242 The Lije Story of the Fish 



place the wild trout with hatchery-reared brood fish as a 

 source of eggs, so that the resulting offspring would be an 

 addition to the native stock, not merely a processing of the 

 native stock by man instead of by nature. The third step was 

 to find ways of increasing the survival of the hatchery fish 

 after they were placed in natural waters, the most obvious 

 way being to plant them at a much larger sizej and here a 

 radical change in thinking had to come about. 



As long as the principal object of the hatchery was to 

 hatch a great number of eggs and turn out a great number 

 of small fingerlings, no large volume of water was needed, 

 and the belief that the best source was a pure spring with a 

 temperature of around forty degrees was justified by the 

 high percentage of hatch and the freedom from disease. But 

 at that temperature growth is painfully slow 5 rainbows, for 

 instance, held throughout the' summer after hatching and 

 the whole of the following winter, will not have reached 

 catchable size by the opening of the fishing season. At sixty 

 degrees they will, if properly fed, attain that size in less than 

 six months. The hatchery man has had to change his ideal. 

 The small, pure, forty-degree spring gives way to a source 

 of water with a constant temperature of around sixty de- 

 grees and a large volume of flow. Such sources, it may be 

 added, are very few and hard to find. 



Strains of fall-spawning rainbow have been developed and 

 maintained in hatcheries as brood stocks j under ideal condi- 

 tions eggs taken from them in October turn into catchable 

 fish at the opening of the season in the spring. These fish 

 cost more to produce than the fingerlings — they eat more 

 and are more susceptible to disease. Inexpensive foods and 

 methods of mass disease prevention and cure have had to be 

 developed. The diehards have argued that even under the 

 best conditions, the cost of producing the large fish was so 

 great as to more than offset their higher survival. Experi- 



