Taxonomy & naming
Centromochlus orca was described in 2017 by Sarmento-Soares, Lazzarotto, Rapp Py-Daniel and Leitão. It belongs to the subfamily Centromochlinae within the family Auchenipteridae, the driftwood catfishes, a South American group distinguished from most other catfishes by internal fertilisation. The Catalog of Fishes treats Centromochlus orca as the valid name, and it has not been placed under any other genus in the literature reviewed here.
The genus name Centromochlus is a long-standing name for these small driftwood-dwelling catfishes; the species epithet orca directly references the killer whale, Orcinus orca, for the fish's bold black ground colour sharply set off from a white underside by a conspicuous wavy border — the same high-contrast patterning associated with orcas. It is one of several recently described dwarf Centromochlus species distinguished largely by colour pattern and fin details.
Morphology
This is a genuinely small catfish: males and unsexed individuals reach only about 2 in standard length, among the more diminutive members of the driftwood catfish family. The body carries the family's slender, tapering profile and, as in virtually all catfishes, no scales — the naked skin is a factor to bear in mind for medication (see "In the aquarium").
The defining feature is colour: a black ground colour sharply delimited from a white belly by a distinct wavy border running along the flanks, the pattern that earned the species its common and scientific names. Like other auchenipterids it bears barbels around the mouth and stiff, serrated spines at the leading edge of the dorsal and pectoral fins that can lock erect — spines that snag readily in a net, so this fish is best moved in a cup or container rather than netted.
Habitat
Centromochlus orca is known from the Tocantins-Araguaia River drainage, part of the wider Amazon basin in northern Brazil. The type locality is the igarapé Jamari, in its lower reaches, described as a transition zone between flowing river channel and floodplain lake — the kind of structurally complex, wood- and root-tangled habitat typical of Amazonian blackwater and clearwater streams.
It is a freshwater, benthopelagic species and strongly nocturnal, sheltering by day in driftwood, submerged root tangles and rock crevices and feeding near shorelines after dark. In the aquarium it does best in dim lighting with driftwood and similar cover replicating that structure.
Feeding
As a nocturnal benthic micro-predator and omnivore, Centromochlus orca forages the bottom and near shorelines mostly after dark, taking small invertebrates, detritus and other opportunistic food items in the wild.
In the aquarium it accepts sinking pellets and frozen foods readily. Because it is strongly nocturnal and rests in cover through the day, it is best fed after lights-out so it is not out-competed by more active, diurnal tankmates for food that reaches the bottom.
Mating
Centromochlus orca follows the reproductive strategy of the entire family Auchenipteridae: internal fertilisation, a genuine rarity among catfishes. The male's anal fin is modified into an intromittent organ used to inseminate the female directly, rather than the sexes releasing eggs and milt together over open substrate.
Following insemination, the female is able to store sperm and lay fertile eggs later, even in the male's absence — a strategy documented across driftwood catfishes that decouples mating from spawning in time. No further detail on courtship behaviour in this species specifically is available in the sources reviewed here.
Breeding
Because fertilisation is internal and the female can store sperm, spawning in Centromochlus orca and its relatives is not tied to a single mating event — she lays fertile eggs from stored sperm once conditions are suitable, without needing the male present at that moment. No documented parental care follows egg-laying in the family.
This unusual biology, combined with the species' small size and specific driftwood/crevice habitat requirements, means Centromochlus orca is not an established home-aquarium breeding project; data on captive spawning is sparse. Keepers should not expect the readily observable courtship and guarding seen in, for example, callichthyid armoured catfishes.
In the aquarium
At under 2.5 in standard length, Centromochlus orca is genuinely diminutive for a catfish and suits a modest aquarium — around 20 US gal is workable — furnished with driftwood, roots and rock crevices for daytime cover and kept under dim lighting. It is reported to be peaceful with similarly sized tankmates.
Two care points follow directly from its biology. It is a scaleless catfish, so it is more sensitive than scaled fish to copper and to some medications — dose conservatively. And like other auchenipterids it carries stiff, locking pectoral and dorsal spines that can snag a net and jab the handler, so it is safer to move in a container. Suggested water parameters are 73–82 °F and pH 6.0–7.5 with soft to moderately hard water (roughly 1–6 dKH); this is not documented as an extreme-softwater blackwater specialist, so the moderate range above is the more reliable guide until further data emerges.
Conservation
The IUCN Red List assesses Centromochlus orca as Least Concern, based on an assessment dated 2020. As a small, recently described species restricted to part of the Tocantins-Araguaia drainage in Brazil, its status should be read as reflecting currently available data rather than an exhaustive population survey.
No major species-specific threats are documented in the sources reviewed here. As with other Amazonian tributary specialists, habitat pressures on the wider Tocantins-Araguaia system — damming, deforestation and water-quality change — are the relevant long-term concerns for the drainage as a whole, even though the species itself is not currently flagged as threatened.