American Fisheries Society 425 



tity and therefore a fertilization with superphosphates is 

 especially to be recommended. 



Potash can also be had in water-soluble form as well as in 

 40 per cent salts of potash and in about 14 per cent kainit. 

 Both these fertilizers can be spread on the bottom before 

 letting on the water or in the pond later. 



In the use of nitrogenous fertilizers in pond-culture the 

 greatest care is enjoined. Most pond-floors have naturally 

 a pretty high nitrogen-content. There are often great 

 masses of humus accumulated, and for the pond-culturist it 

 only remains to make this store of nitrogen active. The 

 means to this end are : 



1. Thorough drainage and deoxidation for the pond-bot- 

 tom, since water and humic acids are antiseptic in their 

 influence. 



2. Laying the pond completely dry during the winter, to 

 crumble the bottom. 



3. Liming of the pond, to induce a more rapid decomposi- 

 tion of the humic constituents of the bottom and a chemical 

 fixation of the pernicious humic acids. 



In feeding-ponds there is at first no nitrogenous manuring 

 necessary since the nitrogenous content of the food, gen- 

 erally abundant, is only partly digested by the fish, and the 

 undigested remnant suffices for the fertilization of the 

 water. Only in case of ponds poor in humus without suffi- 

 cient fructifying flooding from outside, is a trial of fertiliza- 

 tion with water-soluble nitrates to be advised. 



The liming of the pond should not be omitted on earths 

 containing little or no lime, for reasons already given, and 

 also because the lime is an important constituent of plants, 

 indispensable to suspended algse ; not to mention the destruc- 

 tive influence of the quicklime or burnt lime on the disease- 

 inciters and parasites in the pond. If burnt lime is used 

 for pond fertilization, wait at least fourteen days after its 

 application. Ponds occupied by fish should be dressed only 

 with ground lime-carbonate to avoid endangering the fish. 



How much of each kind of commercial fertilizer should 



