Taxonomy & naming
Pseudancistrus asurini was formally described by Silva, Roxo & Oliveira in 2015 in ZooKeys (volume 482, pages 21–34), from specimens collected in the Rio Xingu basin, Pará State, northern Brazil. The Catalog of Fishes (Eschmeyer, CAS) recognises Pseudancistrus asurini as a valid species, with Silva, Roxo & Oliveira (2015) as the authorship.
The genus Pseudancistrus is placed in subfamily Hypostominae, tribe Ancistrini, within the family Loricariidae. It holds a peculiar position in the tribe: unlike virtually all other Ancistrini, Pseudancistrus lacks evertible cheek plates (interopercular odontodes are present but the plates do not evert), making it the only ancistrinine genus without this otherwise diagnostic character.
The species epithet asurini is a dedication to the Asurini indigenous people (also spelled Asurinis), who inhabit the right margin and median portions of the Rio Xingu near Altamira, Pará State, and whose territory lies close to the type locality. The combination Pseudancistrus comes from the Greek pseudes (false) and agkistron (hook), denoting a perceived resemblance to Ancistrus while being distinct from it.
Morphology
Pseudancistrus asurini reaches up to approximately 10 in total length (TL), making it a moderately large species by loricariid standards. The body is elongated and fully armoured in overlapping bony scutes in the typical loricariid fashion. Dorsal fin count is two spines plus seven soft rays; anal fin count is one spine plus five soft rays.
The single most diagnostic character of P. asurini is the whitish tips of the dorsal fin and caudal fin — a pale margin absent in all congeners examined to date. The body bears conspicuous whitish spots; in contrast to the closely related P. kayabi, these spots do not span more than one lateral dermal plate, and they increase gradually in diameter from head (approximately 0.5 in) to body (approximately 0.5 in). The snout odontodes are yellowish rather than the reddish-brown seen in P. depressus and P. barbatus.
Metric proportions that further identify the species include: predorsal length 39–43% of SL (shorter than P. zawadzkii and P. nigrescens); dorsal-pectoral depth 23–27% SL; caudal peduncle depth 9–11% SL; barbel length 5–9% of head length; and head depth 57–66% SL. Pseudancistrus reus and P. kayabi share most of the genus-level characters but differ in the colour pattern — P. reus has bars rather than spots, and P. kayabi has spots that can straddle more than one plate.
Habitat
Pseudancistrus asurini is known from the Rio Xingu, a major right-bank tributary of the Amazon in Pará State, Brazil. The Xingu is a large, fast-flowing clearwater river characterised by an intricate cascade of rapids, rocky outcrops, and narrow channels, particularly in the Volta Grande reach near Altamira — the region from which the type specimens originate.
Loricariids in this system typically occupy rock faces and boulders swept by strong current, where they graze epilithic biofilm and algae and shelter in crevices or beneath submerged slabs. Water in the lower Xingu rapids is warm, generally well-oxygenated due to turbulence, and relatively low in dissolved solids compared with the whitewater Amazon mainstream. No specific temperature or pH data for P. asurini collection sites are reported in the available literature.
Facultative air-breathing, a genus-level trait in Pseudancistrus, allows these fish to gulp atmospheric air through the mouth and extract oxygen across a modified posterior stomach region when dissolved oxygen in stagnant backwaters falls during dry-season low water — an adaptation shared with several other loricariid lineages.
Feeding
Like other members of Pseudancistrus, P. asurini is presumed to be primarily an epilithic algae and biofilm grazer — rasping attached algae, diatoms, fine detritus, and microbial mats from hard surfaces using the laterally positioned, bicuspid teeth characteristic of the genus.
In captivity, members of Pseudancistrus accept standard loricariid herbivore fare: algae wafers, spirulina-based sinking discs, and blanched vegetables such as courgette (zucchini), cucumber, and spinach leaves. Occasional protein supplementation with live or frozen invertebrates is consistent with opportunistic feeding on small invertebrates trapped in biofilm in the wild. Access to smooth river pebbles or slate on which biofilm can develop naturally is beneficial in the aquarium.
Mating
No mating observations for Pseudancistrus asurini are on record in the available literature or in hobbyist databases. The species is not known to be established in the ornamental trade at this time.
Based on the general biology of Pseudancistrus and close relatives within Ancistrini, males are expected to develop enlarged interopercular odontodes (cheek bristles) during reproductive condition — a character used in sexing many ancistrinine species. Males would typically compete for and defend cave or crevice sites before attempting to court females.
Breeding
No breeding records for Pseudancistrus asurini in captivity are known. The species was described only in 2015 and has not been reported in the aquarium trade.
By analogy with the broader Ancistrini, cave-spawning with paternal brood care is the expected reproductive mode — the male guarding adhesive eggs within a rock crevice or narrow cavity and fanning them until hatching. Any confirmation of captive reproduction would represent a significant new record for this recently described species.
In the aquarium
Pseudancistrus asurini is not established in the ornamental fish trade as of the date of this article. Its large maximum size — approaching 10 in TL — and origin in the highly oxygenated, current-swept Rio Xingu rapids indicate that any successful aquarium husbandry would require a spacious, well-filtered tank with strong water movement and high dissolved oxygen, smooth rock work and slate for grazing, and a diet centred on algae and plant-based foods.
Given the hydroelectric development pressures on the Xingu (the Belo Monte dam complex altered flow regimes near Altamira), wild-caught specimens are unlikely to enter trade through routine commercial channels. Should the species ever become available, care requirements would closely follow those of other mid-to-large Pseudancistrus: clean, warm, oxygen-rich water; ample rock structure; and a predominantly herbivorous diet.
Conservation
The IUCN Red List has not yet evaluated Pseudancistrus asurini; its status is Not Evaluated (NE). The species was described in 2015, and formal assessment had not been conducted as of the available data.
The type locality in the Rio Xingu near Altamira falls within one of the most heavily impacted stretches of any major Amazon tributary, owing to the construction of the Belo Monte hydroelectric complex. Altered flow regimes, changes in sediment transport, and disruption of rapids habitats in the Volta Grande reach are substantive concerns for endemic rheophilic fish communities in this system. Pseudancistrus asurini, with an apparently restricted range tied to this rapids-dependent habitat, may face localised pressure even in the absence of formal threat assessment.