[9] UTILIZING WATER BY FISH-CULTURE. 1109 



every board a strong ring of galvanized iron is firmly fixed by screws, 

 so that the boards can easily be raised with a hook. It is not advisable 

 to make these boards higher than 20 centimeters, as in that case they 

 are difficult to handle, and whenever a board is raised the water rushes 

 into the " monk " with too great force. The very circumstance that the 

 water always flows off at the top, and consequently flows oft' with little 

 pressure, thus neither carrying fish away with it, nor injuring the bot- 

 tom or sides of the outflow ditch, is one of the principal advantages of this 

 arrangement. Another advantage is this, that by means of the boards 

 the level of the water can easily be brought to the desired height, at 

 which it will remain j and when the opening of the " monk " is sufficiently 

 large, even large masses of water, occasioned by violent rains, are easily 

 led out in a very short time. To exclude the possibility of the fish es- 

 caping, a grate of galvanized iron is inserted in a wooden frame above 

 the upper board. To prevent any unauthorized person from meddling 

 with the boards, the top of the "monk" is closed by a lid on hinges. 

 To prevent the stopping up of the grate by aquatic plants, dead leaves, 

 and other articles of the kind carried along by the current, which mostly 

 float on the surface, or immediately below it, it may be recommended to 

 place a box constructed of two boards joined at a sharp angle in front of 

 the pond side of the perpendicular outflow pipe. This box should rise 

 20 centimeters above the highest water-mark and be as far distant from 

 the bottom of the pond. The water will then unhindered flow into the 

 " monk," whilst all objects floating on the surface will gather in the box, 

 whence they can easily be removed from time to time. After it has been 

 ascertained what time it takes the level of the pond — after one of the 

 boards has been removed — to sink to the edge of the next board, one 

 will always know in what time the pond can be drained, which is of con- 

 siderable importance, as sometimes the fisheries have to take place at 

 a certain time. 



The outer end of the horizontal outflow pipe (both in the "monk," and 

 in the tap outflow), after it has left the dike, is generally extended 1 to 

 2 meters, in order to prevent damage to the dike such as being washed 

 out from below. It will also be well to cover the first 5 to 10 meters of 

 the bottom of the ditch with stones to prevent the ditch from being 

 washed out, which might easily cause its walls to tumble down. 



As wooden pipes will keep best when under water, it is advisable to 

 place a small sluice in the outfldw ditch, high enough to keep the out- 

 flow pipe under water all the time. When the pond is drained this 

 sluice must, of course, be removed, so that the bottom of the pond may 

 be laid entirely dry. 



In ponds located in level country " monks " of suitable width will 

 suffice to quickly lead out the superfluous water and maintain the uoji-- 

 mal level of the pond, even during violent rains or when the snow melts 

 in spring. Ponds located between mountains or hills, or those fed by 

 brooks or rivers which are apt to overflow, must be protected against 



