Taxonomy & naming
Ancistrus lineolatus was described by Charles Tate Regan in 1904 in the Annals and Magazine of Natural History (series 7, volume 13), based on material from the Río Orteguaza (spelled 'Orteguasa' in the original) at Florencia, Caquetá, Colombia. The type locality lies in the upper Japurá (Caquetá) drainage, where the eastern Andean foothills meet the Amazonian plain — an area of high but poorly surveyed loricariid diversity. The Catalog of Fishes (Eschmeyer, CAS) recognises A. lineolatus as a valid species.
The original combination followed the convention of the era; the name was subsequently placed firmly in Ancistrus as the genus was consolidated and synonyms such as Xenocara subsumed. Within Loricariidae, the species belongs to subfamily Hypostominae, tribe Ancistrini — the larger grouping that includes all Ancistrus along with genera such as Baryancistrus, Hypancistrus, and Peckoltia. Armbruster's (2004) phylogenetic analysis of Loricariidae placed Ancistrus as paraphyletic but retained it pending further revision.
The specific epithet lineolatus is a Latin adjective meaning 'with fine lines' or 'finely striped', referring to the longitudinal pattern of pale lines or rows of spots on the dark body. This pattern is useful for preliminary field identification, though it overlaps with markings seen in other western-Amazonian Ancistrus. No subspecies are recognised. The species is not synonymous with other nominal Ancistrus from the region and is treated as a distinct biological entity in recent Loricariidae checklists.
Morphology
Ancistrus lineolatus is a small to medium-sized bristlenose, reaching approximately 3–3.5 in standard length (SL) in adults. The body is strongly dorsoventrally flattened, as in all Ancistrus, covered in overlapping keeled bony scutes, and equipped with a ventral suckermouth bearing multiple rows of bicuspid teeth suited for grazing biofilm and algae from rock surfaces.
The most distinctive Ancistrus character — the elaborate fleshy tentacles or cirri of mature males — is fully developed in A. lineolatus. Adult males carry branching tentacles across the rostral plate and along the snout margin; females may develop tentacles only at the very tip of the snout, or lack them entirely. The interopercular odontodes are the hook-shaped spines characteristic of the tribe Ancistrini and are used in male–male combat and as a defensive mechanism against predators or rival males attempting to displace them from a spawning cave.
The coloration that gives the species its name is a pattern of pale whitish or yellowish narrow lines or rows of small spots running longitudinally across a dark brown to greyish-black ground colour on the body and fins. This lined pattern is more pronounced on juveniles and young adults and may fade to a more uniformly dark appearance in large, old males. The caudal fin is slightly emarginate (shallowly forked). Detailed published meristics for A. lineolatus are limited, and the species has not been the subject of a modern morphometric revision.
Habitat
Ancistrus lineolatus is known from the Río Orteguaza basin in Caquetá, Colombia — a piedmont tributary system of the upper Caquetá–Japurá drainage that descends from the eastern Andean foothills onto the Amazonian plain. These rivers are characterised by steep gradients in their upper reaches, seasonal variation in discharge driven by the very high piedmont rainfall, and substrates of exposed bedrock, boulders, and coarse gravel in faster sections transitioning to sandy or muddy deposits in lowland stretches.
Like most Ancistrus, this species favours rocky or hard-substrate habitats where biofilm, algae, and periphyton accumulate — waterfalls, rapids, bouldered runs, and the undersides of large flat rocks in moderate current. The water in these Andean-piedmont rivers is typically clear to lightly turbid, with moderate to slightly acidic pH in headwater areas and near-neutral conditions downstream. Temperatures are warm-tropical year-round (roughly 68–82 °F).
No detailed ecological survey has been published specifically for A. lineolatus, and precise records of depth preference, microhabitat use, or population densities are lacking. The species is part of the Andean-Amazon piedmont ichthyofauna of Colombia, one of the region's most diverse and least surveyed freshwater fish assemblages.
Feeding
Ancistrus lineolatus is a periphyton grazer, using the ventral suckermouth and fine bicuspid dentition to rasp algae, diatoms, and organic biofilm from hard surfaces — boulders, bedrock outcrops, submerged roots, and woody debris. The oral disc functions as an adhesive holdfast, allowing the fish to remain attached to the substrate in significant current while feeding, a capacity essential in the rocky, fast-flowing habitats it occupies.
No gut-content analysis has been published specifically for this species. By analogy with the well-studied diet of congeners from comparable habitats, the diet consists primarily of epilithic algae (including green algae and diatom mats), cyanobacterial films, fine detrital particles, and small invertebrates or organic fragments incidentally ingested while grazing. Periphyton biomass and community composition vary with season, light, and current, and benthic grazers like Ancistrus may shift feeding locations accordingly.
