Figure 2. --Voltage gradient pattern in experimental area. Lines 

 connecting points of equal voltage gradient (volts per inch) 

 have been smoothed. Water temperature: 50° F. (10 C.) 

 Water resistance: 6, 300 ohms per cubic inch (16,000 ohms 

 per cubic centimeter). 



possible so that the fish, having 

 little or no visual orientation, 

 tended to move downstream to the 

 electrical field without being 

 crowded or forced. The fish which 

 passed through the field were cap- 

 tured in the wide channel, while 

 those which avoided the field were 

 collected in the narrow channel. 

 Previous observations showed that 

 five minutes of darkness were suf- 

 ficient time for the majority of 

 the fish to move downstream; at the 

 end of five minutes the traps were 

 closed, the lights turned on, and 

 the fish counted. We counted and 

 removed those fish which had not 

 moved down but did not consider 

 their numbers in the guiding re- 

 sults. The results were measured 

 by a comparison of the number of 

 fish in the narrow channel with the 

 total number of fish that moved 

 downstream, expressed as a percent- 

 age. 



cm. in length, averaging 10.3 cm. (3 to 5 

 inches, average 4 inches). 



EXPLORATIONS 



In order to provide experimental conti- 

 nuity we used pulsed direct current, found 

 most promising by Raymond (1956) cind pre- 

 vious investigators. Water resistance was 

 controlled by the addition of fresh water or 

 table salt as required to maintain a resist- 

 ance of 6300 to 7500 ohms per cubic inch. 

 The electrical array was set at an single of 

 40° to the direction of water flow, and the 

 voltage was maintained at 210 volts across 

 a 30-inch electrode spacing. The current, 

 when interrupted, was pulsed at a frequency 

 of 3 per second with a duration of 30 milli- 

 seconds — a duty cycle of 0.09. 

 The measured voltage gradients 



We conducted preliminary trials in which 

 the electrode array was energized in six 

 different ways. This exploration was for 

 two purposes: (1) To provide some compari- 

 son of 60-cycle alternating current with 

 steady and pulsed direct current, a compari- 

 son not previously made here or reported 

 elsewhere, and (2) to provide a basis for 

 the design of another experiment involving 

 the role of field polarity in electrical 

 guiding. The six methods of array energiz- 

 ing are listed below, with a short title 

 for each: 



ge 



(volts per inch) —'are pre- 

 sented in figure 2 as lines 

 connecting points of equal 

 voltage gradient. 



All tests were conducted 

 in as near total darkness as 



A/ The electrode spacing and 

 voltage gradient sire ex- 

 pressed in English imits 

 in Einticipation of prac- 

 tical field studies. 



60-cycle alternating current, 

 peak to peak 



210 volts 



3. 



5. 



Continuous direct current, 210 volts 



Pulsed direct current in which the polarity 

 of the field was constant, 210-volt pulses 



Pulsed direct current with the field polar- 

 ity alternated, 210-volt pulses 



Pulsed direct current, electrodes sequen- 

 tially energized with the positive polarity 

 upstream 



Pulsed direct current, electrodes sequen- 

 tially energized with the positive polarity 

 downstresun 



A.C. 



D.C. 



Pulsed D.C, 



Alternate 

 Polarity 



Positive 



Upstream 



Positive 



Downstream 



