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"
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
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.