Taxonomy & naming
Brachyplatystoma capapretum was described by John G. Lundberg and Sifundo Akama in 2005, in a paper that also reclassified several allied goliath catfishes within the family Pimelodidae. For decades specimens of this species were folded into Brachyplatystoma filamentosum, the piraíba, because the two are superficially similar giant long-whiskered cats sharing Amazonian river channels; the 2005 description separated them on tooth-row structure, fin shape and colour pattern. The Catalog of Fishes recognises Brachyplatystoma capapretum as the valid name, and it remains in the genus Brachyplatystoma within Pimelodidae.
The genus name Brachyplatystoma derives from Greek roots meaning roughly "short, flat mouth", a nod to the broad, depressed head typical of these giant cats. The specific epithet capapretum is a Latinised nod to the Portuguese "capa preta", meaning "black cape" — a direct reference to the fish's dark dorsal countershading, and the source of its common name "dark caped goliath catfish" as well as the Brazilian trade name "filhote da capa preta".
Morphology
This is a true goliath: Seriously Fish records an adult maximum length of about 34.5 in SL, with the species possibly growing larger still, while FishBase's older figure of 23 in SL is now considered an underestimate. Like other Brachyplatystoma it has the classic long-whiskered-catfish build — a broad, flattened head, a streamlined torpedo-shaped body, and very long maxillary barbels trailing well past the body. The original description notes fine, densely spaced outer jaw teeth and relatively few rows of straight, depressible inner teeth, features used to separate it from its close relative B. filamentosum.
Colour is the species' signature. Juveniles carry large dark blotches on and above the lateral line, while adults become exceptionally dark — almost black — across the entire dorsal surface, with an abrupt, well-defined line of countershading where the dark cape meets the pale flank below. The caudal fin is broad and shallowly forked. As in all catfishes the skin is naked and scaleless, which has direct consequences for medicating this species (see "In the aquarium"), and the dorsal and pectoral fins carry stiff, serrated, locking spines that must be handled with care.
Habitat
Brachyplatystoma capapretum is native to the Amazon basin of Brazil and Peru, where it inhabits the larger, deeper channels of major rivers rather than small tributaries or floodplain lakes. It is a fish of open, flowing water in the main river channels, living alongside other big pimelodid catfishes in a habitat defined by strong current, considerable depth and turbid or clear-flowing conditions depending on the river reach.
Water conditions reported for the species span a broad range: temperatures of 72–82 °F, pH from about 6.0 to 8.0, and hardness from roughly 18 to 357 ppm. This breadth reflects the diversity of Amazon river types the species and its relatives range across, from softer blackwater-influenced tributaries to harder, more mineral-rich whitewater channels, rather than a single narrow niche.
Feeding
This is a large, nocturnal piscivore. In the wild it preys on other fish, including loricariid catfishes and bottom-dwelling species, hunting mostly under cover of darkness in the deep river channels it inhabits. As an apex-level predator in its size class, it will consume essentially any fish or large invertebrate it can fit in its mouth.
In captivity — almost exclusively public aquaria and very large private systems — it adapts readily to dead and prepared foods: whole prawn, mussel, squid and whitebait are all taken. Adult specimens need feeding only about once a week given their size and slow metabolism. Any tankmate must be far too large to be swallowed whole; this is not a fish that can share space with anything it can eat.
Mating
Detailed observations of courtship and spawning behaviour in Brachyplatystoma capapretum have not been documented from the wild or captivity. Given its enormous adult size and its life history as a deep-channel giant of the main Amazon river system, natural reproduction almost certainly involves long-distance migration to spawning grounds, a pattern documented in other large Brachyplatystoma species, but this has not been specifically confirmed for B. capapretum.
There is no record of this species pairing off or spawning under aquarium conditions. Seriously Fish states plainly that it has never been bred in captivity, and nothing in the available literature suggests otherwise.
Breeding
Brachyplatystoma capapretum has never been bred in the home aquarium, and there is no realistic prospect of that changing: this is a large, commercially important Amazonian food fish, and any captive propagation of goliath Brachyplatystoma species in the region relies on hormone-induced spawning at fisheries or aquaculture facilities rather than natural pairing in a tank. The species' huge adult size, deep-river habitat and probable long-distance spawning migration make natural reproduction in captivity essentially impossible outside a wild river system.
Hobbyists and even public aquaria should not expect to breed this species. Any aquarium specimens seen in the trade are wild-collected juveniles, not captive-bred stock, and the species' conservation and management is tied to wild river populations rather than aquaculture broodstock.
In the aquarium
Brachyplatystoma capapretum is a textbook size-trap fish: it is occasionally sold as an appealing, boldly patterned juvenile a few centimetres long, but it is capable of reaching around 34.5 in SL — pushing a metre in total length — and no home aquarium can house an adult responsibly. Aquarium care sources recommend a minimum tank volume in the tens of thousands of litres, essentially public-aquarium or outdoor-pond scale, with massive, reliable filtration and rigorous ongoing maintenance. This is a fish for zoological institutions and the rare private keeper with a truly enormous system, not a community or even a standard large-tank setup.
Where it is kept, provide a soft sandy substrate, large driftwood for cover, and sparse or dim lighting to suit its nocturnal habits; it becomes more active after dark. Because it is scaleless like all catfishes, it is more sensitive than scaled fish to copper-based medications and many standard treatments — dose conservatively. It also carries stiff, serrated, locking pectoral and dorsal spines that can snag a net and jab the handler, so any necessary handling should use a container rather than a net. Feed it whole fish, prawn, mussel or squid roughly weekly once mature, and never house it with anything small enough to be eaten.
Conservation
The IUCN Red List assesses Brachyplatystoma capapretum as Near Threatened, an assessment made on 14 December 2020. The listing reflects concern over potential future declines driven by pressures similar to those affecting its congeners — heavy commercial fishing pressure on large Amazonian catfishes, together with the cumulative effects of dam construction and habitat alteration across the Amazon and its major tributaries, which can disrupt the long-distance migrations these goliath catfishes are thought to depend on.
As a large, slow-growing predator near the top of its food web, B. capapretum shares the vulnerability common to big migratory Amazonian catfishes: populations recover slowly from overfishing, and barriers to river connectivity pose a long-term risk even where current numbers appear stable. It is a food fish across its Brazilian and Peruvian range, and continued monitoring of catch levels and river connectivity will determine whether its status improves or worsens.