Rainbow Trout

Characteristics

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 have 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.

Distribution

Not native to Iowa; originating west of the Rocky Mountains from southern California to Alaska. Rainbow Trout populations depend on hatchery production with no known natural reproduction in our streams. All rainbows are raised in hatchery confinement to catchable-size; 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 stopped in streams when water temperature exceeds 70 degrees.

Foods

The diet of released rainbows is highly variable, with some fish feeding very little on natural foods, while others taking nearly anything that drifts by. A large part of the diet is made of mayflies, caddisflies, stoneflies and their larvae, small mollusks and fish.

State Record

19 pounds, 8 ounces - French Creek, Allamakee County, July 1984 - Jack Renner, Waterloo, Iowa

Expert Tip

Use small jigs (1/16 - 1/32 ounce) fished in the deeper part of the pool for exciting rainbow fishing in Iowa.

Details

While the Rainbow Trout tolerates slightly higher water temperatures than other trout, it prefers temperatures below 70 degrees. It lives in streams with 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. 

Rainbow Trout do not reproduce in Iowa streams. Two strains of Rainbow Trout, fall and winter spawners, are raised at the Manchester Trout Hatchery. Fall strain fish spawn during September and October, and the winter strain spawns in 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. 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- to 11-inch fish, within 17 to 24 months after spawning. Rainbow Trout adapt well to the hatchery environment and are disease resistant; thus, they are the most economical to raise.

Rainbow Trout live in open water in streams more than other trout species. They also tend to turn in a vertical posture within the water column.

Rainbow Trout will continue to be our most numerically important fish for stocking as catchable-sized trout. They are easily caught by anglers and 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.

Sources:

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.