Brown Trout

Characteristics

As its name implies, this trout is generally brown, shading into a background of green and yellow. Spots on the sides are larger and more prominent than on other trout, and they are often bordered with a light-colored "halo". Few, if any, dark spots are found on the tail fin. The leading edge of all belly fins on Brown Trout is yellow or about the same color as the body. Lower portions of young Brown Trout are yellow, fading to gray or white underneath. Males, during the breeding season, often have vivid yellow to reddish-yellow colors along the belly and a sharply hooked lower jaw. The vomer, a bony structure in the roof of the mouth, has sharp teeth in an alternating "zig-zag" row. There are 115 to 150 scales in the lateral line.

Distribution

Introduced into Iowa from Europe in the late 1880’s; restricted to northeast Iowa. Some limited natural reproduction of this exotic species occurs. The Iowa DNR stocks Brown Trout to maintain its abundance. Brown Trout fingerlings are stocked each year in put-and-grow streams. Almost all trout streams in Iowa receive Brown Trout, with some trout streams being stocked only with Brown Trout.

Foods

aquatic insects and their larvae, other aquatic life

State Record

15 pounds, 6 ounces - North Prairie Lake, Blackhawk County, June 1995 - Gerold Lewis, Gladbrook, Iowa

Expert Tip

Try fly-fishing around fallen trees and undercut banks.

Details

Brown Trout thrive in clear, cold water streams and lakes to a lesser extent. It is typically found in streams around dense cover, such as submerged logs, undercut banks or in deep water below riffles. It can be found in similar places throughout the Midwest where it is stocked.

Brown Trout spawn in October and November, depositing their eggs in saucer-shaped nests called redds, which are dug by the female in the clean gravel lining the bottom of spring-fed streams. The redd is made by the fish while lying on its side and rapidly beating its tail in an up-and-down motion, letting the current move the gravel slightly downstream. Up to two males then move alongside the female and the eggs and sperm are deposited at the same time into the redd. The female then moves to the upstream edge of the redd, again beating its tail on the stream bottom, burying the eggs in gravel.

The eggs are abandoned after spawning is complete. The eggs incubate through the winter, hatch during late winter, and the tiny fry emerge from the gravel during the first warm days of spring. This whole process is temperature dependent. With a constant water temperature of 50 degrees, hatching occurs in 41 days. The number of eggs produced depends on the size of the fish. An 8-inch mature Brown Trout may spawn 200 eggs, while a 10-pound female might spawn over 8,000 eggs.

Fingerling Brown Trout released at 2 l/2-inches long in May will average about 7 l/2-inches one year later and start entering the catch that summer. Browns grow almost one inch per month during mid-summer, with much slower growth in spring and fall, and like most fish, they usually don't grow in the winter. Growth of hatchery-raised fish is constant when water temperature and feeding levels are uniform, averaging slightly over one-half inch per month. A 10-inch Brown Trout stocked from an Iowa hatchery is probably about 18 months old. Trophy-sized fish over 3 pounds have probably survived in our streams for at least three years.

Brown Trout move to hiding cover at the first sign of movement on the bank. They can survive in many cold water streams as long as there is protective cover and the water temperature does not continuously exceed 70 degrees. Brown Trout feed largely on terrestrial and aquatic insects, worms and small crayfish. Fish become important in the diet of larger browns. Daily eating patterns change seasonally with varying water temperature and light intensity. Peak insect drifts will often happen after dark, and browns are well-known for their night feeding. Brown Trout can switch from life in a hatchery to that in a stream and easily adapt to a diet of natural food items.

Brown Trout will remain our most important fish for fingerling stocking and for our special regulation trout streams because they survive well under different stream conditions. They provide the greatest challenge to dedicated trout anglers.

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.