(III). Capacitor discharge pulses with a 

 duration equivalent to that of a 20-msec. "rec- 

 tangular" pulse (fig. 4b). 



For all the tests reported here, water 

 temperatures ranged from 17.1 to 18.1 C. 

 and resistivities from 15,000 to 20,000 ohm- 

 cm. Resistivity of the water was measured by 

 an Industrial Instruments conductivity bridge, 

 Model RC-1B. 



The squawfish were taken by gill nets in 

 Drano Lake, transported to Seattle in a fish 

 tank truck on August 4 and 11, 1953, and held 

 and fed initially in outdoor concrete rearing 

 ponds at the College of Fisheries, University 

 of Washington, Seattle. During the tests the 

 fish were kept in wooden troughs at the BCF 

 Biological Laboratory, Seattle. The 300 squaw- 

 fish ranged in total length from 28 to 47 cm. 

 (average, 36 cm.; 86 percent of the fish were 

 30 to 42 cm. long). 



Exploratory tests were made to determine 

 the combination(s) of electrode arrays and 

 electrical conditions that warranted systematic 

 tests. 



An exploratory test consisted of 10 trials, 

 each with a different fish, subjected individually 

 to the electrical field. The initial behavior of the 

 fish when it was first exposed to the field 

 was recorded. A fish was recorded as blocked 

 by the electrical field if it was deflected 

 before entering the positive row of electrodes, 

 or deflected out of the field after entering it, 

 or immobilized within the field. We also noted 

 whether a slight, moderate, or complete loss 

 of equilibrium occurred before or after a fish 

 entered the field, or after it passed through 

 the field. Fish that were apparently unaffected 

 by the electrical field or that showed very 

 slight or moderate loss of equilibrium were 

 retrieved as quickly as possible for use in 

 later tests. We did not test the effects of length 

 of fish on response to the electrical fields. At 

 least 1 day elapsed between trials with in- 

 dividual fish. 



2. Parallel and staggered arrangements of 

 electrodes in the two rows. 



3. Distances of 100 and 200 cm. between 

 rows of electrodes. 



4. Voltage gradient. 



5. The three sets of electrical conditions. 



The effects of voltage gradients of 0.50 volt/cm. 

 through 1.75 volt/cm. (at intervals of 0.25 

 volt/cm.) were explored at distances of 100 and 

 200 cm. between rows of electrodes. 



Exploratory tests were made on (1) spacing 

 and patterns of electrodes (tests 1, 2, and 3, 

 table 3); (2) distance between rows of electrodes 

 (tests 3 and 4, table 3); and (3) electrical 

 conditions and wave form (tests 4, 5, and 6, 

 table 3; figs. 4a and 4b). Pulse frequency was 

 held constant at 8 pulses/sec. in all the tests. 



Spacing and patterns of electrodes (tests 1, 2 , 

 and 3, table 3) .- -Electrode arrays A and B, 

 each combined with electrical conditions of 

 set I (rectangular pulse with a duration of 

 40 msec. --see table 2 and fig. 4a), were 

 tested with voltage gradients of 0.50 through 

 1.75 volts/cm. (at intervals of 0.25 volts/cm.) 

 and a distance of 100 cm. between rows of 

 electrodes. Arrays A and B differed in numbers 

 of positive and negative electrodes in the two 

 rows, but in both arrays the electrodes were 

 30 cm. apart and the electrodes in opposite 

 rows were parallel (tests 1 and 2, table 3). 



The combination of array C (distance between 

 electrodes 61 cm. and electrodes in opposite 

 rows staggered, see fig. 2) and electrical 

 conditions of set I (table 2 and fig. 4a) was 

 tested with voltage gradients of 0.50 and 0.75 

 volts/cm., 100 cms. between rows of elec- 

 trodes (test 3, table 3). The purpose of this 

 test was to compare (with tests 1 and 2, table 

 3) the effects of the two voltage gradients when 

 the spacing of the electrodes within each row 

 was increased from 30 to 61 cm. and electrodes 

 in the two rows were staggered. 



TESTS OF ELECTRICAL FIELDS 



Limited time and holding facilities precluded 

 extensive testing of all possible combinations 

 of electrode arrays with the three sets of 

 electrical conditions. We made exploratory 

 tests, therefore, to determine the combinations 

 that warranted systematic tests. 



Exploratory Tests 



Various electrical fields were created by a 

 combination of the electrode arrays (A, B, and 

 C in fig. 2 and table 1) with the three sets of 

 electrical conditions (sets I, II, and III in table 

 2) and two pulse shapes (fig. 4). The factors 

 tested were: 



1. Spacings of 30 and 61 cm. between 

 electrodes in each row. 



Distance between rows of electrodes (tests 

 3 and 4, table 3) .- -The combination of array C 

 with electrical conditions of set I (table 2 and 

 fig. 4a) was tested with voltage gradients of 

 0.50 and 0.75 volts/cm. and a distance of 100 

 cm. between rows of electrodes (test 3, table 3), 

 and with voltage gradients of 0.50 through 

 1.00 volts/cm. when the distance between rows 

 of electrodes was increased to 200 cm. (test 4, 

 table 3). 



Electrical conditions (tests 4, 5, and 6, table 

 3^. --Array C was combined with each set of 

 electrical conditions and each combination was 

 tested with voltage gradients at a distance of 

 200 cm. between rows of electrodes as follows: 



1. The combination of array C and electrical 

 conditions of set I was tested with voltage 



