can be used; and the manpower required for 

 continuous control of squawfish population 

 by gill netting makes that method imprac- 

 tical also. The failure of these controls 

 makes clear that there is need for an 

 economical and practical method for continu- 

 ously removing squawfish from the area in 

 which the fingerlings are released. 



In an effort to meet this need, Max- 



-5/ 



field and Volz in 1953 — ' conducted a labo- 

 ratory study of controlling squawfish by 

 electricity. This study involved the use of 

 a single electrical field as a barrier to 

 block the entrance of sqawfish into a desig- 

 nated area. Direct current was supplied to 

 two rows of electrodes, the positive row 

 being located downstream. The individual 

 squawfish swimming up to the barrier would 

 feel the electrical field and, usually, 

 would be deterred from entering the strong 

 field between the two rows of electrodes. 

 If, however, a squawfish did enter the 

 strong field between the two rows, its re- 

 action was to swim back toward the positive 

 row and out of the array. This reaction of 

 the fish can be explained by the principle 

 of electrotaxis — movement of the fish toward 

 the positive pole in a direct-current field. 

 Fingerling salmon, being shorter than the 

 adult Squawfish, were less affected by the 

 potential difference in the field and passed 

 safely through this electrical barrier when 

 released on the upstream, or negative, side. 



Preliminary Experiment 



In recent laboratory studies at Seattle, 

 we attempted to use electrotcixis to lead 

 the squawfish into a net enclosure or trap- 

 ping area. The square-wave form of pulsat- 

 ing direct current was used with an array 

 of several rows of electrodes in which the 

 electrical fields were sequentially created 

 in one direction between successive rows of 

 electrodes. 



However, initial attempts to lead indi- 

 vidual Squawfish into a trapping area in 

 the laboratory required basic knowledge of 

 the effect on squawfish of the electrically 

 variable factors of potential, pulse fre- 



2/ Maxfield, Galen H. , and C. D. Volz. An 

 electrical barrier for controlling squaw- 

 fish ( Ptychocheilus oregonensis ) preda- 

 tion, U. S. Fish and Wildlife Service, 

 Seattle, Washington. (Unpublished ms.) 



quency, and pulse duration. A preliminary 

 experiment, therefore, was set up to deter- 

 mine the extreme ranges of these three 

 variable factors. 



The results showed that the following 

 conditions should be the limits and ranges 

 of further experiments: 



Potential: The range of potentials 

 studied extended from (1) the minimum 

 potential at which the squawfish re- 

 sponded to (2) the minimum potential 

 at which the squawfish were in obvious 

 distress. This range was 60 to 90 

 volts, respectively, when applied to 

 two rows of electrodes spaced 17 inches 

 apart in rows 18 inches apart. 



Pulse frequency : Employing the two 

 experimentally determined values of 

 potentiail of 60 and 90 volts, we used 

 the above procedure to arrive at a 

 suitable range of pulse frequencies: 

 2 to 8 pulses per second. 



Pulse duration : Finally, employing 

 combinations of the two potentials cind 

 the two pulse frequencies, we also 

 used the same procedure in an attempt 

 to arrive at a suitable range of pulse 

 durations. Variations in pulse dura- 

 tion, however, in the range of 10 to 

 90 milliseconds did not have any ob- 

 servable different effects on the in- 

 dividual squawfish. A range of pulse 

 duration of 10 to 30 milliseconds, 

 therefore, was selected arbitrarily 

 for use in the following experiments. 



After gaining knowledge of the extreme 

 ranges, we wished to determined the optimum 

 electrical conditions for leading adult 

 squawfish. Therefore, we designed the ex- 

 periments reported below in which we tested, 

 under rigorously controlled conditions , the 

 effects on squawfish of extreme and inter- 

 mediate values of the electrical variables. 

 In addition, we had observed in the prelim- 

 inary work that the direction of movement 

 of the electrical fields in the laboratory 

 tank might be a significcint variable. Ac- 

 cordingly, we also tested the effect of 

 this variable on squawfish. 



Objectives 



The objectives of the present study 

 were to determine by systematic testing, 

 (A) the optimum values of (1) potenticil, 



