[19] UTILIZING WATEE BY FISH-CULTUEE. , 1119 



continued rainy seasons, likewise disturbs the carp and causes them to 

 seek the surface, where frequently large numbers of them perish, if 

 severe frosts set in late in the winter season. Winter-ponds located 

 among hills should, therefore, in all cases be provided with ditches for 

 carrying off the superfluous water. 



Ponds which have a regular and abundant supply of water may 

 safely keep their fish during an entire winter without air-holes in the 

 ice. it is, however, advisable even in such ponds (as it is necessary in 

 ponds whose supply of water is scant) to make 3 or 4 large air-holes at 

 some distance from the fish-pit. These holes should be kept open all 

 the time so as to admit air into the water. The freezing of these holes 

 may be prevented by sticking into them large bunches of straw in a 

 perpendicular position. It is still better, after a firm cover of ice has 

 formed on the pond, to lower the level of the water from 10 to 20 cen- 

 timeters, so that extensive places filled with air may form near the 

 banks under the ice which slopes towards the center of the pond. In 

 these air-holes, which should be examined every day, there will show 

 themselves, wherever any deterioration of the water has taken place, 

 gas-bubbles of different size, rising from the bottom, dead beetles, and 

 other insects ; the water will gradually assume a dingy color, and the 

 fish" will come to the surface trying to catch a breath of air. If aid can- 

 not be afforded, by quickly airing the water or renewing it in part, the 

 ice should at once be broken all over the pond, and the water let off, so 

 as to save at least some of the fish by transferring them to other winter- 

 ponds. 



The airing of a pond is done in the most primitive manner, by re- 

 peatedly and violently pushing into the water large brooms or pieces 

 of wood or leather fastened to long poles. A more satisfactory method, 

 however, is to use a force-pump, whose hose is led to the bottom of 

 the pond. In order to distribute the air in as many small particles as 

 possible, the end of the hose is filled with a sponge, through which the air 

 escapes in numberless small bubbles. 



As winter-ponds are only used for harboring carp at a time when they 

 do not take any food whatever (their loss of weight being only 2 to 3 

 per cent, during this period, owing to the pause in all the functions of 

 life) they can receive quite a large number of fish — all the more the more 

 abundant the supply of air and water. More small than large fish may 

 of course be placed in the same pond area. As a general rule one may 

 count per hectare 50,000 to 100,000 one-summer's carp, 30,000 to 40,000 

 two-summers' carp, 15,000 to 20,000 three-summers' carp, and still fewer 

 older carp. 



The carp had best be removed from the winter-ponds when the water 

 in the raising-ponds has reached a temperature of 10 degrees C. or more; 

 therefore, generally towards the end of April or the beginning of May. 

 For wintering the spawning carp which are already selected when the 

 other ponds are fished, special small winter-ponds are constructed, 



