32 Americmi Fisheries Society. 



FOOD 



A factor which has not had sufficient consideration in 

 fish propagation under natural conditions is the amount of 

 food. Even men old in fisheries work sometimes appear to 

 overlook the fact that fish cannot live on pure water alone, 

 any more than land animals can live on fresh air. We have 

 probably seen waters stocked with many more fish than 

 could possibly find sustenance there. Furthermore, it is not 

 only the amount of water, at its lowest stage, that is con- 

 cerned, for the food crop of a lake or stream depends upon as 

 many different factors as a crop on land and the chemicals 

 in solution, the amount and kind of organic matter, the tem- 

 perature, the amount of light, the character of the bottom 

 and various other factors affect the productivity of any body 

 of water. In the end this goes back to the production of 

 aquatic plant life, for, just as upon land, the amount and 

 character of animal life is conditioned by the plant life that 

 furnishes the primary food source. Clear water will grow 

 more food than muddy water on account of the amount of 

 light which penetrates. Warm water will produce more 

 than cold. A stream or lake that maintains a fairly con- 

 stant level will produce more than the one which fluctuates 

 greatly. To judge the productivity of a body of water, 

 therefore, it should be studied at its worst and all the un- 

 satisfactory conditions known. Many streams and some 

 lakes become so low in dry seasons that they cannot support 

 a fish fauna commensurate with their size at other seasons. 

 Streams which are muddy for a considerable portion of the 

 year cannot support as many game fish, nor as much life in 

 general, as Vv^aters that are clearer. This is one of the 

 reasons why lakes are more generally productive than 

 streams, for they are seldom roiled to any extent. 



The natural limit of fish production is therefore not con- 

 ditioned by the reproductive capacity of the fish, which al- 

 ways produce an overplus of young if not interfered with, 

 but upon the various factors which check the development. 



ARTIFICIAL CHECKS 



These are in the nature of the unsatisfactory conditions 

 which the industry, the carelessness and the short-sighted- 

 ness of man have thrown in the way of the natural balance 

 of aquatic life. It is a sad commentary on human behavior 

 that very few of our waters produce any where near as 

 many fish as they did in a state of nature. "Increased pro- 

 duction" has been the slogan of the farmer, the manufac- 



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