American gizzard shad
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The American gizzard shad (''Dorosoma cepedianum''), also known as the mud shad, is a member of the
herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Oceans, i ...
family of fish, and is native to large swaths of fresh and brackish waters of the United States of America. The adult has a deep body, with a silvery-green coloration above fading to plain silver below. The gizzard shad commonly resides in freshwater lakes, reservoirs, rivers, and streams, but can reside in brackish waters, as it does on the Atlantic coast of the United States. Their range is across most of the continental United States, although they typically go no further north than New York and no further west than New Mexico. They are a large part of many of the ecosystems they inhabit, and can drive changes in phyto- and
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, thereby indirectly affecting other planktivorous fishes. The gizzard shad has been widely used as a food source for game fish, with varied success in management and effectiveness.


Physical description

The gizzard shad's dorsal fin starts behind the insertion of the pelvic fins, and the last ray is greatly lengthened. They have a long anal fin, with 25 to 36 long,
soft rays Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology co ...
on the fin. The mouth of the gizzard shad has a short, wide, upper jaw with a deep notch along the ventral margin, and a weak, relatively smaller, lower jaw. The mouth itself is subterminal to inferior (on the lower portion of the head), and the adults possess no teeth. The gizzard shad also has 90 to 275
gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of the ...
s along the lower limbs. Their ventral (pelvic) fins are in the thoracic position, or in the chest region of the fish. The gizzard shad can range from very small size when fry to a maximum recorded length of and maximum weight of . The average length is typically larger in northern waters, and ranges from at age three years to at age 10. They have a branched lateral line system that is confined to the head and anterior body, similar to the lateral line systems of other clupeids. The gizzard shad is brown or gray dorsally, becoming whitish ventrally. A
humeral spot Humeral spot (from Latin ''humerus'', pertaining to the shoulder) is a mark or pattern found on several species of fish, typically above the pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding fro ...
, sometimes with purple iridescence, may be faintly visible posterior to the upper operculum. The fish is often slimy.


Range and habitat

Gizzard shad have historically ranged from North Dakota in the northwest of the United States south to New Mexico in the southwest, east to Florida in the southeast, and north to 40°N latitude (they have historically been seen no farther north than the lower New York Harbor). They were not seen in many of the Great Lakes until the late 1800s and early 1900s, although they are suspected to be native to
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has t ...
, reaching it after the last ice age. Gizzard shad typically live in lakes and reservoirs, although they can live in rivers and streams, and brackish waters. They reside in the
limnetic zone The limnetic zone is the open and well-lit area of a freestanding body of freshwater, such as a lake or pond. Not included in this area is the littoral zone, which is the shallow, near-shore area of the water body. The key difference between the ...
, and can comprise up to 80% of fish biomass in certain lake systems. They prefer shallow lakes with muddy bottoms and relatively high turbidity. This may be due in part to their breeding preferences, but it probably arises from the fact that they have lower survival rates in clear waters and waters with high vegetative cover.


Diet and feeding habits

Gizzard shad are planktivorous in early life, feeding mainly on
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...
and
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
as larvae. Consumptive demand of young of year fish (including larvae) can be intense enough to cause collapses in the zooplankton community, which has far-reaching effects through the ecosystem of which they are a part. In midwestern USA reservoirs, where gizzard shad are often the most abundant fish (by biomass), they usually switch to diets dominated by sediment detritus during the first year of life, whereas in some natural lakes they may rely heavily on zooplankton throughout their lives. As zooplankton are a nutritionally superior food than detritus, if large zooplankton (e.g., ''
Daphnia ''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembl ...
'') are available, gizzard shad probably prefer to feed on this resource. However, in many reservoirs, large zooplankton are scarce so gizzard shad rely on detritus. Gizzard shad growth rates may be lower when they feed only on detritus (compared to zooplankton), and in reservoirs they may consume more zooplankton (and less detritus) when density of conspecifics is low and the abundance of large-bodied zooplankton is high. In such cases,''
Daphnia ''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their saltatory swimming style resembl ...
'' and other
crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
make up a large portion of some gizzard shad diets. Gizzard shad feed mainly during the day, with minimal activity at night. They have been observed at night in
Lake Mead Lake Mead is a reservoir formed by the Hoover Dam on the Colorado River in the Southwestern United States. It is located in the states of Nevada and Arizona, east of Las Vegas. It is the largest reservoir in the US in terms of water capacity. ...
, Arizona congregating in schools in very shallow water two to three feet deep during the fall.


