The fish were released in the center 

 of the array (between rows 5 and 6) from a 

 rectangular enclosure made from small-mesh 

 wire screen fitted with wooden laths for 

 support, the inside dimensions being length, 

 4 feet; width, 4 inches; and height, 15 1/2 

 inches. The enclosure was raised out of 

 the water by means of a bridle and a line 

 running through pulleys on the ceiling. 

 After the array was energized, the operator 

 stationed at the electronic switching unit 

 pulled the line to release the fish within 

 the moving electrical fields. 



By means of an electronic switching 

 unit developed in the Seattle laboratory, 

 pairs of the rows of the electrodes were 

 energized successively to establish a se- 

 quence of pulsating, direct-current fields 

 that moved in the direction of positive 

 polarity. In the north block, the positive 

 row of a pair of energized rows was always 

 to the north. Figure 1 shows for the north 

 block the start of the sequence when the 

 first set of electrical fields is estab- 

 lished by energizing the second and third, 

 and the sixth cind seventh rows of electrodes 

 simultaneously. The progress of the entire 

 sequence through the electrode rows is indi- 

 cated in table 1. As the table shows, the 



Table 1. — Sequence for energizing electrode rows to set up 

 moving electrical fields in laboratory array. 



Polarity 



Change in 

 polarity 



First 



Second 



Third 



Fourth 



Sequence 



begins 



again 



Row Row Row Row Row Row Row Row How Row 

 1 23456789 10 



(-) (♦) (-) (♦) 



{-) (♦) (-) (♦) 



(-) (♦) (-) (♦) 



(-) (♦) (-) (♦) 



(-) (♦) 



(-) (♦) 







sequence is automatically repeated after the 

 tenth row of electrodes has been energized. 

 The frequency and duration determine the 

 rate and length of time each pair of rows of 

 electrodes is energized. For example, at a 

 setting of 30 milliseconds pulse duration 

 and frequency of 2 pulses per second, a pair 

 of rows is energized 30 milliseconds with a 

 lapse of 470 milliseconds before the next 

 pair is energized. The total time to ener- 

 gize the four sets of electrical fields in 



the desired sequence (from rows 2 and 3 

 through row 10) at the cibove conditions of 

 frequency and duration is 2 seconds. With 

 pulse frequencies of 5 and 8 pulses per 

 second, at a pulse duration of 30 milli- 

 seconds, it required .8 and .5 seconds, 

 respectively. 



The direction of movement of the elec- 

 trical fields shown in figure 1 was reversed 

 for the south block of tests. Upon rever- 

 sal, row 10 in figure 1 became row 1 (the 

 electrode row not energized). In the south 

 block, the positive row of a pair of ener- 

 gized rows was always to the south. 



Although the end zones of the experi- 

 mental area were not electrically charged 

 except for fringe effects from the electri- 

 cal fields, it was convenient in conducting 

 our tests to name the zones "positive" and 

 "negative". The "positive" end zone was 

 beyond row 10 (the last positive charge row) 

 of the array, and the "negative" end zone 

 was before row 1 (which was uncharged). 



A schematic description of the switch- 

 ing unit designed to perform this operation 

 is shown in the block diagram (fig. 3). A 

 detailed description of the electrical cir- 

 cuits controlling the square-wave pulses 

 throughout this experiment and determining 

 the sequence of firing will be published 

 later.i/ 



The direct current was provided by a 

 10-kilowatt motor-generator set, with a 

 maximum output of 500 volts at 20 amperes. 

 A calibrated oscilloscope operated from a 

 voltage-regulating transformer was used for 

 setting potential and observing wave form, 

 and a vacuum-tube volt meter for plotting 

 the field with a voltage gradient probe. 

 As a safety device, an overload relay with 

 push-button reset was installed to prevent 

 serious damage to the electrical apparatus. 



Areas to hold the fish prior to and 

 following each test were constructed from 

 plywood at the north end of the tank. A 

 plywood wall separated these holding areas 

 from the experimental area of the tank to 

 eliminate any possible visual effect that 



4/ Dale, Harry P., and C. D. Volz. A 



pulse generation and distribution sys- 

 tem for electrical fish guiding. 

 United States Fish and Wildlife Service. 



