Taxonomy & naming
Pseudotocinclus parahybae was described by Takako, Oliveira and Oyakawa in 2005. It belongs to the subfamily Hypoptopomatinae, the group of small suckermouth catfishes within Loricariidae that are distinct from the larger, more familiar bristlenose and common plecos. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
The genus Pseudotocinclus is a small assemblage of Brazilian hypoptopomatines. The specific epithet parahybae refers to the Rio Paraíba do Sul (historically rendered "Parahyba"), the coastal river basin to which the species is endemic.
Morphology
Pseudotocinclus parahybae is a small loricariid, reaching a maximum recorded length of about 2 in total length. As a hypoptopomatine it has the slender, dwarf body plan typical of the subfamily, covered in the overlapping bony plates (scutes) characteristic of armoured catfishes, with a ventral suckermouth adapted for grazing surfaces.
Detailed published descriptions of live coloration are sparse in the sources available here, and fine diagnostic features are not reproduced. No data on this species' coloration in life is reproduced here beyond its small, plated, dwarf-loricariid form.
Habitat
The species is endemic to the Rio Paraíba do Sul basin in southeastern Brazil, a large coastal drainage flowing through the states of São Paulo, Rio de Janeiro and Minas Gerais. It is a freshwater, demersal fish of tropical waters, living on or near the bottom.
Specific microhabitat data — substrate, current, water chemistry at collection sites — is not detailed in the sources available here. No data is published in these references on the precise stream conditions it occupies.
Feeding
As a small hypoptopomatine loricariid with a ventral suckermouth, Pseudotocinclus parahybae is presumed to graze biofilm, algae and associated micro-organisms from submerged surfaces in the manner typical of the subfamily. However, no diet study specific to this species is published in the sources available here, and its precise feeding ecology is undocumented.
Mating
No data on the courtship or mating behaviour of Pseudotocinclus parahybae has been published in the sources available here.
Breeding
No data on the reproduction, spawning mode or parental care of Pseudotocinclus parahybae has been published in the sources available here.
In the aquarium
Pseudotocinclus parahybae is not an established aquarium species, and no husbandry data is published in the sources available here. It is a small, range-restricted Brazilian endemic of conservation concern rather than a trade fish; any keeping would, by analogy with other small hypoptopomatines, require clean, well-oxygenated water and abundant grazing surfaces, but no species-specific guidance exists in these references.
Conservation
The IUCN Red List assessed Pseudotocinclus parahybae as Near Threatened (NT) in 2018. The species is endemic to the single Rio Paraíba do Sul basin, one of the most densely populated and heavily industrialised river systems in southeastern Brazil, where pollution, damming, water abstraction and habitat alteration place pressure on its restricted range. Its narrow distribution is the principal driver of its elevated extinction risk.