Table 2. — Description of electrical conditions supplied to 

 electrode arrays 



Figure 3. — Adult northern squawfish being deflected out of 

 electrical field near row of positive electrodes. 



Squawfish were introduced into the end of the 

 channel nearest the positive row of electrodes 

 to take advantage of the known directional 

 properties of the field in blocking the progress 

 of the fish. If the electrical fields were actually- 

 directional, any fish penetrating the fields 

 would tend to become oriented toward the posi- 

 tive row of electrodes and be deflected out 

 (fig. 3). 



Distances of 100 or 200 cm. between rows of 

 electrodes permitted the use of voltages well 

 below the capacity of the generator. We com- 

 puted the voltage gradients by dividing the total 

 voltage by the distances between the two rows 

 of electrodes. 



The following three sets of electrical condi- 

 tions were used indifferent tests (sets I, II, and 

 III of table 2; pulse frequency was held constant 

 at 8 pulses per second; voltage gradients used in 

 each test are given in the text): 



(I). Pulse direct current of "rectangular" 

 configuration (fig. 4a) with a duration of 40 

 msec, (milliseconds). This set of electrical 

 conditions was most effective in directing the 

 movements of fingerling salmon in the labora- 

 tory (see footnote 2). 



(II). Capacitor discharge pulses with a dura- 

 tion equivalent to that of a 40-msec. "rectangu- 

 lar" pulse (fig. 4b). 



The orientation and movement of fish in a direct cur- 

 rent field to the positive electrode (anode) are well docu- 

 mented in the literature (see Applegate, Macy, and Harris, 

 1954). 



Figure 4. — Pulse shapes on oscilloscope, as used with 

 three sets of electrical conditions in tests: 4a — 

 rectangular pulse (d.c.) used with set I; 4b — capacitor 

 discharge pulse used with sets II and III. 



