Karen A. Brinkley, James B. Sickel, and Leon Duobinis-Gray, Department of Biological Sciences, Murray State University, Murray, KY 42071

Abstract. Zebra mussels were collected from 2 sites in Kentucky Lake and 1 site in the Ohio River monthly between March 1996 and February 1997 with the aid of SCUBA. Specimens were fixed in 10% buffered formalin, dehydrated, embedded in paraffin, sectioned and stained with hematoxylin and eosin. Sections from each specimen were histologically examined, sexed and assigned to gametogenic stages based on gamete morphology and gonad maturity. Gonad maturity was determined by types and arrangement of tissue in the gonad. Six gametogenic stages were observed during the reproductive season. The stages were identified as resting, early development, later development, ripe, spawning, and redevelopment. Kentucky Lake zebra mussels matured and spawned slightly later than those in the Ohio River. By June, zebra mussels in both rivers were at approximately the same stage in reproductive development. Redevelopment of eggs in the gonad suggested that eggs were continually shed until the redevelopment stage was reached in mid-October. Gonad development of males and females appeared to be synchronous. The reproductive season lasted approximately one month longer in Kentucky Lake than in the Ohio River. Supporting funds for this project were received from the Mussel Mitigation Trust, Murray State's Center for Reservoir Research, and the Shell Exporters of America, Inc.