These fish come out of the water to lay eggs
Nutan Shukla

Along southern California’s sandy beaches, from March through September, one of the most remarkable fishy lifecycles in the sea is completed. Watched by thousands of people; the California grunion, member of the silverside family, comes ashore to spawn.

These small silvery fish in the full moon night leave their safer haven in the ocean and invade alien place – the land – to breed. Unlike other fish, they come out of the water completely to lay eggs in the wet sand. Grunion make these excursions only on particular nights, and with such regularity that the time of their arrival can be predicted a year in advance. Shortly after high tide, on certain nights, the beaches along the Pacific coast of southern California become silvery shiny due to the presence of millions of spawning grunions, five to six inches long slender fish with bluish green backs, silvery sides and bellies. They strand themselves in huge mass and the beaches along the water’s edge become covered with a silvery carpet. As each wave breaks over the sand, it brings in a fresh cargo of wriggling fish to the shore.

Spawning runs usually begin with single fish (usually males) swimming in with a wave and occasionally stranding itself on the beach. Gradually, more and more fish come in with the waves and by swimming against the outflowing wave strand themselves until the beach is covered with a blanket of grunion. Peak activity is reached about an hour after the start of the run and lasts from 30 to 60 minutes. Finally, when the tide has dropped a foot or more, the run slackens and then stops as suddenly as it started. No more fish will be seen that night, and they will not appear again until the next night or the next series of runs.

Adapted to tidal cycles in precise manner grunions spawn only when there are high tides, but after they have started to recede. Reason is the strong waves of the rising tide erode sand from the beaches whereas receding tide deposits it. In such a case it is obvious that if the eggs were laid while the tide is rising the succeeding waves would wash the eggs out prematurely. This danger is eliminated only by taking the advantage of the falling tide.

Females ride a far-reaching wave on to the beach accompanied by as many as eight males. If no males are present, the female will return to the ocean with the outflowing wave. In the presence of males, she swims as far up on the beach as possible and literally drills herself into the sand as the wave recedes. This is accomplished by arching her body with the head up, and at the same time vigorously wriggling her tail back and forth. As her tail sinks into the semifluid sand, she twists her body and drills herself downward until she is buried up to the pectoral fins.

Occasionally she may bury herself completely. The male (or males) curves around her as he lies on top of the sand, with his vent close to or touching her body. The female continues to twist, emitting her eggs 2 or 3 inches beneath the surface of the sand. Males discharge their milt onto the sand near the female and then immediately start to wriggle towards the water. The milt flows down the body of the female and fertilises the eggs. The female then frees herself from the sand with a violent jerking motion and returns to the sea with the next wave to reach her. This entire process takes about 30 seconds. Larger females are capable of laying up to 3,000 eggs every 2 weeks. As the mature eggs are deposited in the sand, another group of eggs are developing that will be spawned during the next series of runs. This cycle continues throughout the season.