Fish Out of Water
from the book, "Petrified Lightning"
Fish Out of Water
To keep their eggs safe from snapping jaws, drifting into unsuitable waters, or any of the other fates that may befall small creatures in the sea, many fish have devised unusual tricks. They may keep the eggs in their mouths, bury them, build many sorts of nests, cement them to some stationary or floating object, or deposit them in a pouch appropriately provided by the male.
Fish that have no such safety net for their fry must lay a sizable number of eggs. This is the case with fish that range the seas and lay pelagic (floating) eggs. The female cod and turbot, for example, lay between two million and nine million eggs at a single spawning. The oceans are not overrun with cod and turbot because, by the time the tiny fish are two inches long, fewer than a dozen will have survived from each million eggs: one survivor out of 83,000 eggs. Most of the rest become dinner for the many creatures of the sea.
Among the most remarkable fishes are those that, knowing the dangers of the waters, lay their eggs on land.
Miniature Sprinkling Systems!
One fish that lays eggs on land is a species of characin, Copeina arnoldi, whose family includes such aquarium favorites as the tetras, x—ray fish, and pencil fish and such sinister aquarium rejects as the piranha. C. arnoldi is a three—inch blue—gray fish that lives in slow—moving South American rivers.
This little fish is spectacular only because it lays its eggs out of the water. The male steers a willing female to a spot where the leaves of a hanging branch are just an inch or two above the water. The pair then hook their fins together, leap out of the water, and cling to a leaf for about 10 seconds. During this brief period the female lays a dozen or so eggs in a jelly mass that adheres to the leaf. The pair return to the water and repeat this maneuver until all the eggs are deposited and then fertilized by the male. The spawning completed, they unlock fins, and the female swims off in the never—ending search for food. The male, as a fish version of a househusband, is stuck with minding the nest.
Laid out of water, the eggs are safe from menacing jaws but are in danger of being dried up by the sun. Keeping the eggs moist is a job for the male C. arnoldi. He returns to the egg mass every quarter of an hour and splashes water on the brood with his tail. If he fails to return, the nest will dry up. The only thing that will sabotage his standing appointments with the offspring is an invitation to dinner by a larger fish—he being the dinner. But by and large dad returns faithfully as scheduled, joyfully splashing water on the eggs to keep them healthy and wet. Fortunately for him they hatch in three days (288 trips, in case he is keeping score). The fry then drop into the water and swim away without so much as a nod of appreciation for their exhausted father.
At certain times of the year around midnight, under a full moon, for several hundred miles along the California coast, the sea virtually explodes with thousands of silvery fish that appear to perform a mysterious dance on the beach. They sparkle like diamonds in the moonlight. When this spectacle is at its highest intensity, so many fish may be visible on the sand that they create the illusion of a silver canopy covering the beach.
The fish's weird antics give the impression that they are dancing, from which grew the Native American legend of the Dancing Fish. But the dance is actually their unusual spawning ritual, for these are the grunion.
Because grunion eggs will die if kept immersed in water, an alternative, nonwatery haven must be found for them. Therefore the fish have selected a 100—mile strip of beach, from Point Conception, California, to Baja California, Mexico, for their haunting natural drama. These six— to seven—inch fish, Leuresthes tenuis, have a long breeding season, from late February until early September. But actual breeding can take place only on the three or four nights that follow the highest tides during a new or full moon.
As the time to spawn nears, the grunion stops growing. Instead, its energy is channeled into reproduction, and its sexual organs grow larger. Within the female the first eggs begin to ripen. Yearling females produce only about 1,000 eggs per spawning, but the number is tripled in older fish. Since a single female can spawn up to eight times a season, many thousands of eggs can be left ashore by one fish.
With incredibly precise timing and a knowledge of tides that the U.S. Coast and Geodetic Survey might envy, the female prepares for her trip ashore. She must lay her eggs in the sand after the peak tide or they will be washed away by higher tides, and the eggs must be protected for at least 10 days while they are incubating.
The grunion gather offshore for an hour or more before the run. When the time and tide are right, the grunion allow themselves to be flung high on the beach by an incoming wave. The sand is immediately carpeted with quivering silvery bodies twisting, squirming, shimmying, or (as legend would have it) frolicking in a frenzied dance.
The fish strive mightily to reach a point on the beach just below the high—water mark. Stranded high and dry, unable to breathe, the females nevertheless arch their bodies vertically and burrow violently into the sand with their tails until only their heads and pectoral fins are clear. This takes about 10 seconds. Several males writhe around each female and discharge their milt (sperm—containing fluid), which trickles down to fertilize the eggs deposited in the sand. The males will wriggle back to the safety of the sea, but the female will rest for a moment, making a tiny, high—pitched grunt. (This behavior gave the species its name, derived from the Spanish word grunion, for "one who grunts.") She will shortly follow the males back into the sea. Depositing and fertilizing a cluster of 1,000 to 3,000 eggs is a 30—second task—with arrival and departure time, one minute.
The water of the tides for the days following doesn't reach the buried eggs but does add more layers of sand. This gives the eggs extra protection from sun, storm, and probing beaks of predatory shorebirds.
The eggs are ready to hatch in about 10 days, but nothing happens until the next flood tide about a fortnight later. Then incoming waters swirl the sand around the eggs, which hatch with explosive suddenness. The young grunion shoot into the water on the wave that uncovered them. And there they remain, not far from shore, at depths of no more than 60 feet, until spring tide of the next year, when it will be their turn to become a dancing fish in the light of the moon.
How do these remarkable fish know when and where to spawn, and what triggers the spawning runs? What activates the extremely accurate internal clock that makes them beach themselves with such precise timing? Do they sense variations in the force of gravity that produces the high tides, or changes in water pressure? Or do they somehow respond to changes in the intensity of the moon's light? When the survival of their young hangs in the balance, animal species instinctively know whatever they need to know in order to survive. Those that do not will face extinction!