244 T^h^e Life Story of the Fish 



nels which would otherwise go dry. He has tried the trans- 

 plantation of beavers in the hope that their dams would 

 accomplish the same result, but whether the net effect of 

 this animal is helpful or harmful to trout has not yet been 

 decided. He has tried introducing certain organisms which 

 form fish food into lakes where they were absent, but with- 

 out much success. A body of water, like a piece of land, has 

 a limited capacity to produce. Efforts in a more fundamental 

 direction, fertilization, he has also tried, but so far without 

 proven results in natural waters. One of his most successful 

 inventions is a method of nullifying the effects of the sports- 

 men's own negligence. Trout lakes sometimes become over- 

 run with minnows which have been brought from other 

 waters for bait. When this happens, the whole fish popula- 

 tion — usually a very few trout and hundreds of thousands of 

 useless fish — ^is poisoned with a chemical which is compara- 

 tively cheap, does no harm to warm-blooded animals nor to 

 many of the invertebrates which form trout food, and loses 

 its effectiveness in a comparatively short time. The lake can 

 then be re-stocked, and if catchable fish are used not one 

 season's fishing need be missed. All goes well until the un- 

 desirable minnows return through the carelessness of anglers 

 and again over-run the lake. 



The present-day thinking of trout culturists and conserva- 

 tionists may be summarized along these lines: 



1. Brood stocks, hatchery-reared and maintained, should 

 be the main sources of t^g supply. Eggs should be taken 

 from wild fish only where facilities are inadequate for them 

 to spawn naturally. 



2. The most economical method of stocking heavily fished 

 waters is with catchable-sized fish planted just before and 

 during the season. Fingerlings are more economical for 

 lightly fished waters. 



3. The old type, cold spring hatcheries must be retired 



