Taxonomy & naming
Characidium wangyapoik was described in 2021 by Jonathan Armbruster, Nathan Lujan and David Bloom in Ichthyology & Herpetology, as part of a wider revision of Guiana Shield darters that also redescribed the related Characidium crandellii. It belongs to the family Crenuchidae — the South American darters and their allies — within the order Characiformes, and to the large genus Characidium, which the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises as holding roughly 60-plus valid species distributed across South and Central America.
The species epithet wangyapoik is drawn from the Patamona language of the indigenous people of the Guiana Shield region: wang ("honey") and yapoik ("seated"), a reference to the fish's yellowish-honey colouration and its characteristic habit of resting propped on the substrate rather than swimming freely. The holotype measures 3 in SL, with type series specimens ranging 0.5–3 in SL, collected from the first shoal upriver of the confluence with Sukwabi Creek on the Ireng River, Guyana (5.07711°N, 59.97423°W).
Morphology
Characidium wangyapoik shows the typical crenuchid-darter build: an elongate, slender, sub-cylindrical body rather than the laterally compressed shape of open-water tetras, a flattened underside and low-set paired fins adapted for perching and pushing off the substrate. The type series reaches up to 3 in SL (about 3 in), with most individuals in collected samples considerably smaller, in the 0.5–2 in SL range — a genuinely small, nano-scale fish for most of its life.
The original description notes the honey-yellow ground colouration reflected in the species name, consistent with the muted, cryptic patterning typical of Characidium — mottled or barred flanks that blend against sand, gravel and leaf litter rather than the flash colouration of shoaling tetras. As with most darters, the reduced or modified swim bladder that limits sustained mid-water swimming and favours short, darting bursts followed by resting on the fins is inferred from the genus rather than specifically described for this species.
Habitat
The species is known only from the upper Ireng River and its tributary the Sukwabi River, on the Guiana Shield along the Guyana–Brazil border, within the Branco River basin of the Amazon drainage. Records span the stretch of the upper Ireng below Orinduik Falls up to falls on both the Ireng and Sukwabi, a rapids-and-shoal habitat typical of Guiana Shield headwaters — clear, well-oxygenated, moderately to fast-flowing water over rock and gravel substrate rather than slow floodplain water.
No specific water-chemistry measurements were recorded in the type description. Given the genus's well-documented preference for fast-flowing, well-oxygenated water in similar Guiana Shield and greater Amazonian habitats, C. wangyapoik very likely occupies comparably clear, moderately soft, circumneutral-to-slightly-acidic water, but that inference should not be read as a measured fact for this specific species — data here is genuinely sparse.
Feeding
No diet study has been published specifically for Characidium wangyapoik. Across the genus, Characidium are documented micro-predators that pick tiny aquatic insect larvae, microcrustaceans and other invertebrates from the substrate and drifting current, rather than grazing algae or taking large prey; several are noted to largely ignore dry flake food in aquaria.
In the absence of species-specific data, keepers should plan around that genus-wide pattern: small live or frozen foods sized to a fish that tops out around 3 in — bloodworm, mosquito larvae, brine shrimp, daphnia and cyclops — rather than relying on prepared flake or pellet as a primary diet.
Mating
Courtship and pairing behaviour have not been documented for Characidium wangyapoik. No sexual dimorphism was reported in the type description, and the species is too recently described and too poorly known in the hobby for external sex differences to have been established with confidence.
For the wider genus, and for its crenuchid relatives such as Crenuchus and Poecilocharax, courtship is typically a quiet, substrate-oriented affair rather than an open-water chase — but attributing that specifically to C. wangyapoik would be guesswork beyond what the source material supports.
Breeding
There is no published or hobby record of Characidium wangyapoik being bred in captivity. Characidium as a genus are generally understood as egg-scatterers that release eggs over fine substrate or among plants in soft, acidic water, without the nest-building or brief male-guarding behaviour documented in some of their crenuchid cousins (Crenuchus spilurus and Poecilocharax species are cave- or leaf-spawners with brief paternal care); Characidium themselves are not reported to guard their eggs.
Given the complete absence of species-specific breeding data, this account does not assign a confirmed breeding mode for C. wangyapoik beyond noting the genus-typical pattern — any aquarium spawning would be a genuinely notable, unrecorded first, and a keeper attempting it should treat the tank as an experiment rather than follow an established protocol.
In the aquarium
Characidium wangyapoik is not established in the aquarium hobby — it was described from scientific collections in 2021 and there is no evidence of it being traded or kept. Anyone encountering it, whether through a specialist importer or a Guiana Shield biotope project, should treat it as a nano/small-species proposition: adults reach only about 3 in SL, and the genus as a whole does well in modest, well-filtered tanks with fine gravel or sand, current, and strong oxygenation to mimic its rapids-and-shoal home water.
As with most Characidium, expect a bottom-oriented, perching fish rather than a mid-water shoaler, and expect it to largely ignore flake in favour of small live and frozen foods. Given how narrow its known range is — a single headwater stretch on the Guyana–Brazil border — any wild-collected specimens should be treated as coming from an extremely localised, potentially vulnerable population, and this species is not a candidate for casual or high-volume collection.
Conservation
Characidium wangyapoik has not been evaluated by the IUCN Red List; its conservation status is Not Evaluated. This is unsurprising for a species described only in 2021 from a remote Guiana Shield headwater system, and the absence of an assessment should not be read as evidence of either safety or risk.
The species' entire known range — the upper Ireng River and Sukwabi Creek, below Orinduik Falls — is narrow and specific, which is typical of many Guiana Shield endemics and is itself a reason for caution: single-river or single-headwater ranges are inherently more exposed to localised pressures such as mining, damming or water-quality change than widespread species, even though no specific threat has been documented for this fish to date.