conditions for primary reproduction (of the kind of vegetation) and on the other hand, to 

 provide a favorable condition of supplementary metaboliam to the ultimate consumers, i.e., 

 the fishes. It is not possible to directly increase the small life forms upon which the 

 fishes feed. 



ikside from these fundamental considerations for proper sustenance, it is necessary 

 to have favorable conditions of existence for the different kinds of organisms, involved 

 in the catabollc chain (sufficient oxygen, approximate neutral reaction of the water, 

 absence of injurious substances) for the vital functioning of the catabolic cycle. 



The means to achieve these ends are none other than fertilization, water conditioning^ 

 care of the pond, proper rate (limitation) of stock planting and feeding. (See chapters VI 

 to VIII) 



The links of the catabolic cycle of the pond rest ultimately upon the primary pro- 

 ductivity of plants, the rate of which determines, in great measure, the rate of total 

 productivity. 



This primary productivity again is correlated to a great number of complex factors 

 and our problem is to discover which of these factors exercises a controlling influence 

 i^xxi this productivity. 



In regard to vegetable foodstuffs Liebig ' s law of minlmiima is still helpful here. 

 This law, in its essence, reads as follows: 



"If one of the indispensable nutriments of plant life is present 

 in only relatively small amounts (in minimal amounts), the total 

 productivity will be lowered." 



It has been proven that the pond is especially lacking in nitrogen and phosphoric 

 acid combinations; therefore, any fertilization of the pond should tend to ameliorate 

 this deficiency, 



Thienemann (1926), by also taking into account other factors (light and heat) has 

 f emulated a general " law of effects of environ mental factors" and »hich I partly quote 

 here verbatim: 



"The mass development of an organism within a biological community is 

 dependent upon necessary environmental factors which during its most 

 exacting stadium of development (which has the least strength of 

 adaptability) deviate the most from their optimum in amounts as well 

 as in strength." 



This means that an over-abundance of a certain factor may very well be detrimental 

 to general productivity. Within a larger region, the different factors are mostly equally 

 strongly or weakly developed. 



In this respect, that is, from the "regional" angle, we differentiate first between: 



Ponds and pond bottoms rich in foc)dstuffs (eutrophic) and ponds and pond bottoms 

 foodstuff-poor (oligotrophic). Each one of these two groups has to be subdivided again 

 into the. folloTri.ng categories: 



alpha-trophic 



beta-trophic 



ypsilon-trophic. 



The division into foodstuff-rich and foodstuff-poor pertains originally only to the 

 available amounts of nitrogen and phosphorus combinations. 



But aside from ordinary "harmonious oligotrophy", we have to reckon, in pcmd culture, 

 with a certain oligotrophy due to slightly acidulous water, that is, an overabundance of 



30 



