Taxonomy & naming
Klausewitzia ritae was described by the French ichthyologist Jacques Géry in 1965 and remains, per the Catalog of Fishes and GBIF taxonomic backbone, the only valid species placed in the genus Klausewitzia — a monospecific genus within the family Crenuchidae, the South American darter characins, in the order Characiformes. GBIF and ITIS both confirm the name and placement as current and undisputed; there is no indication in the available sources of a recent revision or split affecting this species.
Crenuchidae itself sits close to the sailfin characins Crenuchus and Poecilocharax (subfamily Crenuchinae) and the larger group of stream-bed Characidium darters (subfamily Characidiinae), and the family as a whole is informally known among hobbyists and ichthyologists as the "darters" for their characteristic perch-and-dart behaviour rather than continuous swimming. Klausewitzia ritae is a genuinely obscure species outside specialist and academic circles — most of what little is documented about its biology draws on comparisons with better-studied relatives in the same family.
Morphology
Klausewitzia ritae is diminutive even by characin standards: FishBase records a maximum standard length of just 1 in for males and unsexed individuals, placing it firmly in nano-fish territory alongside other small crenuchid darters. Detailed morphological description is sparse in the available sources, but its family placement and small size are consistent with the slim-bodied, elongate build typical of stream-bed and leaf-litter darters in Crenuchidae, built for hovering and short, precise bursts of movement rather than sustained cruising.
Data on this species' specific colouration, fin shape and any sexual dichromatism is sparse in the cache available for this account; readers should treat any photographs or trade descriptions with caution given how rarely the species is documented or offered.
Habitat
The species is known from the upper Amazon basin, specifically documented from the Brazil–Peru frontier region, where FishBase describes it as an inhabitant of blackwater river systems. Within that setting it occupies a freshwater, pelagic-to-benthic niche typical of small darter characins — holding station near submerged wood, leaf litter or fine vegetation and making short darting movements rather than swimming continuously in open water.
FishBase gives a water chemistry envelope of roughly 73–82 °F, pH 5.0–6.0 and a hardness of 1–8 dH, consistent with the soft, acidic blackwater conditions typical of much of the upper Amazon. This is genuinely soft, acidic water — not merely a generic "Amazon" assumption — and any aquarium attempt at this species should aim to replicate it closely.
Feeding
No species-specific diet study for Klausewitzia ritae was found in the available sources, but its family placement strongly indicates it is a micro-predator in the same mould as the well-studied sailfin characin Crenuchus spilurus, whose stomach contents are dominated by small aquatic invertebrates — mayfly (Ephemeroptera) larvae, copepods and ostracods — rather than plant matter or detritus. Fish of this size and lifestyle typically take prey small enough to fit their correspondingly tiny mouths.
In the aquarium, related crenuchid darters accept small live and frozen foods readily — Artemia nauplii, Daphnia, Moina and grindal worms — but frequently refuse dry flake, at least initially, and may only take prepared foods once well settled. Any keeper attempting Klausewitzia ritae should plan on live or frozen micro-foods as the dietary mainstay rather than assuming flake will be accepted.
Mating
No courtship description specific to Klausewitzia ritae exists in the available sources. However, its closest well-studied relatives in Crenuchinae, the genus Crenuchus (and the related Poecilocharax), show size-assortative pairing and mutual courtship signalling between a territorial male and a receptive female ahead of spawning, along with a degree of sexual dichromatism that helps pairs recognise one another. Whether Klausewitzia follows the same pattern is not documented, and this account does not assume it does.
Given the near-total absence of published biology on this species' reproductive behaviour, prospective breeders should treat any pairing and spawning cues as inferred from relatives rather than confirmed for Klausewitzia ritae itself.
Breeding
There is no direct documentation of Klausewitzia ritae being bred in the aquarium, and this account does not claim otherwise. Its subfamily relatives Crenuchus and Poecilocharax, however, are cave- and leaf-spawners with pronounced brief male parental care: the male tends and guards a modest clutch (documented at roughly 100 eggs in Crenuchus spilurus) at the spawning site for an extended period — around eight days of active care has been recorded — fanning and defending the eggs and newly hatched fry, during which time he feeds little or not at all.
If Klausewitzia ritae follows the same crenuchid pattern — which is plausible given its family placement but not confirmed by any source reviewed here — a would-be breeder should expect a cave-or-leaf-oriented spawning site, male-only guarding of a small clutch, and free-swimming fry that need infusoria-scale foods before graduating to newly hatched brine shrimp and microworm, as documented for its relatives. This should be read as an informed inference from the genus's relatives, not an established breeding record for this species.
In the aquarium
Klausewitzia ritae is essentially unrecorded in the mainstream aquarium trade, and this account makes no claim that established husbandry protocols exist for it. Anyone who does encounter it — most likely as an incidental catch in a mixed blackwater import from the upper Amazon rather than a targeted offering — should treat it as an advanced, nano-scale proposition: a small, densely planted or leaf-litter-furnished tank with soft, acidic water (roughly pH 5.0–6.0, 73–82 °F) mirroring its native blackwater habitat, gentle flow, dim lighting and no boisterous or larger tankmates that could outcompete it for the tiny live foods it likely needs.
Given its 1 in adult size, it should never be housed with anything that could see it as a snack, and given how little is documented about its captive requirements, keepers attempting it should be prepared to observe closely and adjust rather than follow a proven recipe. It is not aggressive, not a shoaling schooler in the way many other characins are, and not remotely related in temperament or care needs to piranhas or pacus despite sharing the broader characin lineage.
Conservation
The IUCN Red List assesses Klausewitzia ritae as Least Concern, an assessment dated 29 May 2020 according to FishBase. This reflects the absence of documented major threats to the species across its known upper Amazon range on the Brazil–Peru frontier, though as a poorly studied, monospecific genus restricted to a specific blackwater river system, its population trend and finer-scale distribution are not well characterised in the sources available for this account.
Because the species is not meaningfully present in the aquarium trade, collection pressure for the ornamental market is not a relevant conservation factor here; the more general, unquantified pressures facing upper Amazon blackwater systems — regional deforestation and water-quality change — would be the plausible long-term watch items, though no source reviewed for this account documents specific pressure on this species.