In the trout ponds at Eberswalde, i\dth a II and III class production rate (30 to 70 

 kilograms per hectar) were found about 1,000 aquatics per square meter of a weight of 5 

 grams • 



The fish biologist is familiar, of course, vdth the methods of such investigations. 

 For the practical fishbreeder, we recommend the use of a certain net, as furnished by the 

 National Hatcheries at Berlin- Friedrichslmgen, by means of which he will be able to 

 ascertain the relative fertility of his ponds and also their varjoxig productivity at 

 different times. 



This loiowledge is especially valuable in regard to hatching-ponds. 



3. The Flora of the Pond . 



From the viev;point of biology and v,ith regard to pond-cultural importance, the flora 

 of ponds may be best divided into the three classes of; 



(1) Surface plants 



(2) floating plants 



(3) Submerged plants 



Surface plants 



The surface plants are rooted in the bottom of the pond and their leaves and floral 

 shoots rise far above the vjater level. It is for this reason that they choose — preferably — 

 the more shallow parts and shores of ponds. Almost vdthout exception, the surface flora is 

 noxious from the viewpoint of pond culture, therefore should be kept down and for the 

 following, pidncipal reasons: 



(1) They contribute to "Lelta formation" by raising the bottom of the pond 

 (especially bull rush, reed mace, horsetail) or by starting floating lawns 

 which event\ially will also raise the bottom by sinking down to it. 



(2) They shade the water to such an extent that ponds (or parts of it) covered 

 by them make development of fish and productivity of aquatics practically 

 impossible. Also the oxygen content of the water is often reduced by the 

 growth of these plants. 



(3) They make it difficult for fish to find their food, even in not too-thickly 

 overgrown ponds. In this respect we quote the findings of Lundbeck. who 

 arrived at the follov.'ing figures for bottom aquatics — non consumed because not 

 discovered — in all of the ponds in Bemeuchen: 



Upon clear bottom 6.28 gram per sq. meter 



In case of submarine flora 6.41. " " " " 



In case of surface flora 8.29 " " " " 



(4) They deprive the pond of valuable plankton and work it into almost non- 

 decomposable cellulose, while their own decayed remnants form quite an amount 

 of cellulose and by themselves. This mud finally covers the bottom in 

 gradually thickening layers, and since it can hardly be decomposed even by 

 mud dwellers, it is of no food vailue v.'hatever and soon leads to desolation 



of the bottom. (In a nondrainable pond of only a few hundred square meters 

 and which v/as thickly covered Tdth reeds, I found a layer of cellulose mud 

 of 1.30 meter thickness and a water depth of only 60 centimeterl And this 

 condition is not unusual.) Also, extensive penetration of the bottom with 

 roots reduces the productive layers of decomposed matterand thus makes the 

 pond still more unproductive. 



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