The variations in the galvanotaxic response of the brook trout 

 with respect to voltage gradient and duty cycle are also shown in 

 Figure 5. At low voltage gradients the response of the brook trout in- 

 dicated only discomfortj whereas at a higher voltage gradient^ but one 

 still below those which stimulated movement toward the anode^ the reac- 

 tion of the majority of the brook trout was persistent alignment along 

 equipotential planes or at right angles to the flow of current. In con- 

 trast^ the white suckers appeared to assume this position only by chance 

 and could be easily driven from it. At still higher voltages, brook 

 trout showed good response after a period of violent circling. With ad- 

 ditional increases, voltage levels were reached which produced immediate 

 and determined movement to the anode. 



Laboratory tests on rainbow trout ,— Two hundred seventy=nine 

 adult rainbow trout, ranging in length from 9^2 to 2I4.5 inches, were used 

 in a series of tests to determine the relationship between voltage gra- 

 dient producing the desired response and the size of the fish. Duty cycle 

 and repetition rate were held constant at 0.66 and 3 pulses per second, 

 respectively. The water resistivity throughout the tests was approxi= 

 mately 3,000 ohms per inch cube. For the purpose of testing, the fish 

 were divided into 16 one-inch length classes. 



It would have been desirable to test each individual fish through- 

 out a range of voltage gradients. This procedure was inadvisable because 

 fish that had been subjected to a series of exposures were electronarcotized 

 in subsequent exposiires at a lower voltage level than that which originally 

 would produce the same condition. Therefore, each rainbow trout was sub- 

 jected to only one voltage gradient. 



The response of each fish could be classified into one of 7 rea- 

 sonably distinct types of reaction as listed below? 



1. None No response to polarity. 



2. Poor. Fish meandered and circled considerably 



before displaying response to polarity, 



3. Fair Fish, with little circling, went to the 



anode . 



h- Excellent Response immediate and determined. 



5. Good. Good response, but movement weak — voltage 



a little too high. 



6. Over-control. .... .Voltage excessive, movements exaggerated 



and devious, electronarcosis imminent, 



7. Immediate electronarcosis. 



12 



