**FILE PHOTO** A captured snakehead fish is displayed at Wheaton Regional Park in Wheaton, Md., Wednesday, April 28, 2004, where the fish was caught by a fisherman. Maryland officials said a second northern snakehead has been caught by a fisherman in the Potomac River, a sign that the destructive alien species may have invaded the Washington area's largest river. (AP Photo/Leslie E. Kossoff) Second Snakehead Found in Potomac River Fri May 14, 10:17 AM ET By STEPHEN MANNING, Associated Press Writer ROCKVILLE, Md. - A second northern snakehead has been caught by a fisherman in the Potomac River, Maryland officials...