Taxonomy & naming
Hyphessobrycon klausanni was described by Carlos A. García-Alzate, Alejandro Urbano-Bonilla, and Donald C. Taphorn in 2017 in a paper published in ZooKeys (vol. 668, pp. 123–138, DOI 10.3897/zookeys.668.11489). The type locality is the upper Guaviare River drainage of the Orinoco River basin in Colombia. Eschmeyer's Catalog of Fishes is the authority for the valid name; the species is placed in Hyphessobrycon, one of the largest genera in Characidae.
The post-2017 molecular revision of the broader tetra assemblage reassigned many genera formerly considered Characidae to the family Acestrorhamphidae as recognised by some authorities, and FishBase places H. klausanni there accordingly. The top-level family field on this site follows the Catalog of Fishes' current placement. The genus name Hyphessobrycon combines Greek roots loosely meaning 'little bite' or 'lesser bite', describing smaller relatives of Brycon, and the species epithet klausanni is a patronym formed from the first names of Klaus and Anni Lang, parents of the collector Klaus-Peter Lang.
Morphology
Hyphessobrycon klausanni is a miniature tetra, with the maximum recorded standard length of 1 in for male or unsexed specimens reported by FishBase. The dorsal fin carries 9 soft rays; the anal fin has 19–20 soft rays, ray counts documented in the original description.
Detailed colour and body-shape descriptions beyond the meristic data in the cache are sparse in accessible sources. Like other small Hyphessobrycon the fish is presumably laterally compressed with the family's characteristic adipose fin, but specific pigmentation patterns, lateral-line scale counts, and other morphological details are best drawn from the original ZooKeys publication.
Habitat
The species is known from the upper Guaviare River drainage, Orinoco basin, in Colombia — a freshwater pelagic microhabitat of shallow, well-oxygenated streams. Reports from the type locality describe clear water flowing over substrates of rock, sand, and gravel with leaf litter, and the fish is found among aquatic vegetation, tree roots, and submerged logs.
Water-chemistry measurements at the type locality span a notably wide range: temperature 78–79 °F and pH 6.47–8.7. The pH breadth likely reflects different microhabitats sampled across the drainage rather than a single homogeneous water body. FishBase classifies the species as tropical and freshwater-pelagic.
Feeding
The trophic level of H. klausanni is recorded at 2.9 ± 0.3 in FishBase, consistent with a diet dominated by small invertebrates, algae, and fine organic matter — typical of small characids in lowland tropical streams. Specific gut-content studies for this species are not documented in available sources.
In captivity, very small tetras of this size class are generally fed on fine-grade dried foods, small live or frozen invertebrates such as freshly hatched brine shrimp, micro-worms, and Daphnia nauplii, and possibly finely powdered prepared foods. Data specific to H. klausanni in aquarium conditions are sparse given the species' rarity in the hobby.
Mating
No specific observations of courtship behaviour in H. klausanni have been published in sources available to this account. Based on the biology of closely related Hyphessobrycon species, egg-scattering open spawning behaviour is expected: males likely court receptive females with fin displays and pursue them into fine-leaved vegetation or among submerged plant matter where eggs are deposited.
As with most small characids, no pair bond or territorial defence of a spawning site is expected, and spawning probably occurs in loose group activity among multiple individuals in the presence of suitable spawning substrate.
Breeding
Breeding details specific to H. klausanni in captivity or in the field are not documented in sources accessible to this account. By analogy with other small Hyphessobrycon, the species is assumed to be an egg scatterer depositing small adhesive eggs among fine-leaved plants or over substrate, with no parental care — adults would be expected to consume eggs if not separated.
Given the species' very small adult size (under 1 in SL), fry at hatch would be extremely small and would require infusoria-grade first foods or commercial liquid fry preparations before graduating to newly hatched brine shrimp. The species is not established in the aquarium trade and captive-breeding records are not known to the authors of this account.
In the aquarium
Hyphessobrycon klausanni is not an established aquarium fish and is essentially absent from the ornamental trade. No specific husbandry guidance exists in hobby literature for this species. As a 1 in tetra from soft, slightly acidic to circumneutral Colombian blackwater streams it would likely require a well-planted nano or small aquarium, stable water quality, and suitably small tank mates if ever kept.
The water conditions at the type locality (78–79 °F, pH 6.47–8.7) suggest reasonable tolerance across a moderate pH range, though captive preferences may differ. Any aquarist encountering this species would be working largely from first principles and from knowledge of closely related Colombian Hyphessobrycon.
Conservation
Hyphessobrycon klausanni is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment dated 14 November 2020. Data Deficient means there is insufficient information to make a direct or indirect assessment of extinction risk — the species is known from a restricted portion of the upper Guaviare drainage but population size, range extent, and threats have not been adequately quantified.
The upper Guaviare basin in Colombia faces pressures common to Amazonian and Orinocoan lowland ichthyofaunas, including deforestation, agricultural expansion, and artisanal gold mining, though the specific impact on this species is undocumented. The small adult size and restricted type locality suggest the species could be vulnerable to localised habitat change, but formal reassessment awaits broader surveys.