gradients of 0.50 through 1.00 volts/cm. 

 (test 4). 



2. The combination of array C and electrical 

 conditions of set II (capacitor discharge pulse 

 [table 2 and fig. 4b] with a duration equivalent 

 to that of a 40-msec. "rectangular" pulse) was 

 tested with voltage gradients of 1.00 and 1.25 

 volts/cm. (test 5). 



3. The combination of array C and electrical 

 conditions of set III (capacitor discharge pulse 

 [table 2 and fig. 4b] with a duration equivalent 

 to that of a 20-msec. "rectangular" pulse) was 

 tested with voltage gradients of 0.50 through 

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

 (test 6). 



The voltage gradient of 0.50 volts/cm. ap- 

 parently had little blocking effect on the adult 

 northern squawfish when either array A or B 

 (30 cm. spacing of electrodes, distance of 100 

 cm. between rows, parallel pattern of elec- 

 trodes, see fig. 2) was combined with electrical 

 conditions of set I (test 1 and 2, table 3). The 

 blocking at this voltage gradient was more 

 effective when the electrode pattern was stag- 

 gered (array C; see fig. 2) and the spacing 

 between electrodes in each row was 61 cm. and 

 the distance between rows was 100 or 200 cm. 

 (tests 3 and 4, table 3). When array C at 61 cm. 

 spacing of electrodes in each row and a 200-cm. 

 distance between rows of electrodes was com- 

 bined with electrical conditions of set III, the 

 blocking effect was the most effective at this 

 voltage gradient (test 6, table 3). 



The number of squawfish blocked at 0.75 

 volts/cm. closely approximated the numbers 

 blocked at all of the higher gradients (table 3, 

 tests 1 through 6). Above 1.25 volts/cm., 

 immobilization and in many instances, subse- 

 quent death of the fish resulted. 



Chi- square tests applied to the results of 

 these exploratory tests at each of the voltage 

 gradients indicated no significant differences 

 among the various arrays and sets of electrical 

 conditions in blocking the adult squawfish. 



On the basis of the above tests, we eliminated 

 the following from consideration for the sys- 

 tematic tests: 



1. A distance of 100 cm. between rows of 

 electrodes. 



2. A spacing of 30 cm. between electrodes 

 in the same row. 



3. Voltage gradients of 0.50, 1.50, and 1.75 

 volts/cm. 



4. Arrays A and B (because they required 

 more electrodes than array C). 



5. Sets I and III of electrical conditions (be- 

 cause set II--capacitor discharge, 8 pulses/ 

 sec. equivalent to 40-msec. "rectangular" 

 pulse- -has a wave form similar to the output 

 of certain commercial devices used in fish 

 screens and is more economical than pulsed 

 current of "rectangular" configuration under 

 field conditions). 



Systematic Tests 



The systematic tests were performed by the 

 use of electrode arrays C, D, E, and F (table 1 

 and fig. 2), with capacitor discharge pulses at 

 8 pulses/sec. and a pulse duration equivalent to 

 that of a 40 msec, "rectangular" pulse (set II 

 of electrical conditions, table 2). At least 

 five tests, each with 10 fish, were performed 

 under each of the above combinations of con- 

 ditions; voltage gradients used were 0.75, 1.00, 

 and 1.25 volts/cm., and the distance between 

 rows of electrodes was 200 cm. 



Table 3. — Numbers of adult northern squawfish blocked in exploratory tests at indicated con- 

 ditions, to determine conditions for systematic tests. Single fish were used in each of 

 10 trials. 



1 (P) = parallel; (S) = staggered. 



2 As indicated in table 2. 



3 Fish immobilized. 



* Four fish tested — all immobilized. 



