How to Identify a Rainbow Trout (Oncorhynchus mykiss)

• Tail spots: The tail is heavily spotted — one of the key traits separating it from the brown trout.
• Body markings: Adults usually have a pinkish lateral stripe.
• Spot pattern: Rainbow trout also have many small, black spots on the body.
• Adipose fin: The adipose fin (the small fin behind the dorsal fin) has a black edge.
• Fin edge color: The inner mouth and gums are white.
• Body shape: The tail is forked.

Whether the tail is heavily spotted is the main distinguishing feature: the rainbow trout's tail is covered in small black spots while the brown trout's tail usually has few or none; the rainbow trout often has a pinkish lateral stripe, which the brown trout lacks. See the Brown Trout page for its full mark list.

The rainbow trout has dark spots on a lighter body, the opposite of the brook trout, which has light spots on a dark background with worm-like markings on the back; the rainbow trout's tail is forked and heavily spotted, while the brook trout's tail is nearly square. See the Brook Trout page for its full mark list.

Found in lakes, ponds, reservoirs, large lakes such as Lake Michigan, and rivers and streams; widely stocked. Native to the Pacific coast of North America; now widely stocked and introduced elsewhere in North America.

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.