(2) Minimum voltage gradient requirements 



Experimentation in 19^2 substantiated the fact that a minimum 

 voltage gradient of 0.75 volt per inch must exist in the water on a 

 line between electrodes if the electrical field is to effect a complete 

 block of the lamprey run. This statement applies specifically to gra- 

 dients existing between electrodes of the center and upstream rows com- 

 prising the upper half of an incremental field barrier, and between 

 electrodes of any two adjacent rows of a uniform field barrier created 

 by either a 3-row or 2-row electrode system. It applies further to any 

 2-row electrode system regardless of whether both rows consist of sus- 

 pended electrodes or whether one row is suspended and the other is re- 

 placed by a single, lateral submerged electrode. It was also substan- 

 tiated that if an adequate margin of safety is desired, the minimum 

 voltage gradient between the aforementioned electrodes must be at least 

 1.0 volt per inch. 



The above minimal gradients have been established on the basis 

 of an electrical field created in depth by a system of electrodes distri- 

 buting the electrical field over at least k feet of stream length (i.e., 

 center and upstream rows of incremental field barrier., or any two rows 

 of uniform field barrier). A simple system of electrodes (i.e., one row 

 with every other electrode wired alternately to grounded and ungrounded 

 sides of a. 110 VAC circuit) would require much greater voltage gradients 

 particularly if located in sluggish waters. Furthermore, it is extremely 

 doubtful whether such a single row structure utilizing practical input- 

 voltages would provide a completely lamprey-tight barrier. 



It seems pertinent to point out here that migrant sea lampreys 

 are not only highly resistant to electrical shock ^/but display little or 

 no avoidance reaction to an electrical field in the water. Whereas other 

 migrant fishes react sensitively to very weak gradients at the fringe of 

 an electrical field (and tend to avoid same), the lampreys show no such 

 reaction. Characteristically, the lamprey swims into a field of increas- 

 ing intensity, laboring against oncoming paralysis until complete para- 

 lysis prevents any muscular movement whatsoever. This resistance to elec- 

 trical stimulation, the determined nature of their migration, and their 

 ability to swim very rapidly at least over short distances, would as a 

 rule permit some escapement through a barrier creating only a relatively 

 thin electric field in the water. 



Th 



5/ Apple gate, Vernon C. and William L. Stahl. Use of electricity in 



he control of sea lampreys : Experimental electrocution of downstream 

 migrants. MS. 



31 



