trout-perch, either of two species of small, dark-spotted fishes of the genus Percopsis (family Percopsidae), found in freshwaters of North America. The larger species, P. omiscomaycus, grows about 15 cm (6 inches) long and is found in central North America. The second, P. transmontana, is about 10 cm long and lives in the Columbia River system. Trout-perch are notable in being structurally intermediate between the more primitive soft-rayed fish, such as trout, and the more advanced spiny-rayed fishes, such as perch.