Acanthicus adonis, the adonis pleco, is a species of armored catfish endemic to Brazil. Though originally described from the lower Tocantins River, it is found more widely in the Amazon Basin. It is among the largest armored catfish species and reaches a length of 1 m (3.3 ft).
The adonis pleco is dark brown to black with numerous white spots as a juvenile. As the fish matures, the spots fade. These plecos have slender, rough bodies, a lyre-tail, and a pointed snout. These fish are omnivores, and will feed on anything from fruits and vegetables to bits of frozen meaty foods. Driftwood is also appreciated for grazing. Adonis plecos reach a considerable size and adults can be aggressive; it is only suitable for very large aquariums.