Eggs in plankton samples from lower Chesapeake Bay indicated that the spawning season of the bay anchovyAnchoa mitchilliin 1988 extended from early May to mid-September. Oocyte stages in adults were used to determine daily spawning time and frequency as well as batch fecundity. Spawning was temporally synchronized and lasted for about 1.5 h each night. Spawning time became later each month (2000 hours on 6 June to 2330 hours on 31 August). Spawning frequency per individual was every 4 d in early June and every 1.3–1.9 d in other months. Batch fecundity was a linear function of fork length and of body weight; regression slopes on 6 July and 4 August were significantly higher than those on 6 June and 31 August. Estimated mean total spawnings per female in 1988 was 54. Total egg production for a fish of average size was 45,110, which is equivalent to 346% of body biomass energy. Age determinations based on lagenar otoliths showed that some fish spawned when as young as 2.5–3 months. The bay anchovy has a greater reproductive potential than is known for other anchovy species.