Gizzard Shad, Dorosoma cepedianum
Gizzard Shad, Dorosoma cepedianum. Fish caught from Lake Pleasant, Peoria, Arizona, May 2019. Length: 20 cm (7.9 inches). Catch, photograph and identification courtesy of Chris Moore, Peoria, Arizona.
Gizzard Shad, Dorosoma cepedianum. Fish caught from the Carlyle Reservoir, Carlyle, Missouri, June 2017. Length: 12.7 cm (5.0 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com).
Gizzard Shad, Dorosoma cepedianum. Fish caught from the Carlyle Reservoir, Carlyle, Missouri, May 2017. Length: 15 cm (5.9 inches). Catch, photograph and identification courtesy of Marc Eberlein, Grand Rapids, Michigan.
The Gizzard Shad, Dorosoma cepedianum, is a member of the Herring or Clupeidia Family, and the Gizzard Shad or Dorosomatinae Sub-family, that is also known as the American Gizzard Shad, the Eastern Gizzard Shad, the Hickory Shad and the Mud Shad and in Mexico as sardina molleja. The possess a gizzard, for which they are named. There are five global members of the Dorosoma Genus, of which two are found in Mexican waters, one in the Atlantic and this species which is found in the fresh water systems of the southern United States and Mexico.
The adult Gizzard Shad has a short deep moderately to strongly compressed oblong body with a depth that is 31% to 35% of standard length. The juveniles are slender, minnow-like and nearly cylindrical. Dorsally they are silvery-green in color with 6 to 8 horizontal stripes transitioning to silvery ventrally. The juveniles have a dark shoulder spot. Their fins are dusky. The males cannot be separated from the females visually. Their head is rounded with a blunt snout with a small subterminal mouth that lacks teeth with the upper jaw projecting beyond the short lower jaw. Their anal fin has 29 to 35 long rays and a long base; their caudal fin is deeply forked; their dorsal fin has 10 to 13 rays and is found behind the pelvic fins with the last ray being elongated in mature fish; their pectoral fins have 12 to 17 rays and small and found just below the gill cover and low on the body; and, their pelvic fins have 8 rays and low on the body and in front of the dorsal fin. They have 90 to 275 closely packed gill rakers on the lower limbs. Their body is covered with small cycloid scales and scutes along the lateral line. Their lateral line is weak.
The Gizzard Shad are found in freshwater lakes, reservoirs, and slow-moving rivers and streams that are not vegetated and have muddy bottoms and relatively high turbidity, but also reside in brackish waters along the Atlantic coast of the United States and Mexico. They have a high reproductive capacity, are abundant, fast-growing and short-lived. They are found at depths up to 30 m (100 feet) in waters that are between 10oC (50oF) and 21oC (70oF) and have the ability to survive in waters up to 35oC (95oF) and salinities of 34 ppt. They reach a maximum of 52 cm (20.5 inches) in length and 1.56 kg (3 lbs 7 oz) in weight. The Gizzard Shad is active diurnally. During certain periods of the year they congregate in schools in very shallow water. The juveniles consume larval phytoplankton and zooplankton. The adults are omnivorous filter feeders that consume phytoplankton and zooplankton and detritus. They are also known to consume the fry of other fishes found within their environment and very quickly become the dominant fish in the majority of water bodies in which they have been introduced. In turn the juveniles provide forage for at least 17 important game fishes most game fish as-well-as a large number of birds. Reproduction occurs in the spring with fish migrating to shallow waters and is dioecism with each female spawning several times and mating with several males and releasing between 20,000-550,000 eggs per year that adhere to submerged and floating objects. The eggs are demersal and hatch within 7 days. The juveniles reside in large schools for up to one year and then become solitary migrating to brackish waters (when access is available) until mating time. The have a very high fecundity rate and rapid grown rates, however, the Gizzard Shads are prone to massive die-offs when water temperatures drop to below 3oC (37oF) and when water temperatures elevate significantly. They have the ability to breach. They have lifespans of 10 years.
The Gizzard Shad is a resident of Mexico’s coastal fresh water systems being along the northwest section of the Gulf of Mexico from the Texas boarded south to the Río Pánuco drainage, Tampico, Tamaulipas.
The Gizzard Shad is easily confused with the Threadfin Shad, Dorosoma pretenense (pointed snout, projecting lower jaw, yellow fins, 20 to 25 anal fin rays).
From a conservation perspective the Gizzard Shad is currently considered to be of Least Concern with stable, widely distributed populations. They have been widely introduced as a food for game fish. The juveniles are heavily preyed upon but they quickly become too large and quickly become very established and a nuisance fish that outcompete native fishes. They are utilized at a modest level as a live bait targeting catfish and striped bass but die fairly quickly when hooked. They are not an esteemed human food fish with tasteless flesh and the numerous fine bones. They are utilized as an animal feed, trout feed and as plant fertilizers. They are utilized in toxicology testing of chemical products and water quality.