Rainbow Trout

central mudminnow

What's In a Name?
Rainbow trout, aka Steelhead: "rainbow" refers to the colors on the sides of the stream-dwelling type; "steelhead" refers to the steel-gray head color of the type that runs to the ocean (in Lake Superior in our case)

Oncorhynchus (on-co-wren´-cuss) means "hooked snout" in Greek
mykiss (me´-kiss) an old Russian name for the species

Where Do They Live?
The rainbow trout or steelhead is an introduced exotic species. It is native to the West Coast and some of the streams west of the Rocky Mountains. Rainbow trout have been introduced into many of Minnesota's streams and lakes, especially in the northern half of the state. A migratory strain that normally lives in the Pacific Ocean was introduced long ago into Lake Superior and it has become naturalized. We call it the steelhead. Steelheads begin and end their lives in streams and live in Lake Superior during their major growth period. A different hatchery strain was introduced more recently. Non-migratory rainbows typically live in fast-running clean streams with gravel bottoms and in deep, cool, soft water lakes. The Missouri strain of rainbows do especially well in warmer streams where brown and brook trout cannot survive.

How Big Do They Get?
How Long Do They Live?

In Lake Superior, steelhead used to exceed 750 mm (30 in) and 6.8 kg (15 lbs), but now most angler catch ones 600-700 cm (24-28 in) and 1.4-3.6 kg (3-8 lbs). Inland rainbows are considerably smaller fish, 375 mm (15 in) long and 2.5 kg (5.5lbs) are lunkers. Most rainbows live for 3-4 years.

What Do They Eat?

Young rainbow trout first eat waterfleas and then add aquatic (water) insects, like caddisflies, mayflies, and midges, to their diet. As they grow larger they include small fish, but continue to consume larval and adult insects. They also supplement the diet with other kinds of food, such as snail, leeches, fish eggs, sideswimmers, and algae.

What Eats Them?
Young rainbow trout often are eaten by a variety of piscivorous (fish-eating) fishes, such as sculpins, smallmouth bass, and larger trout. When in shallow water, they also are fed upon by kingfishers, herons, eagles, osprey, otters, and raccoons. Humans are the most frequent predators of larger rainbows.

How Do They Reproduce?
Rainbow trout are usually 3 - 4 years old when they spawn. Stream-dwelling rainbows migrate upstream to spawn. Those in lakes migrate into tributary streams or spawn in shallow areas of rock or gravel if no streams are available. Some steelhead spawn in the fall, but most spawn in the spring mostly in April in Minnesota. Water temperatures must go above 5°C (41° F) and streams must rise (from rain) or the steelhead will not spawn. The female scrapes out a nest in the gravel and is joined by one or two males. The males lay side by side with the female in the middle and the fish release their eggs and sperm at the same time. The female covers the eggs with the gravel she removed to build the nest. She will spawn repeatedly until all her eggs are released. There is no parental care of the nest or the eggs. A single female may lay 400-3,000 eggs depending on her size. The embryos develop for 20-80 days depending on the water temperature. They hatch into what are called alevins (free-swimming embryos with huge yolk sacs) and stay down in the gravel for another 2-3 weeks while their fins develop. After that time, they swim up and begin feeding in the stream or lake. Migrating rainbows live and grow in the stream for 2-3 years before they migrate downstream or out into a lake.

Conservation and Management
Rainbow trout are probably the most important sport trout in Minnesota. They are a part of both coldwater lake and stream fisheries. More rainbows are stocked each year in Minnesota waters than any other trout or salmon.

Natural History of Minnesota Fishes

Photograph by John Lyons WiDNR
Text by Nicole Paulson & Jay T. Hatch in cooperation with
the Minnesota Department of Natural Resources' MinnAqua Aquatic Program

Go here to find MN DNR Rainbow Trout Management reports and annual summary data.