Taxonomy & naming
Creagrutus paraguayensis was described by Volker Mahnert and Jacques Géry in 1988. The species is placed in Creagrutus, a genus of characid fishes belonging to the subfamily Stevardiinae (sensu lato) within the family Characidae and order Characiformes. The valid name as confirmed by the Integrated Taxonomic Information System (TSN 640853) is Creagrutus paraguayensis Mahnert & Géry, 1988.
Creagrutus is a speciose and taxonomically complex genus, with the number of recognised species having grown considerably through systematic revisions over recent decades. Many members are superficially similar small-bodied fishes separated by subtle meristic and morphological characters. The specific epithet paraguayensis refers to the country of Paraguay, from which the type material was collected, following a common convention in the genus of naming species after the drainage or region of origin.
Morphology
Creagrutus paraguayensis is a small, slender-bodied characid with a standard length of approximately 2.5 in. Like other members of the genus, it conforms to the general characid body plan: a laterally compressed, fusiform body, a forked tail, an adipose fin between the dorsal and caudal fins, and a small to moderate mouth. The species is a ray-finned fish (Actinopterygii) in the diverse order Characiformes.
Detailed morphometric and meristic data for this species are not widely available in the accessible literature. Creagrutus species in general tend to be silvery to pale tan on the flanks, often with a lateral stripe or series of markings, and lack the vivid colouration that characterises many aquarium-popular characids. Without a thorough revision comparing it to close congeners, the specific diagnostic characters of C. paraguayensis are best established by reference to the original description.
Habitat
Creagrutus paraguayensis is documented from the Paraguay River basin in central and northern Paraguay. The Paraguay River is one of the major tributaries of the La Plata system, draining a vast interior lowland that includes the Pantanal — one of the world's largest tropical wetland complexes — as well as adjacent cerrado and dry Chaco landscapes. The species occurs in freshwater habitats within this drainage.
Surveys of fish diversity in the upper Paraguay River basin have documented the species as part of a rich ichthyofaunal assemblage. The Paraguay system is characterised by seasonal flooding dynamics that strongly influence habitat availability, with water temperatures varying seasonally through the subtropical and tropical ranges typical of the interior of South America. Anthropogenic pressures on the Paraguay River basin — including agricultural expansion, deforestation, and hydrological modification — have been noted as ongoing threats to fish diversity in the system.
Feeding
No specific feeding data for Creagrutus paraguayensis appear in the accessible literature. By inference from the genus and family, it is expected to be an opportunistic omnivore or invertivore — a feeding guild common among small characids of its size class. Creagrutus species in general likely consume small aquatic invertebrates, microcrustaceans, insect larvae, and organic detritus available in the water column and substrate of river and stream habitats.
The small mouth size and modest body length are consistent with a diet focused on small prey items rather than larger fishes or robust plant material. In rivers and streams of the Paraguay basin, potential food sources include invertebrates associated with leaf litter, sandy substrates, and the edges of flooded vegetation during seasonal inundation.
Mating
No specific mating observations exist in the literature for Creagrutus paraguayensis. The genus Creagrutus belongs to Characidae, a family in which the predominant reproductive strategy is egg-scattering with no parental care. Small characids of this type typically form loose aggregations or pairs during the spawning act, with eggs scattered over vegetation, substrate, or open water and abandoned immediately after fertilisation.
In South American characids of similar ecology, spawning is often triggered or synchronised with seasonal cues — rising water temperatures, increased flow, or the onset of the wet season's flooding pulse — though the specific triggers for C. paraguayensis have not been documented. Adhesive or semi-adhesive eggs among fine-leaved vegetation or leaf litter would be the expected spawning medium for a riverine species of this type.
Breeding
Breeding in the wild for Creagrutus paraguayensis has not been described in detail. Given the reproductive mode typical of Characidae, spawning is assumed to involve free-scattering or loosely adhesive eggs deposited without nest construction, with both parents abandoning the spawn entirely after fertilisation. Incubation time and fry development data are not available for this species.
Creagrutus paraguayensis is not known to be kept or bred in the aquarium hobby, so captive breeding records do not supplement the wild biology. Data on clutch size, fecundity, and juvenile development would require targeted field or laboratory study. The seasonal hydrological cycle of the Paraguay River basin likely plays a role in coordinating reproduction across the ichthyofaunal community, as is typical for floodplain-associated characids throughout South America.
In the aquarium
Creagrutus paraguayensis is not an established aquarium fish. The genus Creagrutus as a whole is almost entirely absent from the hobby; the species that have appeared in specialist collections are typically collected incidentally during targeted surveys or by hobbyists specifically interested in characid systematics rather than colour or display.
For aquarists who obtain specimens — most likely as bycatch from wild-caught shipments from Paraguay — husbandry by analogy with other small, riverine characids of the La Plata system would be appropriate: soft to moderately hard freshwater, subtropical to warm temperatures broadly consistent with the Paraguay basin range, a well-filtered tank with some current, and a diet of small live or frozen invertebrates supplemented with fine-particle dry foods. The small adult size (under 2.5 in SL) makes it compatible with micro-scale aquaria, though schooling conspecifics would likely be needed to observe natural behaviour. Given the paucity of published information, keepers should treat care parameters as working hypotheses rather than established facts.
Conservation
Creagrutus paraguayensis has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). No dedicated conservation assessment, population estimate, or threat analysis has been published for the species. Its documentation in the scientific literature is limited to taxonomic records and ichthyofaunal checklists for the Paraguay River basin.
The Paraguay River system faces significant and ongoing anthropogenic pressure. Research on fish diversity in the upper Paraguay basin has highlighted habitat degradation linked to agricultural conversion, deforestation within the cerrado and Chaco catchments, and hydrological alteration. The Pantanal — the core of the Paraguay drainage — is itself subject to increasing threats from land-use change and climate variability. Whether C. paraguayensis has a restricted range within the basin or is broadly distributed, and how sensitive it may be to these pressures, cannot be determined from available data. A formal IUCN assessment would require targeted surveys and population data.