Taxonomy & naming
Creagrutus caucanus was described by Carl H. Eigenmann in 1913 on the basis of material from the Cauca River system of Colombia. The genus Creagrutus Günther, 1864 is one of the larger and more taxonomically complex genera in the subfamily Stevardiinae (family Characidae), encompassing a diverse array of small, silvery characins distributed across the drainages of Central America and South America, from lowland rivers to Andean headwater streams.
Eschmeyer's Catalog of Fishes is the authority for the valid name Creagrutus caucanus Eigenmann, 1913. Because the species was described in Creagrutus, where it remains, no parenthetical authority is used. Revision of Creagrutus has been ongoing; the genus has undergone considerable taxonomic attention in recent decades, and some species limits have shifted. The caucanus epithet refers to the Cauca River, the type-locality drainage.
Morphology
Creagrutus caucanus is a small, slender to moderately compressed characin, with published standard lengths in the range of approximately 1–1.5 in. The body plan is typical of the genus: elongate and somewhat fusiform, with a relatively pointed snout, a terminal or slightly subterminal mouth, and the characteristic adipose fin of the Characidae.
Coloration in life is not well documented in the accessible literature. As with most Creagrutus species, the fish is likely silvery to pale straw-colored on the flanks, with a darker dorsal surface and a mid-lateral stripe or dusky lateral band. Detailed meristic and morphometric data distinguishing C. caucanus from congeners in the Cauca drainage are available in the ichthyological monographic literature on the genus but are not reproduced in hobby or aggregator sources.
Habitat
Creagrutus caucanus is endemic to the Cauca River drainage in Colombia. The Cauca is a major left-bank tributary of the Magdalena River, draining the inter-Andean valley between the Central and Western Cordilleras. Species of Creagrutus in this region typically inhabit clear to slightly turbid streams and smaller rivers, often in hilly or montane terrain, where they are associated with substrates of sand, gravel, or bedrock and moderate to swift current.
Water conditions in Andean and sub-Andean Colombian streams are generally cool to warm depending on altitude, typically soft to moderately hard and slightly acidic to neutral. FishBase notes clear to slightly acidic water for this species. Precise temperature and chemistry data specific to Cauca River populations of C. caucanus have not been compiled in the accessible literature, but conditions typical of mid-elevation Colombian streams — temperatures roughly in the low-to-mid 20s Celsius, pH near neutral or slightly below — are a reasonable inference.
Feeding
Creagrutus species are generally regarded as opportunistic omnivores or micropredators in their natural streams, feeding on small invertebrates — aquatic insect larvae, terrestrial insects falling to the water surface, and small crustaceans — along with algae, detritus, and organic particles. The feeding ecology of C. caucanus specifically has not been described in detail in the accessible literature.
In the aquarium, related Creagrutus species accept small live and frozen foods such as Daphnia, brine shrimp, and bloodworm, as well as fine-grained dried foods. Given the small adult size, food particle size is an important consideration.
Mating
No detailed observations of courtship behavior specific to Creagrutus caucanus have been published or recorded in hobby literature. Characins in the family Characidae are broadly egg-scatterers, and Creagrutus species are expected to follow this pattern: open-water or vegetation-associated spawning with no pair bond and no parental care.
As with other small characins, males likely display to females with fin extension and lateral positioning prior to spawning. The small adult size suggests that spawning groups rather than isolated pairs would occur in nature, with eggs deposited among fine-leaved plants, roots, or substrate crevices and left to develop without further parental investment.
Breeding
Captive breeding of Creagrutus caucanus has not been documented in the accessible aquarium hobby literature, and the species is essentially absent from the ornamental trade. By analogy with other small characins, breeding would likely involve egg-scattering among fine-leaved plants or over substrate, with adhesive or semi-adhesive eggs requiring separation from adults to prevent predation.
Incubation period, fry size, and first-food requirements are unrecorded for this species. Breeders working with closely related Creagrutus species have reported standard small-characin protocols: soft, slightly acidic water, dense planting or spawning mops, removal of adults post-spawning, and infusoria or commercial liquid fry food as first foods for newly free-swimming fry.
In the aquarium
Creagrutus caucanus is not an established aquarium fish and does not appear in mainstream hobby literature or trade lists. Occasional specimens may reach specialist hobbyists through Colombian ornamental-fish exporters, but the species has no history in the hobby comparable to more popular Characidae.
For hobbyists working with this or related Creagrutus species, a small aquarium of 23.5–31.5 in with soft to moderately hard, neutral to slightly acidic water and good oxygenation would approximate natural conditions. The species' small size makes it suitable for a biotope setup representing Colombian Andean stream fauna, and it would likely do best in a group with similarly sized, non-aggressive tankmates. Specific care notes are data sparse.
Conservation
Creagrutus caucanus has not received a formal assessment by the IUCN Red List; its status is Not Evaluated (NE). The species is endemic to the Cauca River drainage of Colombia, a system that has experienced significant human impact through agriculture, urban development, mining, and water extraction over recent decades. The Cauca valley is one of Colombia's most heavily modified river systems.
Without an IUCN assessment, the conservation situation of C. caucanus cannot be formally characterized, though the pressures on the Cauca drainage are well documented. The species' apparently restricted range within an impacted system warrants monitoring. It is not collected for the ornamental trade in significant numbers and therefore does not face the collecting pressures that affect some Colombian characins.