Taxonomy & naming
Hypostomus rondoni was described by Alípio de Miranda Ribeiro in 1912, from specimens collected in the Tapajós River basin of Brazil during one of the Rondon Commission's telegraph-line expeditions through Mato Grosso and Amazonas. The holotype (MNRJ 741, 2.5 in SL) is held at the Museu Nacional in Rio de Janeiro. The Catalog of Fishes (Eschmeyer, CAS) recognises Hypostomus rondoni as a valid species within the large and species-rich genus Hypostomus Lacépède, 1803.
Hypostomus is the most speciose genus in the family Loricariidae and one of the most diverse in all of Siluriformes, encompassing well over 140 valid species distributed across South America east of the Andes. Placement within the genus is based on the combination of ventral mouth, plated body armour, and the arrangement of teeth and scutes characteristic of the Hypostominae lineage. Within the vast Hypostomus radiation, H. rondoni is a small-bodied species from a tributary of the Amazon whose precise phylogenetic affinities within the genus have not been formally resolved in published molecular work accessible to date.
Morphology
Hypostomus rondoni is a small species, with FishBase citing a maximum recorded length of 3 in total length (TL) — notably small for the genus, where many species exceed 8–12 in. Like all members of Hypostomus, the body is encased in rows of overlapping bony scutes that provide mechanical protection; the number and arrangement of these plates are important taxonomic characters. The ventral surface is largely unplated and pale, in contrast to the armoured and typically brownish or olivaceous dorsal side.
The mouth is directed ventrally and is equipped with spatulate, bicuspid teeth suited for rasping algae and biofilm from hard substrates. The genus as a whole includes members capable of facultative air-breathing — an adaptation to low-oxygen conditions in dense, warm Amazonian waters, accomplished via a modified stomach that can extract oxygen from gulped air. Whether H. rondoni employs this capacity in the wild has not been confirmed in the accessible literature, though it is a widespread trait across the genus.
Detailed colour pattern data for H. rondoni specifically are not available in accessible published sources; as is typical for many Hypostomus species, the ground colour is likely a muted brown or grey with darker spotting or mottling.
Habitat
Hypostomus rondoni is recorded from the Tapajós River basin, a major southern tributary of the Amazon draining the Brazilian Shield through the states of Mato Grosso and Pará. The Tapajós is a clear-water river system with comparatively low turbidity and moderate acidity, flowing over ancient Precambrian basement rocks that contribute little mineral load to the water.
Specific habitat data for H. rondoni at the microhabitat level are not documented in sources accessible at the time of writing. As a small loricariid of the genus Hypostomus, it would be expected to occupy benthic substrates — rocky outcroppings, submerged wood, and hard-substrate surfaces — in riverine environments where periphyton and algal growth provide the nutritional base. The Tapajós basin spans a large latitudinal range and encompasses a variety of habitat types from upper highland tributaries to the broad lower river approaching its confluence with the Amazon.
Feeding
Detailed dietary studies for H. rondoni are not available. Members of Hypostomus are broadly characterised as algivores and periphyton scrapers, using their ventral rasping mouth to dislodge algae, diatoms, cyanobacteria, and associated organic matter from hard substrates. The spatulate bicuspid teeth are well adapted for grazing on hard, biofilm-covered surfaces such as rocks and submerged wood.
Some Hypostomus species also ingest detritus and fine organic particles, and opportunistic consumption of invertebrates within algal mats has been recorded in the genus. In the absence of species-specific feeding data, the assumption that H. rondoni is a benthic biofilm grazer is consistent with both its morphology and the feeding ecology typical of small Hypostomus from Brazilian shield rivers.
Mating
No species-specific mating or courtship observations for Hypostomus rondoni have been published in sources accessible at the time of writing. Reproductive behaviour in Hypostomus as a genus typically involves cave spawning, with males selecting and defending suitable cavities — undercut banks, rock crevices, or burrows in soft substrate. Territorial competition between males in the vicinity of breeding sites is common across the genus.
Given H. rondoni's small body size (maximum ~3 in TL), any breeding cavity it uses would be correspondingly modest in dimension. The species is not recorded in the ornamental fish trade, so aquarium observations that might supplement the sparse field record are unavailable.
Breeding
Breeding data for Hypostomus rondoni are not documented in the accessible literature. Across Hypostomus, the reproductive pattern that has been studied in other species involves adhesive eggs deposited inside excavated or pre-existing cavities, with the male providing parental care by guarding and fanning the developing brood. Clutch sizes vary considerably among species in relation to body size.
Given the dearth of ecological and captive data, nothing specific can be stated about clutch size, incubation duration, or larval development in H. rondoni. Any account would be extrapolation from congeners rather than documented fact.
In the aquarium
Hypostomus rondoni does not appear to be established in the ornamental fish trade under this name, and no captive husbandry records have been located. Its small maximum size of approximately 3 in TL would, in principle, make it one of the more manageable Hypostomus species for aquarists — a meaningful contrast to the large common plecos that frequently outgrow modest home aquaria.
For any small Hypostomus from a Brazilian clear-water system, a soft-water, slightly acidic to neutral setup (pH 6.5–7.2, low conductivity, temperature 75–82 °F) with ample rocky or woody structure and good water movement would likely replicate essential habitat features. Algae growth on hard surfaces, supplemented with algae wafers and blanched vegetables, would constitute an appropriate diet. These are general inferences from the species' origin and generic biology, not confirmed husbandry data.
Conservation
The IUCN Red List assessed Hypostomus rondoni as Least Concern (LC) in November 2018, reflecting no identified population declines or major threats at the time of assessment. The Tapajós River basin supports a diverse ichthyofauna and, compared to some Amazon tributaries, has historically experienced somewhat lower deforestation pressure across portions of its range — though headwater areas in Mato Grosso have faced agricultural expansion.
The Tapajós basin has been subject to hydroelectric development pressure in recent decades, with proposed and constructed dams raising concerns about altered hydrology and sediment dynamics that could affect species dependent on hard substrates and clear-water conditions. The species' small size and presumably localised microhabitat requirements warrant continued monitoring, though no current evidence suggests it is facing significant threat across its range.