166 FISH CULTUEE 



desired to change them. A natural habit of mid 

 trout is to rise towards the surface for food, and to 

 ignore anything excepting living creatures on the bot- 

 tom. The initial food for young trout in captivity, 

 as I have said, is liver and thick milk, both of which 

 sink rapidly to the bottom. When they begin to feed, 

 the advanced fry seize the liver or milk as it sinks, 

 and soon learn to pick it up from the gravel. They 

 keep this up after being transferred to the ponds. 

 After the lapse of several months the young trout, 

 having reached the dignity of fingerlings, have their 

 food changed to chopped lungs. Now lungs are 

 lighter than water, and therefore float. When first 

 introduced to this food the young trout pay little at- 

 tention to it, not coming freely to the surface for it, 

 but apparently waiting for it to sink; and it some- 

 times requires two or three weeks of very patient work 

 to teach the youngsters to rise to the surface for their 

 food. 



After the young fish have remained in the 

 nursery ponds or races until their size has ap- 

 preciably increased, it is important that they be 

 sorted according to size, and transferred to the 

 rearing-ponds v^here they must be fed by hand, 

 and regularly given as much food as they will 

 consume, but no more. 



Feeding Yearlings. — ^When the trout reach 



