Acanthicus hystrix should not be confused with Pseudacanthicus histrix.
Acanthicus hystrix, the lyre-tail pleco,[1] is a species of armored catfish native to the Amazon, Tocantins–Araguaia and Orinoco basins.[2] It is typically found at various depths on a rock or rock–gravel bottom in the main channel of rivers in places with moderate to strong current,[2] although it also occurs in slow currents.[1] The species is occasionally seen in the aquarium trade, but its adult size and territorially aggressive behavior means that a very large tank is required.[1]
It grows to in standard length,[2] but may possibly reach .[1] Its color ranges from medium-brown to near-black (especially those from the Madeira, Branco and Xingu rivers are dark), and the underparts often have a vermiculated pattern.[2] Some of the variants are commonly considered as separate, undescribed species in the aquarium trade (e.g., L193 from the Orinoco basin and L407 from the Branco basin; in the L-number system), but there is extensive overlap in the morphometrics of the different populations.[2] Unlike the polka dot lyre-tail pleco (A. adonis), A. hystrix never has white spots.[2] Adult males are especially spiny with extensive odontodes on the cheeks and opercle.[2]