power outputs at optimum pulse characteristics. 

 In addition, this review pointed out the 

 advantages of designing a circuit using SCR 

 (silicon-controlled rectifier) static switching in 

 conjunction with capacitor-discharge pulses. 

 This design would allow us to produce fast rise 

 flat-topped rectangular pulses with exponential 

 trailing edges of durations of 1 msec or more. 

 Pulses having this shape are considered to give 

 the optimum neurophysiological effect for fish 

 taxis (Vibert, 1970). 



As a result of our literature survey, we con- 

 cluded that a versatile research tool could be 

 devised to study ways of increasing the catching 

 efficiency of freshwater fishing gear using elec- 

 tricity. Consequently, developmental work was 

 started on the Freshwater Fish Electro-Motiva- 

 tor (FFEM) system. Four basic modes of oper- 

 ation were considered in the initial design. These 

 operating modes were: 1) phased array — use of 

 electrical stimuli to herd or direct fish into 

 active or passive fishing gear; 2) increasing net 

 aperture — use of stimuli to increase the effec- 

 tive aperture of a net by confining the fish to a 

 region wherein they will be caught by the me- 

 chanical fishing gear; 3) confinement — use of 

 electrofishing techniques to prevent fish from es- 

 caping once they are trapped by the fishing gear; 

 and 4) concentric spheres — use of electrical 

 stimulus in conjunction with a fish pump-light 

 for removing fishes that are positively photo- 

 tactic. 



To achieve this goal, we contracted with the 

 University of Michigan to work with us on the 

 development of an FFEM. Two main studies 

 were conducted: the development of a proto- 

 type FFEM and its field testing. In this paper we 

 will cover the design characteristics and oper- 

 ation of the FFEM and give a summary of the 

 field test. Another report covers the field test in 

 detail (Ellis and Pickering, in press). 



CHARACTERISTICS AND OPERATION 



OF THE FRESHWATER FISH 



ELECTRO-MOTIVATOR 



The FFEM system as shown in Figure 1 is 

 divided into a pulser and a power supply. The 

 physical and electrical parameters of each 

 system are as follows. 



Pulser 



The FFEM pulser is by far the most complex 

 portion of the system (Figure 2). Its physical 

 characteristics are shown in Figure 3. The pulser 

 housing is an aluminum tube, 165.1 cm in 

 length, 20.3 cm nominal diameter with 1.3 cm 

 walls, and weighs 116.1 kg including electronic 

 components. It consists of three bulkhead 

 plates, PI, P4, and P8 along with two tubes, Tl 

 and T2, as shown in Figure 3. The bulkheads 

 and tubes are held in compression by two sets of 

 four aluminum connection rods, Rl and R2. 



The right bulkhead end plate has an air check 

 valve which permits the pulser to be pressurized 

 with air to about 13.6 kg/cm". This pressuriza- 

 tion tests the O-ring seals for leaks before 

 submerging the unit. A cap is placed over the 

 check valve to prevent water from entering the 

 housing since external water pressure will at 

 times exceed the internal air pressure. The left 

 bulkhead end plate has six bulkhead electrical 

 connectors and mating plugs. One connector is 

 for supplying external electrical power to the 

 pulser while the other five connectors are for 

 supplying power to the electrode arrays in 

 sequential or single mode firing orders. 



The firing circuits and power silicon-con- 

 trolled rectifiers (SCR) of the FFEM pulser 

 contained within the aluminum housing are 

 shown schematically in Figure 4. The pulser has 

 a maximum voltage of 300 volts^ peak output 

 with the capability of any intermediate voltage 

 level. A minimum load resistance presented by 

 the electrodes to the pulses should be 1.5 to 2.0 

 ohms. For an "effective duty cycle" of 100% 

 (equivalent to an on-time of 1 msec and an 

 off-time of 7 msec) at full voltage, the pulser is 

 capable of an average output of 7,500 watts 

 with a peak pulse power output of 60,000 watts. 



Pulse control logic— The pulse control logic 

 (Figure 1, items 8 and 9) generates the gate 

 input pulses to the firing circuits (Figure 1, item 

 6) which controls the firing of the SCR for the 

 desired output pulse parameter. To achieve the 

 basic 8-msec timing cycle, a l-KH^, clock is used 

 with a three-stage binary counter which divides 



This maximum was dictated by the size and 

 availability of electrolytic capacitors. 



