Once limited to the Northern Hemisphere, they are valued as game and food fish and have been introduced into a number of areas in the Southern Hemisphere. Although predominantly a freshwater fish, some species migrate to the ocean after spawning upriver. The trout has a moderately long, unspecialized body that is laterally compressed, smooth, and muscular. Axial and paired fins are without spines. The softer, fleshy adipose fin, between the dorsal and caudal fin, is an indicator that the trout is a salmonid.
All scales are small except for the elongated axial scale at the base of each pelvic fin.
The trout's diet changes with age. Fry, or newly hatched fish, feed on aquatic insect larvae for the most part. They progress to eating winged insects. As adults, small fishes, shrimp, and winged insects constitute the bulk of their diet. Most trout breed in early spring in running water.