Dorosoma is Greek for “lance body,” referring to the lance-like shape of young shad. The word petenense refers to Lake Peten in the Yucatan, the species type locality. Threadfin shad are usually easily distinguished from gizzard shad by the fact that the upper jaw does not project beyond the lower jaw. The anal fin usually has 20-25 rays, as opposed to 29-35 rays found in gizzard shad. The upper surface is silver-blue and grades to nearly white on the sides and belly. All fins have yellow tint except the dorsal. In this species, unlike gizzard shad, the chin and floor of the mouth is speckled with black pigment.
Threadfin shad and gizzard shad both have a thread-like filament at the end of the dorsal (top) fin, so this thread-like fin does not distinguish the threadfin. The best way to tell the two species apart is that the upper jaw of the gizzard shad extends beyond the lower jaw and has a deep notch in the center. The upper jaw of the threadfin does not extend beyond the lower jaw and it is not notched. Both species have a dark spot on the shoulder, although it is typically darker on the gizzard shad. Another difference is that the gizzard shad does not have any yellow on the fins, although it may have a distinctive yellow spot in the white of the eye that is not found in threadfins. The fins of the threadfin usually have a yellowish tint, and the tail fin is often distinctly yellow. The chin and the floor of the mouth of the threadfin have black specks, while there are none on the gizzard shad.
Threadfin shad are used as forage fish because they remain relatively small, usually less than 7 inches. Threadfin are a schooling, open-water fish and grow well in productive ponds. Shad are filterfeeders and feed mainly on zooplankton and some larger phytoplankton. Larger threadfin may consume some detritus as well. They eat fish feed only incidentally.
Often used as a bait fish. Threadfin shad almost never bite on a hook.
Like gizzard shad, threadfin shad are most commonly found in large rivers and reservoirs. However, threadfin shad are more likely to be found in waters with a noticeable current and are usually in the upper five feet of water. They are quite temperature sensitive, with die-offs reported at temperatures below 45°F. Spawning begins in the spring when water temperatures reach approximately 70°F, and may continue into the summer. During spawning, one or more emales are accompanied by several males. Adults are considerably smaller than gizzard shad adults, rarely exceeding 6 inches in length.
Threadfin shad naturally occur in waters west of the Appalachian Mountains, north to Kentucky, west to East Texas, south to the Rio Grande drainage, and east to Florida. The species has been widely ntroduced in California and Arizona, as well as Appalachian and southern Atlantic states. Threadfin shad are common in all East Texas streams and have been introduced as forage fish in many eservoirs statewide.
Other Names for Threadfin Shad: