Taxonomy & naming
Hypostomus macrops was described by Carl H. Eigenmann and Rosa Smith Eigenmann in 1888, making it one of the earlier Hypostomus descriptions from the prolific Eigenmann partnership. The type locality is southeastern Brazil, in the region of coastal Atlantic drainage rivers. The species epithet macrops is straightforward Greek for 'large-eyed' (makros = large; ops = eye), referring to the comparatively prominent eyes that Eigenmann & Eigenmann considered a distinguishing feature. Catalog of Fishes (Eschmeyer/CAS) lists Hypostomus macrops as a valid species. It belongs to the subfamily Hypostominae, tribe Hypostomini. The Atlantic Forest drainage of southeastern Brazil hosts a diverse and largely endemic loricariid fauna, and Hypostomus macrops belongs to this regional assemblage. Several nominal species described in the late nineteenth and early twentieth centuries from this area have been synonymised over time, but H. macrops has retained its validity.
Morphology
Hypostomus macrops is a moderately sized pleco, with published records suggesting adults can reach approximately 8–11 in standard length, though most individuals encountered are smaller. The most notable feature for which it was named is the relatively large eye compared to many congeners — a character that may be linked to clearer-water habitats where visual acuity offers greater utility. Body coloration is generally brownish to olivaceous, with a darker pattern of spots or blotches over the dorsum, flanks, and dorsal fin. The ventral surface is pale. The body is covered in the characteristic keeled, bony scutes of the genus; the dorsal fin spine is robust, and the pectoral-fin spines bear recurved odontodes. The caudal fin is slightly lunate to forked. The sucking disc is broad with papillose lips adapted for rasping biofilm from surfaces. Meristic and morphometric details diagnostic for the species relative to sympatric congeners are provided in the original description and subsequent revisional literature.
Habitat
Hypostomus macrops is associated with the Atlantic coastal drainage rivers of southeastern Brazil — river systems that drain the escarpment of the Serra do Mar and Serra Geral mountain ranges into the Atlantic Ocean. These rivers are typically clear to slightly turbid, well-oxygenated, and exhibit a rocky to gravelly substrate in the mid and upper reaches. They are characterised by a subtropical to warm-temperate climate with marked seasonality: water temperatures range from approximately 61–64 °F (61–64 °F) in winter to 77–82 °F (77–82 °F) in summer. pH tends toward the slightly acidic to neutral range (pH 6.5–7.2) in undisturbed tributaries. Hypostomus macrops is a benthic species, occupying the littoral and sublittoral zones of rivers, sheltering beneath rocks and woody debris during the day. The Atlantic Forest biome that surrounds its river systems is critically endangered due to extensive historical deforestation.
Feeding
Like other Hypostomus, H. macrops is primarily a herbivorous grazer that uses its inferior sucking disc to rasp aufwuchs — the community of algae, diatoms, cyanobacteria, and associated micro-invertebrates that colonises hard surfaces in clear-water rivers. Rocky substrates in the clear rivers of the Atlantic Forest drainage typically support dense benthic algal communities, particularly during the low-water dry season (May–September in this region) when reduced turbidity allows greater light penetration. Organic detritus and fine particulate matter are also consumed. The bicuspid, spatulate teeth typical of Hypostomus are efficient for scraping rather than nipping or biting. Gut-content studies specific to H. macrops have not been published, but dietary data from co-occurring loricariids in southeastern Brazilian coastal rivers consistently show algae and detritus as dominant items.
Mating
Reproductive behaviour of Hypostomus macrops in nature has not been described in the published literature. The genus Hypostomus broadly employs cavity spawning, with territorial males guarding burrows or rocky crevices used as nest sites. In the seasonal rivers of southeastern Brazil, spawning activity is expected to coincide with rising water temperatures and increasing day length during the austral spring (September–November). Male H. macrops, as with congeners, likely develop more pronounced odontodes on the pectoral-fin spines and possibly the opercular region at reproductive maturity — features that may function in male-male competition for nest sites or in courtship signalling. The females' role is limited to egg deposition; subsequent parental care is handled exclusively by the male.
Breeding
No confirmed captive breeding records for Hypostomus macrops have been published. The species is not a regular aquarium fish, so captive reproduction has had little opportunity to be documented. For hobbyists who might acquire this species (e.g., from Brazil-sourced stock), the same approach used for other subtropical Hypostomus would apply. Providing suitably sized spawning caves — PVC pipes or clay tubes of 2–3 in internal diameter and 12–15.5 in length — is essential for triggering nest occupation by the male. A seasonal temperature reduction to around 64–68 °F (64–68 °F) over winter followed by gradual warming in spring can simulate natural seasonal cues. Clutch sizes in related species range from 50 to 200+ eggs; eggs are adhesive and yellow-orange. The male guards and fans the brood; the fry initially subsist on yolk before grazing algal films. Soft water and high oxygen levels during incubation support best hatching rates.
In the aquarium
Hypostomus macrops is not commercially available through the mainstream ornamental fish trade and would be unusual to encounter outside of Brazil. Any specimens would most likely originate from incidental collection alongside other Brazilian loricariids. As a subtropical species, it tolerates and may require a moderate winter temperature drop — cooler conditions (64–72 °F / 64–72 °F) in austral winter simulate the natural seasonal cycle and keep the fish in good health. Summer temperatures up to 79–81 °F (79–81 °F) are tolerated. A tank of at least 55–65 US gal with good filtration and oxygenation is appropriate for an adult. Rocky décor with multiple hiding places should be provided; driftwood and smooth flat rocks mimic natural substrates. Diet should be plant-based: algae wafers, spirulina, and blanched vegetables form the core diet, with sinking pellets as supplement. This species is not strongly territorial with non-loricariid tankmates, but two males in close proximity may engage in competition for shelter sites.
Conservation
Hypostomus macrops has not been formally assessed on the IUCN Red List and its status is Not Evaluated (NE). The Atlantic Forest drainage of southeastern Brazil, where H. macrops occurs, is one of the most threatened river systems in South America. The Atlantic Forest biome retains less than 12–15% of its original extent due to centuries of logging, agricultural conversion, and urban expansion, and many of the smaller coastal river systems that drain it have been severely altered. Deforestation removes riparian shade and increases erosion and sedimentation, which directly damages the rocky benthic habitats that Hypostomus depends on. Water extraction for agriculture and urban use reduces dry-season flow in smaller tributaries. Point-source and diffuse pollution from agriculture and urbanisation are additional stressors. H. macrops's apparent restriction to southeastern Brazilian coastal drainages means that its range may be naturally limited, which compounds these anthropogenic threats. A precautionary conservation concern is warranted, though formal assessment is absent.