Alosa sapidissima

American shad have a strongly compressed body and no scales on their head, no lateral line, and one dorsal fin. They have a fatty eyelid in front of their eye, no spines in their fins, and sharply pointed scales on their belly; adults have no teeth. Their cheeks are deeper (top to bottom) than they are long (front to rear). Their mouth is not strongly oblique (slanted), and their lower jaw extends to the tip of their snout or slightly beyond. These shad have a green or blue back and silvery sides and a blue-black spot near the upper edge of the gill opening that is usually followed by one or two rows of smaller spots. Their total length can reach up to 75 cm (29.5 inches).
 

The native range includes the Atlantic coast from Labrador to the St. Johns River in Florida. In the 1870s, this species was introduced in the Sacramento River in California; subsequently, it spread north to Alaska and eastern Asia (Kamchatka Peninsula) and south to Mexico. An introduced, landlocked population occurs in Millerton Lake in California.

American shad migrate up to thousands of kilometers (or thousands of miles) between their spawning habitats in rivers and their feeding habitats in the ocean. In the Atlantic, most American shad are in the Gulf of Maine in summer and fall and move southward to the mid-Atlantic region during the winter.

The time when American shad migrate upstream to spawn varies across the range. In the south, they spawn in February, but not until June or July in the far north. The timing of migration and spawning also varies among years; shad migrate and spawn later when the water is colder. Eggs hatch in about a week. Larvae and juveniles spend the summer in rivers, then enter the ocean by fall. They return to fresh water when they are mature (3-5 years old). Shad in southern populations tend to die after they spawn, whereas those in more northerly populations survive to spawn in multiple years.