Brook trout have a long, streamlined body with a large mouth that extends past the eye. Color variations include olive, blue-gray, or black above with a silvery white belly and wormlike markings (vermiculations) along the back. They have red spots sometimes surrounded by bluish halos on their sides. The lower fins have a white front edge with black and the remainder being reddish orange. The tail fin is square or rarely slightly forked. During breeding time in the fall male brook trout can become very bright orange-red along the sides.