Shad, also known as river herring, is a type of fish in the genus Alosa. They are native to North America and can live in saltwater or freshwater. There are many different types, including the American shad and the gizzard shad.
The many varieties of this fish include the American, gizzard, threadfin and hickory shad, as well as the blueback herring and the shipjack herring. Some of these fish live in the ocean, while others live in fresh or brackish waters. Different varieties can be found in the oceans around North America as well as in many North American rivers. Some of the varieties are not good to eat and are mainly used for sport fishing and then released.
Many, although not all, varieties of shad are andromous. This means that they spend much of their life in the ocean but return to fresh water rivers once a year to spawn. It is not unusual for these fish to return every year to the river where they were born. Depending on the region, spawning may occur as early as November, in warm climates, or as late as July, in cooler climates such as Canada.
The American shad is the largest variety and typically reaches 20-24 inches (50.8 – 60.96 centimeters) in length. It has been known, however, to be as long as 30 inches (76.2 centimeters). These fish are silver with dark spots on their sides and scutes, or sharp, saw-like scales, on their underside. The mouth closes in a “V” shape with the lower jaw not extending beyond its upper jaw. The American shad is also known as the white, common, or Atlantic shad and is a popular fish for cooking and eating.
The gizzard shad is found in eastern North American rivers. Unlike the andromous American shad, the gizzard shad lives year round in rivers and reservoirs. These fish are not considered good for eating but are caught for sport and used as bait for other types of fish. Typically, these fish grow to be between 9-14 inches (22.86-35.56 centimeters) long, though they may reach 20 inches (50.8 centimeters), and rarely exceed 3 pounds (1.36 kilograms). Their scales are sliver-blue at the top but become white on the sides and underside.
Historically, shad was a very popular fish for both commercial reasons and for sport. Over time, however, their numbers in North America have dropped significantly. This is mainly due to human modifications to their habitat. Dams block the ability of fish to swim upriver to spawn, and water pollution has also prevented spawning. They are threatened by overfishing as well.