THE VERTEBRATE ANIMALS 283 



Problem XXXVI (OpHomil). Tlir <trf ijicial propagation of 



fishes, (Laboratory J\I diinal , I'roh. .V.V.VJ 7.) 



The Work of National and State Governments in protecting and 

 propagating Food Fishes. But the profits from the fisheries 

 are steadily decreasing because of the yearly destruction of untold 

 millions of eggs which might develop into adult fish. 



Fortunately, the government through the Bureau of Fisheries, 

 and various states by wise protective laws and by artificial prop- 

 agation of fishes, are beginning to turn the tide. Certain days of 

 the week the salmon are allowed to pass up the Columbia unmo- 

 lested. Closed breeding seasons protect our trout, bass, and other 

 game fish, and also prohibit the catching of fish under a certain 

 size. Many fish hatcheries, both government and state, are en- 

 gaged in artificially fertilizing millions of fish eggs of various species 

 and protecting the young fry until they can be placed in ponds or 

 streams at a size when they can take care of themselves. This 

 artificial fertilization is usually accomplished by first squeezing out 

 the ripe eggs from a female into a pan of water; in a similar manner 

 the milt or sperm cells are obtained, and poured over the eggs. The 

 fertilized eggs are carefully protected, and, after hatching, the 

 young fry are kept in ideal conditions until later they are shipped, 

 sometimes thousands of miles, to their new home. 



State and government interposition, however, is in many cases 

 coming too late, for at the present rate of destruction many of our 

 most desirable food fishes will soon be extinct. The sturgeon, the 

 eggs of which are used in the manufacture of the delicacy known 

 as caviare, is an example of a fish that is almost extinct in this part 

 of the world. The shad is found in fewer numbers each year, 

 and in fewer rivers as well. The salmon will undoubtedly soon 

 meet the fate of other fishes which are taken at the spawning 

 season, unless conservation of a radical sort takes place. 



Classification of Fishes. The animals we recognize as fishes are 

 grouped by naturalists into four groups : 



1. The Elasmobranchs. These fishes have a skeleton formed of 

 cartilage which has not become hardened with lime. The gills com- 

 municate with the surface of the body by separate openings instead of 

 having an operculum. The skin is rough and the eggs few in number. 



