shad

Any of several marine fishes, especially the genus Alosa, the largest (60 cm/2 ft long and 2.7 kg/6 lb in weight) of the herring family (Clupeidae). They migrate in shoals to breed in rivers.

The American shad A. sapidissima, once common along the Atlantic coast, was badly affected by stream pollution but is now making a comeback. It was successfully introduced along the Pacific 1870. The gizzard shad Dorosoma cepedianum has been widely introduced into fresh waters of the US as food for other fishes.