Taxonomy & naming
Pareiorhina cepta was described by Roxo, da Costa e Silva, Mehanna and Oliveira in 2012, in Zootaxa (3512: 64–74). The type material was collected in headwater streams of the upper Rio São Francisco basin in Minas Gerais State, Brazil. The Catalog of Fishes (Eschmeyer, CAS) recognises the species as valid within the genus Pareiorhina.
The genus belongs to the subfamily Neoplecostominae, a group of small, often torrent-associated loricariids concentrated in the highland streams of southeastern Brazil. (FishBase's classification line lists the genus under Hypoptopomatinae, reflecting an alternative arrangement; the original description and the subfamily assignment used here follow Neoplecostominae.) The species is diagnosed from its congeners by a suite of fine characters, most conspicuously the presence of small odontode-bearing plates scattered across the abdomen — in contrast to the naked abdomen of other Pareiorhina — together with a caudal fin that is entirely dark except for a single clear (hyaline) bar, a minute lateral cusp on the teeth, and pointed odontodes on the ventral surfaces of the leading pectoral, pelvic and anal-fin rays.
Morphology
Pareiorhina cepta is a small fish, reaching about 1.5 in in standard length in the known material. The body is elongated, in keeping with the slender build typical of stream-dwelling neoplecostomines.
The most diagnostic external feature is the abdomen, which carries small odontode-covered platelets distributed somewhat irregularly across the belly — a state that separates it from congeners whose abdomens are naked. The caudal fin is almost entirely dark, broken only by a single hyaline (transparent) bar. The teeth bear a minute lateral cusp, and pointed odontodes line the ventral surfaces of the first pectoral, pelvic and anal-fin rays. No data on sexual dimorphism or coloration in life beyond the preserved-specimen description has been published.
Habitat
The species is known from narrow, shallow headwater streams in the upper Rio São Francisco basin, collected at elevations of roughly 810–1,213 ft above sea level. The streams are small — about 10–16 ft wide and 1–5 ft deep — flowing over a bed of small-to-medium rocks, loose stones, gravel and sand, with marginal vegetation shading the water.
The recorded water conditions are striking: clear, cold water (measured at 62–67 °F), highly oxygenated (5.91–13.05 mg/l dissolved oxygen), poorly conductive, and remarkably acidic, with pH readings of 2.78–2.87. Flow ranged from moderate to fast. The species was found alongside Astyanax rivularis, Neoplecostomus franciscoensis, Trichomycterus macrotrichopterus and Characidium fasciatum.
Feeding
No direct dietary study has been published for Pareiorhina cepta. Like other small loricariids of fast, rocky highland streams, it is presumed to graze the biofilm — algae, diatoms, microorganisms and fine detritus — coating stones and gravel, using its ventral suckermouth to hold position in current while rasping the substrate. Specific gut-content or feeding-behaviour data are not available.
Mating
No data on courtship or mating behaviour have been published for this species.
Breeding
No breeding report exists for Pareiorhina cepta, in the wild or in captivity. Reproductive mode, clutch size and parental care are all undocumented.
In the aquarium
Pareiorhina cepta has no aquarium history. It is a small, specialised inhabitant of cold, fast, exceptionally acidic mountain headwaters, and is not part of the ornamental trade. The combination of low temperature, very low pH, high oxygenation and strong flow recorded at its collection sites would be difficult to reproduce and maintain, and there is no husbandry literature to draw on. It is documented here as a scientific record rather than a hobby fish.
Conservation
The IUCN Red List assessed Pareiorhina cepta as Least Concern, with the assessment dated 7 November 2018. As a small-bodied species restricted to highland headwaters of the upper Rio São Francisco basin, its long-term prospects depend on the integrity of those streams; headwater systems in this region face pressures from land-use change, water abstraction and habitat degradation, though no specific decline has been documented for this species.