PROPAGATION OF FISH 373 



deposits milt, consisting of millions of sperm cells, in the water 

 just over the eggs, and fertilization follows. Some fishes, as 

 sticklebacks, sunfish, toadfish, etc., make nests, but usually the 

 eggs are left to develop by themselves, sometimes attached to some 

 submerged object, but more frequently free in the water. In 

 some eggs a tiny oil drop buoys up the egg to the surface, where 

 the heat of the sun aids development. Both the eggs and young 

 fish are exposed to many dangers ; they are eaten, not only by 

 birds, fish of other species, and other water inhabitants, but also 

 by their own relatives and even parents. Consequently, a very 

 small percentage of eggs ever reach maturity. 



The Relation of the Spawning Habits to Economic Importance 

 of Fish. — The spawning habits of fish are of great importance to 

 us because of the economic value of fish to mankind, not only 

 directly as a food, but also indirectly as food for other animals in 

 turn valuable to man. Many of our most desirable food fishes, 

 notably the salmon, shad, sturgeon, and smelt, pass up rivers from 

 the ocean to deposit their eggs, swimming against strong currents 

 much of the way, some species leaping rapids and falls, in order 

 to deposit their eggs in localities where the conditions of water 

 and food are suitable and the water is shallow enough to allow 

 the sun's rays to warm it sufficiently to cause the eggs to develop. 

 The Chinook salmon of the Pacific Coast, w^hich is used in the 

 Western canning industry, travels over a thousand miles up the 

 Columbia and other rivers, to the headwaters where it spawns. 

 The salmon begin to pass up the rivers in early spring, and reach 

 the spawning beds, shallow deposits of gravel in cool mountain 

 streams, before late summer. Here the fish, both males and 

 females, remain until the temperature of the water falls to about 

 54° Fahrenheit. The eggs and milt are then deposited, and the 

 old fish die, leaving the eggs to be hatched out later in the water 

 warmed by the sun. 



The instinct of salmon and other species of fish to go into shallow 

 rivers to deposit their eggs has been made use of by man. At 

 the time of the spawning migration the salmon are taken in vast 

 numbers, to the value of over $40,000,000 annually. 



Need of Conservation. — The need for conservation of this 

 important national asset is great. The shad within recent times 



H. NEW CIV. BIOL. — 25 



