Amblyopsidae (cavefishes) Aphredoderidae (pirate perch) Percopsidae (trout-perches) The Percopsiformes /pɜːrˈkɒpsɪfɔːrmiːz/ are a small order of freshwater teleost fishes measuring less than 20 cm in length, comprising the trout-perch and its allies.

[4][1] Most species in this order are known from the eastern and central regions of North America, although the two Percopsis species have a primarily boreal and western distribution, with P. omiscomaycus reaching as far north as the Arctic Circle and P. transmontana being restricted to the Pacific Northwest.

They are generally small fish, ranging from 5 to 20 cm (2.0 to 7.9 in) in adult body length.

They are grouped together because of technical characteristics of their internal anatomy, and the different species may appear quite different externally.

They are more closely related to the cods, dories, and the deep-sea tube-eye, and fossil evidence suggests that their closest relative was the extinct order Sphenocephaliformes, comprising two enigmatic genera of Late Cretaceous marine fish, as well as Omosomopsis, another Cretaceous marine fish from Morocco.