TO STRIP-SWITCH 



HUBBELL 

 TWIST LOCK 



0.05\ii 0.022 (jf. 



Figure 2. — Schematic diagram of the Type IV shocker. 



of the 12-v., double-pole, single-throw relay. 

 One set of contacts on this relay also controls 

 the running of the timer motor. 



A normally closed momentary switch located 

 on the front panel, is used to open the plate 

 lead of the OA4G to allow for de ionization of 

 the tube and to restore normal pulsing opera- 

 tion after a misfire. A misfire can be caused 

 by accidental shorting of the electrodes in the 

 water. 



A four-position selector switch connects 

 different values of capacitance into the trigger 

 anode circuit to vary the frequency of the 

 oscillator. 



A running-time meter and a small neon 

 indicator lamp are installed on top of the unit. 

 The lamp is wired directly across the output 

 of the unit and gives visual indication of the 

 output pulse. The running-time meter records 

 cumulative time that the unit runs, to assist 

 in determining catch per unit of effort, 



A 12-v. battery with a 50-ampere-hour 

 rating is generally sufficient as a power 

 source for 4 to 5 hours of use. (If inter- 

 mittent automobile trips are made, the battery 

 can be recharged en route by a connection to 

 the 12-v. car system.) 



CHARACTERISTICS AND EFFECTIVENESS 

 OF THE ENERGY OUTPUT 



The more desirable forms of electrical 

 energy for electrofishing have not been care- 

 fully determined, although some research on 

 various neurological phenomena resulting from 

 electric shock do suggest the optimum energy 

 output for electrofishing. These findings are 

 used here to establish a basis for evaluating 

 the shock produced by the Type IV instrument. 



Effects of Basic Electric Currents 



The three types of electrical energy con- 

 sidered here are alternating current (a.c.-- 

 usually 60-cycle), direct current (d.c), and 

 pulsed d.c. The continuous reversal of fields 

 in a.c, current in equal magnitudes along a 

 sine curve eliminates unidirectional physio- 

 logical response in animals. In electrofishing 

 with a,c,, the voltage gradient decreases with 

 distance from the electrode (fig. 3), and a 

 typical set of fish reactions occurs within the 

 graduated intensities. The weaker voltage 

 gradients along the periphery of the field 

 invoke fright and flight, resulting in escape; 



