FISHERY BULLETIN: VOL. 72, NO. 3 



inducing fright, taxis, or even tetanus. These 

 various responses have successfully been used to 

 commercially harvest marine animals. The prin- 

 cipal applications include an electrical fish pump 

 for hardening menhaden in a purse seine 

 (Kreutzer, 1964), an electrical fish trawl (McRae 

 and French, 1965), and an electrical shrimp trawl 

 (Klima, 1968; Seidel, 1969). 



MATERIALS AND METHODS 



Test Procedure 



Field experiments were performed in the near- 

 shore waters off Panama City, Fla. The test 

 equipment used in evaluating fish response to an 

 electrical field consisted of a deck-mounted pulse 

 generator and an electrode array deployed in the 

 water alongside the vessel. Salinity and tempera- 

 ture ranged from 29.5 to 33.8%oand 28.0° 

 to 29.6°C, respectively. 



Two separate groups of experimental animals 

 were used in the experiments and are referred to 

 as captured fish and wild fish, respectively. The 

 first group consisted of 393 Spanish sardines, 

 Sardinella anchovia Valenciennes; 397 round 

 scad, Decapterus punctatus (Agassiz); 390 scaled 

 sardines, Harengula pensacolae Goode and Bean; 

 228 Atlantic thread herring, Opisthonema og- 

 linum (Lesueur); and 37 Atlantic bumper, Chloro- 

 scombrus chrysurus (Linneaeus). They were 

 attracted by lights at night and caught with a 

 5-m lift net in the northern Gulf of Mexico and 

 held in a tank of circulated seawater. Prior to 

 testing, each fish was inspected for damage, and 

 only fish in good condition were used. Each fish 

 was exposed to a preselected combination of pulse 

 rates, voltage, and pulse widths by carefully 

 dropping them into the electrical field facing 

 toward and within 1 m of the negative electrode. 



The second group (wild fish) was not handled by 

 the investigators but rather was attracted by 

 lights at night to an area between the electrodes 

 positioned next to the boat. When five or more fish 

 were between the electrodes, they were exposed to 

 preselected combinations of pulse rates, pulse 

 widths, and voltage. Visual observations were 

 used to estimate species composition, approximate 

 size, and responses. 



To evaluate the in situ effectiveness of the pulse 

 characteristics tested, we measured the percent of 

 fish which escaped from the electrical field and the 



percent which swam the length of the field to the 

 positive electrode. The captured fish were intro- 

 duced into the field 'in such a way that they 

 were forced to turn 180° in order to swim to the 

 anode, whereas the wild fish schools were ran- 

 domly oriented. Fish not electrically stimulated 

 when placed between the electrodes exhibited 

 immediate escape movement toward the cathode, 

 the side, or down, but usually did not escape 

 by swimming toward the anode since they were 

 dropped into the electrode array facing the 

 cathode. Test fish would occasionally mill between 

 the electrodes for several seconds before slowly 

 moving away and to the side. Wild fish not 

 electrically stimulated would mill between the 

 electrodes. Consequently, the reactions of the 

 electrically stimulated fish were evaluated in 

 terms of electrotaxis or a positive response by 

 their directed behavior to the anode. We con- 

 sidered swimming to the anode a positive response. 

 All other responses were designated negative. 



Description of Test Equipment 



The pulse generator providing electrical energy 

 to the electrode array had an output capability 

 of 12 kVA at a pulse rate of 50 pulses/s with a 

 peak output voltage of approximately 150 V at a 

 pulse width of 0.8 ms (millisecond). The pulse 

 rate could be varied from 4 to 55 pulses/s, and 

 three different output widths were available with 

 the unit; 0.3, 0.5, and 0.8 ms measured at the 

 10% power points. Pulse rise time was around 

 0.05 ms with a sloped decay. The pulse generator 

 output was designed to operate into load resistance 

 of either 0.05 or 0.2 ohm, since the operational 

 array resistance could not be predicted for all 

 variations in field conditions. At these loads, the 

 output pulse was relatively smooth and undis- 

 torted, exhibiting only slight imperfections in the 

 decay portion of the waveform. The waveform was 

 distorted with other array resistances (Figure 1). 



In Figure ID, both the output pulse and the 

 recharging compensating pulse are shown. ^ The 

 compensating pulse is an important feature of 

 the pulse generator and is designed to significantly 

 reduce both electrode electrolysis and electrolysis 

 of any incidental metal within the electrical field, 

 such as a ship's hull. Essentially, the same 



^Kreutzer, Patent No. 3,363,353; 16 January 1968. 



658 



