grunion
n.,
pl. 3ion or 3ions 5prob. < Sp gruO<n, grumbler < L grunnire, to grunt < IE *gru3, echoic6 a silverside fish (Leuresthes tenuis) of the California coast: it spawns on sandy beaches during high tides in the spring

I remember a wonderful TV nature program showing grunion by the thousands mating in the
shallows of a California beach.