Taxonomy & naming
Hypostomus simios was formally described by Hollanda Carvalho and Weber in 2005 in the Revue Suisse de Zoologie (volume 111, number 4, pages 953–978), as one of five new species of the Hypostomus cochliodon group from the middle and lower Amazon system. The holotype, MZUSP 82268 at 6 in SL, and a single paratype, MHNG 2652.018 at 4.5 in SL, were both collected from the Rio Cupixi, Amapá State, northern Brazil — the only known locality for the species.
The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hypostomus simios Hollanda Carvalho & Weber, 2005. The species belongs to the Hypostomus cochliodon group — a clade characterised by the possession of spoon-shaped (spatulate) teeth on both jaws and a blunt, compressed snout. H. simios was described alongside H. fonchii, H. macushi, H. paucipunctatus, and H. waiampi in the same publication.
Within the family Loricariidae, Hypostomus is the largest genus, comprising several hundred valid species. H. simios is placed in subfamily Hypostominae, the dominant grouping in the family. The cochliodon species group within Hypostomus shares a wood-eating ecology convergent with the Panaque lineage, though the two are not considered closely related.
Morphology
Adults reach 6 in standard length (SL) based on the holotype at 6 in. The most distinctive character of H. simios within the cochliodon group is the snub-nosed (blunt, compressed) snout profile that gives the species its name. The head is broad and depressed, with the mouth positioned ventrally and armed with the spoon-shaped spatulate teeth diagnostic of the cochliodon group — teeth adapted for rasping wood and encrusting biofilm from hard substrates.
The body is covered in the overlapping bony scutes typical of all loricariids. Exact details of coloration, keeling of scutes, and fin ray counts were established in the original description but are not replicated here from secondary sources. As with other members of the cochliodon group, the trunk is robust relative to the pointed caudal region.
Sexual dimorphism has not been specifically documented for this species in published sources consulted. In the genus Hypostomus broadly, breeding males often develop interopercular odontodes and odontodes along the first pectoral fin ray.
Habitat
Hypostomus simios is currently known exclusively from the Rio Cupixi, a right-bank tributary of the lower Amazon in Amapá State, northernmost Brazil. The Cupixi basin is a lowland Amazonian system draining a region of terra firme forest and associated sandy and rocky stream beds that characterise the Guiana Shield fringe of the lower Amazon.
No water chemistry data specific to H. simios collection sites appear in published records consulted. Members of the Hypostomus cochliodon group in the lower Amazon system generally inhabit clear to black-water rivers over rocky or wood-rich substrates, where the fish exploit submerged logs and root tangles as both feeding substrates and refuge sites. The Cupixi is a seasonally variable river subject to Amazonian flood pulses, and like most lower Amazon tributaries likely experiences temperature ranges in the tropical band (approximately 75–86 °F) with moderately acidic, soft water typical of the region.
Feeding
The cochliodon group affiliation of H. simios strongly implies a wood and hard-substrate diet. Members of this clade possess spatulate teeth — broad, spoon-shaped at the tip — that are adapted for gouging into submerged wood to access cellulose fibres, fungi, bacteria, and other biofilm components colonising wood surfaces. This is a fundamentally different feeding strategy from the aufwuchs (algae-scraping) approach of the majority of Hypostomus species, which carry fine, bidentate teeth.
Diet specifics for H. simios in the field have not been published in the sources consulted. By analogy with other cochliodon-group species (e.g., Hypostomus cochliodon, H. pyrineusi), the species is expected to be primarily xylophagous and biotrophic on encrusting wood biofilm.
In any aquarium context, quality hardwood driftwood should be regarded as a dietary requirement rather than optional decor, supplemented with vegetable matter (algae wafers, blanched vegetables).
Mating
Mating behaviour has not been documented for Hypostomus simios in the published literature consulted. Courtship and pair formation in the genus Hypostomus generally follows a male-territorial pattern in which males claim and defend cave or crevice sites — frequently within submerged wood structures — and attract females through positional display and odontode elaboration.
Given the species' rarity in the wild, inferred only from two type specimens, no aquarium breeding records have been traced. Any account of specific mating behaviour for this species would be speculative and is not presented here.
Breeding
No breeding data for Hypostomus simios have been published in sources consulted, nor have aquarium spawning records been traced. The species appears to be unknown in the ornamental trade.
Hypostomus as a genus is broadly characterised by cave-spawning with paternal brood care: the male selects and defends a tight cavity, eggs are deposited on the cavity walls, and the male fans and guards the clutch until hatching. This is a general expectation for H. simios based on genus-level biology, but has not been confirmed for this species specifically.
In the aquarium
Hypostomus simios does not appear to be established in the ornamental trade, and no aquarium husbandry accounts have been traced. The species is known from only two museum specimens.
Were it to become available, the cochliodon-group biology points to an aquarium approach similar to that used for other wood-eating Hypostomus: a spacious tank with abundant quality driftwood, good filtration to handle the substantial waste output of a 6 in-class catfish, and soft to moderately soft water with a slightly acidic to neutral pH reflecting the blackwater character of Amapá waterways. Temperature in the 75–82 °F range would be appropriate for a lower Amazonian species.
As a putatively rare, range-restricted species, any specimens encountered should be treated with care; sourcing from captive-bred stock would be strongly preferable if the fish ever enters the trade.
Conservation
The IUCN Red List assessed Hypostomus simios as Least Concern in 2018, based on available distributional data. The species is treated as endemic to the Rio Cupixi basin in Amapá State, northern Brazil — a relatively intact region of Amazonian forest with lower deforestation pressure than many other parts of the Amazon catchment at the time of assessment.
The restricted range is a potential vulnerability: a species known from a single river basin has limited buffering against localised habitat degradation. Amapá faces incremental pressures from agricultural expansion, mining activity, and road development. Ongoing monitoring of the Cupixi basin would be warranted to ensure the LC assessment remains valid as land-use change progresses.