Taxonomy & naming
Pseudotocinclus juquiae was described by Aléssio K. Takako, Cláudio Oliveira and Osvaldo T. Oyakawa in 2005, in a revision of the genus Pseudotocinclus published in Neotropical Ichthyology (volume 3, number 4, pages 499–508). The type material comes from the rio Juquiá basin in São Paulo State, southeastern Brazil, part of the larger Ribeira de Iguape coastal drainage. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Pseudotocinclus juquiae.
The species sits in subfamily Hypoptopomatinae, the group of small armoured catfishes commonly known as dwarf suckermouths or 'otos' in the broad hobby sense. Pseudotocinclus is a small genus of southeastern Brazilian coastal-drainage endemics, and the 2005 revision that introduced this species clarified the boundaries between its members.
The genus name combines the Greek pseudes ('false') with otos ('ear') and kygklos (the name of a small fish), echoing the related genus Otocinclus; the construction signals a superficial resemblance to, but distinction from, that better-known dwarf genus. The specific epithet juquiae is a toponym referring to the rio Juquiá, the basin from which the type specimens were drawn.
Morphology
Pseudotocinclus juquiae is a very small loricariid, reaching a maximum recorded size of about 1.5 in standard length. As in other Hypoptopomatinae, the body is encased in rows of bony lateral plates, the head is depressed, and the mouth is ventral and modified into a suckermouth disc suited to clinging to firm surfaces in current.
The original description and revision of the genus document the diagnostic features that separate P. juquiae from its congeners, including details of plate arrangement, snout shape and coloration. Beyond the formal description, little published detail on live coloration or fine morphological variation is available, and no reliable hobby-derived photographs of confirmed wild specimens circulate. Sexual dimorphism has not been documented in detail for this species in the literature consulted; in many dwarf hypoptopomatines mature females are simply broader-bodied when carrying eggs.
Habitat
The species is endemic to the Ribeira de Iguape basin, a coastal Atlantic drainage of São Paulo (and adjacent Paraná) State in southeastern Brazil, with type localities in the rio Juquiá system. These are tropical, freshwater, demersal habitats — typically clear, flowing streams and small rivers draining the Serra do Mar and surrounding lowlands.
Dwarf hypoptopomatines of this region are generally associated with riffles, submerged vegetation, leaf litter and firm substrates where they graze biofilm in moderate current. Specific physico-chemical measurements (temperature, pH, hardness) for P. juquiae's habitat were not published in the sources available, so precise field water parameters are not given here rather than estimated. The Ribeira de Iguape is a comparatively well-preserved basin in parts, but faces localized pressures from agriculture, urbanisation and water abstraction.
Feeding
Like other dwarf suckermouth catfishes, Pseudotocinclus juquiae is a grazer, rasping the aufwuchs — the film of algae, diatoms, bacteria and fine detritus — that coats rocks, wood and plant surfaces in flowing water. Its low trophic level (estimated around 2.4) is consistent with a diet dominated by periphyton and associated micro-organisms rather than animal prey.
No detailed gut-content study or captive feeding observations specific to this species were found in the available sources. Inferences from the genus and subfamily suggest a continuous, low-intensity browsing habit on biofilm-rich surfaces.
Mating
No courtship or mating behaviour has been documented for Pseudotocinclus juquiae in the literature consulted. The species is known almost entirely from preserved type and survey material, and it is not established in the aquarium hobby, so no spawning observations are available.
Among dwarf hypoptopomatines generally, reproduction tends to involve adhesive eggs deposited on firm surfaces such as plant leaves or stones, but extending that pattern to this species would be speculation; the honest position is that its reproductive biology is unstudied.
Breeding
No published breeding records exist for Pseudotocinclus juquiae, in the wild or in captivity. There is no documented clutch size, egg description, incubation period, or evidence regarding parental care. The species has not, to the knowledge available here, been bred by aquarists. This is a clear case where no data has been published, and nothing reliable can be stated.
In the aquarium
Pseudotocinclus juquiae is essentially absent from the ornamental trade and is not a hobby fish in any practical sense — it is a scientifically described, Critically Endangered, narrow-range endemic rather than an aquarium import. No husbandry protocol, recommended tank size, or water-parameter regime has been published for it.
Any hypothetical care would have to be inferred from related dwarf suckermouths, which generally need mature, well-oxygenated, clean water; gentle to moderate flow; firm grazing surfaces coated in biofilm; and stable, low-pollutant conditions. Given its conservation status, deliberate collection for the hobby would be inappropriate. This profile is included for completeness and reference, not as a keeping recommendation.
Conservation
The IUCN Red List assessed Pseudotocinclus juquiae as Critically Endangered (CR), under criteria B2ab(iii,iv), with the assessment dated 7 November 2018. A Critically Endangered B2 listing reflects a very small area of occupancy (under 6 mi² in the threshold sense), severe fragmentation or a single location, and a continuing decline — here in the extent and quality of habitat (iii) and in the number of locations or subpopulations (iv).
The species' entire known range is the Ribeira de Iguape coastal drainage in southeastern Brazil, one of the most densely populated and heavily modified regions of the country. Range-restricted stream endemics like this are acutely vulnerable to habitat degradation from deforestation, sedimentation, water abstraction, pollution and the spread of urban and agricultural land use. With no captive population to buffer it, the persistence of P. juquiae depends entirely on the protection of its narrow native watershed; the CR status should be read as a genuine, severe extinction risk rather than a precautionary placeholder.