Only large pimelodid with numerous spots but no stripes. Large flat barbels. A large black spot is present on the lower caudal lobe. Possibly more than one valid species is currently classified as P. notatus given the reported differences in coloration, habitat, and adult size.

Specimens from the Amazon are reported to reach 50 cm while specimens from the Orinoco are reported to reach one meter. Given the greatly varying reported adult sizes, aquarists wishing to acquire this fish should take great care and assume the fish could reach one meter in length.