might attract the fish during a test. These 

 holding areas were not within the influence 

 of the electrical field. 



The tests were conducted under a con- 

 stant light intensity provided by two 500- 

 watt Icunps suspended 10 feet above the water 

 at each end of the large tank. 



Potential was measured by a calibrated 

 oscilloscope, specific resistance of the 

 water by an industrial conductivity bridge, 

 and temperature of water by a standard mer- 

 cury thermometer. The desired pulse fre- 

 quency and pulse duration for each test were 

 set by dials on the calibrated switching 

 unit. 



The fish were measured for total length 

 (from the tip of the snout to the extreme 

 end of the tail) to the nearest quarter-inch. 

 Each new lot of fish was sorted and counted 

 into two size groups: Group 1 — small fish, 

 10 to 15 inches; Group 2 — large fish, 15 

 through 20 inches. Fish shorter than 10 

 and longer than 20 inches were eliminated. 

 Figure 4 (page 6) shows the length frequency 

 of the jidult squawfish used in the tests. 

 These measurements were taken of fish which 

 died after one exposure and of fish twice 

 exposed to the electrical field. 



The number of fish available was not 

 sufficient to permit testing with one spe- 

 cific size group, or to make a comparison 

 between two or more size groups. Therefore, 

 a ratio of small to large fish was deter- 

 mined for each lot of new fish, and this 

 ratio was used to make up the 10 fish in 

 each test. This size ratio varied as the 

 weeks of testing progressed, but the average 

 ratio was 8 small fish to 2 large fish. 



Experimental Procedures 



We conducted 216 tests (8 series of 

 tests, 27 tests per series) from August 1 

 through October 31, 1956, exposing 1,080 

 fish in 10-fish groups as unshocked and 

 once-shocked fish. Actually a total of 

 1,219 fish was required to perform the tests 

 because of mortalities of some of the once- 

 shocked fish. 



After we released adult squawfish 

 within the sequentijilly pulsed electrode 

 array, we measured the effectiveness of 

 leading for each combination of potential, 

 pulse frequency, and pulse duration by the 

 percentage of fish that entered the "posi- 



tive" end zone of the experimental area 

 during the 7-second period of test. 



We used equal numbers of fish (10 fish) 

 to test each condition to obtain a reliable 

 comparison of the leading effectiveness of 

 various potentials, pulse frequencies, £ind 

 pulse durations, the number of tests per- 

 formed each day being determined by the num- 

 ber of fish available. The squawfish to be 

 tested were placed in holding areas at the 

 north end of the laboratory tank. 



If the lot of fish to be tested con- 

 sisted of unshocked fish (fish not pre- 

 viously exposed to the electrical fields) 

 we sorted it into the two size groups. 



To minimize any chance of a learning 

 response, we used a lot of fish no more 

 than twice. The tests in each series were 

 so arranged that the fish were never exposed 

 to the same combination of variable factors 

 as unshocked and once-shocked fish. 



The experimental tank was drained zind 

 filled with fresh water once a week to main- 

 tain the desired level of resistance (15,000 

 ohms/cm-^) of the water. No facilities were 

 available to control the temperature of the 

 water. The temperature measured 62" P. at 

 the beginning of the tests August 1, 1956, 

 and dropped to 50° F. at the end of the 

 tests on October 31, 1956. 



At the beginning of each test, after 

 the electronic switching unit was turned on, 

 we visually checked whether the electrode 

 array was pulsing properly by observing a 

 series of argon lamps connected across each 

 pair of electrode rows. After determining 

 that the switching unit was performing as 

 desired, we turned the unit off until we 

 had placed the 10 fish to be tested in the 

 fish release enclosure. 



Half the fish for each test were headed 

 toward each end of the fish release enclo- 

 sure, and aligned across the direction of 

 the sequentially pulsed electrical fields. 

 After turning on the switching unit and re- 

 leasing the fish, we determined the duration 

 of exposure by a time clock, meeinwhile count- 

 ing the fish during each test according to 

 (1) the number that were led with moving 

 electrical fields into the "positive" end 

 zone, and (2) the number that went against 

 the moving electrical fields into the "nega- 

 tive" end zone. These two counts were made 

 during the test interval because no traps 



