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The American Bullfrog (Lithobates (=Rana) catesbiana) is the largest true frog native to Eastern North America, from Maine and Ontario to Texas, and west to Kansas and Nebraska. It has been introduced to many western watersheds, and to fresh waters in the San Francisco Delta, and Columbia River estuaries, and probably other estuaries on the Pacific coast. Bullfrogs were once widely used for food, and released for that purpose, and also used for teaching and research, and sometimes released. They reach 90 to 150 mm in length, and can weigh up to 500 g. The loud, deep croaks of males are distinctive. Bullfrogs have been widely introduced around the world, to more than 41 countries. They have a strong preference for freshwater, but tadpoles can tolerate salinities as high as 3 PSU. Bullfrogs were introduced to the San Francisco Bay watershed and Delta at several locations between 1896 and 1932. and are widespread in inner portions of the Delta. They were found along the Columbia River as early as 1925. Bullfrogs are a concern as predators and competitors of threatened native West Coast frogs such as the California Red-Legged Frog (Rana draytoni) and Foothills Yellow-Legged Frog (Rana boylii), and as a vector for amphibian diseases, particularly the chytrid Batrachochytrium dendrobatidis.