Taxonomy & naming
Psalidodon crenuchoides was described by Zarski and Géry in 1999 in the journal Spixiana (vol. 22, no. 1, pp. 91–96), based on material from streams in Goiás state, Brazil. The original description examined holotype and paratype specimens with standard lengths ranging from 1.1–2.52 in. The valid name under Eschmeyer's Catalog of Fishes is Psalidodon crenuchoides Zarski & Géry, 1999.
The species has appeared in the literature and some databases under the synonyms Hasemania crenuchoides and Psalidodon crenuchoides, reflecting the broader uncertainty about generic boundaries within the hyper-diverse Characidae. Regardless of the genus applied in any given classification, the species epithet crenuchoides is the stable identifier. Zarski and Géry chose the epithet for the fish's superficial resemblance to the creeks characins of the genus Crenuchus — the suffix -oides meaning 'resembling' in Latin-derived nomenclature.
Subsequent ichthyofaunal surveys, including work by Langeani and colleagues documenting the fish communities of the upper Paraná tributaries in the Distrito Federal, confirmed the species' presence and formally extended its known distribution into Minas Gerais and the Federal District, though the overall range remained very small.
This fish was long listed as Astyanax crenuchoides; Eschmeyer's Catalog of Fishes places the species in Psalidodon, and the current combination Psalidodon crenuchoides is followed here.
Morphology
Psalidodon crenuchoides is a slender, laterally compressed characin reaching approximately 2.6 in standard length (SL) at maximum recorded size, though most individuals in survey material are considerably smaller — the original description cites specimens from 1.1–2.52 in SL. The body plan is typical of small characids: a fusiform profile, moderately large eyes, a small mouth armed with the fine teeth characteristic of omnivorous Astyanax, a single dorsal fin positioned roughly at mid-body, and the adipose fin diagnostic of the family.
Colouration is modest compared with the showier characins popular in the aquarium trade. The flanks are silvery to pale yellowish with a diffuse horizontal lateral stripe, and no bold spot or vivid pigment band is reported in the original description or subsequent accounts. The species' resemblance to Crenuchus, as indicated by its epithet, lies more in overall body shape and the character of the lateral-line scales than in colour. Sexual dimorphism is not well described in the available literature; females are likely deeper-bodied when gravid, as is common across Astyanax.
Habitat
The species is known exclusively from the upper Paraná River basin in central Brazil, concentrated in the Distrito Federal and possibly adjacent areas of Goiás and Minas Gerais. Its IUCN assessment places its core population within the Reserva Biológica da Contagem, a protected biological reserve on the outskirts of Brasília, with an extent of occurrence of approximately 21 mi². This is an exceptionally small range for any vertebrate, and the fish is effectively an island species in a sea of agriculture and urban development.
The streams it inhabits drain the Brazilian Shield at elevations typical of the central plateau, carrying clear to slightly turbid water over rocky or sandy substrates. These are permanent streams within inland wetland and gallery-forest habitats. The IUCN categorises the habitat type as inland wetlands and permanent rivers and streams, consistent with the cerrado-edge gallery forests of the Distrito Federal, where small stream fish communities have been documented to be both endemic-rich and acutely vulnerable to land-use change.
Feeding
Detailed dietary studies on Psalidodon crenuchoides are not available in the published literature captured by current sources. FishBase assigns the species a trophic level of 3.0, consistent with omnivory at the invertebrate-consumer level — a feeding guild typical of small Astyanax throughout the Neotropics.
By analogy with ecologically similar small characids of the upper Paraná and cerrado streams, the natural diet likely includes small aquatic invertebrates (insect larvae, microcrustaceans), terrestrial arthropods falling onto the water surface, algae, and fine organic detritus. The cerrado stream environment provides seasonally variable food supply: dry-season low water concentrates food resources while the wet season flush delivers allochthonous inputs from riparian vegetation.
Mating
No specific breeding behaviour observations for Psalidodon crenuchoides have been published in the sources available. Like other small characids, the species almost certainly practises open egg-scattering without parental care, following the dominant reproductive mode across Astyanax.
In this pattern, sexually mature adults aggregate and broadcast adhesive or semi-adhesive eggs among fine-leaved aquatic vegetation, over submerged gravel, or into the water column, with no subsequent guarding or tending of the spawn. Male characids typically develop small hooks on the anal fin rays — present in many Astyanax — thought to facilitate close contact during spawning. Spawning in cerrado streams is likely triggered or amplified by the onset of the rainy season, as rising water levels, increased flow, and flooding of marginal vegetation are strong reproductive cues for many Neotropical stream fish.
Breeding
No captive-breeding records for Psalidodon crenuchoides are documented in the available literature, and the species is not held in the ornamental trade in any significant numbers. Captive propagation is likely achievable using methods developed for other small Astyanax: a well-conditioned pair or small group in a moderately sized aquarium with fine-leaved plants or spawning mops, a temperature in the upper-20s Celsius, and a trigger of cooler water change to simulate seasonal rainfall onset.
Eggs in open-spawning characids are typically scattered broadly and left by the parents, which should be removed promptly to prevent predation on the clutch. Incubation times of one to three days are typical for Astyanax at tropical temperatures, producing small fry that initially absorb the yolk sac before feeding on infusoria and then nauplii. Given the species' conservation status, any captive population would have conservation value, and formal ex situ breeding has been recommended as a backup to field protection of the Reserva Biológica da Contagem population.
In the aquarium
Psalidodon crenuchoides is not an established aquarium fish, and specimens are not available in the hobby trade. The restricted endemic population and Endangered status make wild collection inappropriate, and no captive breeding programme has placed it in circulation.
Should the fish become available through legitimate conservation breeding, its care requirements would resemble those of other small, lightly built Astyanax: a well-filtered, moderately flowing aquarium mimicking the clear cerrado streams of central Brazil, slightly acidic to neutral water reflecting the upper Paraná headwater chemistry, temperatures consistent with the central Brazilian plateau (approximately 72–79 °F), and a varied diet of small live or frozen invertebrates supplemented with quality dry foods. A planted aquarium with open swimming lanes and subdued lighting would suit a species from shaded gallery-forest streams. It is a fish of ichthyological and conservation interest rather than a mainstream hobby species.
Conservation
Psalidodon crenuchoides is assessed as Endangered (EN) under IUCN criteria B1ab(iii), based on an assessment dated 7 November 2018 and published in 2022. The criterion reflects a severely restricted extent of occurrence (approximately 21 mi²), presence at very few locations, and a continuing decline in the extent and quality of its habitat. The core population is confined to the Reserva Biológica da Contagem, a protected biological reserve on the periphery of Brasília in the Distrito Federal.
The threats are multiple and intensifying. Residential and commercial development driven by Brasília's expansion degrades and eliminates stream habitat at the edges of the reserve. Agricultural land use in adjacent areas contributes run-off, sediment, and agrichemicals. Two introduced fish species — the Nile tilapia relative Coptodon rendalli and a Xiphophorus swordtail or platyfish — have been recorded in or near the species' habitat and represent potential predation and competition pressure. Water pollution from the peri-urban environment compounds these stressors.
The existence of a formal protected area — the Reserva Biológica da Contagem — provides some buffer, but the biological reserve's boundaries are not a firewall against diffuse pollution, invasive fish spread through connected waterways, or the hydrological effects of surrounding urbanisation. Conservation priorities identified for the species include enforcing the biological reserve's protection status, controlling invasive fish, and investigating the feasibility of ex situ breeding as an insurance population.