Taxonomy & naming
Hypostomus robertsoni was formally described by Dias and Zawadzki in 2021 in Neotropical Ichthyology, based on specimens collected from the Keller River — a tributary of the Ivaí River — near Marialva, Paraná State, Brazil. The holotype measures 5 in standard length (SL); the paratype series of 68 specimens ranged from 3.5–5.5 in SL. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hypostomus robertsoni Dias & Zawadzki, 2021.
The species was described in the same paper as a redescription of Hypostomus hermanni, allowing the authors to clarify the boundaries between these two Paraná-basin Hypostomus. The two species share certain features but are reliably separated by the colouration pattern and by characters of the parieto-supraoccipital region: H. robertsoni has a non-carinate parieto-supraoccipital, distinguishing it from relatives where that dorsal ridge is more pronounced.
Hypostomus is one of the most species-rich genera in Loricariidae, placed within the subfamily Hypostominae. It encompasses the armoured suckermouth catfishes of tropical and subtropical South America, ranging from small Andean foothills streams to large lowland river systems. The vast majority of Hypostomus species are described from single river basins or sub-basins, and H. robertsoni fits this pattern as an apparent endemic of the Ivaí drainage.
Morphology
Adults are reported to reach approximately 5.5 in SL. The body follows the standard Hypostomus plan: dorso-ventrally flattened profile, fully armoured with bony scutes, a ventrally positioned suctorial mouth, and a high dorsal fin arising from near the head. Colouration is described as dark blotches on a clear background — a pattern common within the genus but here used to distinguish H. robertsoni from its congeners, particularly H. hermanni.
The teeth are viliform and bicuspid, the typical configuration for algae- and biofilm-grazing Hypostomus that do not specialise in wood or detritus the way Panaque and related genera do. The parieto-supraoccipital region is non-carinate — flat or only weakly ridged — a character of diagnostic importance within this species group.
Like all Hypostomus, the species possesses the genus's capacity for facultative air-breathing: in hypoxic conditions the fish can surface to gulp air, supplementing gill respiration. This adaptation is widespread across Loricariidae and allows these fish to survive in warm, stagnant, or seasonally deoxygenated backwaters that would be lethal to obligate gill-breathers.
Habitat
Hypostomus robertsoni is known from the Ivaí River basin and the adjoining Piquiri River basin, both tributaries of the Upper Paraná River in Paraná State, southern Brazil. The type locality — Keller River near Marialva — is a mid-sized Paraná-basin tributary flowing through agricultural and mixed-use landscape in one of Brazil's most intensively farmed states.
The Upper Paraná basin is a subtropical system with a strong seasonal temperature cycle. Water temperatures in Paraná tributaries typically range from the low teens in winter to the upper twenties in summer, with most Hypostomus activity concentrated in the warmer months. Substrate in the Ivaí drainage is variable — rocky runs alternate with sandy reaches and slower, more turbid stretches in the lower portions of the system.
As a benthic, armoured catfish, H. robertsoni is likely associated with hard substrate — rocks, submerged logs, and root masses — where it can graze biofilm and seek shelter from the current. The demersal lifestyle is universal within Hypostomus. Beyond the type series collection data, detailed microhabitat information for this species is not yet published.
Feeding
The bicuspid, viliform dentition of Hypostomus robertsoni is consistent with the generalised algae, biofilm, and aufwuchs grazing that characterises most of the genus. These are opportunistic scrapers: the suctorial mouth is pressed flat against rock, root, or submerged wood surfaces, and the teeth rasp off periphyton, diatoms, fine detritus, and the associated microbial mat.
In common with many Hypostomus, the species likely supplements biofilm grazing with incidental organic detritus — fine particulate matter settled on substrate, and perhaps the occasional invertebrate item — though the diet composition for this newly described species specifically has not been published. General Hypostomus dietary studies confirm that plant material and fine detritus form the bulk of gut contents in most species, with algae most abundant in specimens from clear, well-lit reaches.
Mating
No specific mating observations have been published for Hypostomus robertsoni. The genus as a whole is a cave-spawner, with males defending and preparing nest cavities — typically earthen burrows excavated in riverbanks, crevices between rocks, or cavities in submerged wood — and attracting females to spawn inside. Males in reproductively active condition typically display more prominent odontodes on the pectoral spine and interopercular region than females, and broader-bodied females can be distinguished when viewed from above during the breeding season.
Reproductive timing in Paraná-basin Hypostomus is generally tied to the austral spring and summer, when rising temperatures and water levels coincide with the wet-season flood pulse. Seasonal conditioning — cooler, drier conditions in winter followed by warming and increased flow in spring — appears to trigger spawning readiness in many congeners.
Breeding
No captive breeding records have been published for Hypostomus robertsoni. The species was described only in 2021 and has not been documented in the ornamental trade, so aquarium experience is effectively absent.
Breeding biology can be inferred from the broader genus: Hypostomus are cave-spawners with paternal brood care. The male guards adhesive eggs deposited on the cavity wall, fanning them to maintain oxygenation and removing dead eggs. Fry are miniature versions of adults, capable of grazing biofilm shortly after absorbing the yolk sac. Successful captive breeding of Hypostomus generally requires appropriate cave structure, high water quality, and conditioning on a varied vegetable-rich diet.
In the aquarium
Hypostomus robertsoni is not established in the ornamental trade and is not known from hobbyist collections as of its description in 2021. It originates from a subtropical drainage with a marked seasonal temperature cycle, which suggests it would tolerate cooler conditions than many tropical Hypostomus — though specific aquarium temperature requirements cannot be stated from available data.
For aquarists who might encounter or work with this species in the future, standard Hypostomus husbandry principles apply: a spacious tank with robust filtration to handle the significant waste load of these fish, flat stones or driftwood for grazing surfaces, and a varied diet of algae wafers, blanched vegetables, and sinking pellets. Cave structures or hollow logs are appropriate enrichment. Adults at roughly 5–5.5 in SL are medium-sized within the genus and would require at minimum 40–55 US gal for a single specimen.
Conservation
Hypostomus robertsoni has not been evaluated by the IUCN Red List. The species was described in 2021, and newly described taxa typically enter the assessment queue with a delay of several years.
The naming of this species carries a conservation dimension baked into its etymology: it honours Robertson Fonseca de Azevedo, a Brazilian environmental attorney who devoted his career to opposing unnecessary hydroelectric development on Upper Paraná tributaries and preserving natural landscapes in Paraná State. The Ivaí River basin — the entire known range of H. robertsoni — has faced significant pressure from dam proposals and the ongoing transformation of the watershed by intensive agriculture. Endemism at the sub-basin scale makes this species inherently vulnerable: any large impoundment or severe degradation of the Ivaí or Piquiri drainages could threaten populations that have nowhere else to go.