There are just 10 extant (living) species in this order of freshwater fish, grouped into three families.

Found only in North America, they are often called “trout-perch-like fishes” because they share features with both perch and trout, though they are not closely related to either.

These fish are typically small, ranging from about 2 to 8 inches (5–20 cm) in length. They have slender bodies, large eyes, and fins. Many species are well adapted to dim or murky water, and some are most active at night.

Most members of this order live in cool freshwater habitats such as lakes, streams, and rivers. They tend to stay near the bottom, where they feed on small insects, crustaceans, and other tiny organisms.

The fossil record shows that this group has a long history in North America, dating back roughly 100.5 to 66 million years ago during the Late Cretaceous period.

The Ozark cavefish (Troglichthys rosae), one of the species in this order,  is a small freshwater fish that lives underground in caves. It is found in northeastern Oklahoma, northwestern Arkansas, and southwestern Missouri. Because of its limited habitat and environmental threats, it has been listed as a threatened species in the United States since 1984.

This unique fish has adapted to life in complete darkness. It has no pigmentation, giving it a pale, almost translucent appearance. The Ozark cavefish is tiny, growing to only about 2 inches (5.1 cm) long.