Taxonomy & naming
Hypostomus nigromaculatus was described by Othon Henry Schubart in 1964 in Boletim do Museu Nacional do Rio de Janeiro, Zoologia, Nova Série No. 251 (pp. 2, figs. 2 and 5). The type locality is Cachoeira de Emas, Rio Mogi Guassu basin, Brazil — a well-known collecting site in the state of São Paulo on the upper Paraná drainage. The Catalog of Fishes (Eschmeyer, CAS) recognises the valid combination Hypostomus nigromaculatus; the original combination was Plecostomus nigromaculatus, reflecting the historical practice of placing most Hypostominae in Plecostomus before modern revisions separated out the genera. The species is listed in ITIS under TSN 680209.
Hypostomus is the largest genus in Loricariidae, with well over 130 valid species, and is defined by Armbruster (2004) by a suite of osteological and external characters within subfamily Hypostominae. Molecular work by Montoya-Burgos and Weber (unpublished at the time of FishBase entry, represented by GenBank accession AJ318355) placed H. nigromaculatus within a mitochondrial D-loop phylogeny of Hypostomus and related genera, though no major reclassification has followed from that work. The species remains unambiguously assigned to Hypostomus. Its L- or LDA-number is LDA012, reflecting registration in the German aquarium magazine 'Das Aquarium'.
Morphology
Maximum size is recorded at 4 in standard length (SL; FishBase, citing Burgess 1989), making H. nigromaculatus a compact member of a genus that elsewhere reaches 15.5 in or more. The body follows the standard Hypostomus plan: heavily armoured with keeled scute rows, a broad, depressed head with a ventral suckermouth, and a powerful caudal fin. The dorsal fin is tall with a rigid leading spine and seven soft rays; the pectoral fins are large and fan-like.
The diagnostic feature is the coloration: the dorsal and lateral surfaces carry a dense field of dark brown to black spots — the specific epithet nigromaculatus means 'black-spotted' — on a pale yellowish-brown to grey-buff ground colour. The spots are present on all fins as well. The ventral surface is paler and largely unspotted. This high-contrast pattern holds into adulthood, though the ground colour can shift depending on substrate and stress.
Sexual dimorphism in Hypostomus is subtle. Mature males typically develop odontodes along the pectoral spine and along the posterior body flanks more prominently than females, and females are somewhat broader across the abdomen when gravid. Genital papillae provide the most reliable sex-determination method in hand.
Habitat
The species is distributed across the middle and upper Paraná River basin in Brazil, with records confirmed from the states of Goiás, Minas Gerais, São Paulo, Paraná, and Mato Grosso do Sul (IUCN geographic range, ICMBio 2018). The Rio Mogi Guassu basin (type locality region) falls within the upper Paraná drainage in São Paulo state. The Paraná basin is among the best-studied river systems in South America, characterised by subtropical to tropical temperatures, clear to moderately turbid waters, and a mix of rocky, sandy, and muddy substrates.
The IUCN habitat classification records the species in permanent rivers, streams, and creeks (wetlands, inland). The species is demersal, spending its time on the bottom in association with rocky substrate, submerged wood, and hard-bottom channel margins. The facultative air-breathing capacity recorded for the genus (FishBase ref. 126274) allows temporary survival in poorly oxygenated water, an adaptation of value during the dry season when some Paraná tributaries drop in level and water quality declines. Field records span multiple sub-basins, including the Mogi Guassu, consistent with a species common and widespread through the upper and middle Paraná.
Feeding
The IUCN habitat and ecology summary for H. nigromaculatus states directly that the species 'feeds by rasping benthic algae' (Portuguese: 'se alimenta raspando as algas bentônicas'). This confirms it as a typical periphyton grazer in the Hypostomus mould: the ventral suckermouth provides adhesion to current-swept surfaces while the jaws work in a rocking motion to dislodge attached algae, diatoms, and associated biofilm organisms.
Hypostomus species in general are not xylophagous (wood-eating) in the manner of Panaque and Panaqolus, though they commonly rest on and rasp wood surfaces. Gut-content studies on closely related species in the Paraná basin typically show a predominance of diatoms, green algae, detrital plant matter, and mineral particles (sand grains consumed with the algae on the substrate). Invertebrates form a minor dietary fraction.
