Taxonomy & naming
Knodus orteguasae was described by the American ichthyologist Henry Weed Fowler in 1943. The authority is written in parentheses because Fowler originally placed the species in a different genus; it was subsequently transferred to Knodus, which is maintained as its valid placement by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Van der Laan).
The genus Knodus belongs to the family Characidae and encompasses a suite of small, slender South American tetras distributed across the Amazon and Orinoco drainages and adjacent river systems. The specific epithet orteguasae refers to a geographic locality — likely the Río Orteguaza, a tributary of the Caquetá (Japurá) River in Colombia — suggesting the type locality lies within that drainage. Exact type-locality details follow Fowler's original description and are not independently verified here.
Morphology
Members of the genus Knodus are small, laterally compressed characids with a streamlined, fusiform body, a typical tetragonally shaped head, and the adipose fin characteristic of most characiforms. Detailed morphometric data for K. orteguasae specifically are not widely documented in accessible literature, and published measurements should be sought in Fowler's original description.
Like congeners, K. orteguasae is presumed to be a silvery fish with a faint lateral stripe or midlateral dark marking, a pattern common across the small Amazonian Knodus species. The presence and extent of any humeral spot, caudal marking, or fin pigmentation would be diagnostic features distinguishing it from related species, but these specifics are data sparse for this species in secondary sources.
Habitat
The species is associated with the Amazon basin, most probably the Caquetá-Japurá drainage or closely adjacent systems based on the etymology of its name. Knodus species as a group inhabit small to medium-sized rivers and streams, typically in lowland and foothill environments, often in clear or blackwater settings with moderate to swift current over sandy or rocky substrates.
Water conditions in the likely range of K. orteguasae are typical of western Amazonian tributaries: soft, acidic to slightly acidic, warm water with low conductivity. Exact habitat and water-chemistry records for this species are not available in the sources consulted, and field data from the original collecting locality should be considered authoritative.
Feeding
Like most small characids in the genus Knodus, K. orteguasae is presumed to be an omnivore feeding opportunistically on small invertebrates, zooplankton, and organic matter in the water column and at the surface. Specific dietary studies on this species have not been located in the literature reviewed.
In captivity, small Knodus species generally accept a range of prepared foods — fine flake and micro-pellets — supplemented with small live or frozen invertebrates such as Daphnia, Artemia nauplii, and micro-worms, which likely improve condition and coloration.
Mating
No published observations of mating behaviour in K. orteguasae are available. Based on the reproductive biology of related Knodus species and small Amazonian characids generally, the species is expected to be an egg-scattering open spawner that deposits adhesive eggs among fine-leaved plants or over sandy substrate, with no parental care from either sex.
Male courtship in small tetras typically involves pursuit of females and lateral displays. Spawning is likely triggered by slight temperature increases, water changes, and a photoperiod transition mimicking the onset of the rainy season.
Breeding
No captive-breeding records for K. orteguasae have been located in accessible hobbyist or scientific literature. By analogy with other small Knodus, breeding in captivity would involve a small species tank or a fine-mesh-bottomed breeding tank with soft, slightly acidic water, fine-leaved plants or a spawning mop, and conditioned adults.
Eggs of small characids are typically small, semi-adhesive, and vulnerable to fungus; adults should be removed promptly after spawning. Fry would require infusoria or other fine first foods for the first days before graduating to newly hatched brine shrimp. Given how rarely this species appears in the hobby, captive-breeding experience is essentially undocumented.
In the aquarium
Knodus orteguasae is essentially unknown in the aquarium hobby. It does not appear in mainstream hobbyist literature or major retailer stock lists, and care information specific to this species is not available. The notes below are extrapolated from general Knodus and small Amazonian characid husbandry and should be treated as provisional.
Like other small tetras from soft-water Amazonian drainages, K. orteguasae would likely do best in a species tank or community of similarly sized, peaceful fishes, in soft, slightly acidic, warm water (approximately 75–82 °F, pH 6.0–7.0), with subdued lighting, a fine-grained or sandy substrate, and some surface cover or floating plants to reduce stress. A school of six or more individuals is recommended to promote natural behaviour. Any aquarist who keeps or breeds this species would be contributing genuinely novel observations to the hobby record.
Conservation
Knodus orteguasae has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). No conservation-specific data — population estimates, threat assessments, or range-change information — have been located for this species.
The Caquetá-Japurá basin, the likely range of this species, faces ongoing pressures from deforestation, agricultural runoff, and hydroelectric development in parts of its Colombian and Brazilian extent. Without a formal assessment it is not possible to characterise the species' status beyond noting that small, range-restricted Amazonian characids can be locally vulnerable to habitat change even when not formally listed.