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Rainbow Trout are olive to greenish-blue over most of the upper body, fading to a silvery-white along the belly. They are most easily separated from the other trout species by the strikingly prominent pink-red horizontal stripe that extends down each side of the fish. The sides, back, dorsal and caudal fins are profusely spotted with small black spots continuing to the distal end of the caudal fin. Like most trout, there are sharp teeth on the vomer in the roof of the mouth. Scale counts along the lateral line range from 135 to 155.
The Rainbow Trout is not native to Iowa, originating west of the Rocky Mountains from southern California to Alaska. Perpetuation of Rainbow Trout populations in this state depends completely on hatchery production with no known natural reproduction occurring in our streams. All rainbows are presently raised in hatchery confinement to catchable size, and distribution is controlled in a predetermined schedule based mostly on angler use of a stream -- heavily used streams are stocked more often than lesser used streams. High water temperature is the most limiting factor affecting trout distribution in Iowa, and stocking is terminated in streams when water temperature exceeds 70 degrees F.
aquatic insects and their larvae, small mollusks and fish
19 pounds, 8 ounces - French Creek, Allamakee County, July 1984 - Jack Renner, Waterloo, Iowa
use small jigs (1/16 - 1/32 ounce) fished in the deeper part of the pool for exciting rainbow fishing in Iowa
The Rainbow Trout is found in the cold water streams of northeast Iowa. No wild populations are known to occur and the presence of this fish in Iowa is dependent entirely on hatchery production.
While the Rainbow Trout tolerates slightly higher water temperatures than other trout, it prefers temperatures below 70° F. It inhabits streams where there are stable riffles of rocks and gravel, for nursery and spawning areas; deep pools, overhead cover, and swift current. Rainbow Trout have adapted to areas of cool, deep reservoirs as well as cold tailwaters below dams. In Minnesota, Rainbow Trout migrate downstream after spending its first 1-3 years in smaller headwaters.
Rainbow Trout do not reproduce in Iowa streams. Two strains of Rainbow Trout, fall and winter spawners, are reared at the Manchester Trout Hatchery. Fall strain fish spawn during September and October, and the winter strain spawns during January. Both strains are semi-domesticated fish. Egg production from mature female rainbows is fairly constant, a 3 year-old fish weighing 4 pounds will produce about 2,500 eggs; a 4 year-old fish weighing 8 pounds yields 5,000 eggs; and a 5 year-old, 12 to 15-pound fish gives close to 10,000 eggs. Eggs are removed from the females by hand stripping since the trout will not spawn naturally in cement raceways.
After spawning, the eggs are incubated for 30 days at a water temperature of 50 degrees F. Growth, when on a full-food ration of 1 to 10 percent of the body weight per day, averages about three-fourths of an inch per month. The amount of food supplied to the fish is used in the culture process to control growth. Feeding schedules are designed to produce a one-half pound, 10-11 inch fish, within 17 to 24 months after spawning. Rainbow Trout adapt very well to the hatchery environment and are disease resistant; thus, they are the most economical to raise.
Rainbow Trout inhabit the open water habitat in streams more than the other trout species. They also tend to orient in a vertical posture within the water column.
The diet of released rainbows is highly variable, with some fish feeding very little on natural foods while others seemingly taking nearly anything that drifts by them. A large part of the diet is comprised of mayflies, caddisflies, stoneflies and their larvae, small mollusks and fishes.
Rainbow Trout will continue to be our most numerically important fish for stocking as catchable trout. They are readily caught by fishermen and so provide the greatest amount of fishing recreation for the least cost.
Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.
Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.
Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames.
Illustration by Maynard Reece, from Iowa Fish and Fishing.