Taxonomy & naming
Centromochlus macracanthus was described by Soares-Porto in 2000. It belongs to the family Auchenipteridae, the driftwood catfishes, within the subfamily Centromochlinae, and to the genus Centromochlus, a group of small South American wood-dwelling catfishes. Molecular and chromosomal work on the Centromochlinae has found the boundary between Centromochlus and the closely related genus Tatia to be unsettled, and hobby literature sometimes confuses the two genera in trade — a mislabelled fish offered as a Tatia species may in fact be C. macracanthus, and vice versa. The Catalog of Fishes currently treats macracanthus as a valid species under Centromochlus.
The genus name Centromochlus combines Greek roots referring to a spine or bolt (kentron) and a lever or bar (mochlos), an allusion to the stiff, locking fin spines typical of the group. The species epithet macracanthus is likewise Greek-derived, from makros ("long") and akantha ("spine" or "thorn"), describing a notably long or prominent spine in the type material.
Morphology
Like other Centromochlus, this is a small, soft-bodied catfish with a broad, somewhat flattened head, large eyes suited to nocturnal activity, and long, sensitive barbels used to feel out food and shelter in the dark. The body tapers to a slender caudal peduncle and forked tail. Reported maximum size is modest, around 3 in standard length, so this stays one of the smaller driftwood cats.
As in all catfish the skin is scaleless (naked), which has direct care consequences — see "In the aquarium". Centromochlus and its relatives carry stiff, serrated pectoral and dorsal spines that lock erect; in sexually active males the anal fin is further modified, its rays thickened and reshaped into an intromittent organ used for internal fertilisation, a structural oddity unique to this catfish lineage.
Habitat
Centromochlus macracanthus is endemic to the upper Rio Negro drainage in Amazonas, Brazil, a blackwater system known for tannin-stained, mineral-poor water. The type locality is São Pedro on the Rio Negro. Within this system the species shelters by day among submerged driftwood and root tangles, emerging to forage after dark — the classic "driftwood cat" lifestyle that gives the group its common name.
Upper Rio Negro water is soft and can range from moderately acidic to circumneutral, with recorded parameters spanning roughly pH 4.0–7.0 and temperatures of 72–82 °F, and moderate hardness by blackwater standards (around 18–179 ppm). Cover in the form of wood and root structure appears to be a consistent habitat requirement rather than an incidental detail.
Feeding
This is a nocturnal benthic micro-predator and omnivore, foraging mostly after dark for small invertebrates, detritus and other opportunistic food items around wood and root structure. In the aquarium it will take sinking dried and prepared foods, but does best on small live or frozen fare such as bloodworm and Tubifex, and well-acclimated individuals will feed actively even at the surface once settled.
Because it is shy and nocturnal by nature, food is best offered after lights-out or with attention to timing so it is not out-competed by more assertive, day-active tankmates.
Mating
Centromochlus macracanthus follows the reproductive pattern of its family, and it is one of the more distinctive stories in the catfish world: driftwood catfishes (Auchenipteridae) use internal fertilisation rather than external egg-scattering. In sexually active males the anal fin is remodelled into an intromittent organ, and sperm is transferred to the female as discrete packets (spermatozeugmata) via a modified urogenital opening. The female stores the sperm internally in a specialised oviductal structure, and fertilisation of the eggs is delayed until the moment of spawning, which can occur well after mating took place.
This internal-fertilisation strategy is rare among catfishes generally and is a defining feature of the driftwood cat subfamily Centromochlinae, shared with relatives such as Tatia and Trachelyopterus.
Breeding
Because fertilisation is internal and delayed, breeding biology in this genus does not follow the pair-spawning or nest-building patterns seen in many other catfish families. Mating and egg-laying are decoupled in time, which makes reproduction difficult to observe or control in captivity, and there is no evidence of parental care after eggs are laid — no nest, no guarding male, no bubble raft.
Centromochlus macracanthus is not established as a regularly captive-bred species; specimens reaching the hobby are believed to be wild-collected from the upper Rio Negro. Given the internal-fertilisation strategy and the scarcity of published husbandry data, aquarists should treat successful home breeding as unlikely rather than a realistic goal.
In the aquarium
This is a genuinely small catfish — around 3 in maximum — so it does not present the size trap that catches out keepers of larger driftwood cats and pimelodids; a modestly sized aquarium with soft, tannin-stained, blackwater-style conditions (roughly pH 4.0–7.0, 72–82 °F) suits it well, echoing its Rio Negro origin. Provide driftwood and root tangles for daytime cover; this species is nocturnal and shy, and will rarely be seen foraging in open water during the day.
Two care points follow directly from its biology as a catfish. It is scaleless, so it is more sensitive than scaled fish to copper and to many medications — dose conservatively. It also carries locking, serrated pectoral and dorsal spines that can snag in a net and jab the handler, so it is best moved in a container rather than netted. Given how little is published on this species, treat any husbandry recommendation as provisional and favour a stable, well-established blackwater tank over experimentation.
Conservation
Centromochlus macracanthus has not been formally assessed by the IUCN Red List and is currently listed as Not Evaluated. As a narrow-range endemic of the upper Rio Negro system, its conservation status is essentially undocumented, and there is no published population trend or threat assessment to draw on.
The upper Rio Negro basin faces general Amazonian pressures — deforestation, mining-related sedimentation and, regionally, the ornamental fish trade — but no species-specific data exists to say how this catfish is faring. Any aquarium specimens in trade should be assumed wild-collected rather than captive-bred.