Taxonomy & naming
Pareiorhaphis hypselurus was described by Eduardo Pereira and Roberto Reis in 2002, originally placed in Hemipsilichthys. The type locality is the Forqueta River, a tributary of the Maquiné River, at approximately 29°32′42″S, 50°14′21″W, in the municipality of Maquiné, Rio Grande do Sul state, Brazil — a coastal Atlantic drainage of the southern Brazilian shield. Pereira's 2005 revision of the hemipsilichthyine assemblage transferred the species to Pareiorhaphis Miranda Ribeiro, 1918, the combination currently recognised by the Catalog of Fishes (Eschmeyer, CAS).
Pareiorhaphis is the dominant genus of the subfamily Neoplecostominae in southern Brazilian Atlantic-slope drainages, with highest species richness concentrated in Rio Grande do Sul and Santa Catarina. The species epithet hypselurus derives from the Greek hypselos (high, tall) and oura (tail), in direct reference to the distinctly deep caudal peduncle that is a diagnostic character separating P. hypselurus from congeners with a shallower caudal taper.
No L-number, LDA-number, or established common name exists for this species. It has not entered the ornamental trade to any documented degree.
Morphology
Adults of Pareiorhaphis hypselurus reach approximately 2.5 in standard length (SL), placing it among the smaller species in the genus. The body is typical of the rheophilic neoplecostomine bauplan: strongly dorsoventrally flattened, fully armoured with keeled bony scutes, and equipped with a large ventral sucker mouth adapted for adhering to smooth rock in fast current.
The defining external character is the notably deep caudal peduncle — the narrowing region of the body between the anal and caudal fins — which gives the fish a subtly different silhouette compared to congeners. Published meristic data include 74–98 teeth per dentary, 7 dorsal soft rays, and 5 anal soft rays. Ground coloration is dark brown on the dorsal surface, paler ventrally, with the cryptic pattern common to fast-water benthic loricariids.
Male Pareiorhaphis develop hypertrophied odontodes on the snout, cheeks, and pectoral spines during the breeding season — a consistent sexual dimorphism across the genus. These bristle-like projections are used in male–male competition for spawning sites and may also function in mate assessment. Females are generally more robust in body depth when gravid.
Habitat
The type locality — the Forqueta River in Maquiné municipality, Rio Grande do Sul — is a coastal Atlantic drainage stream lying east of the Serra Gaúcha escarpment. The Maquiné River and its tributaries flow across fractured basalt and granite toward the coastal lowlands of RS, discharging into the Atlantic coastal plain north of Porto Alegre.
This region receives high rainfall year-round, keeping streams relatively clear, cool, and well-oxygenated. The streams are typically shallow to moderate in depth, fast-flowing over rocky substrates, with natural gallery forest providing shade and allochthonous leaf and wood input. The IUCN assessed this species as Least Concern in 2018, implying that at the time of assessment the Maquiné/Forqueta drainage population was considered stable.
No measured water parameters (temperature, pH, conductivity) have been published specifically for the Forqueta River at the type locality for this species.
Feeding
Pareiorhaphis hypselurus is inferred to be a periphyton scraper and epilithic biofilm grazer consistent with the neoplecostomine body plan and the rocky, fast-water habitat it occupies. The papillose oral disc and rasping teeth characteristic of the genus are adapted to graze the thin layer of algae, diatoms, and microbial film coating cobble and bedrock surfaces in high-velocity stream reaches.
No stomach content analyses or specific field diet data have been published for this species. Benthic invertebrates (chironomid larvae, micro-crustaceans) swept into the fish's path likely supplement the algal diet, as is typical for small rheophilic loricariids of comparable size and ecology.
Mating
No observations of mating behaviour in P. hypselurus — either wild or captive — have been published. The reproductive context can be inferred from the strong sexual dimorphism in male odontode expression: breeding males invest substantially in odontode growth on the snout, cheeks, and pectoral spines, which serve as contact weapons in bouts between rival males competing for crevice spawning sites in the rocky streambed.
In the fast-flowing coastal streams that P. hypselurus inhabits, suitable sheltered spawning cavities (the underside of flat stones, tight rock crevices, submerged root tangles) are likely distributed patchily, and male competition for the best sites may be pronounced during the reproductive season.
Breeding
No captive breeding records exist for Pareiorhaphis hypselurus. The species is not established in the hobby, and no published reports from aquarium collections or research facilities document its reproductive biology.
By analogy with related neoplecostomines, the species is expected to deposit adhesive eggs in a sheltered substrate cavity — beneath a cobble or in a rock crevice — with some degree of male brood guarding. Clutch size, incubation period, and fry development are entirely undocumented for this species.
In the aquarium
Pareiorhaphis hypselurus is not available in the ornamental fish trade and is not kept in aquaria. No husbandry information has been published.
As a small (under 3 in SL) benthic loricariid from clean, fast, cool Atlantic-slope streams, the species would require high dissolved oxygen, strong water movement over a rocky substrate, and cool temperatures reflecting the Serra Gaúcha highland climate of its native range. In the complete absence of any captive experience with this species, no specific care parameters can be honestly stated beyond these broad inferences from ecology and family-level biology.
Conservation
The IUCN Red List assessed Pareiorhaphis hypselurus as Least Concern (LC) in November 2018. The assessment reflects stable conditions in the Maquiné/Forqueta coastal drainage of Rio Grande do Sul at the time of evaluation. The species has a naturally restricted range confined to this small Atlantic-slope watershed, but the catchment retains relatively intact Atlantic Forest vegetation compared to heavily deforested inland drainages of comparable size.
The Maquiné valley is partially within or adjacent to protected areas associated with the Atlantic Forest Biosphere Reserve, which may afford some degree of habitat continuity. Nevertheless, the species' restricted extent of occurrence means it has limited resilience to any major disturbance — road construction, riparian clearing, intensive agriculture, or point-source pollution in the catchment could significantly reduce populations. The LC assessment should be interpreted in the context of the species' inherently small range rather than as evidence of abundance.