p\ilsated direct current at a duty cycle of 0.66 and a repetition rate 

 of 3 pulses per second. Tests were made at two levels of electrode volt- 

 age, 1^0 and 170 volts peak. The electrode current at l50 volts was 3.5 

 amperes resulting in a peak load of 525 watts. The resultant voltage 

 gradient which was produced in the water between the electrodes is illus- 

 trated in Figure 2. A fairly intense electrical field existed near each 

 electrode with the lowest voltage midway between them. The gradient 

 could have been made more uniform between electrode centers by increasing 

 the immersed area of both electrodes. The presence of a higher voltage 

 gradient at the cathode in both of the field installations (Carp Creek 

 and Little Ocqueoc River) is probably due to the greater effective immersed 

 area of that electrode. 



The 11 suckers were tested individually. Eight of them defin- 

 itely responded to polarity by displaying an immediate movement toward 

 the anode. Of the three that failed to respond, one escaped upstream from 

 the center of the electrical field, and 2 were electronarcotized imme- 

 diately upon the application of power. In addition, 2 "free" suckers 

 accidently entered the area and both went directly to the anode. 



Although the number of tests at Carp Creek was so small that 

 conclusions are limited, the behavior of the few fish indicated beyond 

 any reasonable doubt that a suitable galvanotaxic response could be in- 

 duced among suckers. The low water temperatures may have been the reason 

 for the failure of suckers to respond in the test tank, especially in 

 view of the fact that electrical conditions in the laboratory were exper- 

 im.entally more ideal. 



Laboratory tests on brook trout . — The second series of tests in 

 the laboratory was made with brook trout, ranging in length from 7.3 to 

 11.5 inches. The water temperature during the tests remained between 36 

 and 38° F. Brook trout swam immediately and persistently to the positive 

 pole when subjected to the proper voltage gradient of pulsated direct current, 



Voltage levels causing electronarcosis in brook trout varied in- 

 versely as the duty cycle. A similar relationship existed in the attain- 

 ment of a good response (Fig. 5); therefore, a duty cycle of 0.66 was con- 

 cluded to be the most desirable since it permitted the use of the lowest 

 voltage levels. 



Within limits, the repetition rate (pulses per second) was not 

 extremely critical. Elxcellent responses were obtained from the brook trout 

 at, 2 to U pulses per second. However, a lower repetition rate often al- 

 lowed the fish to make a turn during the "off" period, and a higher repe- 

 tition rate resulted in galvanotaxic reactions comparable to those encoun- 

 tered in tests with continuous direct current. In general, an application 

 of continuous DC will produce a response to polarity but the ability of 

 the fish to move appears restricted. 



10 



