a certain factor and which plays a well defined role. Together with Nauaann (1932), we 

 apeaic in this case of " azidotrophy" » 



Aside from eutrophlc and oligotrophic pond types, we have further the so-called 

 " dystrophic " type, which is easily recognised by the yellowish-brownish color of its 

 water, due to a rich, humus soil, a "brown-water pond". 



Ein. Naumann (1928) has gone still lUrther in the division of pond types, namely 

 from a nutritive-biological angle. 



He differentiates from geographical viewpoints and which determine the factor of 

 warmth between ponds of temperate zones, ponds of arctic zones, and ponds of tropical 

 zones. Tlithin each group he differentiates again between autotrophic ponds and 

 hetarotrophic ponds. 



Into the last category — not directly producing organic substances but supplied with 

 them from the outside — belong a great number of trade waste (sewage) ponds. 



Other principles of differentiation — also in regard to nutritive physiology — are 

 based lyjon the form of water supply, water percolation and upon the age of ponds. 



I will deal with these questions later. Be it said, though, already, that newly 

 planted ponds are much richer in foodstuffs than older ones. In the experimental station 

 at Sachsenhausen, for instance, the newly planted ponds suipassed in productivity the ponds 

 of secondarj' order by L.'i per cent after fertilizaticm even by 100 per cent. 



Running water is also relatively richer than stagnant water, and will yield, accord- 

 ing to their nature, ftorn 2 to 10 times greater "crops", 



2. Aquatic Animals in Ponds . 



The small animal life of the pond, important for the alimentation of fish is deter- 

 mined by two chief factors: 



(1). By the numerous and varying conditions of existence, 

 and whidi are similar to these at the sea shoi-e; 



(2). by the periodical changes of replanting and drainage. 



On account of the time and duration of various drainage procedures, according to the 

 different kinds of ponds (nursing ponds, rearing ponds, holding ponds, and hibernation 

 ponds), rather different aquatics are to be expected in the different kinds of ponds. 



Also, the cool, rapidly flowing trout ponds differ from carp ponds, in this respect, 

 VTe have a free-current loving (reophile) water fauna which prefers cool trout ponds, and 

 a stagnation-loving (stagnophile) irater fauna which finds the warmer carp ponds better to 

 their liking. 



In the following pages, v;e will tell briefly the most important forms of aquatic life, 

 especially found in larger carp ponds which are drained during the vrinter months, and in 

 which natural food plays the greatest role. Its natural history should be essentially 

 knoTn in advance. 



Vforms 



Valuable foodstuffs are such bristle worms as Stylaris and Nais (of the Chaetopodae ) 

 which are often found upon Potamogeton vegetation and milfoil; also red mud-tube worms as 

 Tubifex and Limnodrilus . which dwell in the mud. 



31 



