Isolating the Parentals of the late Summer Spawn of Threadfin Shad in Hugo Reservoir, Oklahoma

Kurt E. Kuklinski
500 E. Constellation, Norman, OK 73072, University of Oklahoma, (405) 325-7288, kuk@ou.edu

Jeff Boxrucker
Oklahoma Fishery Research Laboratory, Oklahoma Dept of Wildlife Conservation, 500 E. Constellation, Norman OK 73072 (405) 325-7288 jboxrucker@odwc.state.ok.us

The presence of larval threadfin shad (Dorosoma petenense) in summer trawl collections from Hugo Reservoir, Oklahoma in 1997 and 1998 established evidence of multiple spawning bouts. The first spawn occurred in the spring with an ensuring spawn following during late July and into August. Weekly gill net samples were collected from March through August 1999. It is hypothesized that age-1 and older shad spawn in the spring and that parentals of the summer spawn are the fish from the summer spawn of the previous year. Threadfin shad were grouped into 20-mm length classes, and ovaries and otoliths of 10 fish from each length class were removed and examined. A gonadal somatic index (GSI) was created for each length class to follow ovarian development over the course of the entire spawning period. GSI patterns showed a peak in ovary weights from late April through May in all length classes. A secondary increase in ovarian weight occurred during the second week of July in all length classes. Ova diameters are being measured to determine maturation rates by size and age over time.