Taxonomy & naming
Ancistomus spinosissimus was formally described by Cardoso and Lucinda in 2003 in Ichthyological Exploration of Freshwaters (volume 14, number 1, page 79), from specimens collected in the Rio Maranhão near the mouth of the Rio Tocantinzinho, on the border of Niquelândia and Campinaçu municipalities, Goiás State, Brazil (13°05'25"S, 48°19'08"W). The original generic placement was Hemiancistrus, and the species has also circulated under the combination Hemiancistrus spinosissimus before transfer to Ancistomus. The Catalog of Fishes (Eschmeyer, CAS) and FishBase currently recognise Ancistomus spinosissimus as the valid combination.
The taxonomic status of this species deserves honest qualification. Armbruster et al. (2015) found no reliable distinguishing characters separating A. spinosissimus from the closely related Ancistomus micrommatos and Ancistomus spiloma, concluding that the three may represent a single biological taxon. As of 2026, however, formal synonymisation has not been published, and all three are retained as separate valid species on FishBase and the Catalog of Fishes pending a revisionary study. This article follows current nomenclature while acknowledging that the species limits within this complex remain unresolved.
Ancistomus belongs to subfamily Hypostominae within Loricariidae, one of the most species-rich catfish families in the Neotropics. No L-number has been assigned to this species, and it has not entered the ornamental trade in any documented capacity.
Morphology
Adults reach a maximum known size of approximately 5 in standard length (SL), though museum series may include variation. The most diagnostic feature, commemorated in the species name, is the extraordinary proliferation of odontodes — the tooth-like projections derived from modified scales that cover the body, head, and fins of all loricariids, but here developed to a notably pronounced degree.
Beyond this defining character, the available literature does not provide a detailed morphological description accessible in English-language hobbyist sources, and the original 2003 description is the primary source. General body plan follows the Ancistomus grade: a depressed, fusiform catfish with heavily armoured flanks, a ventrally placed suctorial mouth, and paired pectoral and pelvic fins braced for resting on hard substrates in flowing water. The precise colour pattern, plate row counts, and fin ray formulae in the type series are recorded in the original description but are not reproduced here due to data-density constraints.
Sexual dimorphism has not been reported in the literature or in hobbyist records.
Habitat
The type locality — Rio Maranhão at the confluence with Rio Tocantinzinho, Goiás, Brazil — places this species in the upper Tocantins River system. FishBase records the species from the middle and upper Rio Tocantins and its tributaries. The Tocantins is a large South American river draining the central Brazilian plateau (Planalto Central), ultimately flowing north to join the lower Amazon estuary via the Pará River.
No water chemistry data specific to the collection sites of A. spinosissimus are available in the literature. The Tocantins in this region generally carries clear to slightly turbid water, with characteristics typical of central Brazilian Cerrado streams: moderate temperatures, near-neutral to slightly acidic pH, and variable conductivity depending on season and catchment geology. Ancistomus species are typically benthic, associated with rocky substrates and moderate to fast current, consistent with their heavily armoured body plan and robust pectoral fins.
Feeding
No specific dietary studies or hobbyist feeding observations are on record for Ancistomus spinosissimus. Based on general loricariid biology and the broad feeding ecology of Hypostominae, the species is presumed to be an aufwuchs grazer and biofilm scraper, rasping algae, diatoms, detritus, and associated microorganisms from hard substrates using its suctorial mouth and dentition.
In the unlikely event that specimens entered captivity, the diet appropriate for Hypostominae of similar size and ecology would apply: high-quality algae wafers, spirulina-based foods, blanched vegetables, and sinking pellets formulated for herbivore-omnivore catfishes.
Mating
No mating behaviour has been recorded in the wild or in captivity for this species. Ancistomus is a genus with limited reproductive data across most of its members. Loricariids in the Hypostominae broadly display cave-spawning or crevice-spawning behaviour with paternal brood care, but whether A. spinosissimus follows this pattern is unknown. The species has not been bred in captivity, and no keeper records exist on PlanetCatfish or comparable hobbyist databases.
Breeding
No breeding observations have been documented for Ancistomus spinosissimus. The species is unknown in the ornamental trade and has not been maintained in captivity in any recorded instance. Information on clutch size, incubation period, or parental roles cannot be offered without fabrication.
In the aquarium
Ancistomus spinosissimus is not known in the hobby. No keeper records, import records, or captive-care observations appear in the PlanetCatfish database or other major hobbyist resources as of the time of writing. The species has no assigned L-number and no established common name in the trade.
Should specimens ever become available, the general framework for a Tocantins-basin Hypostominae of approximately 5 in SL would apply: a well-oxygenated aquarium with significant water movement, rocky or woody substrates, pH in the moderately acidic to neutral range, and temperatures reflecting Cerrado stream conditions — broadly 72–81 °F. The heavily armed body suggests an affinity for rheophilic (fast-water) microhabitats, and tank design would need to accommodate that.
No tank size recommendations, compatibility notes, or specific care parameters can be offered with confidence given the complete absence of captive data.
Conservation
The IUCN Red List assessed Ancistomus spinosissimus as Least Concern in 2018, indicating that available data do not suggest the species is under immediate threat. The assessment was published 7 November 2018 (FishBase records this date).
The Tocantins River basin has, however, experienced significant hydrological alteration through dam construction — most notably the Tucuruí Dam, one of the world's largest hydroelectric facilities, which inundated a substantial portion of the lower Tocantins and fundamentally changed downstream flow regimes. The type locality of A. spinosissimus lies in the middle and upper reaches above the main reservoir, but ongoing hydroelectric expansion in the Tocantins basin represents a relevant long-term pressure on rheophilic species with restricted ranges. The possible synonymy with A. micrommatos and A. spiloma, if confirmed, could affect how the combined range and conservation status is evaluated in a future assessment.