[9] 



POND CULTURE. 



i7i 



to be used lor one poutl, a suitable depth of water uiay be obtained by 

 Ibrniiijg- several ponds by constructing dikes rising on terraces one 

 above tlie otlier. 



Taking, for example, an area 700 meters long, a c, and 200 meters 

 broad, equal to 14 hectares, whose grade per 700 meters is 5 meters, 

 c f?, and therefore 2.5 meters in the middle, we would have to divide 

 it. into five parts by constructing dikes at the points marked a, whereby 

 we would obtain a maximum depth, a h, of 1 meter and a medium depth, 

 e e, of 50 centimeters. (In order to show these depths in the limited 

 space of the illustration different scales had to be adopted for the lines 

 a c and o cl, which, however, will not prevent it from being sufQciently 

 intelligible.) The ground should not slope too abruptly, as, in spite 

 of terraces, the water could not be prevented from rising too high, 

 and as, moreover, very high and therefore expensive dikes would be 

 required. In such cases it may be recommended to utilize the uj^per 

 parts as meadows. Wherever the above-mentioned conditions, de- 

 scribed as either necessary or favorable, do not exist at all, or only in 

 part, the laying out of a pond (if not entirely impossible) will be very 

 expensive, and will also render fish-culture a costly experiment. 



3. The quantity of water. — It should, in all cases, be possible 

 to furnish the i)ond with a suflicient quantity of water, which, if possi- 

 ble, should be fresh. Ponds generally are found in plains or on low 

 ground, and receive their water either from springs, brooks, rivers, or 

 from other ponds and swamps, or their sui)ply is furnished by the rain 

 and snow water flowing from hills and mountains. Ponds which are 

 su])])lied with water in the last-mentioned way are termed "sky ponds," 

 I as tliey are entirely dependent on the jjioisture of the atmosphere. 

 I Ponds should at all seasons of the year have the necessary and un- 

 varying, as far as possible, depth of water, so as not to endanger the 

 j life of the fish during hot and dry summers. Before laying out a pond 

 ' special attention should be paid to the way in which water is generally 

 j supplied to the ground which has been selected ; and it will be neces- 

 sary to ascertain wiiat was the average (puuitity of water supplied 

 ' durinj^^a number of years, and more especially what were the conditions 

 j of such supply during the last months of summer. The most reliable 

 dei)th of water will be found in those ponds w^hich are filled by canals 

 j from neighboring brooks and rivers, or through which rivers flow, or 

 ' which draw an ami)le supply of water from never-ceasing springs. 



