96 FISH CULTUEE 



from a common open race or sluice are most 

 desirable for many reasons. They are more 

 easily worked and attended and, what is much 

 to be desired, a simple drainage system can be 

 more easily provided. In this way also there 

 can be more ponds, with a less amount of water 

 per minute than when built separately. Al- 

 ways, in laying out ponds, care should be taken 

 to make them suitable for various sizes and 

 ages of trout, and to arrange them with a view 

 not only to their being worked conveniently but 

 also for the advantageous growth of fish. 



Ponds for trout which have arrived at full 

 maturity can be built nearest the spring or 

 where the water is coldest, because, having at- 

 tained their growth, warmer water is no longer 

 desired, and also because fish three or more 

 years old naturally spawn before the two-year- 

 olds, and cold water has a tendency to retard 

 the ripening of their eggs. The longer this 

 function can be delayed within reason, the bet- 

 ter are the chances for hatching healthy young. 



It is advisable to construct ponds for two- 

 year-olds next; those for yearlings still farther 

 away; and those for fingerlings and nursery 



