Gizzard shad grow quickly and attain a much larger size than threadfins.
Some adults can reach over 18 inches long and weigh over 2-pounds.
The gizzard shad has the typical herring family shape, but with a distinctive dorsal fin. Its short, soft-rayed dorsal fin is located at the center of its back. It has a long, trailing filament as the rear ray, longer than any of the other rays. The gizzard shad's back is silvery blue-green to gray. The sides are silvery or reflect blue, green, brassy or reddish tints. There is no lateral line. The tail is deeply forked, and the lower jaw is slightly shorter than the upper jaw. The snout is blunt. The mouth is small, and there is a deep notch in the center of the upper jaw. The gizzard shad's eye is large. There is a big, purplish-blue spot near the edge of the upper gill in young gizzard shad and small adults. This spot is faint or disappears completely in larger, older fish. The fins are dusky and there are the usual herring sawtooth - edged belly scales. Gizzard shad grow rapidly and can reach a maximum size of about 18 inches.
Gizzard shad are omnivorous filter feeder taking both phytoplankton and zoo plankton. The adults have more than 400, fine gill rakers that can catch minute plankton.
Gizzard Shad have an unusual digestion process for fish. The vegetable material they eat is ground in a gizzard like stomach. Some bottom material is often ingested while feeding.
Lake and reservoir populations use both the shoreline and open water areas.
Essentially it is an open water species, living at or near the surface, however, they have been collected at depths of up to 100 feet.
They will hybridize with the threadfin shad.
Gizzard shad of all ages are extremely fragile, and handling them or keeping them in captivity for controlled laboratory testing is difficult even under the best of circumstances (Shoemaker 1942; Bodola 1965; Reutter and Herdendorf 1974); consequently, many specific habitat requirements can only be assumed from field observations, and few or no quantitative data are available for most habitat variables. Comprehensive life history and habitat information was given by Bodola (1965), Jester and Jensen (1972), and Miller (1960).
Conditions for gizzard shad populations are optimal in warm, fertile, shallow bodies of water with soft mud bottoms, high turbidity, and relatively few predators (Miller 1960; Zeller and Wyatt 1967).
Factors contributing to this problem are the gizzard shad's high reproductive capacity, rapid growth rate, and efficient and direct use of plankton (Hubbs 1934; Miller 1960; Bodola 1965).
Moderate to heavy predation by large game species, fluctuating water levels, deep clear water, and steep shorelines (factors that are less than optimal for many species) tend to be associated with lower gizzard shad populations.
A schooling fish their range Range extends from southeastern South Dakota and central Minnesota, throughout the Mississippi and Great Lakes drainages to about as far north as the St. Lawrence River, near Quebec. From southern New York along the Atlantic Coast to the Gulf of Mexico; and west through the Gulf Coast States to the portions of New Mexico and Colorado.
Found in the backwaters of sluggish rivers and the deep, slow pools of smaller streams.
Gizzard shad become more abundant as a lake gains fertility through natural aging or added pollutants.
They are often found over a mucky bottom, which they filter when feeding.
Unlike many other herrings, gizzard shad are non-migratory and stay near their home areas.
The gizzard shad spawns in spring, May to June, when water temperatures reach the mid 60s to mid 70s. Will start at 50 degrees.
Usually has a Six week spawning period.
The gizzard shad spawn begins at night in shallow water.
As early as age two they gather in large schools to broadcast their eggs and milt in shoreline shallows.
Females produce up to 400,000 eggs that are randomly scattered adhere to plants, rocks or firm substrate.
When conditions are perfect, gizzard shad can actually spawn a second time.
Eggs hatch in two to three days.
No nesting behavior or parental care is shown by adults.
Growth rate of Gizzard Shad:
Growth is rapid, up to seven inches in the first year have been recorded.
Their Rapid growth means that largemouth and smallmouth bass are able to eat them for only a short time each spring.
After the spawn, the gizzard fry just explode in growth.
They will be 1 1/2 to 2 inches in midsummer, but by late fall, they're often 5 inches long and a little large for the majority of largemouth bass.Shad school up as juveniles in quiet surface waters, adults near bottom.
Striped bass are the dominant predator for the large Gizzards and keep them under control so that young Largemouth bass and Large shad don't have to compete for the same limited planktonic food allowing the fingerling black bass to grow quicker.
Life span 3 - 11 years, few live beyond age 3.
In general, short life spans are correlated with rapid growth rates in the first year of life.
In more northern parts of its range, gizzard shad typically live to ages 5 to 7 and may live to ages 10 or 11
(Miller 1960; Jester 1962).
Gizzard shad are filter feeders straining small organisms particularly from organic deposits.
Adults have fine gill rakers to strain these minute plant plankton; the food is ground and digested in their gizzard-like stomach, hence the name.
Back silvery blue, somewhat iridescent; sides silvery above, whitish below; abdomen white.
Dark purplish spot about the size of the eye present immediately behind the upper end of the gill opening.
Spot becomes obsolete and disappears with age.
Small sub-terminal, slightly overhung by the rounded snout.
Centrally notched upper jaw protrudes slightly beyond lower jaw.
Upper jaw reaching below the front margin of the eye. Gill rakers long, slender
Deep strongly compressed laterally.
Average length 8.5 -13.5 in.
Scales large, thin, rounded and smooth-edged , Falling off or shed at a specific season or stage of growth.
Lateral line lacking.
Median lateral series of scales 61 (52-70).
Ridge of sawlike scales close to the abdomen.
Gizzard Shad differ from Threadfin Shad by:
lower jaw shorter than upper jaw;
a much shorter dorsal fin filament;
absence of black pigment on the chin and floor of mouth; more than 17 midventral scutes in the prepelvic series;
more scales in the lateral series; more anal fin rays.
Williamson, K. L., and P. C. Nelson. 1985
Gizzard Shad Habitat suitability index models and instream flow suitability curves:
online library feeding of Shad.