Spawning begins after high tide and continues for several hours. As a wave breaks on the beach, grunion swim as far up the slope as possible. The female arches her body and excavates the semifluid sand with her tail to create a nest. She twists her body and digs until she is half buried in the sand with her head sticking up. She then deposits her eggs in the nest.
Males curve around the female and release milt.
As many as eight males may fertilize the eggs in a nest. After spawning, the males immediately retreat toward the water while the female twists free and returns with the next wave. While spawning may take only 30 seconds, some fish remain stranded on the beach for several minutes. Spawning occurs from March through August, and occasionally in February and September. Peak spawning period is between late March and early June.