Taxonomy & naming
Creagrutus amoenus was described by Henry Weed Fowler in 1943 from specimens collected in Peru. Fowler, a prolific describer of South American fishes working at the Academy of Natural Sciences of Philadelphia, contributed extensively to the early documentation of Peruvian ichthyofauna. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises Creagrutus amoenus Fowler, 1943 as the valid name; the authority is not parenthesised because the species was placed in Creagrutus from its original description.
The genus Creagrutus was established by Günther in 1864 and belongs to the subfamily Stevardiinae within Characidae, a grouping of small South American characids that has been substantially revised in recent decades through molecular and morphological study. Creagrutus is one of the most species-rich genera of small Neotropical characids, with well over a hundred described species spread across drainages from Panama south through much of South America west of the Andes and into trans-Andean systems. Many species have narrow ranges tied to individual river drainages or elevation bands, and the genus has been an active area of taxonomic research, with numerous species described since 2000.
Data on C. amoenus specifically are sparse in the published literature beyond the original description, and no subsequent taxonomic revision has moved it from Creagrutus.
Morphology
Like other members of its genus, Creagrutus amoenus is a small, laterally compressed characid with a moderately deep body and a blunt snout — the robust, somewhat chunky body plan typical of Creagrutus distinguishes the genus from the more slender Astyanax-like tetras of similar habitats. Specific size data for C. amoenus are sparse; Creagrutus species are generally small fishes, with most species reaching 1.5–3 in standard length, though some exceed this. No reliable maximum length figure for C. amoenus is available in the published sources consulted here.
Colouration in life is not well documented for this species. Creagrutus species are typically silvery with a lateral stripe or band of variable width and intensity, sometimes with a dark humeral spot and a caudal spot; preserved specimens used in taxonomic accounts lose much of the live colouration. As with many small characids, sexual dimorphism in body colour is subtle, though females may be deeper-bodied when ripe.
Habitat
Creagrutus amoenus is known from Peru. Members of the genus are characteristically associated with clear, well-oxygenated streams and rivers in Andean foothill and piedmont drainages, ranging from the lowland Amazon basin edge up into the montane zone depending on species. They are typically found in flowing water over gravel or rock substrates, often in areas with moderate current and riparian vegetation providing shaded cover along the banks.
Specific habitat data for C. amoenus from the type locality and any subsequent collection sites have not been thoroughly documented in the literature available for this account. Based on the general ecology of the genus in Peruvian drainages, water conditions at collection sites are likely cool to warm-temperate, soft to moderately mineralised, and slightly acidic to neutral, consistent with Andean foothill streams. Data sparse — confirmed locality and ecological parameters await comprehensive treatment of the species.
Feeding
Creagrutus species are generally considered opportunistic omnivores of the stream drift and benthos. Studies on closely related congeners and sympatric Stevardiinae indicate that small characids of this type feed on aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and adult insects falling onto the water surface — as well as algae and organic detritus. Some Creagrutus have been noted to take small fishes.
No specific dietary study for Creagrutus amoenus has been located. In captivity, small characids of this build do well on a varied diet of small live and frozen invertebrates (Daphnia, Artemia, chironomid larvae), supplemented with quality small pellets or flake. A varied menu with protein-rich live or frozen items supports condition and colouration.
Mating
No specific observations on the mating behaviour of Creagrutus amoenus have been published. Based on the reproductive biology of the family Characidae broadly and on accounts of related Stevardiinae, Creagrutus species are expected to be egg-scattering spawners with no parental care — the default mode for small South American characids in open or vegetated stream environments.
Males of small characids in this group typically display to females with fin spreading and lateral positioning; spawning likely occurs over fine substrate, gravel, or among aquatic plants in flowing water. Adhesive or semi-adhesive eggs are probable given the stream-dwelling habits. No aquarium spawning account for this species has been documented in the hobby literature available.
Breeding
Creagrutus amoenus has not been reported as established in the aquarium hobby, and no captive breeding account has been located. General expectations for the genus, based on the breeding of other small Stevardiinae in captivity, would be egg-scattering over fine-leaved plants or substrate with no parental care, and removal of adults from the eggs after spawning to prevent predation.
Fry of small characids of this type typically require very small first foods — infusoria or rotifers — before graduating to newly hatched brine shrimp nauplii. Growth rates and brood sizes for C. amoenus are undocumented. Any hobbyist successfully breeding this species would be making a genuine contribution to knowledge of the genus.
In the aquarium
Creagrutus amoenus is not a species currently available in the mainstream aquarium trade, and no established care literature exists for it specifically. The species is known primarily from scientific museum collections rather than from hobby sources. Should it become available, care expectations based on congeners and the general ecology of Andean stream characids would point toward a species suited to cooler, well-oxygenated, soft to moderately hard water with good current simulation and a sandy or fine gravel substrate.
Small characids of this type do best in groups, which reduces individual stress and elicits more natural schooling and displaying behaviour. Tankmates should be similarly sized and peaceful. A biotope-style setup with South American stream aesthetics — rounded river stones, fine sand, driftwood for cover, and restrained planting with Amazonian species — would suit the genus well. As a rarely traded scientific-collection species, C. amoenus is an example of the enormous diversity of small characids that advanced hobbyists occasionally encounter through specialist importers.
Conservation
Creagrutus amoenus has not been evaluated by the IUCN Red List; its status is listed as Not Evaluated (NE). Like many narrowly distributed Andean-foothill characids, it may face pressures from habitat degradation in Peruvian river systems — deforestation, agricultural runoff, and water extraction affect small streams throughout the Andean piedmont — but no formal assessment of population status or trend has been carried out for this species.
The broader genus Creagrutus contains several species with restricted ranges, and the taxonomic complexity of the group means that undescribed species and overlooked populations are still being discovered. Conservation attention for small stream characids in Peru is limited relative to larger, commercially important species, and C. amoenus is likely to remain formally unassessed until targeted ichthyological surveys are conducted in its range drainages.