[3] UTILIZIKG WATER BY FI8H-CULTURE. 1103 



it is preferable to have the spriugs located at some little distauce from 

 the edge of the poud. If springs coutaiu much irou, lime or different 

 gases, they will make the water of a poDd entirely unfit for fish-culture. 



Sky-ponds share this advantage with si)ring-i)onds, that, owing to 

 the absence of a supply of water fro/n a, river or brook, they are toler 

 ably well protected against enemies of the lish, although occasionally 

 the spawn of pike and other fish is introduced into them by aciuatic 

 birds. During hot summers these ponds have the disadvantage that, 

 especially if they are not very deep, the water easily becomes too hot, 

 or even evaporates entirely. It is therefore a great advantage for sky- 

 ponds if a number of water-pipes empty into them. 



Ponds may be dug out, or, by using the existing grades of the land, 

 be constructed in such a manner as to prevent the outflow of the water 

 by means of dikes. This last-mentioned method may be specially 

 recommended as being cheap and as the quickest way of reaching the 

 object in view. In this manner large or small, deep or shallow ponds 

 may easily be constructed in any country which is not absolutely level. 

 By a skillful use of the ground small sheets of water measuring but a 

 few meters in length will suffice for the construction of large ponds. 



For centuries pond-culture has been almost exclusively devoted to the 

 raising of carp, which owing to its rapid growth, its hardiness, its quick 

 increase, and its great and general popularity as a food-fish, is on the 

 whole the best paying fish for pond-culture. We shall, therefore, prin- 

 cipally treat of carp-culture, and afterwards give a brief review of the 

 raising of other fish in ponds. 



A distinction should be made between ^kh-culture in ponds and the 

 keeping of fish. The former aims at increasing the number of fish and 

 raising them until they have reached a sufficient size to make them mar- 

 ketable, whilst the latter confines itself to fattening the fish which have 

 been obtained from fish-culturists when quite young. Any pond or 

 puddle having suitable water, and a depth of 4 to 1 meter, is suitable 

 for the keeping of fish, even if there is no chance to let the water off; 

 whilst regular fish-culture in ponds requires a number of different and 

 properly arranged ponds. 



It will be best to construct carp-ponds in the midst of fertile fields, 

 surrounded by gentle hills, protected against the east and north winds 

 and quite open towards the south, so that during the day the sun may 

 shine on them and heat them. The most favorable bottom is clay, which 

 does not allow the water to filter through into the depths of the ground, 

 and which offers the greatest advantage for the development of rich 

 fish-food. Marshy or sandy bottom is not so good ; the latter especially 

 is very poor and particularly apt to let the >vater filter through, unless 

 the entire bottom of the poud is covered with a thin liiyer of clay. Shal- 

 low ponds are preferable to deep ones, because the production of fish- 

 food does not depend on the quantity of water, but on the extent of the 

 bottom, and because deep ponds do not so easily reach the desired de- 



