Taxonomy & naming
Spectracanthicus murinus was formally described by Han Nijssen and Isaäc J.H. Isbrücker in 1987 in the Revue française d'Aquariologie et Herpétologie (volume 13, number 4, pages 94–98, figures 1–3; for 1986). The holotype, MZUSP 22011, was collected at Poça de Pedra, Rio Tapajós, eastern Pará State, Brazil; additional paratypes are deposited at MZUSP and ZMA (Naturalis). The Catalog of Fishes (Eschmeyer, CAS — updated June 2026, spid 6064) recognises the combination Spectracanthicus murinus Nijssen & Isbrücker 1987 as currently valid, placing it in Loricariidae: Hypostominae.
Spectracanthicus murinus is the type species of the genus Spectracanthicus, which Isbrücker erected to accommodate armoured catfishes sharing a dorsal-fin membrane that contacts the adipose-fin spine — a character shared by a small number of other genera (Baryancistrus, Parancistrus) but distinguished in Spectracanthicus by restricted gill openings and a low tooth count (fewer than 25 teeth per jaw). Armbruster's (2004) phylogenetic analysis of Loricariidae placed Spectracanthicus within tribe Spectracanthicini of Hypostominae.
In the hobbyist L-number system, no official DATZ or Das Aquarium code has been stably assigned to S. murinus; the species is listed on PlanetCatfish without any L-number. The name murinus (Latin for 'mouse-grey') is straightforward and descriptive, alluding to the greyish-brown ground colour.
Morphology
Adults of S. murinus reach approximately 4 in standard length (SL) according to the largest specimen recorded in FishBase references (Chamon & Rapp Py-Daniel 2014); PlanetCatfish gives 2.5 in SL as the typical aquarium size, and the original description reports a somewhat smaller adult series. The body is fully armoured with overlapping bony scutes and is noticeably flattened ventrally — the ventral surface from the snout tip to just behind the pectoral girdle is largely unplated (naked), as are the urogenital and surrounding areas. The head is broad and depressed; the snout is covered by numerous small scutes except for a small naked area at its tip.
The ground colour is dark greyish-brown — a colour the epithet directly references. Most specimens show a pattern of small pale spots or a finely reticulated network of pale lines on the body and fins. The dorsal fin membrane connects to the adipose-fin spine, a defining diagnostic feature of the genus. Tooth count is low: fewer than 25 spatulate teeth per jaw ramus, set in a relatively wide, fleshy mouth.
Sexual dimorphism includes the development of interopercular odontodes (cheek bristles) in breeding males, which become noticeably elongated during reproductive condition. Gravid females appear visibly broader across the body when viewed from above, and papilla shape offers a secondary indicator: the male's papilla is small and pointed; the female's is rounded and swollen when ripe.
Habitat
The type locality — Poça de Pedra, Rio Tapajós — places S. murinus in the middle Tapajós, a large clearwater river in Pará State, Brazil, draining the Brazilian Shield. Clearwater rivers of the Tapajós system are characterised by moderate to low conductivity, slightly to moderately acidic pH (often 5.5–7.0), warm temperatures (typically 79–86 °F), and excellent visibility. The riverbed in the Tapajós proper and its tributaries includes extensive rock outcrops, boulder fields, and submerged wood, all providing the cavities and rough surfaces that Spectracanthicus requires.
Field habitat images associated with this species on PlanetCatfish show individuals at Itaituba on the middle Tapajós, resting on rocky substrates with moderate current. Like other Spectracanthicus and Baryancistrus relatives, S. murinus is a rocky-substrate specialist that shelters in crevices and under overhangs; it is not associated with open sand or silt zones. GBIF records (39 occurrences; 21 georeferenced) confirm the Tapajós River basin as the exclusive known distribution (Brazil only).
Feeding
Spectracanthicus murinus is a periphyton and biofilm grazer with a generalist aufwuchs diet in the wild. The restricted gill openings characteristic of the genus (compared with the large opercular openings of Parancistrus) suggest a grazing and rasping ecology rather than a high-flow ram-ventilation mode. In the wild, the fish scrapes algae, diatoms, fungal films, and associated micro-invertebrates from rocky surfaces and submerged wood.
