Threadfin shad. Dorosoma petenense. were first introduced into Bull Shoals Reservoir in 1961. Based on fish collected in 1966 and 1967. weighted average calculated total lengths of females at the end of each successive year of life were 66. 118. 134 and 141 millimeters. and of males 64. 118 and 123 millimeters. Growth of threadfin shad in Bull Shoals was slower than in more southern and temperate regions, but life span was longer. A strong year class in 1964 was indicated by the Presence of a relatively high number of 2-year-old fish in 1966 and 3-year-old fish in 1967. The ratio of females to males in cove rotenone samples was 3.8 to 1. while in midwater trawl samples the ratio was 1.0 to 1. Threadfin shad comprised 80 percent of the total shad population by number. but only 17 percent by weight.