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Gizzard shad have the typical herring body shape with a deep, oblong body that is strongly compressed laterally. Color ranges from bright silvery blue on the back, silvery sides and a dusky white on the belly. A dark shoulder spot is common on younger fish, but may be absent from adults. The front of the head is rounded with a sub-terminal mouth. Teeth are absent. There are about 190 rakers on the lower limb of the first gill arch. The eyes have adipose eyelids with vertical slits. Body scales are cycloid with no lateral line present. The ventral scales are keeled. Dorsal fin rays number 10 to 12 with the last ray elongated into a thin whip-like filament. This fin is inserted slightly behind the pelvic fin. An auxiliary process is present at the base of the pelvic fin. The anal fin has 27 to 34 rays, and the caudal fin is deeply forked.
One of the most widespread and abundant of Iowa’s fishes. With the exception of the far northern central part of the state, it has been found in all the state’s major rivers systems, large reservoirs and man-made lakes. It is found throughout the Mississippi River as well as in parts of the Missouri River.
This species is an omnivorous filter feeder taking both phytoplankton and zooplankton, which are then ground in the gizzard-like section of the gut. Some bottom material is often ingested while feeding; hence, the name mud shad or mud feeder.
State Records are not documented for non-game species.
Shad make great bait for catching channel catfish.
The Gizzard Shad is common in lakes, oxbows, impoundments, sloughs and large rivers with basic or low gradients, but reaches greatest abundance in waters where fertility and productivity are high. It avoids high gradient streams and rivers in the mountains and rivers without large, permanent pools, but can tolerate moderately turbid and occasionally even brackish or salt waters. The Gizzard Shad prefers living in open water, at or near the surface.
In Iowa, this species is synonymous with mud, preferring sluggish, soft-bottomed waters. In Missouri, it is usually found in the deep calm waters of natural lowland lakes, ponds, artificial impoundments, or in the pools and backwaters of streams. It has benefited from the construction of upstream reservoirs in the larger rivers in its range.
The Gizzard Shad spawns in shallow backwaters or near the shore. The fish are random, nocturnal group spawners with no care given to the young. Eggs are released near the surface of the water from late April or early May to early August at 50 to 70 degrees F. The eggs are adhesive and sink. The females produce up to 400,000 eggs that are about .03 inch in diameter.
Shad are intermediate hosts for several species of the glochidiad stages of mussels and in that respect have economic importance in the perpetuation of freshwater mussels with commercial value.
Shad commonly reach 4 inches long during the first year of life. The maximum size in Iowa is about 9- to 14-inches.
Gizzard Shad have little value as a food-fish and are seldom taken by hook-and-line. Its flesh, and particularly the gizzard-like stomach, are occasionally fermented for use as catfish bait. Dense shad populations provide considerable forage as young for other predatory fishes, and their schooling behavior during the first year make them easy prey for larger fish. Some controversy surrounds this forage value, however, as shad quickly outgrow the vulnerable forage size and rapidly assume pest levels in some closed watersheds or when predator populations are insufficient to control their numbers. Evidence is strong that shad compete with young bluegill for food, and when populations reach very dense levels, bluegill survival is lowered. At that time, eradication of the entire fish population and game fish species restocking, particularly in small lakes is the only way to restore acceptable fishing. Massive die-offs of young and yearling shad are commonly reported after spring ice-out as a result of their susceptibility to fluctuating water temperatures.
Recent stream sampling information is available from Iowa DNR's biological monitoring and assessment program.
Harlan, J.R., E.B. Speaker, and J. Mayhew. 1987. Iowa fish and fishing. Iowa Conservation Commission, Des Moines, Iowa. 323pp.
Loan-Wilsey, A. K., C. L. Pierce, K. L. Kane, P. D. Brown and R. L. McNeely. 2005. The Iowa Aquatic Gap Analysis Project Final Report. Iowa Cooperative Fish and Wildlife Research Unit, Iowa State University, Ames.
Photo Credit: photo courtesy of Konrad P. Schmidt, copyright Konrad P. Schmidt.