Taxonomy & naming
Parotocinclus planicauda was described by Garavello and Britski in 2003, in the Brazilian Journal of Biology (volume 63, number 2, p. 254, Fig. 1). The type locality is the Suaçuí Pequeno River at Barra do Rochedo, on the Antônio Pereira de Oliveira farm about 12 mi from Coroaci, Minas Gerais State, Brazil, within the Rio Doce basin. No synonyms are recorded, and the Catalog of Fishes (Eschmeyer, CAS) treats the name as valid.
The species sits in the subfamily Hypoptopomatinae, the group of small grazing loricariids that includes Otocinclus and its relatives. The genus Parotocinclus is distinguished from the superficially similar Otocinclus by the presence of an adipose fin, which Otocinclus lacks — a simple but reliable diagnostic point separating the two genera.
Morphology
Parotocinclus planicauda is a small loricariid, recorded at about 1.5 in in standard length. It shows the compact, dorsoventrally flattened body and ventral suckermouth typical of the dwarf hypoptopomatines, and — like all Parotocinclus — possesses an adipose fin, the feature that separates the genus from Otocinclus. Detailed published data on live coloration and sexual dimorphism are not available beyond the original description.
Habitat
The species is known from the Rio Doce basin in Minas Gerais, southeastern Brazil, with the type material taken from the Suaçuí Pequeno River. Small hypoptopomatines of this region are typically associated with flowing, well-oxygenated stream habitats where they graze firm surfaces, but no specific water-chemistry or microhabitat measurements have been published for P. planicauda.
Feeding
No dietary study has been published for Parotocinclus planicauda. By analogy with other small Parotocinclus and Otocinclus, it is presumed to be a grazer of aufwuchs — the film of algae, diatoms and associated microfauna on rocks, wood and plant surfaces — but specific gut-content data are not available.
Mating
No data on courtship or mating behaviour have been published for this species.
Breeding
No breeding report exists for Parotocinclus planicauda, in the wild or in captivity. Reproductive mode, clutch size and parental care are undocumented.
In the aquarium
Parotocinclus planicauda has no meaningful aquarium history and is not a fixture of the ornamental trade. There is no published husbandry guidance specific to the species. It is recorded here as a described taxon rather than a hobby fish; aquarists encountering Parotocinclus in the trade are far more likely to be keeping other, more widely exported members of the genus.
Conservation
The IUCN Red List assessed Parotocinclus planicauda as Least Concern, last assessed in 2018. As a small fish of the Rio Doce basin, its prospects are tied to the condition of that system, which has faced significant environmental pressures; no species-specific population decline has been documented.