Taxonomy & naming
L391 is a DATZ L-number, a trade code from the system started in 1988 for imported loricariids not yet identified, with no describing authority and no type specimens. The registry lists the fish under the genus Oligancistrus; the atlas follows Catalog of Fishes, which treats that name as a synonym of Spectracanthicus, as PlanetCatfish does in Spectracanthicus sp. (L391). No second code is on record. Starry Sky Pleco is the registry's common name. It names Oligancistrus punctatissimus (L30), which the atlas treats as Spectracanthicus punctatissimus, as a similar fish, and cites the Miniatlas L-Welse (2005).
Morphology
The registry's size is about 6 in total length. Pattern and body shape are not described, so the diagnostic characters of L391 are not on record, and "starry sky" is a trade name, not a description. Oligancistrus punctatissimus (L30) is the one similar fish listed.
Habitat
The registry gives the Rio Curuá at Salto do Curuá in Pará, Brazil, and traces the river system as Rio Iriri, then Rio Xingu, then the Amazon; it describes the spot as "near a waterfall". The water is clearwater, and Hypancistrus sp. L428 is listed as found together with this form. Substrate and depth are not on record.
Feeding
The registry classes L391 as an omnivore and does not say whether it eats plants. Sinking pellets or wafers, frozen foods and some vegetables fit that class in the aquarium. What the fish eats at Salto do Curuá has not been recorded.
Mating
No characters for telling the sexes apart are on record for L391. Spectracanthicus are typically cave spawners in which the male guards the eggs and larvae in the cave, and the registry treats the cave requirement as standard for the genus.
Breeding
Captive breeding of L391 is marked as reported, with Aquarianerportal cited as the place of the report. No spawning details are given, so clutch size, timing and the development of the young are unrecorded.
In the aquarium
The registry's keeping range is 77–84 °F and pH 5.0–7.0, with a recommended tank length of 39.5 in; these are aquarium figures, not field measurements. Keeping in small groups is recommended, though a single fish is possible. A pleco from a waterfall reach needs clean, well-oxygenated water with current and caves or rock cover, and territorial behaviour toward other plecos is common.
Conservation
L391 has not been assessed by the IUCN Red List; an undescribed form has no formal status. The registry records it as not on Brazil's 2012 positive list of species cleared for ornamental export and not on the 2020 negative list. Collecting for the trade and river engineering are pressures on some L-number habitats; nothing specific is recorded for the Curuá population.