In the aquarium, S. murinus accepts a range of foods: algae wafers and spirulina-based tablets form a good dietary staple. Blanched vegetables — courgette (zucchini), cucumber, sweet potato, and peas — are also taken. The species will graze on tank algae and biofilm but does not appear to be a dedicated wood-eater (xylophage) in the manner of Panaqolus or Panaque. Occasional protein foods such as bloodworm, brine shrimp, or carnivore pellets can be offered in small amounts, as the natural aufwuchs diet includes invertebrate components. Overfeeding protein should be avoided. Multiple feeding surfaces (smooth stones, slate, wood) help replicate the natural foraging range.
Mating
Very little published information exists on the specific mating behaviour of S. murinus in captivity. Based on the general Spectracanthicus biology and the broader pattern documented in related Ancistrini, males establish and defend territories centred on cave sites — narrow rock crevices, PVC pipes, or coconut halves. Competition between males for prime cave sites can be vigorous, involving opercular flaring, lateral displays, and interlocking of pectoral spines.
Breeding condition in males is signalled by pronounced elongation of the interopercular odontodes (the cheek bristles). At the same time, breeding females show a noticeably swollen and rounded genital papilla and a broader body profile when viewed dorsally. Conditioning both sexes with a varied diet, regular water changes, and a slight temperature drop followed by warming can trigger spawning attempts, as it does in related cave-spawning plecos. The ratio of one male to multiple females is generally recommended when space allows.
Breeding
PlanetCatfish records no confirmed breeding reports on file for S. murinus as of 2026, and the species is genuinely rarely bred. Given its close relationship to other Spectracanthicus (including S. punctatissimus and S. zuanoni, which have some captive breeding records), the reproductive biology almost certainly follows the standard hypostominae cave-spawning pattern: the male selects a tight cave interior, the female deposits a clutch of adhesive eggs on the cave walls or ceiling, and the male fans and guards the eggs until they hatch.
In related Spectracanthicus species, clutches tend to be moderate in size (typically under 50 eggs). Eggs are pale amber to yellow. The male fans continuously with his caudal fin and pectoral fins to maintain water movement over the clutch. Incubation at typical temperatures takes approximately one week. Fry hatch as yolk-sac larvae and remain in the cave for several more days before becoming free-swimming. As with all cave-spawning plecos, the male should not be disturbed during incubation.
In the aquarium
At under 4 in SL, S. murinus is a manageable pleco for an intermediate-level aquarist willing to provide appropriate conditions. A minimum of 20–30 US gal is recommended for a single adult, with 40–55 US gal preferred for a pair or small group, given the species' territorial tendency around cave sites.
Water quality should reflect the Tapajós clearwater environment: temperature 79–86 °F, pH 5.5–7.5, soft to moderately hard water, and high dissolved oxygen. Regular partial water changes of 25–30% weekly are important. Strong filtration is recommended — the rocky Tapajós habitat is well-flushed.
Decor should include multiple rock structures or slate pieces forming caves and crevices, with at least one suitable cave per fish to reduce territorial aggression. Driftwood contributes both visual interest and biofilm surfaces. Smooth, polished stones are acceptable as grazing surfaces. Plants tolerant of slightly acidic, warm water (Anubias, Java fern) can coexist without damage.
Compatible tankmates are peaceful mid-water species that will not compete for cave sites: small tetras, rasboras, hatchetfishes, and small Corydoras are suitable. Do not keep with other Spectracanthicus or similarly cave-dependent plecos in small tanks without an excess of cave sites. S. murinus is not widely available in the hobby and is rarely seen at retail; hobbyists typically source it through specialist importers or pleco-enthusiast groups.
Conservation
The IUCN Red List assessed Spectracanthicus murinus as Least Concern in 2018 (criterion date: 7 November 2018). The assessment is based on an apparently stable population across the Tapajós River basin and no evidence of major range reduction. GBIF documents 39 occurrence records, with type specimens from Poça de Pedra and additional records from the Itaituba area and surrounding middle Tapajós drainage.
The Tapajós basin faces significant ongoing threats from the ornamental fish trade (harvesting pressure on specialist plecos), gold-mining and mercury contamination (garimpo, which is extensive in parts of Pará), and hydroelectric development. The Tapajós is not fully protected along its length. Although S. murinus is not immediately threatened, its apparent restriction to rocky-substrate habitats in the Tapajós system makes it vulnerable to habitat alteration from dam construction or large-scale sedimentation events. Captive breeding efforts, though rare, would help provide a buffer against trade pressure on wild stocks.