Gizzard shad are currently not in any need of special protections.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Perception Channels: tactile ; chemical
D. cepedianum grows to be about nine to fourteen inches long as an adult, and only four inches long as a juvenile. Usually, the adult eventually grows to be about two pounds.
D. cepedianum juvenile has a different appearance than the adult. The juvenile has a dark spot on its shoulder, but this marking fades as the fish grows. The adult's body is oblong shaped and is laterally compressed. It is usually silvery blue dorsally, silver on the sides, and dusky white ventrally. The last ray of the dorsal fin rays is long and thin; it resembles a whip. Its caudal fin has a deep fork in it. Its head is rounded and blunt on the front and its mouth is subterminal. Like many fish, there are no teeth. This fish has no lateral line.
(Konrad 2001)
Other Physical Features: bilateral symmetry
Average mass: 1089 g.
Average lifespan
Status: wild: 10.0 years.
This is mostly a freshwater fish, usually living in lakes, ponds, rivers, streams, and reservoirs. However, it lives in the Chesapeake Bay, and there it is anadromous, meaning it lives in both salty and freshwaters. In the bay, it spends most of the time in the salty lower region, and migrates up the bay to the freshwater regions to breed in the spring. This fish prefers brakish, not densely vegetated areas of deep waters to live as adults, and juveniles live in the more clear and shallower waters when they are calm. The lakes that D. cepedianum occupy are mostly soft-bottomed with a lot of mud and sediment. The ideal temperature for gizzard shad to live in is between 50 and 70 degrees F, or 10 and 21 degrees C. If the temperature drops to around 2 or 3 degrees C, D. cepedianum will die.
(Konrad 2001, Lippson 1997)
Aquatic Biomes: lakes and ponds; rivers and streams
Dorosoma cepedianum thrives in rivers, streams, reservoirs and lakes in the mid to eastern region of the United States and the middle and south of Canada around the Great Lakes. It can also be found all the way down to central Mexico and Florida.
(Murdy et al. 1997)
Biogeographic Regions: nearctic (Native )
An adult D. cepedianum is primarily an omnivore. It is a filter feeder using the 190 rakers on the first gill arch's lower limb. It feeds mostly on phytoplankton and zooplankton, such as perphyton, chrysophyta, and rotifera. Since this fish filters the surrounding water and sediment for food, it also ingests and digests detritus. The substance on the freshwater bed is known as ausfwulchs assemblage, which is what gizzard shad feed on. Sediment and sand are also ingested by the gizzard shad that helps it to digest food in its muscular gizzard.
(Klingel 1990, Konrad 2001)
Humans use D. cepedianum as bait to catch larger fish. This fish is sold as a basic live or cut bait. Also, larger pelagic sport fishes eat gizzard shad, which keeps the human sportfishing industry up.
(Bonds 1998, SCBASS 2001)
Generally, D. cepedianum is viewed as a trash fish that is simply a nuisance. Not many sports fish eat the adult gizzard shad. Actually, the only fishes that do eat this fish are catfish and striped bass. The young shad is usually in competition with the valuable sports fishes that co-exist in the same habitat. In fact, one study shows that D. cepedianum eats young crappie (a more valuable fish) in Texan reservoirs. This factor decreases the gizzard shad's usefulness to humans.
(Drenner 1990, Konrad 2001, SCBASS Federation 2001)
D. cepedianum reproduces like many fish and even mammals do: one female mates with many males to ensure fertilization. The female is prolific. She mates randomly and does not stay around to care for her young. Gizzard shad reproduce during spawning season, which is in the spring between late April and early August. They mate nocturnally. Also, they prefer to spawn over sandy and rocky substrates so the eggs will have a surface to adhere to once they are laid. Furthermore, the temperature of the water should be around 21 degrees Celsius for optimum breeding conditions. The fish will spawn in shallow water, usually less than 1.2 meters deep. After mating, up to 400,000 eggs are released in the shallow, clear, and calm waters of the freshwater environment. The D. cepedianum incubation period is two to four days, depending on the water temperature and environmental conditions. The young hatch in the larval stage, develop into the juvenile stage, and then on to the adult stage. The young reach sexual maurity after one year. Breeding is random, so there is no social system to D. cepedianum spawning.
(Klingel 1990, SCBASS Federation 2001)
Average age at sexual or reproductive maturity (male)
Sex: male: 730 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 730 days.
The American gizzard shad (Dorosoma cepedianum), also known as the mud shad, is a member of the herring family of fish, and is native to large swaths of fresh and brackish waters of the United States of America.[2] The adult has a deep body, with a silvery-green coloration above fading to plain silver below.[3] 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.[2] They are a large part of many of the ecosystems they inhabit, and can drive changes in phyto- and zooplankton, thereby indirectly affecting other planktivorous fishes.[4] The gizzard shad has been widely used as a food source for game fish, with varied success in management and effectiveness.
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 on the fin.[5] 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.[6] The gizzard shad also has 90 to 275 gill rakers along the lower limbs.[3] 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 477 mm (18.8 in) and maximum weight of 1.56 kg (3.4 lb).[7] The average length is typically larger in northern waters, and ranges from 284 mm (11.2 in) at age three years to 399 mm (15.7 in) at age 10.[2] 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.[8]
The gizzard shad is brown or gray dorsally, becoming whitish ventrally.[5] A humeral spot, sometimes with purple iridescence,[9] may be faintly visible posterior to the upper operculum.[5][9] The fish is often slimy.[5]
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).[2] 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, reaching it after the last ice age.[3] 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, and can comprise up to 80% of fish biomass in certain lake systems. They prefer shallow lakes with muddy bottoms and relatively high turbidity.[7] 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.[10]
Gizzard shad are planktivorous in early life, feeding mainly on phytoplankton and zooplankton 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.[4] 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,[11] whereas in some natural lakes they may rely heavily on zooplankton throughout their lives.[12] As zooplankton are a nutritionally superior food than detritus, if large zooplankton (e.g., Daphnia) 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.[13] In such cases, Daphnia and other crustaceans make up a large portion of some gizzard shad diets.
Gizzard shad feed mainly during the day, with minimal activity at night.[4] They have been observed at night in Lake Mead, Arizona congregating in schools in very shallow water two to three feet deep during the fall.
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.[7] 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.[14] They are capable of hybridizing with the closely related threadfin shad.[2]
Gizzard shad were introduced into many lake and river systems as a source of food for game fish, such as walleye, bass, and trout, 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).[15] 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 herons, as well as raccoons and other wetland predators.[16]
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.[17] Partly as a result of this, large gizzard shad are sometimes labeled as "nuisances" and "unwanted".[18] 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.[16]
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[13] as well as excreting them in more bioavailable forms.[19] 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.[19]
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."[20]
The gizzard shad is so named because it possesses a gizzard, a sack filled with rocks or sand, that aids the animal in the breakdown of consumed food. Its generic 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 name, cepedianum, is a reference to amateur French ichthyologist La Cépède.
The American gizzard shad (Dorosoma cepedianum), also known as the mud shad, is a member of the herring 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, 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.
