How to Identify a Brown Trout (Salmo trutta)

• Spot pattern: Large, dark spots outlined with pale halos appear on the sides, back, and dorsal fin, with reddish-orange or yellow spots scattered on the sides in some individuals.
• Tail spots: The tail usually has few or no spots, a sharp contrast with the heavily spotted tail of the rainbow trout.
• Fin edge color: The fins are yellowish-brown, with no spots and no white edges — quite different from the brook trout's white-edged fins.
• Body shape: An overall silvery color with "X"-shaped markings on the back and upper half of the body, and a squared tail.
• Fin edge color: The inside of the mouth is white.
• Body markings: The belly is white-yellow.

The brown trout's tail usually has few or no spots and no pinkish lateral stripe; the rainbow trout's tail is covered in small black spots and often shows a pinkish stripe. See the Rainbow Trout page for its full mark list.

The brown trout's fins are yellowish-brown with no white edges at all, and its sides show large dark spots with pale halos on a lighter background; the brook trout's lower fins have a distinct white leading edge followed by a black border, with worm-like markings on the back and red spots with blue halos. See the Brook Trout page for its full mark list.

Lives in cold or cool streams, rivers, lakes, and impoundments; more tolerant of siltation and higher water temperatures than brook trout. Native to Europe and western Asia, from Iceland to Afghanistan; introduced into North America as early as 1883 (New York and Michigan), and now widespread across the U.S. and Canada east of the Great Lakes and west of the Rockies to the Pacific coast.

Lay the fish flat on its side in even light and photograph the whole body first, then the details below. Spread the tail fin so its shape (forked, rounded or square) is clear. Raise the dorsal and anal fins fully; ray counts and fin edges only read when the fin is spread. Shoot the side of the body before the fish dries; spots and stripes fade fast out of water. The app reads the photo and names the likely species; use the marks on this page to confirm it.

Size and daily limits for this species differ by state and by water, and some waters are catch-and-release only. Check the current regulations for where you are fishing before keeping any fish; if you are unsure of the species, release it.