(2.47 acres) doubled the increase. But great success vjas also shoim with every organic 

 fertilization in practice. The hi^h productiveness of the villF.r-e pond with its liquid 

 manure inflows is generally known. 



The manner of conducting organic fertilization has already been discussed elsewhere. 

 Since the amounts of organic fertilizers are insufficient they can only be aoplied in 

 few ponds. Extension and brood nursery ponds, which especially permit repeated fertiliz- 

 ation are to be preferred. These ponds act to the growing pond somewhat like the garden 

 to the field and therefore justly merit this preference. The green fertilization which 

 was already discussed, is likewise a form of organic fertilization. A verj' special pro- 

 cedure has been developed in the Luenebere Heath for the fertilization of ponds which are 

 naturally extremely poor in nutritive substance. The pig stalls are erected on poles in 

 the pond. Feces, urine and all food residues flow into the ponds. The method has excell- 

 ent results and reminds of Chinese customs. A good fertilization and "soil cultivation" 

 can also be obtained by keeping pigs in drained fallow fenced-in nursery ponds. 



Stable manure and compost are spread upon the pond bottom in the distribution of 

 fertilizers. They retard at the same time a luxuriant plant growth. For the production 

 of daphnidae, Naumann advises a first time application of manure in a concentration of 

 5:1000 (which would be about 20,000 to 30,000 kg per hectare, 17,813 to 26,720 pounds 

 per acre), and then every week in a concentration of 1:1000 in flat ponds. Fish meal, 

 which has been found especially valuable for the production of cladocerae, is simply 

 strewn about. Liquid manure can be released into ponds only in small portions and only 

 once or twice about every eight days. Slaughterhouse scraps and se-wage fertilizers are 

 to be given as frequently as possible and in small portions. They are simply left on the 

 flat shore in the pond. 



This distribution is necessary, because every organic fertilization aside from its 

 extraordinarily good production increasing action, also harbors a great danger: The pro- 

 duction of oxygen shortage. This naturally occurs especially in warm weather. For the 

 same reason the organic fertilization does not come into question for trout ponds. The 

 progressive pond manager should make frequent early morning tests of organically ferti- 

 lized ponds as to their oxygen content, and should also make especially careful observ- 

 ations on the fishes. The occurrence of gill rot is undoubtedly favored by organic 

 fertilization. 



The successes of organic fertilization have rightfully suggested the use of house- 

 hold and kitchen sewage and especially sewage of municipal canal systems in so-called 

 sewage fish-pcffids for fertilization purposes. The cleansing of sewage vrater in the best 

 industrial manner is naturally in the foj-eground with such establishments. 



The sewage fish-pond procedure is nothing else than one of the many biological 

 sewage cleansing procedures and will be judged in the future according to this economy. 

 Kisker showed that in the consideration of purely operating costs, sewage fish-pond 

 arrangements can shut off with an excess and consequently are superior to all other 

 cleansing procedures. However, in consideration of the total building costs and of the 

 operating costs, the sewage cleansing is more advantageously achieved by an "activated 

 sludge" equipment. 



The construction of sewage fish-ponds must not cause large expenses. In other 

 v;ords, if sewage fish-pond equipments are to be 'profitable, the soil conditions must 

 be favorable. Large soil movements make the construction too expensive. The letting 

 in of fresh water with which the mechanically pre-clarified sewage nust previously have 

 been diluted at least four- fold in mixed canalization, must also not cause any substantial 

 expenses in operation and in the construction. Reserves of fresh water must always be 

 available in optional quantities. It is best if the sewage can be distributed over the 

 entire pond surface. V/here all these prescribed conditions are given, the sewage fish- 

 pond construction must be absolutely recommended, inasmuch as values are hereby created 

 upon the native soil. 



2,000 inhabitants require about 1 hectare (2.^6 acres) of pond surface. The natural 

 yield in sewage ponds amounts to approximately 500 kg per hectare (/iA5 pounds per acre), 

 the losses are hardlj' higher than in usual carp ponds. 



172 



