116 PRACTICAL TROUT CULTURE. 



lated. If too much current is given through the 

 pond the weaker fishes will be carried against the 

 lower screen, their gill-covers closed by the press- 

 ure of the water, and death soon ensue. If too 

 little is afforded, they may die from want of suffi- 

 cient oxygen. The plants previously mentioned 

 here again perform good service in oxygenating 

 the water, a less current being allowable in a pond 

 whose bottom is completely covered with aquatic 

 vegetation than in one in which the bottom is bare. 

 It is well that a constant watch be kept over the 

 pond during the first day after the transfer of the 

 fry, and the current regulated by observation. 

 No rule can be given on this point ; practice and 

 observation can alone suffice. 



As the interstices of the fish screen must, of 

 course, be very small, they will readily become 

 clogged with dirt, which will, spite of all care, 

 find its way into the water. Summer and win- 

 ter, every high wind will blow into the pond a 

 quantity of straws, leaves, and other rubbish 

 which, if allowed to accumulate upon the fish 

 screen, would soon entirely close it, damming the 

 current, and causing an overflow. To prevent this, 

 the leaf screens mentioned on page 38 must be 

 placed above the fish screens, and if much trash 

 finds its way into the pond, two and sometimes three 

 of these will be required. To clean these, raise 



