Forest Preserve District of Cook County, Illinois
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The Trout
Nature Bulletin No. 718   May 18, 1963
Forest Preserve District of Cook County
Seymour Simon, President
David H. Thompson, Senior Naturalist

Illinois is not a trout state. Only the Lake Trout of our Lake Michigan waters is native but it has been almost wiped out during the past twenty years by the depredations of the parasitic marine lamprey (discussed in Nature Bulletin No. 553). For many years small numbers of hatchery-reared Brook Trout, Rainbow Trout and Brown Trout from other parts of the country have been released in the streams and lakes of northern Illinois. These gamy aristocrats are novelties in this region and attract large numbers of fishermen. However, few survive summer water temperatures as high as 70 degrees Fahrenheit and none find conditions suitable for spawning successfully.

As a rule the many kinds of trout are strikingly marked or brightly colored. All have the streamlined bodies found among strong swimmers. Like their near relatives, the salmon, they have tiny scales that are imbedded in the skin.

Trout differ most from other freshwater fish in their breeding habits. Instead of spawning in spring or summer, they lay their eggs in autumn or winter. Trout eggs are large, usually about one-fifth inch in diameter. In the cold water at these seasons the embryos develop very slowly, often requiring 50 or 100 days for the eggs to hatch. In many species the eggs are buried in the gravel of a stream bed, thus giving protection during their long incubation.

Trout hatcheries became popular long ago because of the ease with which eggs can be stripped from a "ripe" female, fertilized with milt from a male, then allowed to incubate in cold running spring water. Within two or three weeks the dark eye spots of the embryos can be seen through the transparent egg shells. At this stage the eggs can be packed in damp moss and stay alive on trips lasting many weeks, if they are kept cool. In this way trout were transplanted all over the world long before the days of air travel. Unlike the European carp which has become a nuisance here, American trout have improved fishing in many foreign countries.

Originally, the Brook Trout, or Speckled Trout, was found only in eastern United States and Canada. Now it thrives in many of our western mountain streams and lakes which previously were barren. This trim, brilliantly colored fish with white edging on the lower fins is one of America's favorite game fish. Because it needs pure cold water, it is disappearing from many waters as a result of pollution, deforestation, soil erosion and warming. Almost a half million pounds which were reared in commercial hatcheries in the northern states and Canada are sold annually in the Chicago market.

The Rainbow Trout is a native of waters draining into the Pacific from Alaska to California. Colored greenish-blue above and silvery below, it is dotted with small black spots and has a prominent red band along the sides. Certain young rainbows go to sea and return to their parent stream after a few years with a quite different coloration -- silvery with a bluish head and back, but without the red band and black spots. Then they are called Steelhead Trout. This has become the most cosmopolitan of all our trout.

The Brown, German Brown or Loch Leven Trout is a native of Europe introduced into America about a century ago. Because it can endure warmer water and stand up under stream conditions that go along with civilization, it often furnishes sport fishing where otherwise there would be none. The back and sides are olive to greenish brown with black and red spots.

The only trout fishing in the forest preserves is at Axe Head Lake located one mile west of Park Ridge between West River Road and the DesPlaines River.

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