Illustration by Steven Schalla, FlyFishingtheSierra.com, used with permission
The Brook Trout is a char, and therefore a cousin of Bull Trout and Dolly Varden. They are generally dark olive green with light spots on the sides. They exhibit wavy marbling on the back, which can appear gold-green. The dorsal fin also has dark wavy lines. No black spots are present on the body but red spots are usually present on the sides. Some of the red spots can have a bluish halo. The Belly is white except during spawning when it turns orange-red, particularly on the males. The leading edge of the pelvic and anal fins is usually a white stripe, followed by a black stripe and orange-red.
Because brook trout are usually living in infertile, headwater streams and lakes, they are often small: under 6 inches. The world record brook trout, however, is nearly 20 pounds, and fish in the 4-6 pound range are common in optimal habitat. Sea run brookies are known as “coasters”.
The Brook Trout is the native trout of the east coast of the US, from Maine to Georgia, plus much of the Great Lakes Region and eastern Canada. Brook Trout require cleaner, colder water than rainbow and brown trout, and are therefore very vulnerable to habitat destruction due to development. As a result, brook trout today inhabit a small fraction of their original range, and are significantly displaced by these exotic species.
That said, the "Eastern Brook Trout" (as they are known west of the Mississippi), is a common exotic species in cold, headwater streams in the Rockies (where it competes with native cutts), the Pacific Northwest (competing with Bull Trout), and California. Eastern Brook Trout reproduce 2-3x as fast as most cutthroat, and are quicker to migrate to find suitable habitat when they are crowded. They have therefore displaced many cutthroat populations across the west.