American shad have sharp scales on their stomach and chest like a saw. Their body is thin from side to side and long from top to bottom. Their backs are shiny blue, and their bellies are white. They have one or more black spots in a row on their shoulder. Once in a while, they have two rows of black spots. American shad get darker in color when they go into rivers to lay their eggs. On average, American shad are 55.85 cm long, but they can be anywhere from 45 to 76.2 cm long. On average, they weigh 2.5 kg, but they can weigh anywhere from 0.9 to 5.4 kg. Females are usually 3 times bigger than males. (Ford, 2006)
American shad live in temperate areas, so they are found north of the tropics but south of the Arctic. They spend most of their lives near the coasts of the Atlantic or Pacific Ocean. When they are ready to breed, which is called spawning, they travel into the rivers of the United States, Canada, or Mexico to lay their eggs. American shad are native to the Atlantic Ocean. They are found from Newfoundland, Nova Scotia and the St. Lawrence River in Canada, down to central Florida. In the late 1800's, they were introduced into the Pacific Ocean, where they now live as well. Today, American shad can be found as far north as Cook Inlet and the Kamchatka Peninsula in Alaska, and down to Baja California in Mexico. (Eddy, 1957)
Adult American shad swim more than 19,000 km in their lifetime, so they travel through many habitats. In summer and fall, American shad are found in waters along the coast, from 0 to 250 m deep. In winter months, they usually stay in deeper water away from the coast up to 375 m. American shad migrate, traveling into rivers to lay their eggs. (Eddy, 1957)
Adult American shad lay their eggs, called spawning, in rivers in the late winter. The eggs usually hatch in 10 days. In warm rivers, they can sometimes hatch in 7 days. When they hatch, larvae are 10 mm long on average. In late fall or early winter, the juveniles travel from the rivers out into the ocean. In 2 to 5 years, they go back to the same river to spawn. (Glebe, 1981)
In late winter, American shad travel into rivers of the United States, Canada, and Mexico to lay their eggs, or spawn. One or more males chase a female up a river. They sometimes nudge her in the belly until she releases her eggs in open water. Then, the males fertilize the eggs in the water. The eggs come apart from each other and sometimes float many kilometers before they hatch. Because the eggs can move, they don't all get eaten if they're found by a predator. (Page, 1991; Wiley, 1986)
Female American shad lay eggs for the first time when they are about 4 years old, but it can be any time from 3 to 7 years old. All together, females release 200,000 to 250,000 eggs every year. Each fish lays 2 to 150 eggs each season. They release the eggs in cycles as they travel up the river. A cycle can last a couple days or up to a week. After the cycle, females rest for 1 to 3 days and start laying eggs again. Juvenile American shad hatch after 6 to 10 days and are able to be independent from their parents right away. (Crossman, 1998; Pfeiffer, 2002)
American shad live about 9 years in the wild, but can live anywhere from 6 to 10 years. Traveling from rivers to the ocean is hard on their bodies, and many of them die. About 60% of females die in the season that they migrate. American shad live about 6 years in captivity, but can live 4 to 7 years. (Eddy, 1957; Ford, 2006; Weiss-Glanz,, 1972)
American shad are social animals that swim in groups, or schools. As juvenile American shad travel to the ocean, they avoid bigger fish which eat them. As they get bigger and reach the ocean, they live closer together with other fish. (Crecco, 1985; Ford, 2006)
American shad are not territorial. They don't stay within the same area, because they travel between rivers and the ocean.
