20 FISH FARMING I 



surement. The ends of the channels are covered by slanting 

 perforated zinc screens'. They atfe slanted, and in the manner 

 shown, to get the greatest aivailaible surface and to prevent, 

 as far as possible, debris accumulating on them. These screens 

 may be made to slide in and! out, but it is not necessary 

 nor advisable, as they are ap<t to be left out.. The supply of 

 water through the channels is controlled by a small hand 

 sluice at M, which in the drawing is 1 shown shut down. The 

 line s T is the highest level to which the water in either the 

 redd A or the channel G should be permitted to rise. This 

 level can always be adjusted at the sluices D D D and D (in Fig. 

 3). Do not attempt to adjust the height of water in the chan- 

 nel G by means of the hand sluices M; they are merely to 

 regulate the supply to the redds. Six inches of water at least 

 is maintained in the channel G above the top of the wooden 

 channels. These wooden channels ought never to block, but 

 should anything of that nature occur, off with the screens at 

 each, end, lift the hand sluice right out, and, if necessary 

 (which can hardly ever be the case) force the obstacle out 

 from either end. The channels are shown parallel to the sur- 

 face, but they may be made to fall from G to A, never from A 

 to G. With a normal supply of water in the main river, only 

 a small quantity need be flowing over the sluice D D D ; but in 

 case of flood adjust all three sluices (in Fig. 3), so that as 

 much water as possible passes through the surplus water chan- 

 nel and out at H and E E (also Fig. 3). Do not forget, how- 

 ever, that no obstruction exists in the main, river, which should 

 be the principal means of disposing of flood water in the ordi- 

 nary way. In the drawing the shape of the redds, the surplus 

 water channel, and the main river are, of course, merely sup- 

 posed ; the real shape depends upon the contour of the banks, 

 but the redds should be formed in as direct line as possible, 

 in order to ensure an even flow of water over them. 



I do not recommend the formation of protected redds in 

 positions that present great natural difficulties. It may 

 happen, however, that the only spawning grounds en one's 

 own estate are so situated, and then it becomes necessary to 



