Taxonomy & naming
Hisonotus notopagos was described by Carvalho and Reis in 2011 in Neotropical Ichthyology (volume 9, number 1), as part of a 'Taxonomic review of Hisonotus Eigenmann & Eigenmann from the laguna dos Patos system, southern Brazil'. The species occurs in the rio Camaquã drainage within the laguna dos Patos system of Rio Grande do Sul, Brazil.
The genus Hisonotus belongs to the subfamily Hypoptopomatinae, the dwarf armoured catfishes, and was erected by Eigenmann and Eigenmann. FishBase and the Catalog of Fishes (Eschmeyer, CAS) list Hisonotus notopagos as a valid species. It was one of several species recognised or redefined in the 2011 revision, which sought to untangle the many similar Hisonotus populations of the laguna dos Patos basin.
Morphology
Hisonotus notopagos is a small fish, reaching about 1.5 in standard length — among the smaller members of an already diminutive genus. It has the elongate, bony-plated body typical of Hisonotus, with the ventral sucker-mouth of the dwarf grazing loricariids. Detailed meristic and plate-count data appear in the original 2011 revision; the broader summary data available here do not enumerate them, and sexual dimorphism is not documented.
Habitat
The species inhabits the rio Camaquã drainage of the laguna dos Patos system in Rio Grande do Sul, southern Brazil. It is a demersal fish of subtropical freshwater streams — a southern, cooler-climate setting than the tropical headwaters of many congeners. Like other Hisonotus, it is capable of facultative air-breathing. FishBase rates its resilience as high, estimating a population doubling time of under fifteen months, consistent with a small, fast-reproducing grazer.
Feeding
No species-specific feeding study has been published for Hisonotus notopagos. The genus consists of aufwuchs grazers that rasp the biofilm — algae, diatoms, bacteria and fine detritus — coating submerged rocks, wood and plants. The fine teeth and ventral mouth of these fishes suit biofilm scraping rather than wood consumption. Specific dietary data for this species are sparse beyond this general pattern.
Mating
No courtship or mating behaviour has been described for Hisonotus notopagos. The species is known from field collections and museum material, without documented aquarium observations of reproduction.
Breeding
There are no published breeding records for Hisonotus notopagos. Its reproductive mode, clutch size, spawning behaviour and parental care are undocumented. While small hypoptopomatines commonly lay adhesive eggs on plants or hard surfaces, no breeding data are reported for this species, and none should be assumed.
In the aquarium
Hisonotus notopagos is not an established aquarium species and is not a regular part of the ornamental trade; no husbandry data exist for it. Aquarists interested in small grazing loricariids of this type usually keep Otocinclus or more widely available relatives, which require mature, biofilm-rich, well-oxygenated tanks. Given its subtropical origin, a species like this would presumably favour cooler, stable conditions, though this remains an inference rather than documented husbandry.
Conservation
The IUCN Red List assessed Hisonotus notopagos as Least Concern (LC) on 7 November 2018. The listing reflects no evidence of significant range-wide decline and a high reproductive resilience, with a population doubling time estimated at under fifteen months. As a small grazer within the laguna dos Patos system, it remains subject to the general pressures on southern Brazilian coastal drainages — agriculture, urbanisation and water-quality change — but is not presently considered threatened. CITES and CMS have not evaluated it.