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 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 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, the salmon used in the Western canning industry, travels over a thousand miles up the Columbia and other rivers, 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 deg. Fahrenheit. The eggs and milt are then deposited, and the old fish die, leaving the eggs to be hatched out later by the heat of the sun's rays. Need of Conservation.--The instinct of this 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, for the salmon fisheries net over $16,000,000 annually. But the need for conservation of this important national asset is great. The shad have within recent time abandoned their breeding places in the Connecticut River, and the salmon have been exterminated along our eastern coast within the past few decades. It is only a matter of a few years when the Western salmon will be extinct if fishing is continued at the present rate. More fish must be allowed to reach their breeding places. To do this a closed season on the rivers of two or three days out of each seven while the shad or the salmon run would do much good. The sturgeon, the eggs of which are used in the manufacture of the delicacy known as _caviar_, is an example of a fish that is almost extinct in this part of the world. Other food fish taken at the breeding season are also in danger. [Illustration: Artificial fertilization of fish eggs.] Artificial Propagation of Fishes.--Fortunately, the government through the Bureau of Fisheries, and various states by wise protective laws and by artificial propagation of fishes, are beginning to turn the tide. Certain days of the week the salmon are allowed to pass up the Columbia unmolested. Closed breeding seasons protect our trout, bass, and other game fish, also the catching of fish under a certain size is prohibited. [Illustration: Early development of salmon. Natural size.]