Taxonomy & naming
Epactionotus bilineatus was described by Reis and Schaefer in 1998 as one of three new Epactionotus species in the same paper. The Catalog of Fishes (Eschmeyer, CAS) recognises it as valid. The species sits in subfamily Hypoptopomatinae of the armoured catfish family Loricariidae — the group of small, slender, grazing 'dwarf suckers' that includes Otocinclus and its relatives.
The genus name Epactionotus combines the Greek 'epaktios', meaning 'at the seaside', with 'noton', 'back' — a reference to the coastal distribution of these fishes along the Atlantic drainages of southern Brazil. There is no L-number or established common name for this species.
Morphology
Epactionotus bilineatus is a very small loricariid, reaching a maximum of about 1.5 in in standard length. As a hypoptopomatine, it has the slender, somewhat flattened body and ventral suckermouth typical of the dwarf grazers, with the body encased in rows of bony plates. Beyond overall size, no detailed colour or meristic description is summarised in the sources available here; the specific epithet 'bilineatus' ('two-lined') points to a paired-stripe element in its patterning.
Habitat
The species is restricted to the Maquiné and Três Forquilhas river basins, coastal drainages of Rio Grande do Sul in southern Brazil. FishBase characterises it as a freshwater, benthopelagic, tropical fish. These are short, clear coastal rivers, and the genus as a whole is associated with such seaside drainages, but specific published data on the water chemistry, current, and substrate of this species' habitat are not available here.
Feeding
No feeding study specific to Epactionotus bilineatus has been published; diet data are sparse. Like other Hypoptopomatinae, it is presumed to be a herbivore and detritivore, grazing biofilm, algae, and fine organic material from plant stems, rocks, and submerged surfaces with its suckermouth. This is the typical pattern for the subfamily rather than a documented observation for this species.
Mating
No data has been published on courtship or mating behaviour in Epactionotus bilineatus.
Breeding
No data has been published on the reproduction of Epactionotus bilineatus. Its spawning mode, clutch size, and any parental care remain undocumented in the sources available here.
In the aquarium
Epactionotus bilineatus is not an established aquarium fish, and no specific husbandry information has been published for it; husbandry data are sparse. As a small, biofilm-grazing hypoptopomatine from clear coastal streams, it would in principle need mature, well-oxygenated water with grazing surfaces, but any detailed keeping advice would be speculation beyond the published record.
Conservation
The IUCN Red List assessed Epactionotus bilineatus as Least Concern (LC) on 7 November 2018. Despite its narrow range across just two coastal basins, the assessment did not find it to be at elevated extinction risk at the time. Coastal drainages of Rio Grande do Sul are nonetheless exposed to general pressures such as land-use change and water-quality decline, which warrant ongoing monitoring of restricted-range species like this one.