Taxonomy & naming
Characidium amaila was formally described in 2013 by Nathan Lujan, Donaldo Agudelo-Zamora, Donald Taphorn, Devya Booth and Hernán López-Fernández, part of a wave of new Characidium descriptions from Guiana Shield rivers published in the early 2010s as ichthyologists surveyed previously under-collected drainages. It belongs to the family Crenuchidae — the South American darters, which also includes the sailfin characins Crenuchus and Poecilocharax — within the order Characiformes, and to the genus Characidium, one of the largest genera in the family with dozens of small, cryptically patterned, benthic species distributed across the Neotropics.
The species epithet amaila refers to Amaila Falls, a striking multi-tiered escarpment on the Kuribrong River that has long been a proposed site for hydroelectric development; the describers named the fish for its type locality specifically because that locality was already under threat. Characidium is distinguished from its close relatives within Crenuchidae by details of squamation, dentition and fin-ray structure rather than by anything visible at a glance, and species-level identification within the genus typically requires close examination of scale counts and tooth counts rather than colour pattern alone.
Morphology
Characidium amaila is a small, slender, cylindrical fish, with FishBase recording a maximum standard length of 3.5 in — modest even by the standards of a genus made up entirely of small species. Diagnostic features noted in the original description include the absence of scales on the isthmus and chest, 8 to 13 premaxillary teeth, a thickened first four rays of the pectoral fin, 34 to 36 lateral-line scales, and branchiostegal membranes that remain free from one another across the isthmus rather than being fused.
Like other Characidium, the body plan is built for perching and darting rather than sustained swimming: a fairly flat ventral profile, pectoral and pelvic fins braced against the substrate to hold position in current, and a body pattern of dark blotches or a broken lateral stripe over a pale background that breaks up its outline against sand and rock. Fine morphological detail of this kind is what separates C. amaila from its many congeners rather than any single obvious external field mark.
Habitat
The species is known only from the upper Kuribrong River, a tributary within the Potaro-Essequibo drainage of Guyana, specifically from the stretch upstream of Amaila Falls. FishBase describes its habitat as shallow sandstone bedrock rapids with attached macrophytes — fast, clear, well-oxygenated water flowing over exposed rock rather than the still, leaf-littered blackwater more often associated with other Guiana Shield fish.
As a benthopelagic species it spends most of its time close to the substrate, using rock and attached vegetation as both anchor points against the current and cover from predators. This is a genuinely narrow-range endemic — the entire known population is confined to a short reach of one river above one waterfall — which is the central fact behind its conservation status.
Feeding
Detailed diet data specific to Characidium amaila has not been published, but the genus as a whole is well characterised: darter characins are micro-predators that feed mainly on aquatic insects and their larvae, particularly chironomid (midge) and other fly larvae, picked from the substrate and current rather than taken from open water. Wild Characidium generally ignore anything resembling flake food and take live or drifting invertebrate prey almost exclusively.
Where related species have been kept, they accept frozen bloodworm, brine shrimp, Daphnia and Cyclops readily once settled, which is consistent with a genus built around small, meaty invertebrate prey rather than plant matter or detritus. There is no published feeding data specific to C. amaila beyond this genus-level pattern.
Mating
No courtship or spawning behaviour has been documented for Characidium amaila itself. In the related and better-studied C. fasciatum, hobby and aquaculture accounts describe males chasing females into vegetation, with spawning following within days of pairing — a pattern of substrate-associated courtship rather than the cave- or leaf-guarding behaviour seen in the genus's sailfin relatives Crenuchus and Poecilocharax.
Without direct observation of C. amaila, and given how narrow its known range is, it would be speculative to describe its courtship in more detail; the safest statement is that its congeners generally scatter eggs over the substrate following a brief chase-and-pair sequence, and there is no reason from morphology to expect otherwise in this species.
Breeding
Characidium species as a group are substrate egg-scatterers: a pair spawns over sand, rock or fine vegetation with no nest construction and no sustained parental care, in contrast to their crenuchid relatives Crenuchus and Poecilocharax, which are cave- or leaf-spawners with brief male guarding of the clutch. There is no published record of Characidium amaila being bred in captivity, and no aquarium population is known to exist.
Given that the species has never been established in the hobby, and that its entire wild range sits above a single waterfall in a river slated for hydroelectric development, any future ex-situ breeding effort would matter primarily as a conservation safeguard rather than as an aquarium trade proposition.
In the aquarium
Characidium amaila is not a hobby fish. There is no evidence of it being collected or traded, and this account exists to document a threatened, single-river endemic rather than to encourage its acquisition. Prospective keepers interested in darter characins as a group should look to more established Characidium species or to the genus's sailfin relatives, Crenuchus spilurus and Poecilocharax species, which are occasionally available and are shy, gentle blackwater nano-fish best suited to a quiet species or community tank with soft, acidic water, fine leaf litter and other calm tankmates.
If C. amaila were ever to appear in the trade, its known habitat — shallow, fast, well-oxygenated water flowing over rock — points to a well-filtered, current-rich, cooler-running setup rather than the sluggish, densely planted blackwater tank suited to its sailfin relatives; but this is inference from habitat data, not a tested aquarium protocol.
Conservation
Characidium amaila is assessed by the IUCN Red List as Endangered (EN), as of a November 2023 assessment, under criteria B1ab(iii)+2ab(iii) — reflecting a very small extent of occurrence and area of occupancy, and a projected or ongoing decline in the quality of its habitat. The core threat is the long-proposed Amaila Falls Hydropower Project, which would alter or inundate the stretch of the upper Kuribrong River that constitutes the species' entire known range.
Because the species is endemic to Guyana and known from nowhere else, any significant change to this single river reach — whether through dam construction, altered flow regimes, or downstream sedimentation — represents a direct threat to its survival, with no other population to buffer the loss. It is a clear case of a narrow-range Guiana Shield endemic whose conservation outlook is tied entirely to the fate of one specific piece of infrastructure.