Taxonomy & naming
Hypostomus macrophthalmus was described by Boeseman in 1968 from material collected in the Sipaliwini River basin of southern Suriname. The Catalog of Fishes (Eschmeyer, CAS) records the valid combination as Hypostomus macrophthalmus Boeseman, 1968; Isbrücker (1980) formalized its recognition at full species rank, resolving earlier ambiguity about its status relative to allied forms.
The species belongs to Hypostomus, the largest genus in Loricariidae and one of the largest vertebrate genera on earth, with well over 150 described species. Hypostomus sits within subfamily Hypostominae and shares the basic loricariid armour-plating, inferior mouth, and benthic lifestyle common to suckermouth catfishes broadly. No L-number or aquarium trade designation has been applied to H. macrophthalmus, which has no documented presence in the ornamental trade.
Two potential points of confusion deserve note. H. macrophthalmus is wholly distinct from Hypostomus macrops Cope, 1874 — a larger Amazonian species described nearly a century earlier and placed in a different species group. It is equally unrelated to Ancistrus macrophthalmus, a different loricariid genus entirely. The epithet macrophthalmus has been applied independently in several catfish genera; context and authority are essential for disambiguation.
Morphology
Hypostomus macrophthalmus is a small species, reaching approximately 3 in standard length (SL). The body follows the typical Hypostomus plan: broad, depressed, and entirely encased in interlocking bony scutes arranged in rows along the flanks and dorsum. The ventral surface is unplated and paler, as is characteristic of the family.
The common name implied by the epithet — large-eyed — points to the most distinctive reported feature: relatively prominent eyes for a benthic suckermouth catfish. Large eyes in bottomdwelling armoured catfishes are sometimes associated with low-light habitats, whether deep or heavily tannin-stained, and the blackwater systems of the Sipaliwini basin would be consistent with such selective pressure. Published coloration and meristic data for this species are sparse; the original 1968 description and subsequent literature have not been widely reproduced in accessible sources.
Sexual dimorphism is not documented in the literature for this species. As a general pattern across Hypostomus, males of many species develop odontodes on the leading pectoral-fin spine and on the interopercular region during the breeding season, and females become visibly deeper-bodied when gravid, but these generalizations should not be attributed specifically to H. macrophthalmus without direct evidence.
Habitat
The Sipaliwini River is a headwater tributary of the Corantijn (Courantyne) River, draining the Tumuc-Humac highland region at the southern border of Suriname and northern Brazil. The Sipaliwini basin is geologically ancient and ecologically distinctive: the Sipaliwini savanna, an open grassland–forest mosaic set among granite inselbergs at roughly 1312 ft elevation, supports a high degree of endemic fauna and flora isolated by surrounding lowland rainforest.
The rivers of this system are characterised as blackwater or clearwater — tea-coloured, ion-poor, and acidic, stained by dissolved humic and fulvic acids leached from organic soils and vegetation. Water temperatures in lowland Suriname rivers are warm year-round (typically 79–86 °F in similar systems), with soft water (low conductivity) and pH commonly in the range of 4.5–6.5. Site-specific measurements for the Sipaliwini have not been located in accessible literature for this species.
H. macrophthalmus is presumed to occupy benthic microhabitats: rocky or root-strewn stream margins, submerged wood, and stone surfaces where biofilm develops. The extreme remoteness of the Sipaliwini basin has limited systematic field work, and the species' microhabitat requirements remain incompletely characterised.
Feeding
No published gut-content analysis or direct feeding observations for Hypostomus macrophthalmus have been found in accessible sources. Diet is inferred from genus-level biology: Hypostomus species are predominantly aufwuchs feeders, rasping biofilm — the complex community of algae, bacteria, diatoms, and fine detritus — from hard surfaces using the inferior, sucking mouth and comb-like teeth. Many species also ingest detritus, fine organic particles, and small invertebrates incidentally.
The soft, acidic blackwater environment of the Sipaliwini likely supports limited algal growth relative to more nutrient-rich whitewater or clearwater systems; biofilm on submerged roots, wood, and rock surfaces would be the principal food resource in such a habitat. Wood rasping, while a specialisation of some Hypostomus lineages, is not documented for this species.
Mating
Mating behaviour in Hypostomus macrophthalmus is undocumented. Across the genus Hypostomus, the predominant reproductive mode involves males excavating or occupying cavities in riverbanks, submerged wood, or rock crevices, which they defend against rival males and use as spawning sites. Males are typically territorial during the breeding season and may develop enhanced odontodes on the pectoral spines or interopercular region as secondary sexual characters.
Given the very restricted and remote range of H. macrophthalmus, no aquarium breeding attempts have been recorded, and field observations of courtship behaviour are absent from the literature. Details provided here reflect general Hypostomus reproductive biology and should not be taken as species-specific documentation.
Breeding
Breeding in Hypostomus macrophthalmus has not been documented in either aquaria or the field. The genus is broadly characterised as cave-spawning with paternal brood care: the male guards and fans the egg clutch within a defended cavity until the fry are free-swimming and capable of independent feeding. This pattern has been confirmed in multiple Hypostomus species across the genus but cannot be attributed to H. macrophthalmus specifically without direct evidence.
Given that the species is not in the aquarium trade and occupies one of South America's most inaccessible river systems, reproductive biology data are likely to remain sparse until dedicated field surveys are conducted in the Sipaliwini basin.
In the aquarium
Hypostomus macrophthalmus is not known to be present in the aquarium trade. Its restricted range — a single remote river basin in southern Suriname — makes collection for export logistically difficult, and the Endangered status of the species would raise serious ethical and regulatory barriers to collection. No hobbyist reports, care guides, or breeding accounts for this species have been located.
For reference, its small adult size (3 in SL) would in principle make it manageable in a modestly sized aquarium by Hypostomus standards, and the blackwater origin suggests that soft, acidic, well-oxygenated conditions with minimal lighting and ample cover would be appropriate. However, this information is provided strictly in a biogeographic context — the conservation status of the species makes its collection from the wild inappropriate, and no captive population is known to exist.
Conservation
The IUCN Red List assessed Hypostomus macrophthalmus as Endangered (EN) under criterion B1ab(iii), with the assessment published on 14 January 2021. The B1 criterion applies because the estimated extent of occurrence (EOO) is below 5,0 mi² and the area of occupancy (AOO) is below 311 mi². The 'a' and 'b(iii)' qualifiers indicate that the range is severely fragmented or represents very few locations, with an observed or projected continuing decline in the area, extent, or quality of habitat.
The species is known only from the Sipaliwini River basin in southern Suriname — a single hydrological unit. The Tumuc-Humac highland region, while currently remote and largely inaccessible, is not immune to the pressures affecting Amazonian and Guiana Shield watersheds more broadly: deforestation, gold mining (garimpo), and climate-driven changes in precipitation and river hydrology all pose potential threats to the narrow-range endemics of this system.
The combination of a tiny AOO, documented habitat quality decline, and absence from aquaculture makes H. macrophthalmus one of the higher-concern Hypostomus species from a conservation perspective, despite — or rather because of — its obscurity in the broader ichthyological literature.