Taxonomy & naming
Hypostomus varimaculosus was originally described by Henry Weed Fowler in 1945 in the Proceedings of the Academy of Natural Sciences of Philadelphia, under the then-current combination Plecostomus varimaculosus. The holotype, ANSP 71707 at 2.5 in SL, was collected from Río Caquetá at Morelia, Caquetá Department, Colombia. The Catalog of Fishes (Eschmeyer, CAS) recognises the current valid combination Hypostomus varimaculosus (Fowler, 1945); the parentheses around the authority indicate the species was originally placed in a different genus.
FishBase notes that 'no recent work' has been conducted on the taxonomy of this species. No revision of the varimaculosus complex or close relatives has been traced in sources consulted. The species belongs to family Loricariidae, subfamily Hypostominae — the largest subfamily in this diverse family of South American armoured catfishes.
The distribution straddles the Colombian–Brazilian border: the Río Caquetá (Colombia) and Río Japurá (Brazil) are the same river, with the name changing at the border. Occurrence records are centred on the Colombian portion near Morelia.
Morphology
The maximum size recorded for Hypostomus varimaculosus is 2.5 in SL (FishBase). This figure likely reflects the holotype or very few specimens and may represent a juvenile or subadult; adult dimensions for this species are not established in sources consulted. Treating 2.5 in as a confirmed adult maximum would make H. varimaculosus one of the smallest valid Hypostomus species — a claim that warrants caution in the absence of a revisionary study.
The specific epithet — combining varius (mottled, variegated) with maculosus (speckled, spotted) — indicates a boldly patterned coloration. The body is armoured with overlapping bony scutes in the loricariid fashion. Detailed morphological data (fin ray counts, scute rows, tooth form, head proportions) are established in Fowler's original 1945 description but are not reproduced here from secondary sources.
Sexual dimorphism has not been documented for this species in sources consulted.
Habitat
The type locality is Morelia, on the Río Caquetá, Caquetá Department, Colombia (approximately 1°29'N, 75°41'W). The upper Caquetá–Japurá system originates in the Colombian Andes and descends through the Andean piedmont before entering the western Amazonian lowlands. Near Morelia the river is in a transitional zone between Andean foothills and the Amazon basin proper — waters in this region tend to be whitewater or mixed, carrying significant sediment load from Andean sources, with temperatures and chemistry that vary seasonally.
No water chemistry data specific to H. varimaculosus collection sites are available in sources consulted. The broader upper Caquetá–Japurá system supports a diverse Hypostomus fauna associated with rocky substrates, woody debris, and gravel beds typical of Andean piedmont rivers in the western Amazon.
Feeding
Diet has not been studied for Hypostomus varimaculosus. In the genus Hypostomus, the great majority of species are aufwuchs grazers — scraping periphyton, algae, and biofilm from hard substrates (rocks, wood, roots) using fine bidentate or multi-cusped teeth. Detritus and fine organic matter are also commonly ingested. Without tooth form analysis of the holotype being available in secondary sources consulted, the precise dietary guild cannot be confirmed.
In an aquarium context, a standard Hypostomus diet would apply: algae wafers, sinking vegetable-based pellets, blanched vegetables (courgette, cucumber, peas), and driftwood as a supplementary grazing and behavioural resource.
Mating
Mating behaviour is undocumented for Hypostomus varimaculosus. No aquarium or field observations have been reported in sources consulted. Based on genus-level patterns, Hypostomus species are territorial cave-spawners in which males compete for and defend suitable crevice or cavity sites.
Breeding
No breeding records exist for Hypostomus varimaculosus in the sources consulted. The species does not appear to be established in the aquarium trade, and no captive reproduction has been reported.
As with the genus broadly, cave-spawning with paternal egg-guarding is the expected reproductive strategy, but this has not been confirmed for H. varimaculosus specifically.
In the aquarium
Hypostomus varimaculosus is not known to be established in the ornamental trade. No specific husbandry information is available.
If the 2.5 in SL maximum figure reflects a juvenile holotype rather than a true adult size, the species could prove to be substantially larger in the wild. Any aquarium care would need to be calibrated accordingly — an aquarium scaled for a compact Hypostomus might be inadequate if the species reaches 6–8 in at maturity, as is typical for the genus.
General Hypostomus husbandry principles apply: spacious aquarium with good water movement and filtration, quality driftwood and rock structures for shelter and grazing, soft to moderately hard water with near-neutral pH reflecting the western Amazonian origin, and temperature in the 75–82 °F range.
Conservation
The IUCN Red List assessed Hypostomus varimaculosus as Least Concern in November 2020, based on a distribution across the upper Japurá–Caquetá basin that spans both Colombia and Brazil and on the absence of evidence of significant population decline. The upper Caquetá–Japurá is a large, biologically rich drainage and the species is not subject to known targeted exploitation.
The upper Caquetá basin in Colombia faces ongoing pressures from coca cultivation, associated deforestation and chemical inputs, cattle ranching, and incremental road development, all of which affect water quality and riverbank integrity. The lack of any recent taxonomic or field study of H. varimaculosus means that population trends cannot be assessed with precision. The LC listing should be considered provisional pending a dedicated field and taxonomic review.