The influence of the amount of stock and of the density of stock within a given pond 

 have been discussed already. Thanks to the valuable investigations of Salter, Nordquist 

 and of Contag, this influence has been more exactly defined, and for the first time. 



Vi'ith regard to other factors — species, stock combinations, etc, — v;e will establish 

 here the respective rules. V.'eather changes, changes in cultivation, etc. will bring about 

 yearly variations in the productivity of ponds. 



The "stock figure", that is, the proper niimber of fish for a given pond is found or 

 estimated through the computed total increase. In case of feeding the fish and by 

 fertilizing the pond this increase is the total of natural increase through feeding plus 

 increase through fertilization. V.'ithout feeding and fertilizing the total increase is 

 just natural increase. The computation can be done through the follov/ing, simple formula: 



"Stock figure" eq. 



_plus allowance for losses. 



total increase kg 



increase in number kg 

 The allowance for losses has to be based upon local experiences. Average figures 

 for same (in percentage) will be found in table 18, The increase in number (weight of 

 fish taken out minus weight of fish put in) is at the discretion of the fishbreeder, of 

 course. For normal estimates see table 18, 



Table 18, 



Normal average weight (per fish) of added stock, yearly weight increase 

 (per fish), and losses of different classes (age) of pond fish. 



A pond of 2 hectar (about 5 acres) of second class productivity (table 17) has 

 an increase per hectar of about 150 kilograms of fish (non fed) and a total increase, 

 that is, natural increase of 300 kilograms altogether. It is to be stocked with 2 

 year old carp of a weight of 350 grams per fish. The carp shall be fished out at a 

 v/eight of 1350 grams. 



The desired stock increase (individual weight) is therefore 1000 grams. Losses 

 are 5 percent. Hence: Stock figure 300 plus loss allowance 300 -f 15 = 315. 



1 

 It follows that 315 carp of a weight of 350 grams are to be set out in this pond. 



If stodcing with mixed stock (yearlings and 2 year old, for instance), the total 

 increase can be divided, so to speak. One can figure, for example, 200 kilograms in- 

 crease for 2 year old and 100 kilograms increase foi' yearlings. Or two yearlings with 

 a v/eight increase of 350 grams per fish are figured per each 2 year old with a weight 

 increase of 1000 grams. 



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