Taxonomy & naming
Lepidocharax diamantina was formally described by Flávio C.T. Lima, Naércio A. Menezes and Irani Quagio-Grassiotto in 2011, in a paper published in Neotropical Ichthyology (volume 9, number 2). The holotype is MNRJ 37509, a 1.5 in SL male collected from the rio Santo Antônio, a tributary of the rio Paraguaçu, near the town of Palmeiras in Bahia State, Brazil, at approximately 12°31'S 41°34'W. Additional paratypes came from the rio Pratinha near Iraquara, in the same drainage basin.
The genus Lepidocharax is placed within the diverse and still-debated family Characidae. Because the genus was erected alongside the species description, no prior genus-level history existed at the time of description. Eschmeyer's Catalog of Fishes recognises the valid name as Lepidocharax diamantina Ferreira, Menezes & Quagio-Grassiotto, 2011. No synonyms have been published. The species is diagnosed by a set of meristic and morphometric characters that distinguish it from all other small characids: head depth 16.7–18.8% of standard length; eight longitudinal scale rows between the lateral line and the pelvic-fin origin; 47–56 lateral-line scales; and 19–22 branched anal-fin rays.
The specific epithet diamantina refers to the Chapada Diamantina, the highland plateau and national park in central Bahia from which the species was collected. The name means "of diamonds" in Portuguese, a reference to the region's historic diamond-mining heritage.
Morphology
Lepidocharax diamantina is a small, slender characid with a maximum recorded standard length of 1.5 in. Like many diminutive stream characids it is laterally compressed with a roughly fusiform body, a relatively deep head (16.7–18.8% SL), and the large eyes characteristic of small tetra-grade fishes adapted to clear, dimly lit waters.
Meristic features are diagnostic: 47–56 scales along the lateral line and 19–22 branched anal-fin rays. Males at sexual maturity develop prominent hooks on the rays of the anal fin and pelvic fins, a secondary sexual character observed in various lineages of South American characids and linked to copulatory behaviour. Males also have proportionally longer pectoral and pelvic fins than females — a further secondary dimorphism. Coloration in preserved specimens shows the standard small-characid pattern of a silvery body with a faint lateral band; live coloration in the wild has not been described in detail in the available literature.
Habitat
The species is known exclusively from the rio Paraguaçu basin in Bahia State, northeastern Brazil, specifically from the upper reaches draining the Chapada Diamantina plateau. Collections were made in the rio Santo Antônio near Palmeiras and in the rio Pratinha near Iraquara — clear, fast-running highland tributaries flowing through the sandstone and quartzite formations of the Chapada Diamantina. These streams are oligotrophic, with low conductivity, soft to moderately hard water, and high clarity typical of highland Brazilian drainages.
FishBase categorises the species as freshwater and benthopelagic, consistent with the notion that it occupies mid-water and near-bottom zones of shallow upland streams. The Chapada Diamantina streams are generally well-oxygenated, seasonally variable in flow, and support a distinctive endemic fish fauna isolated by the plateau's topography. No detailed microhabitat or physical-chemical parameters have been published for the type-locality collections specifically.
Feeding
FishBase assigns Lepidocharax diamantina a trophic level of 3.0, placing it in the broad omnivore category typical of small stream characids. At this trophic level the natural diet is likely to comprise small invertebrates — aquatic insect larvae, microcrustaceans, and similar benthic or drifting prey — alongside algal filaments or organic detritus where available.
No dedicated gut-content study of this species has been published. Given its small size and the oligotrophic nature of its highland stream habitat, it almost certainly exploits whatever invertebrate prey the system offers, supplemented opportunistically by plant material or biofilm. In the aquarium, analogous small Neotropical stream characids accept fine-grade dried foods, small frozen invertebrates such as Artemia nauplii and Cyclops, and micro-pellets.
Mating
Lepidocharax diamantina has an unusual reproductive biology for its size and superficial appearance. The original description documents internal fertilisation: packs of spermatozoa were recovered from female ovaries, and the spermatozoa themselves show a specialised ultrastructure interpreted as an adaptation to internal sperm transfer. Males possess pronounced hooks on the anal- and pelvic-fin rays, structures found in multiple characid lineages and generally associated with grasping females during copulation or with stabilising sperm placement.
The courtship and spawning behaviour in the wild are not described in the literature. Based on the internal-fertilisation evidence, it is assumed that males use the fin hooks to maintain close physical contact with females during sperm transfer, analogous to documented hook-bearing characids in other genera. Whether females retain sperm or embryos internally for any period, or whether fertilised eggs are immediately shed, is not established in available sources.
Breeding
The combination of internal fertilisation and specialised spermatozoa ultrastructure distinguishes Lepidocharax diamantina from most small egg-scattering tetras kept in the hobby. Whether the species deposits fertilised adhesive eggs in vegetation in the manner of typical tetras, or employs a more derived strategy, has not been documented from either wild or captive observations in the published record.
The species is essentially unknown in the ornamental trade and captive-breeding data are absent from the available sources. If it were ever maintained in captivity, its small size and highland stream origin would suggest cool, well-oxygenated, soft-to-moderately-hard water as a starting point, with fine-leaved plants or spawning substrates to receive any eggs that are shed. The absence of parental care is inferred from its characid affinity, but has not been confirmed experimentally.
In the aquarium
Lepidocharax diamantina is essentially absent from the ornamental fish trade and is not maintained in public or private collections to any documented degree. Its restricted range, Endangered conservation status, and the logistical difficulty of collecting from the Chapada Diamantina make it a species of scientific rather than practical aquarium interest at present.
Should captive specimens ever become available through legitimate scientific channels, the species' small size (under 1.5 in), highland stream origin, and apparent preference for clear, well-oxygenated water would suggest a species best suited to a cool, mature, low-flow setup with subdued lighting and soft-to-moderately-hard water. Its internal fertilisation and specialised sperm biology make it of particular interest to researchers studying reproductive evolution in Characidae, quite apart from any aquarium appeal.
Conservation
Lepidocharax diamantina is assessed as Endangered (EN) on the IUCN Red List, with the assessment reflecting the species' extremely restricted range within the rio Paraguaçu basin and the ongoing threats to its highland stream habitat. The IUCN criterion B1ab(iii,iv) applies: the species has a limited extent of occurrence combined with declining habitat quality and number of locations. The 2018 assessment was also recognised by the Brazilian Ministry of Environment (MMA) in the same year.
The primary threats are habitat degradation in the Chapada Diamantina region — including agricultural conversion, altered hydrology, and erosion affecting stream clarity and substrate quality — and the inherently high vulnerability of any species with a naturally restricted range. The Chapada Diamantina National Park provides some protection to parts of the watershed, but areas outside the park boundary, including some collection localities, are under pressure. No ex-situ conservation programme is known for this species. Its continued survival depends on the integrity of the upland stream systems of central Bahia.