[2][3] It was originally described from the lower Tocantins River in Brazil, but individuals resembling the species have also been recorded from Amazonian Peru.

[4][5] The species is occasionally seen in the aquarium trade, but its massive adult size and territorially aggressive behavior means that a very large tank is required.

[2] Acanthicus adonis is among the largest armored catfish species and reaches a length of 1 m (3.3 ft).

As the fish matures, the spots become less numerous and smaller, often disappearing entirely in large adults.

[4][6] In contrast, A. adonis lacks the vermiculated pattern often (but not always) found on the underparts of A.