American gizzard shad
Encyclopedia
The American gizzard shad, Dorosoma cepedianum, is a fish
of the herring family Clupeidae
native to fresh and salt waters of eastern North America
.
Like other gizzard shads, the body is deep somewhat forward of the middle. It is a grayish or silvery blue above, becoming silver on the sides and white below. The dorsal fin
has 10-12 rays; in adults, the last ray is very long, extending beyond the rest of the fin. The caudal fin is deeply forked. They can reach a length of 22.5 inches (57 cm), and weigh up to 4.37 lbs (1980 grams).
American gizzard shad begin life feeding on zooplankton
, using their teeth to catch them. At about 1 inch in length, they lose the teeth, become deeper-bodied, develop the muscular gizzard
, and become filter feeder
s, consuming both small invertebrates and phytoplankton
, as well as some sand
for the gizzard.
They live in a variety of open waters, both clear and silty, including rivers, swamps, lakes, and bays, typically near the surface. They avoid fast-moving water.
Native range extends from the Great Lakes
and St. Lawrence River area west to eastern South Dakota
and central New Mexico
, as well as to the Gulf of Mexico
, where it has been found as far south as Rio Panuco in Mexico
.
The specific epithet cepedianum honors French naturalist Bernard Germain de Lacépède (1756-1825).
, an economically important sport fish, and they reproduce rapidly. For this reason, it is widely believed that bass fishing is best where gizzard shad are abundant. Indeed, the smaller threadfin shad
is a key player in Southern lakes that produce "trophy" bass. However, the practice of introducing gizzard shad to improve bass fishing is controversial.
Gizzard shad do provide large bass with a steady supply of quality food. They grow faster than bluegill
and are easier for bass to swallow, so large bass (approx. five pounds or larger) benefit from shad introduction. Also, by providing bass with alternate prey, they reduce predatory pressure on young bluegill.
However, in public lakes with heavy fishing pressure, gizzard shad are of questionable value. They grow quickly and can easily grow too large for most bass to swallow, so their value as a forage fish is limited. They also compete with hatchling bass for food, reducing their survival rate and preventing many from growing to "replace" the legal-size bass kept by fishermen. If sufficient food is available (e.g., a healthy bluegill population), bass do not grow any faster in the presence of shad.
Although bluegill
enjoy reduced predatory pressure in the presence of gizzard shad, their young also compete with shad for food. As a result, they grow more slowly; it takes four years for a hatchling bluegill to reach six inches in length when gizzard shad are present, compared with three years in the absence of shad.
Gizzard shad contribute to eutrophication
, both by fertilizing algae with their copious feces and by preying on "grazing" zooplankton
that normally feed on algae.
In spite of the possible benefits to trophy-size bass, gizzard shad generally have a negative effect on sport fish. Most wildlife management agencies try to prevent their spread. Using them as live bait is illegal in most public lakes, and deliberately introducing any fish into a public body of water is illegal as well.
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
of the herring family Clupeidae
Clupeidae
Clupeidae is the family of the herrings, shads, sardines, hilsa and menhadens. It includes many of the most important food fishes in the world.-Description and biology:...
native to fresh and salt waters of eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Like other gizzard shads, the body is deep somewhat forward of the middle. It is a grayish or silvery blue above, becoming silver on the sides and white below. The dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
has 10-12 rays; in adults, the last ray is very long, extending beyond the rest of the fin. The caudal fin is deeply forked. They can reach a length of 22.5 inches (57 cm), and weigh up to 4.37 lbs (1980 grams).
American gizzard shad begin life feeding on zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, using their teeth to catch them. At about 1 inch in length, they lose the teeth, become deeper-bodied, develop the muscular gizzard
Gizzard
The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including birds, reptiles, earthworms and some fish. This specialized stomach constructed of thick, muscular walls is used for grinding up food; often rocks are...
, and become filter feeder
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
s, consuming both small invertebrates and phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
, as well as some sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
for the gizzard.
They live in a variety of open waters, both clear and silty, including rivers, swamps, lakes, and bays, typically near the surface. They avoid fast-moving water.
Native range extends from the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
and St. Lawrence River area west to eastern South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
and central New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, as well as to the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, where it has been found as far south as Rio Panuco in Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
.
The specific epithet cepedianum honors French naturalist Bernard Germain de Lacépède (1756-1825).
Forage Fish Controversy
Gizzard shad are a preferred food of the largemouth bassLargemouth bass
The largemouth bass is a species of black bass in the sunfish family native to North America . It is also known as widemouth bass, bigmouth, black bass, bucketmouth, Potter's fish, Florida bass, Florida largemouth, green bass, green trout, linesides, Oswego bass, southern largemouth...
, an economically important sport fish, and they reproduce rapidly. For this reason, it is widely believed that bass fishing is best where gizzard shad are abundant. Indeed, the smaller threadfin shad
Threadfin shad
The threadfin shad, Dorosoma petenense, is a small pelagic fish common in rivers, large streams, and reservoirs of the Southeastern United States. Like the American gizzard shad, the threadfin shad has an elongated dorsal ray, but unlike the gizzard shad its mouth is more terminal without...
is a key player in Southern lakes that produce "trophy" bass. However, the practice of introducing gizzard shad to improve bass fishing is controversial.
Gizzard shad do provide large bass with a steady supply of quality food. They grow faster than bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
and are easier for bass to swallow, so large bass (approx. five pounds or larger) benefit from shad introduction. Also, by providing bass with alternate prey, they reduce predatory pressure on young bluegill.
However, in public lakes with heavy fishing pressure, gizzard shad are of questionable value. They grow quickly and can easily grow too large for most bass to swallow, so their value as a forage fish is limited. They also compete with hatchling bass for food, reducing their survival rate and preventing many from growing to "replace" the legal-size bass kept by fishermen. If sufficient food is available (e.g., a healthy bluegill population), bass do not grow any faster in the presence of shad.
Although bluegill
Bluegill
The Bluegill is a species of freshwater fish sometimes referred to as bream, brim, or copper nose. It is a member of the sunfish family Centrarchidae of the order Perciformes.-Range and distribution:...
enjoy reduced predatory pressure in the presence of gizzard shad, their young also compete with shad for food. As a result, they grow more slowly; it takes four years for a hatchling bluegill to reach six inches in length when gizzard shad are present, compared with three years in the absence of shad.
Gizzard shad contribute to eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
, both by fertilizing algae with their copious feces and by preying on "grazing" zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
that normally feed on algae.
In spite of the possible benefits to trophy-size bass, gizzard shad generally have a negative effect on sport fish. Most wildlife management agencies try to prevent their spread. Using them as live bait is illegal in most public lakes, and deliberately introducing any fish into a public body of water is illegal as well.