110 FISH FARMING I 



enough apart to permit of the fish passing from, pool to pool in- 

 a volume of water flowino- between them (the boulders). The 

 dotted line and arrows show the direction of the current, and 

 also point to one of the many ways through the pass for the 

 fish. If necessary, they can rest ait any pairt of the pass in the 

 slack water caused by the boulders, and this, in practice, they 

 are found to do when the pas is of considerable length. -Need- 

 less to say, the fish mount against the arrows, entering, of 

 course, at the lower part of the pass. In the drawing the num- 

 ber of rows of boulders is less tham would actually occur in a 

 pass, but sufficient to show the method of working. It is net 

 advisable to have more than a foot rise in each pool, and thus 

 an obstacle 10ft. high would be preferably overcome by a suc- 

 cession of 10 pools. In the same way, it is necessary to keep 

 the pools as long as possible, otherwise what is intended for a 



INNER 



oF PASS 



Fig. 23. Section of a Fish-pass. 



steady volume of " dark " water will become a broken, foam- 

 ing, " white " torrent, and no fish would attempt to run, up it, 

 In Figure 23 you will see that the boulders are well let into 

 the bed of the pass and cemented firmly, otherwise they would 

 become washed out of place, and thus the whole scheme of the 

 pass would be destroyed. 



In addition to the proper arrangement of the boulders in 

 the pass, two other matters of importance have to be taken 

 into serious consideration. The first of these is the fact that 

 the intake at the top of the pass must be wider than the pass 

 itself, or otherwise the latter would be short of water half 

 way down. The other point is that, in order to gain greater 

 length and consequently less abrupt " fall " in the pass, it is 

 preferably (although not absolutely necessary) constructed in 

 a curved or serpentine form, and this being so the volume of 

 water naturally flows in the direction of what I have termed 



