October 01, 2021
By FFM Staff
The rainbow trout (oncorhynchus mykiss) is a beautifully colored and speckled freshwater and saltwater fish, and a member of the salmonidae family. It is the most widely distributed trout species in the world. It gets its name from the olive, iridescent pink-ish red, and yellow-ish white hues that drape down its flanks behind a starfield of black spots. They are often considered a very sporting trout for anglers due to their difficulty to catch and their strong fighting ability (including what are often considered the flashiest leaps of any trout species).
Rainbow Trout Size
Adult stream-dwelling (fluvial) rainbow trout usually grow to between 12 and 20 inches in length and between 1 and 4 pounds, depending on a variety of factors mostly related to habitat and genetics. Twenty-plus-inch rainbow are considered a trophy catch for anglers. Adfluvial (lake-dwelling) adults can reach larger sizes on average due to the fact that they burn fewer calories fighting the current to find food.
An exception to this is the steelhead, which are West Coast rainbow trout that evolved to live in the Pacific Ocean but make spawning runs into freshwater tributary rivers. These fish can grow up to 25 pounds and larger in rare instances.
Rainbow Trout Native Range
Rainbow trout are native to the Pacific Ocean watershed of portions of North America and Asia. In North America, rainbow trout are native to the United States and part of the Canadian West Coast, as far inland as eastern Idaho and Northwest Montana and as far south as northwest Baja California, Mexico. In Asia, rainbows are native to Amur River drainage and north into Russia’s Kamchatka Peninsula.
Rainbow Trout Habitat
Rainbow trout habitat includes cold freshwater streams, rivers, lakes, and ponds (with the exception of steelhead, which live part of their lives in saltwater and are covered below) where the average temperature stays below 65 degrees year-round. They prefer well-oxygenated water, often from high-gradient/fast-flowing mountain streams.
Rainbow Trout Life Cycle
Sexually mature adult rainbow trout typically spawn in spring (though there are some known exceptions where rainbow trout spawn in the fall). Rainbows will migrate upstream (usually) to their natal spawning grounds to lay and fertilize thousands of eggs per fish in spawning beds known as redds. In one to two months (depending on habitat), eggs hatch into what are called fry (baby fish), then fingerlings (juvenile fish), and they are considered adults by the end of their first (or second or third, depending up on the strain) year when they are capable of spawning their own eggs. They typically live four to six years.
Rainbow Trout Diet
Rainbow trout feed primarily on all stages aquatic invertebrates (nymph, larva, pupa, etc.) like mayflies, caddisflies, stoneflies, midges, and crustaceans (scuds, sowbugs, and crayfish). They will secondarily eat small baitfish, including using the cannibalistic behavior of preying on small rainbow trout. They also eat fish eggs [J1] when present, worms (both aquatic and terrestrial annelids), zooplankton, and daphnia in stillwaters (lakes, reservoirs, and ponds). They are generally opportunistic feeders, meaning they will eat any attainable food source if it provides more energy than it expends to consume, but they will get selective under certain circumstances of abundance. Because of their feeding habits, they are ideal quarry for fly anglers.
Strains of Rainbow Trout
There are many different “strains” or subtypes of rainbow trout, which means they’re the same species so they can mate with other, but have slight genetic differences that affect when they spawn, how fast they grow, diet, and details in their appearance. They are often named after a native fishery or the location where they’re bred in a hatchery. Some strains include: triploid, Ten Sleep, Sand Creek, Beitey, Shepherd-of-the-Hills, New Zealand, Fish Lake, Desmet, Eagle Lake, Arlee, Kamloops, McConaughy, Columbia River redband, coastal, Gerrard, Pennask, Alaskan, Blackwater, Fraser Valley, Tzenzaicut, Horsefly, Erwin, Colorado River, steelhead, and more.
Rainbow Trout Locations
The rainbow trout is widely regarded as the most widely distributed salmonid in the world, thanks largely to being stocked by humans because of it its adaptable and hardy nature. Rainbow trout are now found in every continent except Antarctica, and nearly every U.S. state and Canadian province.
