EFFECT OF FIELD POLARITY IN GUIDING SALMON FINGERLINGS 

 BY ELECTRICITY 



U. S. 



by 



H. William Newman 

 Fish and Wildlife Service 

 Seattle, Washington 



ABSTRACT 



The relation of field polarity to fish guiding effectiveness was tested under 

 controlled laboratory conditions by using a single -row electrode array sequentially 

 energized so that: (1) positive polarity was always toward the upstream end, (2) posi- 

 tive polarity was always toward the downstream end, and (3) polarity alternated to 

 cancel out polarity orientation. No difference in effectiveness was found demonstrat- 

 ing that fish guiding was due to avoidance rather than to electrotaxis. Variability, 

 measured as variance, decreased as sample size increased but the mean effectiveness 

 was similar for fish release lots of 15, SO, and 100 fish each. 



INTRODUCTION 



The practical application of electrical 

 guiding to the protection of downstream 

 salmon migrants requires a large amount of 

 basic information on the reaction of fish to 

 electrical fields. To provide this back- 

 ground information the U. S. Fish and Wild- 

 life Service has been conducting laboratory 

 research on the lethal effects of electric- 

 ity (Collins et al. 1954), the effect of 

 electricity upon reproductive ability — , 

 the relative effects of various patterns of 

 interrupted direct current in the control of 

 fingerling movements — , and the effective- 

 ness of several types of electrical arrays 



1/ Maxfield, Galen H., and Kenneth Liscom. 

 Manuscript in preparation. "The effect 

 of electricity on reproductive ability 

 of rainbow trout." 



2/ Volz, Charles D, Manuscript in prepa- 

 ration. "Effectiveness of interrupted 

 d.c. in the control of salmon fingerling 

 movements." 



in diverting salmon fingerlings (Trefethen 

 1955), Raymond (1956) measured the effect 

 of pulse duration and frequency in guiding 

 salmon fingerlings. 



The initial laboratory studies, meas- 

 uring the ability of a short segment of an 

 electrical array to divert fingerlings in 

 flowing water, were made with a narrow 

 directional field of pulsed direct current 

 aligned at a relatively small angle to the 

 direction of water flow (Trefethen 1955). 

 The field was created by two rows of elec- 

 trodes connected so that the upstream 

 electrodes were always positive. The elec- 

 trotactic response of the fish to the direc- 

 tional field between the rows of electrodes 

 resulted in the fish being diverted in the 

 desired direction. Several variations of 

 electrical arrays using this principle were 

 investigated. One of the chief disadvan- 

 tages of this type of array was its failure 

 effectively to divert fish of different 

 lengths. The high voltage gradients re- 

 quired to divert small fish were injurious 

 to large fish, while voltage gradients safe 

 and effective for large fish were ineffec- 

 tive for small fish. To overcome this 



