Taxonomy & naming
Psalidodon pessalii was described by Teixeira, Salvador, Mirande and Lima in 2025, based on material collected from headwater tributaries of the Rio Paraopeba in the Rio São Francisco basin, Minas Gerais, Brazil. The holotype measures 1.63 in standard length. Eschmeyer's Catalog of Fishes is the governing authority for the valid name; the parenthetical authority reflects the original description's authorship.
Phylogenetic work surrounding this species placed it as a sister group to Psalidodon crenuchoides, and it has been noted in taxonomic discussions as sitting near the boundary between Astyanax sensu lato and the redefined Psalidodon concept that has emerged from 2024–2025 characid revisions. The Catalog of Fishes currently registers the species under Astyanax, and that placement is followed here.
The specific epithet pessalii honours Brazilian ichthyologist Tiago Casarim Pessali, recognising his contributions to the study of Neotropical fishes.
This fish was long listed as Astyanax pessalii; Eschmeyer's Catalog of Fishes places the species in Psalidodon, and the current combination Psalidodon pessalii is followed here.
Morphology
Psalidodon pessalii is a small characid with males reaching 1.49–1.85 in standard length and females measured at 0.92–1 in SL in the type series — a notable size difference between the sexes, with males substantially larger than females. The holotype is 1.63 in SL.
Diagnostic features noted in the original description include the absence of an adipose fin, an interrupted lateral line, and a scaleless caudal fin — characters that distinguish it from many congeners within the broad Astyanax complex. Beyond these meristic traits, the species' overall appearance is that of a slender, silver-bodied headwater tetra, consistent with the small characids that populate shallow, fast-flowing or marshy upland streams throughout the São Francisco system.
Habitat
The type locality is Córrego Vila Rica, a small stream in the Rio Paraopeba headwaters, Minas Gerais, Brazil, within the upper Rio São Francisco basin. This stream represents a marshland headwater environment — shallow, vegetated, and subject to seasonal fluctuations typical of the cerrado-influenced uplands of central Brazil. At the time of collection, water parameters recorded at the type locality included a temperature of 73 °F, conductivity of 76 µS/cm, pH of 6.82, and dissolved oxygen of 5.84 mg/l — soft, mildly acidic, and moderately oxygenated conditions characteristic of highland Brazilian streams.
The species was found syntopically with Gymnotus cf. sylvius and Callichthys callichthys, indicating a community of small, benthic-adapted fishes sharing the marshy microhabitat. The Córrego Vila Rica type locality is reported as degraded and possibly no longer supporting the species; whether P. pessalii persists in adjacent streams of the same drainage remains uncertain.
Feeding
No specific dietary data for Psalidodon pessalii have been published. By analogy with ecologically similar small Astyanax in headwater cerrado streams, the species is likely an opportunistic omnivore feeding on small invertebrates, insect larvae, microcrustaceans, and plant or detrital material available in the marshy headwater environment it inhabits.
In an aquarium setting, small characids from comparable habitats generally accept fine-grade prepared foods alongside live and frozen invertebrates. Given the sparse data, assertions beyond these inferences would be speculative.
Mating
No published observations on mating behaviour in Psalidodon pessalii are available. Small headwater Astyanax are typically egg-scattering open spawners: males court females and pairs scatter adhesive or semi-adhesive eggs among fine-leaved aquatic plants or over substrate, with no subsequent parental care.
The pronounced sexual size dimorphism documented in the type series — males 1.49–1.85 in SL versus females 0.92–1 in SL — is notable for such a small characid and may reflect selection for male competitive ability or mate-searching in a spatially restricted marshy habitat. Whether display behaviours or territory-holding accompany spawning is undocumented.
Breeding
No captive breeding records for Psalidodon pessalii are known. The general breeding mode of small headwater Astyanax involves the scattering of small, adhesive eggs among fine-leaved plants or in shallow, vegetated microhabitats, with hatching occurring within a few days at typical tropical temperatures and no parental guarding of eggs or fry.
Given the species' precarious status in the wild and the absence of any documented captive population, breeding in aquaria has not been reported. Conservation-minded breeding programs, if the species were ever brought into managed care, would follow protocols used for similar small Neotropical characids: soft, slightly acidic water matching type-locality parameters (pH ~6.8, 73 °F), fine-leaved plants or mops, and prompt removal of adults after spawning.
In the aquarium
Psalidodon pessalii is not established in the aquarium hobby. The species was described in 2025 from a degraded type locality that may no longer support a viable population, and no trade or captive specimens have been documented. It is not available in the ornamental fish trade.
For the purposes of understanding its potential husbandry requirements, the type-locality water parameters — 73 °F, pH 6.82, conductivity 76 µS/cm — suggest a preference for cool, soft, mildly acidic conditions, consistent with high-altitude São Francisco tributaries. A densely planted aquarium with gentle flow and a biotope community of co-occurring small characids and callichthyid catfishes would replicate its natural setting. In practice, the species is known only from scientific collections.
Conservation
Psalidodon pessalii has not been formally assessed by the IUCN Red List; as a species described in 2025, it falls outside the current assessment cycle and carries no official Red List category. The authors of the original description report that the Córrego Vila Rica type locality is degraded and that the species may already be extinct there, with uncertain survival in adjacent tributaries of the Rio Paraopeba system.
The broader Rio Paraopeba basin has experienced significant habitat degradation from agriculture, urban expansion, and the 2019 Brumadinho dam collapse, which released mine tailings into the river system and caused widespread ecological damage. Whether P. pessalii survives anywhere in this basin is unknown. Its narrow endemism to headwater marshy streams in an already-pressured drainage places it among the numerous undescribed or newly described Brazilian characids that face extinction before any conservation response can be mounted. Formal survey work to confirm or refute its persistence, and inclusion in a future IUCN assessment, are urgent priorities.