As much as anglers and wildlife enthusiasts value rainbow trout, and as important as they are to their native ecosystems, their introductions to non-native waters worldwide have been extremely detrimental to certain native fish populations like cutthroat trout and Arctic grayling in the Rocky Mountains. The introduction of non-native rainbows have decimated native cutthroat trout populations due to out-competing them – rainbow trout (along with brown trout, in many locales) are more assertive and dominate prime feeding lies and spawning grounds. The same has happened to the Arctic grayling in the Lower 48. The effect is less pronounced in locations that did not have native trout populations (New Zealand and South America).
The steelhead’s native range extends from southern California to Alaska along the Pacific Coast.
Native Range in North America (Pacific Coast from northern Mexico to Alaska): There are a few distinct strains or populations native of rainbow trout in the native range: coastal rainbow trout, redband rainbow trout, and steelhead. Of these steelhead rainbow trout are the most distinct as steelhead actually live in the ocean for their first two to three years (after hatching in freshwater tributaries to the ocean), and grow to very large sizes (up to 25 pounds – larger in rare instances). Primary locations for native steelhead include Washington, Oregon, California, and British Columbia. Primary locations for the redband include interior portions of northern California, Washington, Oregon, Idaho, and Nevada. The coastal rainbow trout is native to the coastal watersheds of the North American Pacific coastline, from northern Mexico to Alaska, including Baja California, California, Oregon, Washington, and British Columbia. (See Rainbow Trout Native Range above)
Native Range in Asia (China and Russia): In Asia, rainbow trout are native to a few Pacific Ocean tributary rivers. By and large, rainbows are native only to the Amur River drainage, which makes up the far northeastern border of Russia and China, and the Kamchatka Peninsula of far northeastern Russia. Particularly in the Kamchatka Peninsula, rainbow trout grow quite large, where 30-inch specimens are not uncommon.
Non-native range in North America: Rainbow are not native to the Eastern U.S. but have successfully made a home in this area that’s the native range of the eastern brook trout. Much of the rainbow’s habitat here has been created by cold-running tailwater streams (streams that flow below dams). Major states for rainbow trout in the Eastern U.S. include New York, Maine, Pennsylvania.
The Great Lakes and their tributaries also have a lake-dwelling variety of “steelhead” that grow large, and are pursued by fly anglers on their spawning runs, much like the true steelhead of the Pacific Northwest.
Rainbow trout are not native to the Midwest’s Driftless Area (southeastern Minnesota, southwestern Wisconsin, and northeastern Iowa), but have taken hold in this region of small spring creeks due to decades of stocking. Rainbows here rarely exceed 16 inches due to the size of the habitat and biomass/forage base. This is the furthest east of the brook trout’s native range, and brook trout coexist alongside the introduced rainbow and brown trout.
Many other rivers and lakes throughout North America host stocked rainbows as well, particularly tailwaters (rivers below dams), cold spring creeks, and mountain/high gradient streams in cool climates.
Elsewhere: Rainbow were first planted in Australia and New Zealand in the late 1800s, though both countries are better known for their brown trout fishing. Though rainbow trout can get large here given the right conditions, they average 14 to 20 inches as adults.
Rainbow have also successfully been bred and planted in the mountainous regions of Europe, southern and eastern Africa, and portions of the Middle East and western Asia.
Fly Fishing for Rainbow Trout
Rainbow trout are one of the most popular fish to target with fly gear for many reasons, the biggest of which include that they willingly eat aquatic insects and can be challenging to fool.
Three- to 6-weight rods are the most effective for targeting rainbow trout, most often on floating fly lines of the same size. Fly selection will depend on the available bugs in a given fishery or region, and the season. But standard dry flies (Parachute Adams, Elk Hair Caddis, hoppers, etc.), nymphs (Prince Nymphs, Hare’s Ears, Pheasant Tails, Girdle Bugs, etc.), and streamers (Woolly Buggers, Muddler Minnows, sculpin patterns, etc.) should work to catch rainbow trout in most places.