90t 



80-- 



O 70 



60 



o 

 Q: 



UJ 



a. 



z 

 o 

 I- 

 < 



Q 



50-- 



40 



30- • 



t 



-+■ 



-+- 



■+- 



-+- 



-+- 



-I 



40 60 80 100 120 140 



FREQUENCY (PULSES PER SECOND) 



l-'igurc 5. — Th<j optimum frequency-duration combinations 

 for olcctrofishiiig in waters of 5,000 to 30,000 ohm cm.^ 

 resistivity. The lines show the "on" time relation in 

 msecs. 



Wave shape.- -The square wave is con- 

 sidered superior for electrofishing because 

 the maximum voltage is produced throughout 

 its duration. Other wave shapes have a lower 

 efficiency. For example, the triangular wave 

 shown in figure 6 has one-fourth the electric 

 energy of a square wave of the same duration 

 and peak voltage. Condenser discharge waves 

 (fig. 7, A) have low efficiency and require high 

 frequency rates for moderate effectiveness. 



The leading edge of a wave is apparently 

 critical in eliciting the neural response. 

 Haskell, MacDougal, and Geduldig (1954) ob- 

 served that stimulation occurred on the "make" 

 of the impulse. Abe (1935) was able to stimu- 

 late catfish more effectively with fast ascend- 

 ing and slowly descending pulses than with the 



UJ 



< 



o 



> 



TIME 



Figure (\ — Sciuarc and "triangular" waves of Identical 

 peak voltage and duration: the "triangular" wave is 

 capable of producing only one-fourth the power of the 

 square wave into a given load. 



UJ 

 U) 



< 



o 

 > 



400-1 



300- 



200- 



100- 



0- 



400-1 

 300- 

 200- 

 100- 

 0- 



400 

 300- 

 200- 

 100- 

 0- 



-I 1 1 1 1 1 — 



10 20 30 40 50 60 



T-r 



B 



I 1 1 1 1 1 \ r-i 



10 20 30 40 50 60 



—I 1 r- 



10 20 30 



—\ — 

 50 



60 



TIME 



40 

 ( MILLISECONDS ) 



Figure 7. — Wave shapes of Bureau of Commercial Fish- 

 eries shockers: A — the triangular condenser wave with 

 a controllable frequency and an uncontrollable short 

 duration, produced by the Type I shocker; B — the square 

 wave with controllable frequency and duration produced 

 by the Types II and 111 shockers; C — the basic square 

 wave, n, which can be subdivided into groups of pulses 

 with frequency and duration controllable, produced by the 

 Type III shocker. 



inverse. An almost instantaneous pulse rise 

 is probably the most desirable. 



Variations of the basic square wave may 

 be considered. The wave is most easily con- 

 trolled by allowing it to drop to zero volts 

 between impulses. Groups of pulses, or sub- 

 division of the duty cycle (fig. 7, C), appear 



