The reproductive ecology of the tidewater silverside, Menidia peninsulae, was studied during February 1982 through February 1983 along the shoreline of Santa Rosa Island, Florida. Adult Menidia were observed at low tide spawning on a red alga, Ceramium byssoideum, which was growing in the cracks and crevices of a rocky substrate just below the low tide line. Pinfish, Lagodon rhomboides, were noted preying upon newly spawned Menidia eggs; gut analyses revealed a mean number of 191 eggs in five of the predators. The annual reproductive cycle of Menidia extends from February through July or August with the highest spawning activity during March through June at water temperatures of 16.7 to 30.8 C. A single female with ripe ova was collected in November. On eight occasions, minima in female gonadal indices occurred in association with recurring 3- to 4-day periods of tropic tides, suggesting a tidally mediated spawning cycle attuned to periods of very low tidal amplitude and thus low tidal current velocities.