Tony Award-winning actor Jason Alexander is the catch of the day for "Fish in the Dark." On June 9, the "Seinfeld" actor will take over for Larry David in the hit Broadway comedy, the show's publicists announced yesterday. The play, which was written by David, originally had a limited-engagement run scheduled through June 7, but has been extended for six weeks through July 19. Alexander is a longtime friend of David, who was a writer and producer on the classic sitcom "Seinfeld." "Fish in the Dark" also stars Jayne Houdyshell, Rosie Perez, Lewis J. Stadlen and Rita Wilson.