The Gizzard Shad, a member of the herring family, is native to fresh and salt waters of eastern North America. Its natural range includes the Saint Lawrence River and the Great Lakes and extends west into North Dakota. Gizzard shad are found as far south as eastern Mexico, and as far west as New Mexico. Its range has been greatly expanded through stockings throughout the west. Preferred habitat is sluggish rivers and muddy bottomed lakes, avoiding fast waters. Shad are pelagic and frequently feed near the surface. Gizzard shad are sensitive to sudden changes in temperature and oxygen content, which can cause large-scale, unexpected die-offs.
Gizzards have a deep, oblong body. Free of markings, they are grayish or silvery blue on top transitioning to silver on the sides with a whitish belly. The dorsal fin has a long ray that extends beyond the rest of the fin. The tail fin is deeply forked. Their mouth is inferior, sub-terminal, and toothless. Gizzard shad produce excessive slime and have a noticeable strong “fishy” smell.
Eight to fourteen inches is typical for gizzard shad, but can exceed 18 inches.
Gizzard shad spawn in the spring, when water temperatures rise above 50 degrees Fahrenheit. Diverse habitats are utilized for spawning. Eggs and sperm are broadcast simultaneously near the surface. The eggs sink to the bottom and adhere to submerged objects. Reservoir populations often spawn in creeks tributary to the reservoir. Shad are prolific, producing up to 400,000 eggs.
This schooling, pelagic fish is primarily a plankton feeder. They ingest bottom mud and sand to assist grinding of phytoplankton and zooplankton in their thick walled gizzard like stomachs.
Gizzard Shad in Colorado
Description: A fish that is strongly compressed lateraly, body thin and deep; mouth small and subterminal, upper jaw with a deep notch at center, upper jaw extends past lower jaw; dorsal fin with 10-13 rays, last ray of dorsal fin modified into a long, thin filament; 29-35 rays in anal fin; more than 55 scales in lateral line. Adults are silver or silvery-blue on the back, fading to silver on the sides, with a whitish belly. Young have a large purple-silver spot on the sides behind the upper edge of the operculum. Mature fish range from 9-13.5 inches in length and weigh about 12 ounces. Specimens longer than 18 inches have been taken in eastern Colorado.
Range in Colorado: Gizzard shad in Colorado are restricted to reservoirs and mainstem river reaches in the Arkansas and South Platte drainages. Every life stage, from larvae to spawning adults, is found in many eastern plains reservoirs. Immature fish, to five inches in length, may be encountered in the mainstem South Platte River from Greeley upstream to the Saint Vrain River, and in the lower reaches of that tributary (Propst 1982). Wiltzius (1981) indicated that gizzard shad may be native to Colorado since specimens were collected in the Arkansas drainage prior to any known introductory plant of the species. Gizzard shad have been stocked in many eastern plains reservoirs as a forage species.
Habitat: Gizzard shad are found in many diverse Colorado waters, but principally in highly productive impoundments. Traveling in schools which generally are in continual motion, gizzard shad are found in areas of little or no current. This avoidance of current could explain the absence of mature shad in the mainstem South Platte River where low fall and winter flows leave few large pool areas.
Courtesy of NDIS Colorado Division of Wildlife