdalena drainage shows seasonally timed breeding, consistent with the pattern common in Andean-foothill characids where water temperature, discharge, and photoperiod fluctuate with the austral wet and dry seasons. Until formal breeding studies of C. magdalenae are conducted, these details remain inferred rather than confirmed.
In the aquarium
Creagrutus magdalenae is not a species encountered in the ornamental fish trade; it is essentially absent from hobbyist literature, and no dedicated care profile exists in hobby databases such as Seriously Fish. Its small size (under 2.5 in SL) and general hardiness typical of benthopelagic stream characids would in principle make it manageable in a well-maintained biotope aquarium replicating Magdalena valley conditions — moderate current, neutral to slightly alkaline water, and a substrate of fine gravel or sand.
For hobbyists interested in Creagrutus as a genus, the lack of species-specific information means that care would need to be extrapolated from related trans-Andean characids of similar body form. The species' low trophic level and small size suggest it would accept fine-grade prepared foods, small live or frozen invertebrates, and would coexist with similarly sized, non-aggressive tankmates. In practice, it is a species kept only by specialist biotope enthusiasts who can source wild-caught specimens from Colombian ichthyological collections or specialist importers.
Conservation
Creagrutus magdalenae is assessed as Least Concern (LC) on the IUCN Red List, based on an evaluation conducted on 7 October 2014 by Colombian ichthyologists Luz Fernanda Jimenez-Segura (Universidad de Antioquia), Jose Mojica (Universidad Nacional de Colombia), and Juan Carlos Alonso (Museo Nacional de Ciencias Naturales). The Least Concern designation reflects that the species does not meet the threshold criteria for a threatened category at the time of assessment.
The Río Magdalena basin, while one of Colombia's most biodiverse river systems, faces significant pressures from agriculture, urbanization, hydropower development, and water-quality degradation. These threats are ongoing across the basin and affect the diverse community of endemic fishes it harbors. Although C. magdalenae is not currently considered at elevated risk, the long-term status of small, narrowly distributed Andean-basin endemics warrants continued monitoring as land use and water management in the Magdalena valley intensify.