Native to the southeastern United States, the gizzard shad is common in most rivers and lakes. Due to its small size and relative abundance, it is an excellent food source for most large, predatory fish and other piscivorous vertebrates. Its placement in the food chain and its small size places this species squarely in the category of “forage fish,” meaning that it is used in habitat management as a prey item for larger fish. As a result, the gizzard shad is sometimes stocked into lakes and reservoirs to support healthy sportfish populations.
While their status as a prey item may make one think gizzard shad are small fish, that is not always the case. This species averages 6 to 8 inches (15 to 20 cm) in length, although substantial individuals can be up to 22 inches (56 cm) long. Given their relatively large size, humans also enjoy eating gizzard shad.
Where Do Gizzard Shad Live?
Gizzard shads are freshwater fish found in lakes, rivers, reservoirs, ponds, and streams throughout the southeastern United States. Their native range extends from New Mexico to the country’s east coast, with a non-native range reaching as far west as California and north up into the Great Lakes. While these fish are usually found in sluggish waters of lakes and reservoirs, they will venture into areas with a moderate flow in search of food. Additionally, gizzard shad display surprising flexibility when it comes to stress tolerance. For example, they can tolerate low dissolved oxygen levels in the water. However, the lowest they can tolerate is 2mg/L, a trait that makes them more competitive than other native species in areas where gizzard shad are introduced.
Due to their diet, which can include an abundance of algae, gizzard shad are known to be abundant in waterways where excess nutrients encourage algal blooms. On the one hand, their presence helps to reduce algae in the water column, reducing the effects of algal blooms. However, gizzard shad populations can become overabundant and increase the turbidity of the habitat by disturbing the substrate in search of alternative food sources when the algae is depleted. In addition to algae, gizzard shad are associated with typical submerged aquatic vegetation. Submerged vegetation provides refuge and a source of food for adult and juvenile gizzard shad.
How Do I Identify Gizzard Shad?
Gizzard shad have a distinctive elongated and laterally compressed body shape. They are shiny and silver in color, with a single spot behind their operculum or gill covering. Besides this spot, they do not possess any additional markings. The dorsal fin is unique amongst this group of fishes because it includes a long tail extending halfway down the fish’s tail.
The native range of the gizzard shad sometimes overlaps with other shad species, like the threadfin shad (D. petense). To easily distinguish between the two species, examine their mouths. The gizzard shad’s upper jaws extend past the lower jaw. This trait is reversed in threadfin shad.
What Are Shad Used For?
Gizzard shad play a vital role in aquatic ecosystems as forage or prey for many predatory fish, birds, and other aquatic organisms. They are an essential part of the food web, providing a source of nutrition for species like largemouth bass (Micropterus salmoides), catfish (family Ictaluridae), and birds. As a result, anglers commonly use them as live bait in recreational fishing. Gizzard shad are generally abundant where they occur and effectively attract game fish.
Gizzard shad also have uses in research and in maintaining ecological equilibrium. In certain situations, gizzard shad are introduced into bodies of water to help control aquatic vegetation. Their feeding habits involve consuming phytoplankton and small particles, which can reduce excess plant growth and improve water quality. Additionally, gizzard shad are sometimes used in scientific research to explore topics in fish physiology, water quality, and ecosystem dynamics.
Where Does the Name “Gizzard Shad” Come From?
Plant material can be challenging to digest. The gizzard shad has evolved a special stomach to deal with this challenge. Like owls and other birds, the gizzard shad has a muscular stomach that allows this species to grind food items. This trait is uncommon among fish, but birds with a muscular pouch separate from the stomach have a similar digestive feature that allows them to break up their food.
The other part of the common name, shad, is possibly derived from one of several old European words for “herring,” such as schade from German or skadd from Norwegian.
Are Gizzard Shad Invasive?
This species is not considered an invasive species in their native range. Here, they are an integral part of the aquatic ecosystems in these areas and play a role in the food web as both prey and predator.
However, gizzard shad can become problematic when introduced outside their native range. In non-native environments, they may compete with native species for resources, disrupt local food webs, and alter water quality dynamics. They also reproduce quickly and can overwhelm nonnative habitats in only a few generations.
How Do Gizzard Shad Reproduce?
Gizzard shad typically spawn during the spring and summer when water temperatures rise. The exact timing of their spawning can vary depending on local environmental conditions, but it usually occurs when water temperatures reach the appropriate range, often in the range of 68 to 75°F (20 to 24°C). Unlike other shad species that undertake long-distance migrations to spawn in specific areas, gizzard shad typically breed in the waters where they reside.
During spawning, female gizzard shad release their eggs into the water column. The eggs are adhesive and attach to submerged vegetation, rocks, or other objects in the aquatic environment. Gizzard shad produce many eggs in a single spawning event, which increases the chances of successful fertilization. This species does not provide parental care.
