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brook trout

brook trout (Salvelinus fontinalis)
Photo © Sean Landsman/Engbretson Underwater Photography

Features and Behaviors


The brook trout averages five to 15 inches in length, but some individuals will grow larger. The back is green-brown to black with darker blotches. Dark spots can be seen in the dorsal and caudal (tail) fins. Spots are also present on the sides, some of which are bright red with blue edges. There are green or cream, wavy lines on the back and dorsal fin that break into spots on the sides. The breeding male is red or orange along the lower sides. The brook trout’s tail fin is slightly forked. All trout have an adipose fin.


In Illinois, the brook trout lives in streams in the northern one-fourth of the state and in Lake Michigan. Spawning occurs in late fall and early winter over gravel beds in the water. The female excavates a nest on the bottom with her tail. Eggs hatch in early spring. A large female may lay 5,000 eggs during a year and may spawn with different males in the same season. The adult brook trout eats arthropods and small fishes. The young trout eats plankton and insects. The brook trout is native to Lake Michigan but not to the Illinois streams where it has been stocked for many years.

Illinois Range


Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Salmoniformes
Family: Salmonidae

Illinois Status: common, native