[11] UTILIZING WATEE BY FISH-CULTURE. 1111 



III.— FILLING THE PONDS. 



After the construction of the pond has been completed, and the dike 

 has become thoroughly settled, the pond may be filled with water. New 

 ponds whose dikes have not yet been tested had better not be filled to 

 the desired height at once, but gradually. In sky ponds it will of course 

 take the water a longer time to gather, and in order to have them full 

 in spring, water should be allowed to gather in them in autumn. Wher- 

 ever the quantity of water needed for filling the pond can be obtained 

 at any time from springs, brooks, rivers, or lakes, it is advisable, for 

 reasons to which we shall refer later, to let the bottom of the pond be 

 dry during winter and until a short time before the pond is needed for 

 use. 



The filling of the pond is done by closing up the outflow-openings, 

 either by closing the sluice, by putting in the tap, or by placing the 

 flood-boards in the " monk," according to circumstances. In sky-ponds, 

 and those ponds whose supply of water is scant, every opening should 

 be firmly closed,, so as to prevent a loss of water, which, in connection 

 with the loss occasioned by evaporation, might easily prove very inju- 

 rious to the fish. The tap should, therefore, be driven in firmly, and if 

 necessary closed up with clay. The boards should also close firmly. 



Even in filling the pond, the "monk" proves superior to all other 

 outflow arrangements, as it allows the level of the water to be raised 

 quite gradually. For various purposes, however, it is of great advan- 

 tage to keep the water of the i)ond low in the beginning, and to have 

 no more water in it after it has been in use for some time. 



IV.— THE MANNER OF USING THE PONDS. 



For a complete fish-cultural establishment different kinds of ponds 

 are needed — spawning-ponds for propagating the fish, raising-ponds of 

 the first and second class for fish one and two years of age, ponds for 

 older fish (growing-ponds), winter-ponds for wintering fish of difierent 

 ages, and stock-ponds for keeping the fish which are intended for sale. 



1. The spawning-ponds. 



Good spawning-ponds form the basis of well-regulated carp-culture. 

 These ponds should be of such a character as to offer to the fish the most 

 favorable conditions for spawning, and to favor as much as possible the 

 development of the eggs and the young fish. 



The best spawning ponds are small sky-ponds having an area of only 

 one-tenth and, at most, one-half hectare. The bottom of these ponds 

 should be impervious clayey soil or a clayey sand soil. Wherever it is 

 impossible to construct suitable sky-ponds, ponds fed from rivers or 

 lakes may be used ; before entering the spawning-po nd the water should, 

 however, be filtered through large pits or boxes filled with coarse, washed 



