Taxonomy & naming
Paralithoxus raso was described by Silva, Covain, Oliveira and Roxo in 2017 in Zootaxa (volume 4347, number 1, pages 151-168), originally placed in the genus Lithoxus. It is treated as valid by the Catalog of Fishes (Eschmeyer, CAS) and belongs to the Lithoxus group of subfamily Hypostominae, tribe Ancistrini, family Loricariidae.
The species is diagnosed by a distinctive set of characters: large light spots all over the body (comparable in size to the orbit diameter), the presence of an adipose fin, five branched anal-fin rays, fourteen branched caudal-fin rays, and an enlarged, widened cusp on the medial premaxillary teeth. The epithet is a noun in apposition referring to the type locality, the igarapé Balneário Raso.
No aquarium L-number has been assigned, and the species is unknown in the ornamental trade.
Morphology
Paralithoxus raso is small, reaching about 2 in standard length in the largest measured specimens — among the smallest of its group. The body is elongated and flattened, the characteristic profile of the Lithoxus group.
The fin formula given in the original description is two dorsal spines and seven dorsal soft rays, one anal spine and five anal soft rays, with fourteen branched caudal-fin rays; an adipose fin is present. The most conspicuous feature is the bold pattern of large pale spots covering the body, each roughly the diameter of the eye, distinguishing it from the unspotted congeners of the same group. No information on sexual dimorphism has been published.
Habitat
Paralithoxus raso is known from the Rio Raso, in the rio Amapá basin of Amapá State, Brazil — an Atlantic coastal drainage of the Brazilian Guiana shield. It inhabits small- to medium-sized rivers with rocks and sand on the bottom.
It is a freshwater, demersal, tropical species and, like other Paralithoxus, a facultative air-breather. No specific field measurements of temperature, pH or hardness have been published for this species.
Feeding
No dietary study has been published for Paralithoxus raso. As a small, rasping, bottom-dwelling loricariid of rocky-and-sandy streams, it is presumed to graze the biofilm of algae, microorganisms and detritus on rock surfaces, in line with the general ecology of its group. The particulars remain undocumented.
Mating
No data on courtship or mating behaviour have been published for this species.
Breeding
No data on reproduction, spawning mode or parental care have been published for Paralithoxus raso. It is not known to have been bred in captivity.
In the aquarium
Paralithoxus raso is not established in the aquarium hobby, and no husbandry experience has been documented. Its known habitat of rocky, sandy stream bottoms implies that any attempt to keep it would require clean, well-oxygenated water with current and a substrate of rock and sand, as for other rheophilic Lithoxus-group plecos. No more specific recommendations can be made without inventing detail.
Conservation
Paralithoxus raso has not been evaluated by the IUCN Red List, and its conservation status is therefore unknown. It is also Not Evaluated under CITES and CMS. Described only in 2017 from a single small stream in Amapá, its range and population trends are poorly characterised. The Atlantic coastal drainages of the Guiana shield are broadly exposed to pressures from mining, deforestation and sedimentation, but no species-specific assessment exists.