Taxonomy & naming
Knodus borari was formally described by Silva-Oliveira, Canto, and Ribeiro in 2023, in a paper published in the Journal of Fish Biology (vol. 103, no. 1, pp. 136–142, DOI: 10.1111/jfb.13179). The type locality is a stream within the lower Rio Tapajós drainage in the state of Pará, Brazil. Eschmeyer's Catalog of Fishes (CAS) records the valid name as Knodus borari Silva-Oliveira, Canto & Ribeiro, 2023, and the species is classified within the family Characidae under the order Characiformes.
The genus Knodus Eigenmann, 1911 belongs to subfamily Stevardiinae and encompasses numerous small, slender characins distributed across Amazonian and Orinoquian drainages of South America. Members of the genus are typically modest in size and are characterised by certain dental and fin-ray arrangements rather than by vivid colour patterns. K. borari shares the general bauplan of the genus but was distinguished from all previously described congeners by a suite of morphological characters documented in the original description.
Because the species was described so recently, broader taxonomic literature treating the genus has not yet been updated to account for it, and hobbyist resources are sparse. Catalog of Fishes remains the principal reference for confirming its nomenclatural validity.
Morphology
Knodus borari is a small fish, reaching a maximum recorded standard length of 1.5 in (approximately 1.4 in). It is benthopelagic, occupying the lower and middle parts of the water column. The body is elongate and laterally compressed in the typical Knodus fashion.
The original description notes 8 dorsal soft rays and 17–19 anal soft rays, with a vertebral count of 35. The dentition includes conical to tricuspid teeth, a character combination noted in the diagnosis of the species. A distinctive black blotch is present at the base of the caudal fin — a feature that aids visual identification in the field and distinguishes the species from several congeners. Beyond these diagnostic details, no further colouration or scaling data are available in the cached sources.
Habitat
The type locality of Knodus borari is a stream within the lower Rio Tapajós basin in the Brazilian Amazon. The collecting site was described as approximately 13 metres wide and 1–3 metres deep, with moderately fast current and a substrate of rock, gravel, and sand. This combination of clear, well-oxygenated, flowing water over hard substrates is characteristic of many Amazonian stream-dwelling characids.
The Tapajós is a predominantly clear-water river, rising on the Brazilian shield and carrying relatively low levels of suspended sediment and dissolved organic matter compared with whitewater or blackwater Amazonian systems. Stream habitats in the lower basin where K. borari was collected tend toward neutral to slightly acidic pH and warm tropical temperatures, though no specific water-chemistry measurements for the type locality are available in the source material.
Beyond the type locality, the distribution of K. borari has not been documented. Whether it occurs elsewhere in the lower Tapajós catchment or is genuinely restricted to a narrow range is unknown.
Feeding
No specific dietary studies on Knodus borari have been published. Based on the trophic biology of Knodus as a genus and the broader feeding habits of small Amazonian stream characids, the species is presumed to be an opportunistic micro-predator and omnivore, consuming small aquatic and terrestrial invertebrates, insect larvae, microcrustaceans, and organic detritus as available.
The benthopelagic habit recorded for K. borari on FishBase suggests it forages across both the lower water column and the stream bottom, consistent with feeding on benthic invertebrates and drifting particulates. In the absence of gut-content studies, however, these inferences should be treated as provisional.
Mating
No observations of reproductive behaviour in Knodus borari have been published. Small Stevardiinae characids in general are egg-scatterers that spawn over aquatic vegetation or fine substrate without constructing nests or exercising parental care. Males in many small characids establish brief courtship displays involving fin-spreading and rapid pursuit of females before spawning.
Adhesive or semi-adhesive eggs deposited among fine-leaved plants or over gravel are typical of the group, though some Knodus species may broadcast non-adhesive eggs into open water. In the absence of any species-specific observations, these generalisations from close relatives represent the best available inference for K. borari.
Breeding
Captive breeding of Knodus borari has not been reported in the available literature. The species is not known from the aquarium trade and has not been the subject of hobbyist breeding trials. General guidance for breeding small Stevardiinae characids applies by analogy: conditioning adults on varied live and frozen foods, providing fine-leaved plants or spawning mops, and maintaining warm, soft-to-neutral water conditions typically induces spawning.
Eggs would be expected to be small and, in a breeding tank, should be separated from adults to prevent predation. Incubation periods and fry-rearing requirements are unknown for this species specifically. Given its diminutive adult size of 1.5 in SL, first foods would need to be appropriately fine — infusoria or rotifers followed by newly hatched brine shrimp nauplii. All breeding notes here are extrapolated from congeners; no K. borari-specific data exist.
In the aquarium
Knodus borari is not currently available in the aquarium hobby and no husbandry data specific to this species have been published. Any aquarist fortunate enough to obtain specimens would be working largely by inference from other small Stevardiinae characids kept in captivity.
Based on habitat data, a tank replicating the moderate-current, well-oxygenated stream environment of the lower Tapajós — with sandy and gravel substrate, rocks, and good filtration providing some current — would be the appropriate starting point. Neutral to slightly acidic water at tropical temperatures (around 75–82 °F) and a fine-particulate diet of small live and frozen invertebrate foods would align with both the known habitat and the probable feeding niche. As with most small characids, K. borari would be expected to thrive better in a group than in isolation, reducing skittishness and encouraging natural behaviour. Data on compatibility, tank-size requirements, and longevity remain entirely undocumented.
Conservation
Knodus borari has not been assessed by the IUCN Red List. The species was described only in 2023 and is too recently named to have undergone formal evaluation; it therefore carries a status of Not Evaluated (NE). No conservation-specific data — population size, trend, threats, or range mapping beyond the type locality — are available in the published record.
The lower Rio Tapajós basin, while better protected than many Amazonian catchments due to the presence of indigenous territories and conservation units, is subject to ongoing pressures from agriculture, infrastructure development, and artisanal and industrial mining. Whether K. borari has a restricted endemic range or a broader distribution that buffers it from localised disturbance cannot be determined from present data. Formal IUCN assessment and broader survey work across the lower Tapajós drainage would be necessary to evaluate its status with any confidence.