Reproduction

The start of the spawning period is typically between mid-May and early June, and is triggered by rising water temperatures. The number of eggs per individual varies between populations, but typically it is 12,500 eggs for a two-year-old and peaks at 380,000 eggs for a four-year-old. The eggs are laid in shallow water in clumps, with seemingly no pairing off occurring between individuals. They spawn during the evening and the early hours of the night, and the eggs adhere to underwater vegetation and do not receive any parental attention. Feeding begins three to four days after hatching, and most individuals are 3.3 mm long upon hatching. Gizzard shad have very high fecundity and a rapid growth rate, meaning they can become a large part of an ecosystem, in terms of abundance and biomass, very quickly. They are capable of hybridizing with the closely related
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 ...
.


Fisheries management

Gizzard shad were introduced into many lake and river systems as a source of food for game fish, such as
walleye The walleye (''Sander vitreus'', synonym ''Stizostedion vitreum''), also called the yellow pike or yellow pickerel, is a freshwater perciform fish native to most of Canada and to the Northern United States. It is a North American close relat ...
, bass, and
trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salmoni ...
, because of their small size and relatively high abundance. They were thought to be easy food for game fish and could help increase the numbers of fish available, as well as decrease the pressures on prey species (such as the
bluegill The bluegill (''Lepomis macrochirus''), sometimes referred to as "bream", "brim", "sunny", or "copper nose" as is common in Texas, is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and ...
). However, due to their rapid growth, they can quickly grow beyond the size available to many fish. They remain vulnerable to predation by piscivorous birds, such as
great blue heron The great blue heron (''Ardea herodias'') is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North America and Central America, as well as the Caribbean and the Galápagos ...
s, as well as
raccoons The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of . ...
and other wetland predators. In addition, gizzard shad spawn in large numbers and can reach densities high enough to ensure that many of them survive past the first year, making them essentially invulnerable to fish predation. They can also be harmful exploitative competitors to other species, leading to declines in other fish species' populations. Partly as a result of this, large gizzard shad are sometimes labeled as "nuisances" and "unwanted". However, gizzard shad can help to control populations of zooplankton and insect larvae in productive ecosystems through their unique capabilities as predators of small organisms.


Lake management

Gizzard shad can increase productivity in an ecosystem through redistribution of nutrients, particularly in their adult stages when they consume detritus in lower depths of the lake and both make them available to other predator species as well as excreting them in more bioavailable forms. Because of this, gizzard shad can have a strong effect on algal production even when phosphorus loading from watersheds is high, and can counteract management efforts to combat
cultural eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplank ...
.


Aquatic toxicology

Gizzard shad are important to toxicology testing for chemical products. Due to the food web dependencies and fecundity gizzard shad are somewhat the water bound version of "canary in the coal mine."


Etymology

The gizzard shad is so named because it possesses a
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 archosaurs (pterosaurs, crocodiles, alligators, dinosaurs, birds), earthworms, some gastropods, so ...
, a sack filled with rocks or sand, that aids the animal in the breakdown of consumed food. Its
generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...
name, ''Dorosoma'', is a reflection of the fact that, when young, the fish has a lancelet-shaped body (''doro'' meaning lanceolate and ''soma'' meaning body). The
specific Specific may refer to: * Specificity (disambiguation) * Specific, a cure or therapy for a specific illness Law * Specific deterrence, focussed on an individual * Specific finding, intermediate verdict used by a jury in determining the fina ...
name, ''cepedianum'', is a reference to amateur French
ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octobe ...
La Cépède.


References


External links

* {{Taxonbar, from=Q2693645 Clupeidae Freshwater fish of the Southeastern United States Taxa named by Charles Alexandre Lesueur Fish described in 1818 Freshwater fish of North America