American shad can hear sounds with frequencies up to 180 kHz, and they often escape predators that communicate with these same high-frequency noises. American shad communicate with females by chasing them and nudging them in the belly. (Crossman, 1998; Plachta, 2003)
Juvenile American shad eat both plants and animals, mostly zooplankton and larvae of insects. Juveniles eat more after they leave their birthplace. As they get older, American shad start to eat small fish, crustaceans, plankton, worms, and occasionally fish eggs. They eat very little or no food when they are migrating and during the late winter. They start to eat normally again in spring when the water warms up. (Weiss-Glanz,, 1972)
Adult American shad get darker in color when they go into rivers to spawn. This helps them blend into their environment. American shad can hear ultrasound, which are really high frequency noises made by their predators like longbeaked common dolphins and common dolphins. They hide or swim away when they hear these noises. also have the ability to detect ultrasound. They are also eaten by striped bass, blue fish, smallmouth bass, walleye and channel catfish. In addition, they are also eaten by bears and some birds. Finally, humans hunt and eat them. (Crecco, 1985; McPhee, 2003)
American shad are prey for bigger fish, some birds, humans, bears, and dolphins. However, none of these predators depend on American shad to survive. American shad also eat lots of crustaceans and fish that live in rivers while they are migrating. They may help control numbers of some of these animals. American shad get different parasites, like roundworms and flatworms. American shad that spawn in the northwestern United States can also temporarily carry another kind of roundworms. In the southern Atlantic, American shad are often infected by another kind of flatworm. (Shields, 2002; Zool, 1993)
Humans have fished American shad for their meat and eggs for hundreds of years, but the number of them has decreased a lot from overfishing and damage to their habitat. As a result, U.S. and state governments reduced the number that can be fished and passed laws to protect the rivers where they live. In some places, humans have started to raise them. In others, engineers modified dams to allow them to migrate up the rivers. (Dicenzo, 1995; Marcy, 2004)
Sean Kessler (author), Radford University, Karen Powers (editor), Radford University, Gail McCormick (editor), Animal Diversity Web Staff, Catherine Kent (editor), Special Projects.
Crecco, V. 1985. Effects of Biotic and Abiotic Factors on Growth and Relative Survival of Young American Shad, Alosa sapidissima, in the Connecticut River. Canadian Journal of Fisheries and Aquatic Sciences, 43: 1640–1648.
Crossman, S. 1998. The Freshwater Fishes of Canada. Ontario, Canada: Galt House Publications Ldt.
Dicenzo, V. 1995. Relations between Reservoir Trophic State and Gizzard Shad Population Characteristics in Alabama Reservoirs. North American Journal of Fisheries Management, 16: 888-895.
Eddy, S. 1957. How to Know The Freshwater Fishes. Iowa: WMC Brown Company.
Ford, F. 2006. 77 Great Fish of North America. Ontario: Thomas Alen & Sons Limited.
Fowler, H. 1945. Fishes of the Southern Piedmont. Lancaster, Pennsylvania: Wickersham Printing Company.
Glebe, B. 1981. Latitudinal Differences in Energy Allocation and Use During the Freshwater Migrations of American Shad (Alosa sapidissima) and Their Life History Consequences. Canadian Journal of Fisheries and Aquatic Sciences, 38: 806-820.
Marcy, B. 2004. Early Life History Studies of American Shad in the Lower Connecticut River and the Effects of the Connecticut Yankee Plant. CSA, 9: 155-180.
McPhee, J. 2003. The Founding Fish. New Jersey: Farrar, Straus and Giroux.
Page, L. 1991. A Field Guide to Freshwater Fishes. Boston: Houghton Mifflin Company.
Pfeiffer, C. 2002. Shad Fishing: A Complete Guide Species, Gear, and Tactics. United States of America: Stackpole Books.
Plachta, D. 2003. Evasive responses of American shad to ultrasonic stimuli. Journal of the Acoustical Society of America, 4/2: 25-30.
Shields, B. 2002. The Nematode Anisakis Simplex in American Shad (Alosa sapidisima) in Two Oregon Rivers. The Journal of Parasitology, 88: 1033-1035.
Weiss-Glanz,, L. 1972. Water Temperatures and the Migration of American Shad. Society of Certified Senior Advisors, 70: 659-670.
Wiley, H. 1986. The Zoogeography of North American Freshwater Fishes. New York: Wiley-Interscience Publication.
Zool, C. 1993. Parasites of American Shad, Alosa sapidissima (Osteichthyes: Clupeidae), From Rivers of the North American Atlantic Coast and the Bay of Fundy, Canada. Canadian Journal of Zoology, 71/5: 941-946.