Larval threadfin shad (Dorosoma petenense) collected in August trawl samples from Hugo Reservoir raised questions about the spawning potential of the parental fish population. Adult threadfin shad were collected weekly from 24 March to 25 August 1999 to determine their reproductive state. Gonadal somatic index (GSI) values for medium and large size classes increased until mid-May, and then steadily decreased. However, in spite of decreasing GSI values, mature ova (greater than 0.53 mm in diameter) were present in ovaries through mid July. It is likely that threadfin shad were capable of prolonged spawning throughout the spring and summer. A small proportion (4%) of age-0 threadfin shad matured within two to three months of hatching and served as a brood source for the summer larval production.
