Four trout dominate most anglers' conversations. Each has a few features that tell it apart, and those features matter because rules can differ by species.
Identification is more than trivia. Regulations in many places treat species differently. In Idaho, for example, wildlife managers note that harvest of bull trout is not allowed, which is why anglers there need to separate bull trout from similar fish. Other states have their own protected or special-rule species, and the details vary by state and by water.
Being able to tell your catch apart also makes you a better angler, since each species has habits and preferences that affect where and how you fish. Always check your state's species identification guide and current rules, and see licenses and regulations for how to find them.
Rainbows have an olive to greenish-blue back and a white to silvery belly. The signature mark is a red or pink streak along the sides. The pelvic and anal fins usually carry a white tip, and irregular spots are spread fairly evenly from head to tail. Rainbow trout are native to some western waters and introduced to many others.
Browns have a brown or olive back with large black spots. The sides run from light brown to yellowish with brown, black and red spots, and many of the spots are ringed in blue-gray. The adipose fin, the small fin near the tail, often has an orange border, and the tail has few or no spots. Brown trout are an introduced species in much of North America.
Brook trout have a dark green or blue-black back and a white belly. The upper body and dorsal fin show mottled or wormlike markings, and the sides carry pale and reddish spots, with the reddish ones often ringed in blue. The best tell is on the lower fins and tail: they have a distinct white leading edge. Spawning males can develop a bright red belly. Brook trout are technically a char, a close relative of trout, which is why their markings look different from the others.
The cutthroat's name comes from the red to orange slashes on the underside of the lower jaw, and that is the key mark. The back is steel gray to olive green, and the spotting tends to be more closely grouped toward the tail. Several distinct types of cutthroat exist in different waters, and some are protected, so local identification guides matter.
Where cutthroat and rainbow trout share water they can interbreed, and the hybrids are often called cutbows. A hybrid can show both a rainbow's pink streak and a cutthroat's jaw slash, so look closely at several features rather than one.
Use this table as a starting point, not a final answer.
| Species | Best clues |
|---|---|
| Rainbow | Red or pink side streak, evenly spread irregular spots, white tips on pelvic and anal fins |
| Brown | Large dark spots, spots ringed in blue-gray, orange-bordered adipose fin, few spots on the tail |
| Brook | Wormlike markings on back, red spots with blue rings, white leading edge on lower fins |
| Cutthroat | Red to orange slash under the lower jaw |
Some western waters also hold bull trout and lake trout. Bull trout have olive-green to brown bodies with yellow spots above and red or orange spots on the sides, without blue halos, and their fin borders are less distinct than a brook trout's. Lake trout are dark gray or gray-green with light spots and a deeply forked tail, and they live in large, deep lakes. If you cannot identify a fish with confidence, release it carefully, following our catch and release guide.
Trout colors change with age, season, water clarity and diet. A brown trout from a tannin-stained stream can look very different from one in a clear limestone creek, and spawning fish often wear brighter colors than they do the rest of the year. Rely on several features together: spotting pattern, fin edges, the tail and any marks near the mouth or jaw.
Photos can help you check later, but the fish should spend as little time out of water as possible. See the guidance in our release guide before you reach for a camera.
State agencies often publish identification charts with photos of the fish in their own waters, and they usually show look-alikes that matter locally. Keep one on your phone or in your vest. If a chart shows a protected species in the area you fish, learn its marks before your first cast, and when you cannot tell, release the fish gently and quickly.
Some species are native to the waters where you find them, and some were introduced. Rainbow and brown trout, for example, have been introduced to many streams far from their original ranges. Native fish often receive extra protection, and managers sometimes treat introduced species differently. Knowing which is which in your area helps you follow the right rules and understand why a stream is managed the way it is.
Photos help, but live fish change color with age, season and surroundings. A guide can point out the differences in person, and trip planning can include what species and rules to expect on the water you choose.
Practice helps. Look at agency photos before a trip, then compare them with the fish you see, noting spot size, fin color and tail shape each time. Over a season you will start recognizing species at a glance, even in a quick look at a fish still in the net.
Brook trout have wormlike markings on the back and a white leading edge on the lower fins. Browns have large dark spots, often ringed in blue-gray, and orange on the adipose fin.
Cutthroat have red to orange slashes under the lower jaw, which is the source of the name.
They are a type of char, closely related to trout, though anglers treat them as trout.
A hybrid between a cutthroat and a rainbow trout, which can show features of both.
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