Grunion are two fish species of the genus Leuresthes: the California grunion, L. tenuis, and the Gulf grunion L. sardinas. They are sardine-sized teleost fish of the Atherinopsidae family of New World silversides, found only off the coast of California, USA, and Baja California, Mexico where the species is found on both the Pacific Ocean and Gulf of California coasts.
Grunion are known for their unusual mating ritual whereby at very high tides the females come up on to sandy beaches where they dig their tails into the sand to lay their eggs. The male then wraps himself around the female to deposit his sperm and for the next ten days the grunion eggs remain hidden in the sand. At the next set of high tides the eggs hatch and the young grunion are washed out to sea.