In captivity, a diet based around algae wafers, spirulina discs, sinking vegetable pellets, and blanched vegetables (courgette, cucumber, peas) is appropriate. Pieces of driftwood provide a natural substrate for grazing and are beneficial but not the dietary requirement they represent for wood-eating genera.
Mating
No courtship observations specific to H. nigromaculatus have been published. The reproductive biology of Hypostomus in general has been studied in several Paraná basin congeners, and the genus-level picture provides the working model.
Males become territorial and associate closely with suitable nesting sites — typically cavities eroded into riverbanks (burrows), hollow logs, or rocky crevices. Territorial defence of the chosen site intensifies when females are in spawning condition. Aggression between males can be vigorous, involving mouth-locking and body-ramming, though fatalities are uncommon in nature. In aquaria, multiple males in a limited space can lead to fin damage and chronic stress.
Female selection of a brooding male appears linked to the quality of the cavity and the condition of the male. Once a pair has spawned, the female leaves the cavity and takes no further part in parental care.
Breeding
Hypostomus nigromaculatus has no registered breeding report on PlanetCatfish. Within the genus, spawning ecology has been documented most thoroughly for bank-nesting species in the Paraná and Paraguay basins, where the fish excavate burrows in earthen riverbanks during the spawning season — a behaviour that may be restricted to certain Hypostomus lineages and may not apply to all species.
The general Hypostomus reproductive pattern involves the male guarding a clutch of adhesive, demersal eggs inside a cavity, fanning them with the pectoral and caudal fins, and remaining with the fry through yolk absorption. Clutch sizes in the genus vary widely by body size; for a species of around 4 in, a few dozen to perhaps 150 eggs is a plausible range, though no confirmed data exist for H. nigromaculatus specifically.
Reproduction in the Paraná basin appears to coincide with the onset of the warm, rainy season (roughly October–February in southern Brazil), triggered by rising water temperatures and water levels. Attempts to spawn H. nigromaculatus in captivity should simulate these cues: a temperature rise from around 72–73 °F to 79–81 °F, increased water flow, and extended photoperiod.
In the aquarium
Hypostomus nigromaculatus is registered as LDA012 ('Dot Pleco' in the English-language hobby, 'Punktumsugemalle' in Danish). Despite the registration, it appears infrequently in the trade and is not a commonly offered species. Hobbyists in South America — particularly in the Paraná basin states of Brazil — may encounter it locally, but international availability is limited.
At a maximum of around 4 in SL, it is suitable for medium-sized community tanks: 25–40 US gal would comfortably house a single specimen; 200+ litres for a pair or small group. Water parameters should reflect its subtropical Paraná origin: temperature 68–79 °F (the Paraná basin has cooler winter temperatures than most Amazonian systems, so a range extending down to around 64–68 °F in winter is tolerable), pH 6.5–7.5, moderate to moderately hard water.
The species is peaceful toward other fish but will compete with conspecifics over caves and territories. Furnish the tank with flat rocks, terracotta caves, short sections of driftwood, and a sandy or fine-gravel substrate. Algae growth on tank glass and decor will be grazed enthusiastically; supplement with algae wafers and vegetables. The fish is largely nocturnal, becoming active after lights-out. A tight-fitting lid is advisable, as plecos occasionally climb and can exit low-sided tanks.
Conservation
The IUCN Red List assessed Hypostomus nigromaculatus as Least Concern in 2018 (published 2022), based on a review by Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio). The justification states that the species is 'frequent and abundant' across its range in the upper and middle Paraná basin, and no significant threats to its population were identified.
The species is known to occur within the Área de Proteção Ambiental Corumbataí Botucatu Tejupa (Perímetro Botucatu) and the Parque Estadual do Morro do Diabo, providing some level of incidental protection within protected areas. The IUCN assessment identifies a research need for population size, distribution trends, and life-history data — reflecting the general under-study of many Brazilian endemic fishes rather than an acute conservation concern.
The Paraná basin as a whole faces ongoing pressures from hydroelectric dam construction, agriculture-driven sedimentation, and water abstraction. The Mogi Guassu drainage specifically has been heavily modified by agriculture in São Paulo state. These pressures have not yet pushed H. nigromaculatus to a threatened status, but continued documentation of distribution and population trends is warranted.