Taxonomy & naming
Ancistomus spilomma was formally described by Cardoso and Lucinda in 2003, in Ichthyological Exploration of Freshwaters (volume 14, number 1, page 75), from specimens taken at the Rio Tocantins near the mouth of the Rio Lajeado at Porto Franco, Tocantins state, Brazil. The original combination placed the fish in Hemiancistrus — a genus used broadly at the time for spotted ancistrine plecos lacking the character sets of better-defined genera — but subsequent phylogenetic revision moved it to Ancistomus, the combination now accepted by the Catalog of Fishes (Eschmeyer, CAS) and FishBase.
The specific epithet spilomma derives from the Greek spilos (spot) and omma (eye), a reference to the small dark spots occupying the upper portion of the iris; the name functions as a noun in apposition. The hobbyist designation L036 predates the formal description, applied when this fish first appeared in the German aquarium trade from Araguaia collections.
An important caveat: Armbruster et al. (2015) found no unambiguous morphological characters to separate A. spilomma from the closely related A. micrommatos and A. spinosissimus. The three may represent a single polymorphic species, and the Catalog of Fishes retains separate species status pending a formal revision. Authors working with museum material or aquarium specimens from across the Tocantins–Araguaia system should treat identifications cautiously until that revision is published.
Morphology
Adults reach approximately 5.5 in standard length (SL) — a mid-sized pleco by loricariid standards. The body follows the typical compressed-elongate form of the Ancistrini, covered in overlapping bony scutes. Ground coloration is brown to olive-brown on the dorsal and lateral surfaces, with numerous small dark dots scattered across the fins and the lateral and dorsal plates of the head and body. The ventral surface of the head and body is notably free of dark spots — a character listed in the original diagnosis.
The eyes are large and set in a distinctly dorsoventral position, a feature reflected directly in the species name. Lips are well-developed, papillate, and bordered by a smooth band — consistent with the rasping, sucker-mouth lifestyle. The caudal fin is slightly concave with the upper lobe shorter than the lower (a configuration sometimes described as sub-forked). The first anal-fin pterygiophore is greatly expanded and exposed, visible in lateral view — a diagnostic character for the species. Cheek odontodes number 40–60 in the evertible interopercular clusters typical of the tribe. Dorsal-fin formula is not stated in the cache data.
Habitat
Ancistomus spilomma is recorded from the Tocantins and Araguaia drainages of central Brazil — large, geologically ancient rivers that drain the Brazilian Shield into the lower Amazon basin. The type locality is the Rio Tocantins near Porto Franco, Tocantins state; additional specimens photographed in the aquarium trade have been attributed to the lower Tocantins (including sites downstream of the Tucuruí Dam) and to the Parque Estadual da Serra Azul in Mato Grosso, suggesting the species occurs throughout much of the Araguaia drainage as well.
PlanetCatfish temperature data of 73–81 °F brackets the typical seasonal range of these Cerrado-border rivers, which experience pronounced wet and dry seasons. During the dry season water levels drop sharply, concentrating fish in deep channels and rocky riffles; the wet season floods the surrounding gallery forest, dispersing fish into flooded margins. Specific water chemistry data for confirmed A. spilomma localities is not recorded in the available cache; given the Brazilian Shield geology of the Tocantins–Araguaia system, moderately soft, slightly acidic to neutral water is typical, though exact figures should be sourced from field studies.
Feeding
Like other members of the Ancistrini, Ancistomus spilomma is a scraper and biofilm grazer rather than a wood-eater. The ventral, papillate mouth and fine odontodes are adapted for rasping algae, aufwuchs, periphyton, and fine organic detritus from submerged rock and wood surfaces. No specific gut-content analyses are available in the cache, but the morphology is consistent with the generalist scraping strategy seen across most non-xylophagous loricariids.
In aquaria, spirulina-based wafers, blanched vegetables (courgette, cucumber, sweet potato), and sinking algae discs form an appropriate dietary core. Occasional invertebrate-based supplements — frozen bloodworm, daphnia, or sinking carnivore pellets — can be offered to reflect the opportunistic protein intake typical of wild Hypostominae. Driftwood should be provided for grazing and refuge even if this species does not actively rasp it as a primary food source.
Mating
No specific mating observations for Ancistomus spilomma are recorded in the cache, and PlanetCatfish lists no captive breeding reports as of the time of data collection — the species is logged by only three registered keepers and five spotters, reflecting its rarity in the hobby. General patterns from related Ancistrini suggest males become territorial around rocky crevices or hollow wood during the breeding season, developing more prominent interopercular odontodes. Females in breeding condition are typically broader-bodied. Without confirmed in-aquarium observations for this species specifically, detailed mating behaviour remains undocumented.
Breeding
No captive breeding of Ancistomus spilomma has been documented in the available sources. The overall reproductive mode is presumed to follow the cave-spawning, paternal-guarding pattern widespread within the Ancistrini — adhesive eggs deposited in a rocky crevice or hollow, guarded and fanned by the male until hatching. Clutch size, incubation period, and fry behaviour are unknown for this species specifically. Keepers interested in breeding attempts should prioritise providing multiple rocky hiding places or ceramic tubes, stable water quality with periodic small drops in temperature to simulate seasonal cues, and conditioning both sexes on a varied diet.
In the aquarium
Ancistomus spilomma is an uncommon species in the aquarium trade, occasionally available as wild imports from the Tocantins or Araguaia. Its adult size of roughly 5.5 in SL places it in the medium-sized pleco category — larger than a clown pleco but considerably more manageable than the common pleco species that frequently outgrow domestic tanks. A tank of 55 US gal or more with good filtration and regular water changes is appropriate for an adult or a small group.
The species requires well-oxygenated water with moderate flow — consistent with its river-riffle origins. Temperature should be kept in the range of 73–81 °F. Providing flat rocks, slate pieces, and short sections of driftwood for rasping and hiding satisfies its microhabitat requirements. The spotted pattern is attractive and distinctive, and the fish is reasonably peaceful toward dissimilar tankmates. Two males may show territorial interactions, so multiple hiding places should be offered if more than one is kept.
Because wild individuals are collected in a river system that has experienced significant alteration from the Tucuruí Dam (the world's largest hydroelectric dam by reservoir area), wild-caught fish may have been subject to collection pressure below or within the impounded zone. Tank-raised specimens are not currently available commercially.
Conservation
The IUCN Red List assessed Ancistomus spilomma as Least Concern in 2018, finding no evidence of major range-wide population decline despite its association with river systems that have been heavily modified by damming. The Tucuruí Dam on the Rio Tocantins created one of the largest artificial reservoirs in the world and dramatically altered the downstream hydrology; the long-term impact on rheophilic loricariids below the dam remains an area of ongoing ecological concern.
The taxonomic uncertainty raised by Armbruster et al. (2015) — the possibility that A. spilomma, A. micrommatos, and A. spinosissimus are conspecific — has no direct bearing on its conservation status as currently assessed, but a formal revision that synonymises two of these names would affect which populations and localities are considered part of the species' range. Collectors, importers, and hobbyists working with L036 material should retain detailed provenance data to support future taxonomic and conservation assessments.