Lake Texoma Fish Species: Threadfin Shad 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.