"B. capapretum", described in 2005, was previously misidentified as "B. filamentosum". These two species are closely related. However, these species differ in premaxillary dentition, juvenile and adult coloration, and adult maxillary barbel length and caudal fin shape. These two species exhibit spotted juvenile stages, though in "B. capapretum" these spots are much larger than the eye, while in "B. filamentosum" these spots are about the same size as the eye. Also, the cross section of the caudal peduncle is rounded in these two species, as opposed to a deeper, thinner cross section in other "Brachyplatystoma" species. The adult "B. capapretum" has a very dark or even black dorsum (its species name is derived from Portuguese which means "black cape"), as opposed to the lighter dorsal surface of "B. filamentosum".