Taxonomy & naming
Creagrutus maxillaris was originally described by George S. Myers in 1927. Eschmeyer's Catalog of Fishes records the valid combination as Creagrutus maxillaris (Myers, 1927), with the parenthetical authority indicating that the species was placed in a different genus when first described. The genus Creagrutus belongs to the subfamily Stevardiinae within the family Characidae, an arrangement supported by molecular and morphological phylogenies that have substantially reorganised the broader characoid assemblage; some recent sources list Creagrutus under Stevardiidae, reflecting ongoing taxonomic debate about whether Stevardiinae merits family-level recognition, but Characidae is used here in its broad, traditionally accepted sense consistent with the site's editorial convention.
Creagrutus is a diverse Neotropical genus of small, silver-bodied characids distributed across lowland South America from the Pacific-slope rivers of Ecuador and Colombia east through the Orinoco and Amazon systems. Species are distinguished largely by subtle meristic and morphological features, making field identification without specimens difficult. C. maxillaris is defined by the elongated maxillary bone noted by Myers, a character that separates it from congeners with more typical jaw proportions.
Morphology
Creagrutus maxillaris reaches a maximum recorded standard length of 3 in, placing it among the mid-sized members of the genus. The body form follows the typical Creagrutus plan: moderately elongate and laterally compressed, silvery on the flanks with a faint darker lateral stripe, and equipped with the single adipose fin characteristic of most characids. The fins are otherwise unremarkable — a dorsal fin of standard shape, small pelvic and anal fins, and a moderately forked caudal.
The defining morphological character is the maxillary bone, which in this species is noticeably lengthened and sweeps rearward and downward in a concave curve; the ETYFish Project notes that the horizontal extent of this bone is nearly twice its vertical extent. This exaggerated maxillary gives the snout and gape a subtly distinctive appearance compared to other Creagrutus and was the feature Myers chose to name the species. Sexual dimorphism is not well documented in the literature, but as in many Stevardiinae females can be expected to become noticeably fuller-bodied when gravid.
Habitat
The known distribution of Creagrutus maxillaris spans river systems associated with the Guyana Shield: the Orinoco River basin and rivers draining directly off the shield in Venezuela, the upper Negro River in Venezuela and Brazil, and the upper Madeira River basin along the Brazil-Bolivia border. This range encompasses a broad swathe of the northwestern Amazon watershed, all areas draining ancient Precambrian shield rock rather than the more fertile, white-water Andean systems.
FishBase classifies the species as benthopelagic — occupying the lower and mid-water column rather than the surface — in river habitats. Guyana Shield streams are typically blackwater to clearwater, soft, acidic, and low in dissolved minerals, often flowing over sandy or rocky substrates shaded by forest canopy. These conditions, common to many characids of the region, should be considered the baseline for the species even where precise chemical measurements for C. maxillaris collection sites are not available in the literature.
Feeding
No published dietary study specific to Creagrutus maxillaris was found in accessible sources. Based on the feeding ecology of the genus and closely related Stevardiinae, the species is presumed to be an opportunistic microphage, taking small aquatic invertebrates — insect larvae, microcrustaceans, and similar items — from the water column and substrate. The elongated maxillary may influence gape mechanics and prey selection, though the functional significance has not been analysed in the literature.
In the aquarium, congeners and similarly sized Stevardiinae accept a broad range of small prepared and live foods: micro-pellets, crushed flake, frozen bloodworm, Daphnia, and brine shrimp. Offering variety and including some live or frozen invertebrate prey supports good condition. The species is not known to be a plant-feeder or a particular threat to soft-leaved aquatic vegetation.
Mating
Spawning behaviour has not been documented for Creagrutus maxillaris in the primary literature or in detailed hobbyist accounts. By analogy with other small Stevardiinae — the subfamily includes a number of internally inseminating or sperm-storing lineages — the reproductive strategy may differ from simple egg-scattering, but the specifics for this genus are not reliably established in accessible sources. The broader Creagrutus group is generally treated as non-specialised egg-scatterers in the aquarium literature, releasing adhesive or semi-adhesive eggs among fine-leaved vegetation or over the substrate, with no parental care.
Given the paucity of species-specific data, aquarists who work with this fish should treat care accounts for the genus with appropriate caution and be prepared for modest surprises in reproductive behaviour.
Breeding
Captive breeding accounts for Creagrutus maxillaris are absent from published sources. Where congeners have been bred in the aquarium, the approach follows that used for other small soft-water Stevardiinae: conditioning groups of well-fed adults in soft, slightly acidic water, providing fine-leaved plants or spawning mops as egg substrate, and removing adults after spawning to prevent predation on the eggs. Eggs are small and adhesive; incubation and fry development timings are not documented for the species specifically.
Because the species originates from soft, often acidic Guyana Shield drainages, replicating those water conditions — low hardness, pH in the 5.5 to 7.0 range, tannin-stained water — is likely to be beneficial for inducing spawning. Data on clutch size, incubation period, and fry rearing are not available; aquarists attempting to breed the species should document and share their results, as the genus is poorly represented in captive breeding records.
In the aquarium
Creagrutus maxillaris is an uncommon species in the hobby, encountered mainly by aquarists with an interest in Neotropical stream fish from the Guyana Shield or those who receive it incidentally in mixed shipments from Venezuela or Brazil. It is not a commercially important or widely traded species, and purpose-bred captive stock is essentially unavailable. Wild-caught individuals occasionally appear in specialist shipments.
Care should follow the conditions appropriate for small soft-water Stevardiinae: a well-filtered aquarium with gentle to moderate flow, soft and slightly acidic water (pH 6.0 to 7.0, low hardness), temperatures in the 72–82 °F range, dim to moderate lighting, and a substrate that encourages natural behaviour. The species is peaceful toward similarly sized tankmates and does best kept in small groups rather than as singletons. A biotope setup evoking a Guyana Shield stream — sandy substrate, driftwood, dried leaf litter, and dark water — is appropriate and allows the fish to behave naturally. Avoid very large or boisterous tankmates that will outcompete it at feeding.
Conservation
Creagrutus maxillaris is assessed as Least Concern on the IUCN Red List, with the assessment dated 4 March 2021. This status reflects the species' broad distribution across multiple major drainage systems — the Orinoco, upper Negro, and upper Madeira basins — which provides a geographic buffer against localised threats. No specific population declines or habitat-level threats are noted for this species.
The Guyana Shield river systems from which C. maxillaris is known face general regional pressures — deforestation, gold mining (which introduces mercury and increases sedimentation), and in parts of its range, hydroelectric development. These pressures affect numerous co-occurring species. For the moment, however, the species' wide range and apparent habitat tolerances place it in a more secure position than many narrowly endemic Neotropical characids, and no targeted conservation measures are currently identified as necessary.