Taxonomy & naming
Pseudancistrus kayabi was described by Silva, Roxo and Oliveira in 2015 in ZooKeys (volume 482, pages 21–34, Fig. 1; doi: 10.3897/zookeys.482.8747), based on specimens collected from the rio Teles Pires, a major tributary of the Tapajós River, in the municipality of Itaúba, Mato Grosso State, Brazil (holotype: LIRP 9271, 3 in SL, male; type locality coordinates 10°58'30"S, 55°44'03"W). The Catalog of Fishes (Eschmeyer, CAS) recognises Pseudancistrus kayabi as a valid species with no synonyms.
The genus Pseudancistrus groups scrapers and biofilm grazers that superficially resemble Ancistrus but lack the distinctive evertible interopercular plates that define most Ancistrini. The phylogenetic analysis accompanying the original description placed P. kayabi sister to P. pectegenitor within the Pseudancistrus clade. The species is distinguished from congeners principally by a shorter pectoral spine (22–30% of SL — shorter than in P. barbatus, P. depressus, and related species) combined with a dark brown body bearing whitish spots that fade posteriorly, yellowish hypertrophied odontodes on the snout, and dark barring in the caudal and dorsal fins.
The species epithet kayabi honours the Kayabi (Kajabi) indigenous people of Mato Grosso State, whose ancestral territory encompasses the Teles Pires basin from which this species was described.
Morphology
Adults reach approximately 3.5 in standard length (SL) — a relatively small loricariid. The meristic counts recorded in the original description include one dorsal spine and seven dorsal soft rays; one anal spine and five anal soft rays. The body is dark brown overall, with whitish spots that are most apparent anteriorly and fade toward the caudal peduncle. Dark bars are present in the caudal and dorsal fins. The snout bears yellowish, hypertrophied odontodes — a conspicuous feature in life that is useful for field identification.
The pectoral spine is notably short relative to body length (22–30% SL), shorter than in most Pseudancistrus congeners — the key diagnostic character used to distinguish P. kayabi in the original description. Like other Pseudancistrus, the species lacks evertible cheek plates.
Sexual dimorphism follows the general Pseudancistrus pattern: males develop bristle-like odontodes on the snout and sides of the head, which are absent or reduced in females. This dimorphism has been recorded for the genus and is consistent with observations from the holotype (a male) and paratypes.
Habitat
Pseudancistrus kayabi is known from the rio Teles Pires and the broader upper Tapajós River basin in Mato Grosso State, Brazil — a region characterised by clear to slightly turbid fast-flowing rivers with rocky beds. The Tapajós system drains the southern edge of the Amazon basin across the Brazilian Shield, and its clear-water tributaries in the headwater zone are classic habitat for rheophilic loricariids associated with rock surfaces.
The genus Pseudancistrus as a whole favours highly oxygenated, rocky, fast-flowing rivers — rheophilic conditions in which the fish cling to exposed rock faces using their suctorial mouths and scrape biofilm from the substrate. Specific water chemistry data from the type locality have not been published, but Tapajós Shield tributaries are typically soft, acidic, and clear.
Feeding
Pseudancistrus as a genus consists of scrapers and biofilm grazers that rasp aufwuchs (the community of algae, diatoms, bacteria, and fine organic material) from rocky surfaces in fast-flowing water. By analogy with closely related congeners, P. kayabi is presumed to feed primarily on periphyton and fine detritus scraped from rock.
No diet studies specific to P. kayabi have been published. In the rare event of captive husbandry, a diet of high-quality algae wafers, spirulina-based foods, and blanched vegetables would represent an appropriate starting point, with rocky surfaces for natural grazing behaviour.
Mating
No mating behaviour has been documented for Pseudancistrus kayabi. As a recently described species (2015) with no recorded captive presence, all information on reproductive behaviour is extrapolated from the broader genus. Male Pseudancistrus are known to develop pronounced snout and head odontodes, consistent with a role in male–male competition or courtship display. Territory defence around suitable spawning crevices in rocky substrate is the general expectation for the genus.
Breeding
No confirmed breeding records for Pseudancistrus kayabi exist in the published literature or aquarium hobby records. Given the species' description in 2015 and apparent absence from the commercial ornamental trade, captive breeding has not been reported. Cave spawning with paternal brooding is the reproductive norm across Hypostominae, and P. kayabi is presumed to follow this pattern — adhesive eggs deposited in a rock crevice or under a flat stone, guarded and fanned by the male. The species is not bred in captivity at present.
In the aquarium
Pseudancistrus kayabi has no established presence in the ornamental fish trade and carries no L-number designation. As a 2015 description from a remote Amazonian tributary, it is unlikely to be commercially available. Any husbandry notes are therefore tentative, based on the requirements of the genus rather than direct experience with this species.
For keepers who might encounter this or closely related Pseudancistrus species, the overriding requirement is strong water movement and high dissolved oxygen — conditions that replicate the fast, rocky rivers of the Brazilian Shield. A mature filtration system providing significant flow over rocky hardscape, with water temperatures appropriate for the tropical Tapajós watershed (likely 75–82 °F), would constitute a sensible starting environment. Soft, slightly acidic water consistent with Tapajós Shield chemistry is preferable.
The species is small enough (under 3.5 in SL) that large tanks are not a requirement in absolute terms, but the rheophilic temperament means it is not suited to still or slow-moving aquarium conditions. No compatibility data specific to this species are available.
Conservation
Pseudancistrus kayabi has not been evaluated by the IUCN Red List. The species was described in 2015, and its restricted known range in the upper Tapajós basin — specifically the Teles Pires drainage — means that sufficient baseline data for a formal assessment have not yet been compiled.
The upper Tapajós watershed, including the Teles Pires, faces significant and growing anthropogenic pressure. The São Manoel (Teles Pires) and Teles Pires hydroelectric dam complex, constructed in the 2010s, directly altered stretches of the river system from which this species is known, fragmenting habitat and inundating rapids and rocky riverbed that rheophilic loricariids depend upon. The long-term consequences for P. kayabi and co-occurring species in the Teles Pires rheophile fauna are not yet quantified.