[2] Brachyplatystoma are found in the Amazon and Orinoco basins, and other tropical freshwater and brackish habitats in South America.

Brachyplatystoma is derived from the Greek words brachy, platy, and stoma, which mean "short", "flat", and "mouth", respectively.

The subgenus Malacobagrus is characterized by their derived lateral line, Weberian apparatus, a subquadrangular gill cover (as opposed to triangular in the other species), and pectoral spine.

[3] The other, more obvious defining trait of the genus is only reliably found in juveniles and subadults; the single, outermost ray of the caudal fin are extended into long filaments.

In most species, this is consistent throughout life, though there are some exceptions: juvenile B. capapretum and B. filamentosum exhibit dorsal and lateral spots which mostly disappear in the adult form, while juvenile B. juruense and B. tigrinum exhibit lateral spots that expand to form dense vertical stripes as the fish matures;[3] they are not strongly countershaded, but rather are disruptively camouflaged.

[9][10][11] The world record recognized by IGFA for Brachyplatystoma filamentosum belongs to the Brazilian, Jorge Masullo de Aguiar with 155 kilograms (342 lb).

[12] B. filamentosum and B. rousseauxii have a mysterious "milk" gland at the anterior upper part of their pectoral fins.

[13] Brachyplatystoma have specialized pelagic young with greatly elongated barbels and fin filaments, and strongly ornamented pectoral spines.

[18] The young, sometimes referred to as alevins, are carried downstream, during which they develop through their larval stages, which may be hard to distinguish between species.

[17][19] As they drift downriver, they consume animal prey that fits into their mouth; small crustaceans such as cladocerans and copepods, rotifers, the occasional spider and nematode, and insects both aquatic and non-aquatic are taken, with dipterans being the most common food item extracted from the stomachs of larval B. rousseauxii and B.

[20] Juveniles and subadults are commonly found brackish habitats, such as estuaries,[17] staying there for about three years before entering the lower reaches of the river.

Along with Lithodoras dorsalis and "B. flavicans", catfish in this genus were some of the first recorded to have migratory young, at least in the Amazon basin.

In the Amazon Basin, thousands of metric tons of fish from this genus are caught for both local consumption as well as exportation.

may be done in estuaries, where juveniles feed and grow in preparation for their upstream migration, and where bycatch species such as Plagioscion squamosissimus and Sciades herzbergii reside.

[23] Because these fish may migrate back to their original tributary, overfishing in a certain area may diminish overall catches as a whole genetic group is depleted.

[2][6] Human developments are another disruptive factor; dams may impede the migration of these fish both to and from their spawning sites.