Trout biology and identification
The only native Minnesota trout species, the brook trout originally inhabited Lake Superior and many small cold lakes and streams throughout the state. Now common in the upper reaches of North Shore streams, it also is found in some small creeks in southeastern Minnesota and scattered waters elsewhere in the state.
The brook trout takes a lure or bait more readily than the rainbow or brown trout. It is protected less by any innate wariness than the fact that it typically inhabits tiny alder-choked creeks that are difficult to fish.
Brook trout from streams have pale markings on a dark green background. The back is covered with wormlike marks. Lake Superior fish are more silvery with less distinct markings. In both stream and lake fish, the tail is nearly square, and the leading edge of each lower fin often has a white margin. The brook trout rarely exceeds a pound in small streams. Lakes produce larger fish.
Introduced from Europe to much of the United States during the late 1800's, the brown trout has adapted well, tolerating warmer water than the native brookie and supplanting it in many waters throughout the state.
Young brown trout feed on aquatic insects and other invertebrates. As browns exceed a foot in length, they seek chubs, dace and other small fish.
Brown trout are warier and harder to catch than brook trout and can live in streams too warm for brookies. Browns also grow faster and larger. Consequently, they often are stocked in streams that provide marginal trout habitat or where fishing pressure is heavy.
The brown spawns in the fall and occasionally exceeds 10 pounds, even in small streams. It has dark spots and a few red spots on an olive background. Its square tail has few or no spots.
The rainbow trout, stocked in Minnesota a century ago, has become particularly important in Lake Superior and North Shore streams. Fish living in the lake and moving into streams to spawn are known as "steelheads." They ascend tributaries in the fall and spring, spawn in the spring, and swim downstream to the lake. Young trout remain in the streams for up to three years and then enter the big waters of Lake Superior, where they feed on terrestrial insects, various other invertebrates, and small fish.
Considered neither as wary as the brown or as gullible as a brook trout, the rainbow is prized as a game fish because it fights hard, frequently leaping when hooked.
Rainbows stocked in small lakes may exceed 10 pounds; stream fish rarely grow larger than three. The rainbow has dark spots on a light background. Its back is olive and its side carries a pink stripe. The tail is covered with small black spots. The body of a lake-run fish is silvery.