A more intensive and more coiqilete disintegration of mud-products and of by-pz^ucts id 

 one of the purposes of the periodical drainage of ponds, since air becomes thus freely 

 admitted and the work of aSrobic bacteria Intensively decomposes the intermediate and end 

 products of anaerobic decompQsition processes. 



H 



Here also, the temperature is an in^jortant factor. Kastll found in 1 can of pond mud, 

 at a temperature of 3' centigrade, 55>000 germs (in round figures), at a t€ii9)erature of 10* 

 centigrade already 85,000, and at a ten^rature of 15'centigrade over 120,000 bacterial 

 genns. 



Notwithstanding our present-day incomplete knowledge of pcnd oonditians, it is known, 

 nevertheless, that in ponds are also found bacteria which are able to build up protein by 

 extracting water soluble nitrogen. Lantzsch and Demoll have been able to show the presence 

 of azotobacteria and of ami nobacteria — the most inqwrtant nitrogen "fixature" — in large 

 nujnbers at the floor of ponds. They were rarer upon plants and totally absent in the 

 water. Their development is favorably influenced through oocygen, slight alkaline reaction, 

 fine colloidal bottom, slime with high organic contents, and also by phosphatlc fertilizers. 



But aside from their usefulness, pond bacteria may also exercise a noxious influence, 

 and by this we think not only of the fish-pathogenic species* 



The sudden Introduction of dead organic substtmce, for instance, (organic fertilizer, 

 mowed reeds, etc.) can provoke such a rapid, oxygen-consuming decomposition — especially in 

 eusmer — as to consume all the water-soluble oxygen in a peed. 



At the same time, the oxygen consumption on the part of the bacteria (which are always 

 present in small amovints) outweighs their oxygen production and even the admittance of new 

 oxygen from the outside. The consequence of this loss in oxygen is naturally the dying off 

 of fishes, aside from many other disturbances of the metabolic cycle. 



Loss of oxygen must therefore be prevented at all costs . 



Through the presence of organic substances, combined with lad: of oxygen the denltrat- 

 Ing bacteria — especially Pseudomonas fluorescens — ^wlll further exercise a noxious influence 

 by depriving the inqwrtant nitrates of their oxygen and thus destroying them. Conditions 

 for these bacteria are especially favorable under temperatures of over 20* centigrade. 



Tfe are thus confronted with a continuous struggle between nitrogen- fixing or nitrify- 

 ing bacteria and denitrifying bacteria, and it is up to the fiahbreeder to aid in this 

 struggle so as to favoisbly influence the productivity of the pond. 



Unfortunately, at present it is known in cxily nidlinentary fashion that he can accomplish 

 this by carefully controlling the necessary oxygen content, (especially in summer), and through 

 proper care of the pond floor. 



A. The Water 



Fundamental requirements 



Two fundamentally different requirements confront the fishbreeder with regard to the 

 physical and chemical conditions of water, which is, after all, his most important stock in 

 trade. 



(1) The water must offer the fish (as well as all other productive-biologically 

 important organisms) the most favorable conditions of existence. 



(2) The water must contain the necessary nutriments, needed for production and 

 especially primary production, in best possible optimal amounts, or they 

 must be regularly renewed li-om the outside or must be replenished through 

 decomposition processes within the pond. 



46 



