Taxonomy & naming
Hypostomus pseudohemiurus was described by Marinus Boeseman in 1968 in Zoologische Verhandelingen (Leiden), number 99, page 54 (plate 9, figures 1–4), from material collected at the Kabalebo River — a tributary of the Corantijn (Corantyne) River system in Suriname. The name is a compound: pseudo (Greek: false) combined with hemiurus, referencing the earlier species Hypostomus hemiurus; the epithet signals that this fish superficially resembles H. hemiurus but is a distinct taxon.
The Catalog of Fishes (Eschmeyer, CAS) recognises the valid name Hypostomus pseudohemiurus Boeseman, 1968. No synonyms are recorded. No L-number or common name has been assigned. The species belongs to genus Hypostomus Lacépède, 1803 within subfamily Hypostominae of family Loricariidae.
Morphology
At approximately 2.5 in standard length (SL), Hypostomus pseudohemiurus is among the smallest recorded members of Hypostomus — a genus whose members range from a handful of compact species at 2.5–4 in to large specimens exceeding 23.5 in. The body follows the typical Hypostomus architecture: dorsoventrally flattened, covered in keeled bony scutes on the flanks and dorsal surface, with an unplated pale ventral surface, and a broad ventral sucker mouth for rasping substrates.
Beyond size and the collection details from Boeseman's original description, detailed morphometric or coloration data for H. pseudohemiurus are not available in the consulted sources. Given the species' absence from the hobby and the limited post-1968 literature on it, its external appearance beyond the diagnostic characters used to separate it from H. hemiurus remains sparsely documented. Sexual dimorphism has not been described.
Habitat
The type locality is the Kabalebo River in the Corantijn (Corantyne) River basin, Suriname. The Corantijn drains the Guiana Highlands southward into Suriname and Guyana before discharging into the Atlantic, and the Kabalebo is a blackwater tributary flowing through lowland rainforest. PlanetCatfish lists the distribution as covering the Guiana coastal rivers, Suriname coastal rivers, and potentially extending into the Guyana portion of the Corantijn catchment.
Blackwater drainages of this type are characterised by high tannin content (from leaf litter), low pH, very soft water, and low mineral content — a chemical environment distinct from the whitewater Andean-fed rivers that many Hypostomus occupy. Water temperatures in Surinamese lowland rivers are typically warm and relatively stable year-round, consistent with equatorial conditions. Specific field measurements for the Kabalebo are not available in the consulted sources.
Feeding
No feeding data specific to Hypostomus pseudohemiurus exist in the consulted sources. By inference from the genus, it is expected to be an epilithic algae grazer and biofilm scraper, using the ventral sucker mouth to rasp periphyton from submerged rocks, wood, and leaf litter. Hypostomus species also possess the capacity for facultative air-breathing — surfacing to gulp atmospheric oxygen in low-oxygen conditions.
The small size of this species may reflect an ecological niche within fine-textured substrate or smaller microhabitat structures than those used by larger Hypostomus. Nothing further can be stated without field or captive observations.
Mating
No mating behaviour has been documented for Hypostomus pseudohemiurus. No captive records exist, and the species has not been the subject of field behavioural studies. Reproductive behaviour, if consistent with the genus, would involve male territory establishment around shelter sites and courtship leading to spawning within a chosen cavity.
The species' small body size raises questions about whether breeding cavities, clutch size, and fry development differ quantitatively from larger Hypostomus — but these remain entirely open questions without data.
Breeding
No breeding records exist for Hypostomus pseudohemiurus. The species appears to be unknown in captivity, and no hobbyist has reported spawning or rearing fry. Whether it follows the standard Hypostomus cave-spawning strategy with paternal brood care cannot be confirmed from available information.
Given its small size, any future captive breeding attempts would likely require a relatively modest aquarium setup compared to larger Hypostomus — but specific parameters cannot be recommended without more data on its natural history.
In the aquarium
Hypostomus pseudohemiurus has no recorded presence in the aquarium hobby. PlanetCatfish lists no registered keepers, no spotters, and no breeding reports. The species has never been assigned an L-number, and no trade or importation records have been identified.
Its small maximum size — approximately 2.5 in SL — would in principle make it one of the most manageable Hypostomus for the home aquarium. However, the complete absence of captive experience means that tank requirements, diet, water chemistry preferences, and compatibility with other species cannot be specified beyond what is inferred from blackwater loricariid biology in general. Aquarists who encounter this species should treat it as a blackwater fish from soft, acidic, tannin-rich water, avoid hard alkaline conditions, and provide fine-grained substrate or smooth rock surfaces for grazing. Until captive records become available, nothing more specific can be offered.
Conservation
The IUCN Red List assessed Hypostomus pseudohemiurus as Least Concern in January 2021. The Corantijn (Corantyne) River basin spans Suriname and Guyana, both countries with significant areas of intact lowland rainforest. The basin as a whole has not been subjected to the large-scale deforestation that has affected parts of Amazonian Brazil, and the species is not known to be targeted by the ornamental fish trade.
Suriname's interior forests and river systems remain among the least disturbed in South America, and bauxite mining — historically the main extractive pressure in the Surinamese interior — has not extensively impacted the Corantijn watershed. The Least Concern assessment reflects the absence of identified threats rather than detailed population data; biological records for this species remain sparse.