Taxonomy & naming
Xenurobrycon coracoralinae was described by Cristiano R. Moreira in 2005 in the Proceedings of the Biological Society of Washington (volume 118, issue 4, pages 855–862). The type locality is the rio Araguaia basin in central Brazil. Eschmeyer's Catalog of Fishes lists the valid name as Xenurobrycon coracoralinae Moreira, 2005.
The genus Xenurobrycon belongs to the glandulocaudine assemblage within Characidae, a grouping of small South American characids characterised by the presence of caudal glands in males and, in some genera, hooks on the anal-fin rays of mature males. Depending on the classification followed, glandulocaudines have been treated as a subfamily within Characidae or placed in the family Stevardiidae; Catalog of Fishes retains a broad Characidae, which is followed here.
X. coracoralinae was diagnosed as a new species on a combination of characters including anal-fin hook arrangement and meristics; the species name honours Cora Coralina, the pen name of Ana Lins do Guimarães Peixoto (1889–1985), a widely admired Brazilian poet and storyteller who lived beside the rio Vermelho, a tributary of the rio Araguaia system where the fish was collected.
Morphology
Xenurobrycon coracoralinae is a tiny fish, with a maximum recorded standard length of 0.5 in in males — making it one of the smallest members of its genus and among the smaller known characids. The body form is slender and slightly compressed, typical of glandulocaudines.
A key diagnostic character is the anal fin of mature males: hooks are restricted to the last unbranched ray and the first four to five branched rays, a pattern that differs from other Xenurobrycon species and aids identification. Like most glandulocaudines, the species lacks an adipose fin — an unusual absence among characids — and possesses seven pelvic-fin rays rather than the more common six. Teeth are conical. Coloration details from the original description are not widely documented in accessible sources; the species likely shows the subtle silvery to yellowish hues common to small glandulocaudines, with males potentially more intensely marked than females.
Habitat
The species is known from the rio Araguaia basin in the state of Goiás, central Brazil. The Araguaia is a major river of the Brazilian interior, draining the Cerrado and transitional forest zones of central Brazil before joining the Tocantins; the rio Vermelho, the specific locality associated with Cora Coralina and the type series, is a tributary within this system.
The glandulocaudine fauna of the upper Araguaia basin is diverse; small characids in this system typically inhabit shallow, clear-to-slightly turbid streams and marginal areas of the river with abundant aquatic vegetation and leaf litter. No species-specific water-chemistry data for X. coracoralinae have been published in accessible sources, but Cerrado streams are generally warm, with temperatures in the tropical range and chemistry varying from soft and slightly acidic to near-neutral depending on local geology.
Feeding
No detailed dietary study of Xenurobrycon coracoralinae has been published. By analogy with other glandulocaudines and small characids of similar size and habitat, the species is presumed to be a micro-predator feeding on small invertebrates — aquatic insect larvae, microcrustaceans, and other zooplankton — supplemented opportunistically by organic matter and algae.
At 0.5 in standard length, the fish's gape constrains it to very small food items. In captivity, if ever kept, it would require appropriately sized live or frozen foods such as freshly hatched brine shrimp nauplii, micro-worms, or paramecia, along with finely ground prepared foods.
Mating
Glandulocaudines as a group are notable for their use of chemical signals in courtship: males possess specialised skin glands — usually at the base of the caudal fin — that secrete pheromones, and females can distinguish between males partly on this basis. The anal-fin hooks on males of X. coracoralinae, as in other hook-bearing glandulocaudines, are thought to function in holding the female during spawning rather than in combat.
No direct observations of courtship behaviour in X. coracoralinae are documented in accessible literature. The species is presumed to be an egg-scattering, open spawner without parental care, consistent with the glandulocaudine pattern. Spawning likely takes place among fine-leaved vegetation or substrates, with adhesive eggs deposited in small numbers.
Breeding
Xenurobrycon coracoralinae has not been documented in captive breeding, and no hobbyist accounts of successful spawning are available. The reproductive biology is inferred from the glandulocaudine pattern: egg-scattering with no parental investment, adhesive eggs deposited among plants or fine substrates, and fry that are likely tiny and require very small first foods.
At its miniature adult size, the species would presumably produce a small clutch of relatively few eggs. The absence of an adipose fin and the presence of anal-fin hooks in males are fixed characters allowing sex determination in adult specimens, but female-to-male or seasonal variation in spawning condition has not been described for this species in available sources.
In the aquarium
Xenurobrycon coracoralinae is not established in the aquarium hobby and is not commercially available. It is known primarily from museum specimens and scientific collections. Any aquarist encountering the species would face the usual challenges of keeping micro-characids: a species-only or carefully chosen nano-aquarium, very small live or frozen foods, excellent water quality, and fine-leaved plants or spawning substrates.
Given its origin in the warm Cerrado streams of central Brazil, water temperature in the low-to-mid 20s Celsius and a neutral to slightly acidic pH would be a reasonable starting point in the absence of species-specific data. Its extremely small size means it would be vulnerable to predation by or competition with any fish of normal tetra dimensions; dedicated nano keeping would be essential.
Conservation
Xenurobrycon coracoralinae is assessed as Least Concern (LC) on the IUCN Red List, with an assessment date of 7 November 2018 per FishBase. The LC designation reflects a current absence of known major threats sufficient to qualify the species for a threatened category, though data on population size and trend for this small, localised species are limited.
The rio Araguaia basin faces broader pressures common to central Brazilian river systems, including agricultural expansion, deforestation of riparian zones, and sedimentation associated with land-use change in the Cerrado. Small, range-restricted species with limited distributional data are inherently vulnerable to these landscape-level changes even when formally assessed as Least Concern. Continued ichthyological survey work in the Araguaia drainage would clarify the species' distribution and abundance.