Taxonomy & naming
L063 is an L-number: a trade code from the system the German magazine DATZ began for imported loricariids that could not yet be identified. It is not a scientific name, and an undescribed form has no describing authority and no type specimens. The Südamerikafans L-Wels registry lists the fish as Pseudacanthicus cf. serratus "L 63" — compared with, not identified as, that species — while PlanetCatfish files it as Pseudacanthicus sp. (L063). No other code is recorded for the same fish, and no related code is named. Hobby name lists give brown-finned cactus pleco; the registry's bibliography cites the Miniatlas L-Welse (Werner, Lechner and Schmidt, 2005).
Morphology
The registry puts L063 at more than 15.5 in total length; no measured maximum is on record. Like other Pseudacanthicus it is a suckermouth catfish covered in bony plates, with small tooth-like odontodes on the plates and fins. What would separate it from similar forms is not on record, and nothing is said of the colour pattern beyond the trade name, which refers to the fins. Any resemblance to Pseudacanthicus serratus is a cautious comparison, not a diagnosis.
Habitat
L063 is recorded from the Rio Tocantins in the state of Pará, Brazil, in clearwater. The registry assigns the Tocantins to the Rio Pará system, which drains to the north-eastern Atlantic. Habitat place, substrate, depth and current are not recorded, so where in the river the fish lives is unknown. The registry's temperature and pH figures are aquarium keeping ranges; no field water chemistry is on record for the locality.
Feeding
The registry classes L063 as predominantly a carnivore that does not eat plants, and aquarium feeding follows from that. Frozen mussel, prawn and large bloodworm suit it, with sinking carnivore pellets as the staple; sinking foods matter because this is a catfish that feeds on the bottom. What it eats in the Rio Tocantins has not been documented for this code.
Mating
The sexing note is a statement about the genus, not an observation of L063. In Pseudacanthicus the male is said to have a longer, broader head, to be often more attractively coloured and often to carry a larger dorsal fin. Pseudacanthicus are typically cave spawners, the male holding the cave and guarding the eggs and larvae, but no courtship or spawning behaviour has been recorded for L063.
Breeding
No aquarium breeding of L063 is recorded; the registry lists breeding as unknown. Clutch size, egg numbers, incubation and fry development are all undocumented. Related Pseudacanthicus forms are cave spawners in which the male guards the eggs and larvae, which is the working expectation should L063 spawn — a genus-typical pattern, not something observed in this fish.
In the aquarium
Registry guidance for L063 is 77–84 °F and pH 6–7 in a tank at least 78.5 in long — aquarium figures, not field measurements. Small groups are recommended, though a single fish is possible. As with other large plecos, plan on clean, well-oxygenated water with current and rock or wood cover. Territorial behaviour toward other plecos is common, so space and hiding places matter.
Conservation
L063 is Not Evaluated by the IUCN Red List; an undescribed form cannot be assessed until it has a name. According to the registry it is absent from Brazil's 2012 positive list of species cleared for ornamental export, and also absent from the country's 2020 negative list. Its real status is unknown. In general, collection for the trade and river engineering affect some L-number habitats.