Figure h- — The DC power supply and commutator unit of the leading 

 device as used for field tests. 



portion of the suckers were used a second time but only after a lapse 

 of at least 2 days. In tests conducted below the critical voltage level, 

 brook trout ordinarily displayed so much activity that observations of 

 results with 6 specimens became difficult. As a result, the number was 

 reduced to a single fish per test with checks made on groups of 3 or ^ 

 when results indicated the need. 



In general, the fish were placed in the tank, allowed to posi- 

 tion themselves at will, and then the power was applied. Usually the 

 electrode most distant from the fish was made positive. Polarity was 

 reversed at random intervals 2 to U times during each test. 



The second phase of the laboratory experiments was concerned 

 with the relationship between voltage gradient and size of fish. The 

 most effective combination of duty cycle and repetition rate, esta- 

 blished from the first experimental phase, was applied throughout the 

 series of tests. Two hundred seventy-nine rainbow trout ranging from 

 9.2 to 2k. S inches were used as test specimens in these experiments. 

 The test procediire as previously described was followed. Each rainbow 

 trout was subjected to only one test to eliminate the possibility of 

 any residual effect of a previous electrical shock on its reactions. 



8 



