Spawning often occurs near the surface and is accompanied by noisy splashing as the eager males cavort with the roe-laden females. After fertilization, the eggs sink slowly to the bottom and lodge in the gravel where they remain until hatching takes place in five or six days. After hatching, the fry grow rapidly, feeding heavily on freshwater plankton and aquatic insects. Decreasing water temperatures and cool fall rains trigger a mass downriver migration. Once in the open ocean, shad migrate up and down the coast, from their winter range off the mid-Atlantic to their summer range in the Bay of Fundy, off Nova Scotia.
Females follow, maturing at four to five years of age.
Unlike Pacific salmon, not all shad die after spawning. Some shad, particularly in northern rivers, do live to spawn again. Because the majority of the hatchery-reared shad are stocked at 18 to 20 days of age, traditional fish tags such as jaw tags, dart tags and fin clips are unusable. Instead, a sophisticated system of marking using tetracycline antibiotics has been developed. Shad fry, as young as three days of age, are immersed in a tetracycline solution which is absorbed into growing bone tissue.