Taxonomy & naming
Hypostomus pastinhai was formally described by Zawadzki and Penido in 2021, in Ichthyological Exploration of Freshwaters (volume 30, number 4, article IEF-1159, page 365). The type locality is the channel of the Rio São Francisco near Paulo Afonso, Bahia State, Brazil (approximately 9°25'30"S, 38°10'56"W). The species belongs to the family Loricariidae, subfamily Hypostominae, and to the large and taxonomically complex genus Hypostomus Lacépède, 1803.
The paper described two new species simultaneously: H. bimbai and H. pastinhai. Both were recovered from depths of approximately 30 metres in the lower São Francisco, a collection context that the authors termed 'depth-sheltered' — an unusual mode of resource partitioning within a genus otherwise associated predominantly with shallow riffles and rocky marginal substrates. The Catalog of Fishes (Eschmeyer, CAS) recognises Hypostomus pastinhai as a valid species.
The species is distinguished from H. bimbai and other congeners in the lower São Francisco basin by its smaller maximum size, proportionally short dorsal, pectoral, and pelvic fins, and its pale-spotted coloration on a dark background with dark dots on the fins.
Morphology
The largest specimen recorded reached 10 in standard length (SL). The body follows the typical Hypostomus plan: dorsoventrally flattened anteriorly, tapering to a laterally compressed caudal peduncle, and encased in rows of keeled bony scutes. Ground colour is dark, overlaid with pale spots on the body and dark dots on the fins — a pattern common in several lower São Francisco Hypostomus.
The most diagnostically useful character set involves fin proportions: the dorsal, pectoral, and pelvic fins are notably short relative to body length when compared with congeners from the same drainage. The dorsal fin has 2 spines and 7 soft rays; the anal fin has 4 soft rays. These proportionally abbreviated fins may be an adaptation to the reduced current encountered at 98 ft depth, where less fin surface area is needed for bracing against fast water.
Like all members of the family, H. pastinhai is equipped with a ventral sucking disc — a modified mouth — that allows it to adhere to hard substrates. The species is also reported to be capable of facultative air-breathing, an ability found across much of Hypostomus and useful during periods of low dissolved oxygen. Sexual dimorphism has not been documented for this species.
Habitat
Hypostomus pastinhai is known from the lower Rio São Francisco basin in Bahia State, northeastern Brazil. The São Francisco is one of Brazil's major river systems, draining a vast semi-arid to sub-humid interior before reaching the Atlantic coast. The lower reaches, where this species was found, are heavily influenced by the Paulo Afonso hydroelectric complex.
What makes this species ecologically notable is the depth at which it was collected: approximately 30 metres over a rocky bottom in areas of slow water flow. This is unusually deep for a loricariid. Most Hypostomus are associated with shallow, well-oxygenated riffle zones or rocky marginal habitats accessible to divers. Collection at depth likely required survey equipment associated with hydroelectric operations or deep-water sampling gear.
Slow water flow at depth, combined with a hard rocky substrate, suggests the fish maintains contact with the benthos in a relatively stable, dark microhabitat. Water chemistry parameters for this exact depth stratum in the lower São Francisco are not documented in the species description.
Feeding
No diet data specific to Hypostomus pastinhai are available in the literature. General biology of Hypostomus provides a reasonable framework: the vast majority of species in the genus are aufwuchs grazers and detritivores, using the ventral scraping dentition to rasp biofilm, algae, and fine organic matter from hard surfaces.
At 98 ft depth, light levels are low and photosynthetic algal growth on rocky surfaces would be limited. The species may therefore rely more heavily on detritus, microbial biofilm, and organic material settling from shallower water. Facultative air-breathing suggests the fish may also make vertical migrations, though this has not been observed directly.
In an aquarium context, the standard Hypostomus diet — algae wafers, blanched vegetables, sinking pellets, driftwood for rasping — would be a reasonable starting point, but there is no published guidance specific to this species.
Mating
Mating behaviour has not been documented for Hypostomus pastinhai. Across Hypostomus, the general pattern involves males guarding territory around suitable crevices or holes in rocky substrate, with females drawn in during the breeding season. Seasonal cues likely include changes in water level, temperature, and possibly photoperiod, tied to the hydrological cycle of the São Francisco.
Given the deep-water habitat of this species, the dynamics of mate-finding and territory establishment may differ from shallow-water congeners, but no observational data exist to confirm or refute this.
Breeding
Breeding behaviour and reproductive biology are undocumented for Hypostomus pastinhai. The species has not been kept or bred in captivity to the knowledge of the scientific literature. By analogy with other Hypostomus species, it would be expected to be a cave or crevice spawner with paternal guarding of the clutch, but no clutch size, incubation period, or fry data are available.
In the aquarium
Hypostomus pastinhai is not known to be in the aquarium hobby. Its description is recent (2021) and its deep-water type locality makes collection for the trade logistically difficult. No husbandry information exists in the hobbyist literature.
Should specimens become available, the general requirements for a medium-sized Hypostomus would apply: a spacious tank with strong filtration, plentiful oxygenation, rocky decor offering crevices and caves, a sand or fine gravel substrate, and a varied diet of algae wafers, sinking pellets, and blanched vegetables. At 10 in SL — equivalent to perhaps 12 in total length — this is a substantial catfish requiring a correspondingly large aquarium.
The depth-sheltered ecology of this species in the wild (98 ft, slow flow, low light) suggests it may prefer lower light conditions and moderate rather than strong current in captivity, but this remains inference rather than established husbandry practice.
Conservation
Hypostomus pastinhai has not been evaluated by the IUCN Red List. The species was described only in 2021, and the time lag before a newly described species receives a formal assessment is typically several years.
The lower Rio São Francisco is a heavily altered river system. The Paulo Afonso hydroelectric complex, near the type locality, has dramatically changed water flow regimes, flood pulses, and sediment dynamics in the lower basin over decades. The long-term effects of these alterations on deep-water benthic communities — including any Hypostomus populations — are not well studied. Until the species' full range and population status are assessed, its conservation position remains unknown.