Taxonomy & naming
Hisonotus pachysarkos was described by Zawadzki, Roxo and da Graça in 2016, in Ichthyological Exploration of Freshwaters (volume 26, pages 373–383), in a paper presenting a new species of cascudinho from the rio Ivaí basin. The Catalog of Fishes (Eschmeyer, CAS) recognises the name as valid.
The species is placed in the genus Hisonotus within the family Loricariidae. The original description assigned it to the subfamily 'Otothyrinae', a grouping whose limits have shifted with successive phylogenetic revisions; FishBase currently places the species in the subfamily Hypoptopomatinae, the classification followed here. Hisonotus belongs to the small suckermouth catfishes that Brazilian aquarists call 'cascudinhos'.
Morphology
Hisonotus pachysarkos is a small loricariid armoured in the overlapping bony plates typical of the family. A maximum size has not been published on FishBase, so its full adult dimensions cannot be stated with confidence.
The specific epithet pachysarkos is Greek for 'thick-fleshed', alluding to the robust body form noted in the original description. Detailed coloration and any sexual dimorphism are documented in the original description but are not summarised in the sources consulted here, and are not restated to avoid error.
Habitat
Hisonotus pachysarkos occurs in Brazil in the rio Ivaí basin, part of the upper rio Paraná system. It is a freshwater, benthopelagic species of tropical climate.
The genus is associated with rivers carrying marginal or submerged vegetation, where these small catfishes graze on submerged surfaces. Hisonotus, like many Hypoptopomatinae, is a facultative air-breather, an adaptation that helps such fishes tolerate the lower-oxygen conditions that can develop in vegetated and seasonally variable waters.
Feeding
As a member of Hisonotus, H. pachysarkos is a small grazing catfish that rasps biofilm and aufwuchs — algae, micro-organisms and fine detritus coating plants, wood and stones. No gut-content study specific to this species is available in the sources consulted; the feeding profile is inferred from its anatomy and from the well-documented ecology of related cascudinhos rather than from direct observation.
Mating
No data on the courtship or mating behaviour of Hisonotus pachysarkos has been published in the sources consulted. Reproductive behaviour for the species is undocumented.
Breeding
No reproductive data — spawning mode, clutch size, egg deposition or parental care — has been published for Hisonotus pachysarkos. Small Hypoptopomatinae commonly attach adhesive eggs to vegetation or hard surfaces, but no breeding account specific to this species exists in the sources consulted, and the details should not be assumed.
In the aquarium
Hisonotus pachysarkos has no established presence in the ornamental trade and no published aquarium husbandry account. Related cascudinhos generally need clean, well-oxygenated water, gentle to moderate flow, and abundant biofilm and algae to graze, but no species-specific care data is available, so no parameters or recommendations can be responsibly stated for this fish.
Conservation
Hisonotus pachysarkos was assessed by the IUCN Red List as Least Concern, with the assessment dated 30 November 2020 (per FishBase IUCN Red List status, version 2025-2). The Least Concern listing reflects no evidence of significant threat at the time of assessment.
The upper rio Paraná system, including the rio Ivaí, is subject to pressures from dams, agriculture and habitat alteration, but the species is not currently considered at risk.