102 



BXXLLETIN OF THE BUREAU OF FISHERIES 



summary of the results is tabulated in Table 1, tests 1 to 14, inclusive, and shown 

 graphically in Figure 5. These data bring out two very interesting facts. First, 

 the voltage gradient required to produce paralysis is very low. Second, the voltage 

 gradient required to produce paralysis is inversely proportional to the length of the 

 fish. In other words, the long fish require a much lower field strength to paralyze 

 them than the short ones. This is the opposite of the conception held by many 

 previous to these tests. In fact, the most recent patent found covering an electric 

 fish "stop" makes the following statement (Burkey, 1924): 



With the use of the transformer it is possible to have an electric current at the inlet end of the 

 fish "stop" of a low amperage for the purpose of stopping or turning back small fish and thereby 

 obviate any possible chance of injuring or killing small fish by coming in contact i^nth electrical 

 current of too high amperage. The electrodes, being arranged in three series and connected to the 

 transformer, permit electrical currents to be passed through the water of progressively increasing 

 amperage, so that when large fish are not stopped or turned back by the low amperage the intermedi- 

 ate series of electrodes will supply electrical current of sufiicient amperage to turn back or stop such 

 sized fish. 



Table 1. — Voltage gradient required to paralyze fish of various lengths when subjected to a uniform 

 electric field in water having a resistivity of 10,000 ohms per inch cube and at a temperature of 53° F. 



Note.— The rainbow trout were Salma iriiem: the loch leven trout were Salmo laensis: and the Chinook salmon were Oncorliyn- 

 chus Uchawyisctia. 



It is obvious, in the Ught of the facts as given by Table 1 and Figure 5, that the 

 situation is just the reverse of that anticipated by the fish-stop inventor quoted above. 



The equation for the "minimimi" length-voltage gradient for paralysis curve has 

 been calculated and found to be 



g = 3.70L-'>-^ 

 which, within permissible limits of error, may be written 



9- 



3.70 



where </ = voltage gradient per inch to produce paralysis and i = length of fish in 

 inches. 



Thus it is seen that there is a very simple and interesting relation between the 

 length of fish and the voltage gradient required to produce paralysis. This equation 



