REARING 211 



the better for the fish. Much care should be taken 

 in adjusting the shoots. When they are working 

 properly you will see an effervescence of bubbles rising 

 to the surface far down the pond in a line with the 

 current. This shows that plenty of air is being carried 

 into the water. 



To prevent the fish from escaping over the outlet 

 a screen is inserted in front of each dam. These 

 screens are made of perforated zinc stretched on strong 

 frames of oak which reach quite to the bottom of the 

 brick floor of the outlet. They slide in grooves and 

 are made to fit closely, but not so tightly that they 

 cannot be drawn out when necessary. 



As with the screens in the hatching-boxes, so with 

 the screens for the ponds, it is advisable to have them 

 sloping with their lower end up-stream. In this 

 position they are more easily cleaned, and there is no 

 longer the old danger of any weak fish being forcibly 

 sucked against a perpendicular outlet screen. 



In the perspective (fig. 16) a portion of the brick- 

 work is supposed to have been removed, in order to 

 expose the screen and to show the mode in which the 

 water-boards are inserted, and the levels of the water. 



The importance of having the screens ' fish-tight ' 

 will be most fully realised when, through a small hole 

 or an ill-fitting frame, many hundreds uf your trout 



p 2 



