Taxonomy & naming
Oxyropsis acutirostris was described by Paulo de Miranda Ribeiro in 1951, published in the Boletim do Museu Nacional, Zoologia (N. S.) No. 104, pages 1–3 with plates. The holotype (unique specimen, MNRJ 5745) was collected at Paricachoeira on the Rio Taquié, a tributary of the Rio Uaupés (Vaupés), itself a tributary of the upper Rio Negro in Amazonas state, Brazil. The Catalog of Fishes (Eschmeyer, CAS; updated 10 June 2026) records the current valid name as Oxyropsis acutirostris Miranda Ribeiro, 1951. A common variant spelling — acutirostra — appears throughout the literature from Aquino & Schaefer (2002) through Ferraris (2007) and later authors, but CoF treats the original masculine-adjective form acutirostris as the valid epithet.
The species was previously placed in Hypoptopoma (as H. acutirostre) by Isbrücker (1980) before being returned to Oxyropsis. The genus Oxyropsis was erected by Eigenmann & Eigenmann (1889) to accommodate suckermouth catfishes with a notably flattened posterior body and caudal peduncle — a shape that distinguishes them at a glance from the more rounded-section Hypoptopoma. A revision by Aquino & Schaefer (2002, Copeia 2002(2):374–390) confirmed Oxyropsis as a monophyletic assemblage of three species: the type species O. wrightiana, O. carinata, and O. acutirostris. Within Loricariidae, Oxyropsis belongs to subfamily Hypoptopomatinae, the so-called cascudinhos or mini-suckermouth catfishes (Armbruster, 2004; Delapieve et al., 2017).
Morphology
Adults reach approximately 1.5 in standard length (SL) according to FishBase (ref. 36885), making this the smallest species in the genus — O. wrightiana reaches about 2.5 in SL and O. carinata is intermediate. PlanetCatfish records a maximum of 2 in SL in some accounts; ScotCat gives approximately 2 in total length. The body is covered in the typical loricariid bony scute armour, and is strikingly flattened through the posterior body and caudal peduncle — a diagnostic character of Oxyropsis relative to Hypoptopoma, which has a more circular cross-section.
The snout is notably longer and narrower than in Hypoptopoma, giving the head a more pointed, wedge-like profile — the origin of the specific name. Eyes are positioned high on the head, and like other Hypoptopomatinae, the fish uses both eyes and body armour to survey its environment while pressed against vegetation or substrate. A single longitudinal row of enlarged odontodes runs along the body just dorsal to the lateral line, a feature shared by all Oxyropsis species but absent in Hypoptopoma. Ground colour is typically brownish, often with faint mottling or spotting that provides some camouflage; O. acutirostris is reported by ScotCat to be the most attractive of the three species in the genus, with a more contrasted pattern than its congeners. Sexual dimorphism data for this species are not documented in the primary literature; differences would be expected to follow the general Hypoptopomatinae pattern (gravid females broader-bodied), but this is not confirmed.
Habitat
The distribution of Oxyropsis acutirostris spans the upper Orinoco basin (Venezuela and Colombia), and the upper and lower Rio Negro and Amazon basin (Brazil and Colombia), as confirmed by CoF and FishBase. The type locality — Paricachoeira, Rio Taquié, tributary of the Rio Uaupés / Rio Negro — places the species firmly within the classic blackwater river system of the Guiana Shield, characterised by the tea-coloured humic-acid-stained waters and extreme softness and acidity that characterise Rio Negro drainages.
The broader distribution including the Orinoco suggests this species also occupies clearwater and some whitewater-marginal habitats, but the type locality ecology indicates a primary association with soft, acidic, blackwater or dark-clearwater environments. PlanetCatfish notes a temperature range of 77–82 °F and specifically flags the requirement for highly oxygenated water — an important consideration given that blackwater rivers, while soft and acidic, are not uniformly low in dissolved oxygen; flow and surface agitation matter. Microhabitat specifics are poorly documented; the closely related O. wrightiana has been collected clinging to submerged vegetation and leaf litter in slow to moderate currents, and O. acutirostris almost certainly shares comparable associations. The species is described as the most sensitive of the three Oxyropsis species (ScotCat, citing Evers & Seidel 2005), suggesting some intolerance of polluted or poorly oxygenated conditions.
Feeding
Oxyropsis acutirostris, like other Hypoptopomatinae, is principally an algae and biofilm grazer. The ventral, suctorial mouth is equipped with bicuspid teeth adapted for rasping periphyton — the complex community of algae, bacteria, fungi, and fine organic matter that forms on submerged surfaces including plant leaves, wood, and rock. ScotCat describes the diet as algae, vegetables, tablet foods, and small live or frozen foods, which is consistent with the broad aufwuchs-grazing behaviour shared across the subfamily.
