River Tywi these fish to over in weight. In summer and autumn there is also a substantial run of Atlantic salmon ("Salmo salar"). In May the Tywi has a run of the rare and protected twaite shad ("Alosa fallax") and allis shad ("Alosa alosa"). The Tywi also contains brown trout, eels, pike, and a variety of small fish species, and is home to brook lampreys, river lampreys and sea lampreys. The Tywi has the distinction of having accidentally produced by far the biggest fish ever taken on rod and line in fresh water in Britain. This was a sturgeon ("Acipwienser sturio") weighing
American herring gull American herring gull The American herring gull or Smithsonian gull ("Larus smithsonianus" or "Larus argentatus smithsonianus") is a large gull that breeds in North America, where it is treated by the American Ornithologists' Union as a subspecies of herring gull ("L. argentatus"). Adults are white with gray back and wings, black wingtips with white spots, and pink legs. Immature birds are gray-brown and are darker and more uniform than European herring gulls, with a darker tail. It occurs in a variety of habitats including coasts, lakes, rivers and garbage dumps. Its broad diet includes invertebrates, fish, and many other items.