How Are Brook Trout and Rainbow Trout Different? Cousins From the Same Continent

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Close up image of Brook trout in man's hand.

Brook trout and rainbow trout are both members of the Salmonidae family, which means they are related. But brookies aren’t really trout. They are members of the char genus. Rainbows are true trout, however.

A few years ago, while fishing a gorgeous little trout stream outside of Ennis, Mont., my fishing buddies and I were thrilled at the non-stop action we enjoyed. It was “one of those days” when the rainbows in the little creek were relentlessly hitting dry flies. 

After the day on the water, we gathered in a bar in town. Over beers, one of my friends looked at me and said, “I know this sounds odd, but I’m really glad we caught rainbows and not just a bunch of little brookies.”

It’s true. In the West, non-native brook trout tend to take over small streams from native fish. But, I should note, the rainbows we caught that day weren’t native either. Both fish have been introduced into watersheds where they don’t really belong. 

But, most fly fishers would tell you, both fish are now “naturalized” to the Rocky Mountains, having been introduced more than a century ago. 


But are rainbow and brook trout really all that different? Yes. In fact, they’re not even members of the same genus. Rainbows are true trout. Brook trout are a subspecies of char. 

How Can You Tell Them Apart?

Chris caught Rainbow trout in the river.
Rainbow trout will have a pink or red stripe down their sides and often sport a rosé tinted gill plate. They also have white-tipped fins.

Most rainbow trout will sport a tell-tale red or pink stripe down their sides. Often, especially during the spring spawning run, the gill plates of rainbows will be a beautiful shade of rosé. 

Brook trout are equally stunning, if not moreso. They will display green and black worm-like markings on their backs and feature bright orange bellies and white-tipped orange fins. 

Where Are They Native?

Fishing for brook trout where they are native in northwest Ontario.

While it’s certainly possible to catch rainbow trout and brook trout in the same water, the two fish did not evolve together. 

Rainbow trout evolved in the coastal rivers and streams of the Pacific West, from California north to Alaska. Brook trout are native to the Eastern Seaboard of the United States and Canada, with some native populations appearing as far west as Minnesota. 

So, when you see brook trout and rainbow trout in the same waters in the interior West, know that neither fish is really swimming where it belongs. 

Why Are Brook Trout So Small?

Small Brook trout from the West in man's hand.
Brook trout in the West don’t get very big because they spawn so proficiently and eat themselves out of house and home. In the West, their populations are often stunted.

It’s a great question. The reason you rarely catch big brook trout in the West is because they are prolific when it comes to two things: mating and eating. You’d think that would make them bigger, right?

Well, that’s not the case. Brookies are very productive spawners, and each female can lay up to 400 eggs in a single nest, or redd. That’s a lot of baby trout. 

And, with so many trout in the system, the voracious fish do a good job of eating everything they can find. But small streams in the West, where brook trout are prominent, don’t have the same kinds of habitat that brook trout enjoy in their native waters. 

So, they eat themselves out of house and home and they grow to the limits of their habitat. That’s why brook trout populations in the West are often “stunted.” In some waters, a four-inch brookie is a mature fish. 

Why Are Rainbow Trout So Popular?

Rainbows are prolific fighters. They will often jump from the water when they are hooked. That’s very appealing to anglers, particularly fly fishers who love to chase rainbows with dry flies. 

Rainbows, unlike brook trout in the West, do get quite large. This, of course, is appealing to anglers of all stripes. 

Would you rather catch a 20-inch rainbow that rockets from the water or a six-inch brook trout? While the brookie might be absolutely beautiful, the rainbow is going to provide much better sport on the end or your line, right?

Also, likely because they are glorified by anglers of all stripes, rainbows are simply preferred by most anglers.

That said, if you’re very lucky, you’ll one day catch a brook trout in eastern Canada, where they’re native and grow big. That will tilt your perspective. Trust me. 

Final Thoughts

Brook trout and rainbow trout are members of the same taxonomic family, so they’re related. But, even though the fish show up in the same waters sometimes, they are not natural neighbors. Brookies are native to eastern North America. Rainbows are West Coast fish. Both are appreciated by anglers all over the world. 

FAQs

Do Brook Trout Taste Better Than Rainbow Trout? 

Many anglers think so. Brook trout meat is darker and bit more oily than rainbow trout flesh. But it often depends on what the fish are eating.

How Can You Tell Brook Trout and Rainbow Trout Apart?

Rainbows are true trout, so they will have light-colored bodies and dark spots. They’ll also boast the red stripe down their sides that gives them their name. Brook trout are char. They will dark bodies and light spots. They’ll also have orange fins with white tips and worm-like markings on their backs. 

Are Brook Trout and Speckled Trout the Same? 

Yes. In some areas the American Southeast, brook trout are called speckled trout. 

Are Rainbow Trout and Steelhead Related? 

Steelhead trout are rainbow trout that run to the ocean for part of their lives. 

Do Brook Trout Run to the Ocean?

I’m some instances, yes. There are ocean-going brook trout in the Northeast and eastern Canada, and some sea-run brookies in Hudson Bay. 

Chris Hunt Avatar

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