Taxonomy & naming
Knodus ytuanama was formally described by Ferreira and Ohara in 2023. The original description provided a morphological diagnosis distinguishing the species from its congeners, along with type locality data and a full set of meristic and morphometric characters. Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS) records the species as valid under the authority Ferreira & Ohara, 2023.
The genus Knodus Eigenmann, 1911 belongs to the family Characidae and comprises a large assemblage of small, silvery tetras distributed across much of tropical South America. Knodus species are often described as members of a 'trash taxon' in the older literature — a catch-all for small, morphologically generalized characids — but recent revisionary work has clarified the group's boundaries and revealed many undescribed species, of which K. ytuanama is one of the more recently validated. The specific epithet ytuanama is drawn from the type locality region; its precise derivation is given in the original description by Ferreira and Ohara.
Morphology
Like most Knodus, K. ytuanama is a small, slender, laterally compressed characid with a generally silvery body. Species of this genus typically show the classic small-tetra body plan: a moderately fusiform profile, a forked caudal fin, and modest coloration anchored by a lateral stripe or humeral spot. Exact size data for K. ytuanama have not been independently published outside the original description, and the data in that paper have not been widely reproduced in secondary sources.
The original description by Ferreira and Ohara provided the morphological characters used to diagnose the species, including fin-ray and scale counts that distinguish it from close relatives. Given the scarcity of secondary documentation, size and coloration details here reflect the genus-level expectation for a small Knodus: most species reach 1–2.5 in total length, are silvery-translucent with little sexual dimorphism, and lack the vivid coloration of more popular aquarium tetras.
Habitat
The type locality for Knodus ytuanama is given in Ferreira and Ohara (2023) in connection with its name. Knodus species in general occupy a wide variety of Neotropical freshwater environments: small forest streams, creek margins, flooded areas, and the shallower, well-vegetated edges of larger river channels. They are typically associated with clear to moderately turbid water over sandy or leaf-litter substrates.
Given that K. ytuanama is a recently described species with limited post-description literature, specific habitat parameters — water temperature, pH, depth range — have not been independently confirmed in published secondary sources. The broader genus occupies warm Amazonian-type waters, typically in the range of 73–82 °F, with near-neutral to slightly acidic pH values consistent with soft, low-conductivity Amazonian tributaries. These values should be treated as genus-level context rather than species-specific measurements.
Feeding
Knodus species are generally micropredatory omnivores, taking small invertebrates, zooplankton, microcrustaceans, insect larvae, and plant material opportunistically from the water column and substrate surface. This feeding strategy is typical of small characids in Amazonian stream environments, where the diet tracks available prey seasonally.
No specific dietary studies have been published for K. ytuanama. In an aquarium context, small Knodus congeners accept fine flake food, micro-pellets, and frozen or live foods such as Daphnia, brine shrimp nauplii, and micro-worms without difficulty. A varied diet that includes live or frozen invertebrate prey helps maintain condition and natural behavior in captive specimens.
Mating
No specific mating or reproductive behavioral data have been published for Knodus ytuanama. Based on close relatives and the broader Knodus genus, the species is presumed to follow the egg-scattering pattern typical of small characids: males and females spawn in open water or among fine-leaved vegetation, releasing adhesive or semi-adhesive eggs without pair bonding or site preparation.
In small Knodus kept in aquaria, spawning can occur with little ceremony — a brief chase and release of eggs among plant material or over a substrate. No courtship structures, nest-building, or elaborate display have been documented in this genus. As with most egg-scattering characids, there is no parental care, and the adults may consume eggs if not separated from the spawning site.
Breeding
Breeding data specific to Knodus ytuanama are not available in any published or accessible secondary source as of the time of writing. The species is not known to be established in the aquarium trade, and captive-breeding accounts have not been documented.
By analogy with other small Knodus, breeding in captivity would be expected to follow the standard small-characid pattern: egg scattering over fine-leaved plants or a moss-covered substrate, with adhesive or semi-adhesive eggs hatching in approximately 24–48 hours at warm temperatures, fry becoming free-swimming a few days later and requiring very small first foods such as infusoria or commercially prepared liquid fry food before graduating to newly hatched brine shrimp nauplii. No parental care is expected; eggs and fry are at risk of predation from the adults.
In the aquarium
Knodus ytuanama is not established in the aquarium hobby as of 2026 and is not commercially available through the ornamental fish trade. No aquarium care accounts exist in the hobbyist literature. The species was described in 2023 and remains known primarily from its type locality specimens held in institutional collections.
Should the species enter the trade, care requirements would be expected to align closely with other small Knodus: a peaceful, schooling fish suitable for a well-maintained tropical aquarium with soft, slightly acidic to neutral water, temperatures in the low-to-mid 20s Celsius, and a diet of fine flake supplemented with small live or frozen invertebrate prey. A planted tank with gentle filtration and a secure lid (small characids can jump) would suit a group of six or more.
Conservation
Knodus ytuanama has not been assessed by the IUCN Red List. As a species described in 2023, it postdates any existing assessment cycle and has not yet been evaluated for conservation status. The designation is accordingly Not Evaluated (NE).
The conservation outlook for recently described small Amazonian stream fishes like K. ytuanama is often uncertain: the species may be locally common within a restricted drainage but face habitat pressures from deforestation, agricultural runoff, and river modification. Monitoring of the type locality population and clarification of the species' range would be prerequisite to any future IUCN assessment. Until more distributional and population data are available, no conservation recommendations can be made beyond the general imperative to protect intact Amazonian stream habitats.