The Bristle-Tail Filefish (Acreichthys tomentosus) is a marine (saltwater) fish in the Monacanthidae family of Leatherjackets. It is related to Pufferfish.

The Bristle-Tail Filefish has a laterally-compressed, rhomboid-shaped body and rough skin like sandpaper. It has many spines. It can rapidly change colour, skin texture, and even skin patterns to avoid predators. It has a tapered snout (nose) and its orange-brown eyes are located high on its head. It has small fins, so it is not a good swimmer.