37° ZOOLOGY 



destruction. Such fish hatcheries are scattered all over the 

 Union and many of our fresh waters are being restocked with 

 species believed to be hardy and suitable for food. 



2. By determining the foods preferred by special fish and 

 artificially encouraging its abundance. 



3 . By encouraging the destruction of species of animals that 

 prey upon the food fishes, and by the study of fish diseases pro- 

 duced by plant and animal parasites. 



4. By studying the habits of the fishes and by regulation of 

 • the time, place and manner of catching. 



The money value of the annual catch of fish in our waters 

 cannot well be less than $50,000,000. The most valuable fresh- 

 water forms are the lake trout, white fish, cat fish, bass, perches, 

 suckers. The chief marine species are cod, haddock, halibut, 

 mackerel, menhaden, herring, and salmon. The latter, though 

 marine, is caught in fresh waters in its breeding migrations. 



There are numerous species of fish which are destructive to 

 the food fishes, by devouring the young or in other ways. 

 Among these are the gar-pike, pickerel, muscalonge, German 

 carp, the dogfish and other sharks. 



389. Supplementary Exercises for the Library. 



1. Make a report concerning the principal food fishes used by the people of the 

 United States: their habits and geographical range, the mode of their capture and 

 putting on the market. 



2. Make a study of the methods of capturing fish from primitive time to the 

 present and show how the methods have been adapted to the habits of the fish. 



3. A study of the history and work of the United States Fish Commission as 

 shown in the annual reports and bulletins. Its economic side. Its scientific side. 



390. Reproduction and Development. — The sexes are sepa- 

 rate. The sexual elements are produced in great numbers. 

 The ova (spawn) are usually deposited in the water, in shallows 

 on the open bottom, under rocks, or in places specially provided 

 for them by the parents. The sperm {milt) is poured over these 

 by the male, and the fertilization and later development take 

 place in the water usually with little or no care on the part of 

 the parents. Great loss of life occurs among the young from 

 the voracious habits of other species and sometimes of the 

 parents themselves. It is not difficult to believe that the enor- 

 mous number of eggs produced by the female is an adaptation 



