The Forage Problem 387 



When we raise other stock-feed we find a few perfectly 

 definite things to be done: 



1 . We clear a field and prepare it. 



2. We fence it to keep out enemies and undesirable 

 competitors. 



3. We plant it with selected seed; and after a 

 period of growth, 



4. We use the crop at the time of its maximum 

 value. 



All these things we shall have to do if we ever have 

 a real fish culture. The first two of these things are 

 usually cared for in the construction of fish-ponds ; the 

 other two are generally neglected. 



The forage problem is less simple than is the raising 

 of pigs on clover, for at least two reasons: 



1. Plant foods are not eaten directly by the more 

 valuable fishes, and often there are a number of turns- 

 over of the food stuffs before the fishes are reached. 

 For example, diatoms and other synthetic plancton 

 organisms are eaten by water-fleas and midge larva;, 

 that are in turn eaten by little fishes, that are eaten by 

 big fishes. There must be at least two turns-over — 

 one kind each of plant and animal forage — since the 

 desirable food-fishes are carnivorous. 



2. There may be one or more changes of diet during 

 development. Thus the pike when newly hatched eats 

 such water-fleas as Simocephalus, (see fig. 92 on p. 186) 

 picking them one by one with automatic regularly- 

 timed snappings of its jaws. When grown a little 

 larger it eats midge larva;, mayfly nymphs and other 

 small insects. Stih later, it eats large insects and 

 mixes smaU fishes in its diet; and as it attams full 

 stature it restricts its diet to frogs and larger fishes. 

 When grown it takes hardly anything smaller than a 

 golden shiner. 