In captivity, the species should do well on the standard Ancistrus diet: sinking algae wafers, spirulina-based pellets, and blanched vegetables (courgette/zucchini, cucumber, spinach, sweet potato). Protein-rich foods can be offered occasionally but should not dominate the diet, as high-protein regimes can accelerate growth and stress the digestive system in algae-specialist loricariids.
Mating
No published courtship observations exist specifically for Ancistrus lineolatus, but the genus-wide mating system is well documented in captive populations of common bristlenoses and applies here by extension. Ancistrus species are cave-spawners with a polygynandrous or polygynous mating system: males establish and defend cavities — crevices between boulders, spaces beneath flat rocks, hollow sections of driftwood — and actively court passing females by guarding the site and displaying the prominent head tentacles.
Sexual dimorphism is the primary means by which keepers or field biologists distinguish sexes: mature males develop the characteristic fan of branched tentacles from the rostral disc, which are effectively absent or vestigial in females. The tentacles appear to serve multiple roles: inter-male rivalry signalling, female choice assessment, and possibly olfactory/tactile functions during close-range courtship. Gravid females become noticeably broader across the body when viewed from above.
Conditioning for spawning in captivity typically involves feeding varied, nutrient-dense foods and performing regular partial water changes to simulate the increased flow and cooler, oxygenated water associated with the onset of the wet season — the likely natural spawning trigger in these piedmont rivers.
Breeding
Ancistrus lineolatus has not been reported breeding in captivity in the published literature, and PlanetCatfish Cat-eLog records no captive breeding accounts. This reflects the species' rarity in the trade rather than any known biological obstacle to captive reproduction. Based on the reproductive biology of the genus, which is well documented in more commonly kept species such as A. cirrhosus and the trade 'common bristlenose' complex, spawning would proceed as follows.
The male selects and defends a cave — a tight-fitting crevice, coconut shell, ceramic tube, or dense driftwood hollow in the aquarium context — and entices the female to enter and deposit her eggs on the inner wall or ceiling. Clutches in Ancistrus range from roughly 30 to over 100 adhesive, pale amber eggs, arranged in neat clusters. The male remains with the clutch, fanning continuously with his pectoral and ventral fins to maintain water movement and prevent fungal growth.
Incubation typically takes five to seven days at 75–79 °F. The fry hatch with large yolk sacs and remain clustered in the cave under paternal supervision for several more days before emerging to graze independently. First foods are fine biofilm and spirulina paste; microworm or baby brine shrimp can be offered but are not essential for this primarily herbivorous species.
In the aquarium
Ancistrus lineolatus is essentially absent from the international ornamental trade and carries no L-number or LDA designation. It is unlikely to be encountered unless sourced directly from collectors working in the Colombian Amazon piedmont. Hobbyists who acquire it should be aware that accurate identification from trade specimens is difficult given the broad similarity of many small, dark Ancistrus species from the western Amazon.
Care requirements, inferred from the species' piedmont river origin, are straightforward. Temperature: 68–79 °F, reflecting cooler, well-oxygenated foothill waters compared with the sluggish Amazonian lowlands. pH: 6.2–7.4. Moderate water hardness. Strong filtration and regular partial water changes are beneficial; the species would naturally occupy well-oxygenated, rocky-bottomed streams. Avoid stagnant, warm, or heavily silted conditions.
Aquarium size: given adult sizes around 3–3.5 in SL, a single specimen is manageable in 20 US gal; a small group would benefit from 30 US gal or more with multiple rocky caves and driftwood tangles to allow territorial spacing. Males will compete for cave sites and should be provided with more refuges than there are males. Diet: primarily algae wafers, spirulina pellets, and blanched vegetables. Tankmates should be peaceful and not excessively boisterous; avoid keeping with large, aggressive loricariids that compete for caves.
Conservation
The conservation status of Ancistrus lineolatus has not been formally assessed by the IUCN Red List as of 2026, and the species is effectively treated as Data Deficient or Not Evaluated in global databases. This is a common situation for smaller, range-restricted Colombian loricariids that have received little dedicated population research.
The Caquetá piedmont, where the Orteguaza basin lies, is among the most heavily deforested frontiers of the Colombian Amazon: conversion to cattle pasture, agricultural runoff and sedimentation are well-documented pressures on its foothill rivers. A species apparently confined to a single tributary basin is intrinsically more vulnerable to such pressures than species with wide distributions across large basins.
No targeted conservation measures for this species are on record. Documentation of its current range, population abundance, and habitat condition would be a valuable contribution. Any specimens appearing in the trade should ideally come from captive-bred stock rather than wild collection, to reduce pressure on what may be a limited wild population.