In the wild, the extremely flat body profile likely facilitates feeding on the thin, biofilm-covered undersides of broad-leaved aquatic vegetation — macrophytes, floating plants, and leaf litter — rather than on hard surfaces. The long, narrow snout may allow more precise grazing in confined spaces between structures. Detailed published gut-content studies for O. acutirostris specifically are not available; data should be assumed sparse and extrapolated cautiously from congeners and the broader subfamily. In the aquarium, the fish readily grazes algae growing on plant leaves and glass, and benefits from supplemental algae wafers, spirulina-based foods, and occasional blanched vegetables.
Mating
No published observations of courtship behaviour exist specifically for Oxyropsis acutirostris. No captive breeding records are registered on PlanetCatfish, and the species is rare in the hobby. General Hypoptopomatinae biology suggests that, as with the related Otocinclus and Nannoptopoma, mating likely involves a brief courtship phase in which males pursue and nudge females, followed by adhesive egg deposition on flat surfaces such as plant leaves or aquarium glass.
The scattered keeper reports that do exist (five registered keepers on PlanetCatfish, four field-observation records) have not produced documented breeding accounts. ScotCat notes the species is more sensitive than its congeners, which may partly explain the dearth of captive reproduction data. Any account of breeding behaviour for this species as of the 2026 research date would be speculative. Researchers with wild-caught specimens should document any observed pairing or spawning behaviour, as this would represent a novel contribution to the literature on Oxyropsis reproductive biology.
Breeding
Breeding of Oxyropsis acutirostris in captivity has not been documented in any published account or registered on PlanetCatfish as of 2026. This is unsurprising given the species' rarity in trade and its reputation for sensitivity relative to the other two Oxyropsis species. The closely related genus Otocinclus breeds by adhesive egg spawning on plant leaves, with no parental care; the eggs hatch in roughly two to three days at tropical temperatures, and the fry begin free-swimming and grazing within a few more days.
By analogy with other Hypoptopomatinae, it is reasonable to expect O. acutirostris to be a scatterer of small adhesive eggs on broad-leaved plant surfaces, without extended parental care, and with a reproductive cycle linked to seasonal changes in water conditions (temperature drop, rainfall, water softening) that simulate the Amazon-Orinoco wet-season flood pulse. However, none of this is confirmed for the species. Aquarists attempting to breed this fish should aim to replicate blackwater conditions — pH 5.5–6.5, conductivity below 100 µS/cm, temperature around 77 °F with a slight seasonal drop — while providing broad-leaved vegetation (e.g., Amazon swords, broad Echinodorus species) as putative spawning surfaces.
In the aquarium
Oxyropsis acutirostris is a rarely available species that is not recommended for beginners. It has specific water-chemistry requirements — soft, acidic, well-oxygenated water in the blackwater idiom — and ScotCat explicitly notes it is more sensitive than its congeners O. wrightiana and O. carinata. A soft-water setup with pH 5.5–7.0, conductivity below 150 µS/cm (ideally below 100 µS/cm), and temperature 77–82 °F (ScotCat and PlanetCatfish) is appropriate. Highly oxygenated water is specifically noted as a requirement (PlanetCatfish); surface agitation or a good power filter is advised.
The habitat of choice in the aquarium is a planted tank with broad-leaved plants (Echinodorus, Anubias) and leaf litter — conditions that mimic the vegetated margins of its native blackwater rivers. Long-leaved plants or bamboo stalks, as ScotCat suggests for Hypoptopoma generally, provide resting perches. A small group can be kept together; unlike many pleco species, Hypoptopomatinae are not aggressively territorial. Do not house with other loricariids that would compete for grazing surface or disturb the biofilm the fish depends on.
This is not a trade fish and is unlikely to be found at typical pet shops; specimens occasionally appear through specialist importers or collectors. Wild-caught fish may need extended quarantine and acclimatisation to captive conditions. The fish is not suitable for hard-water community tanks or tanks with large, boisterous species that might disturb it.
Conservation
Oxyropsis acutirostris is assessed as Least Concern on the IUCN Red List, first evaluated in 2020 by Salvador (2023, citing IUCN 2023 records). The assessment notes a wide distribution across the Orinoco and Negro basins, with no evidence of significant population decline. The species occurs within several protected areas in both Brazil and Venezuela.
The broader Rio Negro basin is among the better-protected large river systems in Amazonia, but is not immune to threats from gold mining (which deposits mercury and increases turbidity), deforestation, and the growing human footprint around Manaus and other settlements. Climate change may alter rainfall patterns and thus the seasonal flood-pulse dynamics that these soft-water species depend on for reproduction. No targeted conservation measures are in place for O. acutirostris specifically. It is not significantly traded commercially and does not appear on any national threatened-species lists as of this writing. The most pressing unresolved question is the degree to which its reported sensitivity (relative to congeners) reflects a narrow ecological niche that may contract under future anthropogenic pressure.