of such size that a head-to-tail difference in 

 potential of 1 volt will cause the fish to swim to 

 the anode in medium (a). He points out that in 

 fresh water, presuming the resistance of the 

 fish is less than that of the medium, the equipo- 

 tential surfaces will diverge in the vicinity of 

 the fish, requiring a greater potential gradient 

 to elicit response than in (a); however in salt 

 water, presuming the resistance of the fish is 

 greater than the nnedium. the equipotential sur- 

 faces will converge in the vicinity of the fish, 

 requiring a snnaller potential gradient to elicit 

 response than in (a). He thus concludes that the 

 "...voltage gradients need not be so great /in 

 salt water/ as in fresh water. . . " 



This problem was approached independently 

 by the junior author before seeing Cattley's 

 (1955b) paper. Particularly, it was desired to 

 determine the head-to-tail potential in the fish 

 and the current passing through the fish when 

 immersed in freshand salt water with a unifornn 

 electric field. The theoretical approach is given 

 in detail in Appendix II. To simplify the mathe- 

 matics, it has been assumed that the fish forms 

 a sphere. Thus, the formulae which have been 

 developed must be regarded as approximations 

 when applied to a fish which, of course, differs 

 considerably in shape from a sphere. They in- 

 dicate in a qualitative way. however, the results 

 that can be expected with an organism such as a 

 fish. 



In summary, it is concluded that the head- 

 to-tail voltage of this theoretical spherical fish 

 (Vl volts) nnay be expressed as 



'. - (^) V. 



^1- ■ ^o'- TTTI^ 



Where Eq is the uniform electric field (volts /cnn.)^ 

 L is the length of the fish (cm. ), 

 cr^ is the conductivity of the water 



(ohnn-cm. )" , and 

 (Tf is the conductivity of the fish 



(ohm-cnn. )" . 



When the conductivity of the fish is greater than 

 that of the medium, as it may be in some fresh 

 waters, the head-to-tail voltage is less than E^L; 

 when the conductivity of the fish is less than the 

 mediunn, as in salt water, the head-to-tail volt- 

 age is greater than EqL. With reasonable as- 

 sumptions as to the relative conductivities of 

 sea water, freshwater and the fish, it is con- 

 cluded that for a fish of a given size, the electric 

 field intensity in sea water would need to be 

 about 1/10 as large as in freshwater to elicit an 

 equivalent response. It is also shown that the 

 current density in the fish (Jf) is a constant 

 (o-f/L) times the head-to-tail potential: 



L 



Thus, neither current density nor potential, 

 individually, can be said to be responsible for 

 electrically produced responses of the fish. 



The above results are in general agreement 

 with the unsupported discussions of Cattley 

 (1955b) who intimates that the field in sea water 

 would need to be about 1/6 to 1/12 or, again, 

 roughly 1/10 that of fresh water. His connpari- 

 son, however, is given in terms of relative 

 power requirennents. 



PRELIMINARY EXPERIMENTS 

 WITH AHOLEHOLE 



Morgan (1953) initiated experiments during 

 1950 at the University of Hawaii to study the re- 

 sponse of the aholehole, a tropical marine fish, 

 to interrupted direct current insea water. Using 

 a wooden tank 12 x 2 x 2 feet, a mechanical 

 current interrupter, and a 5 kw. direct current 

 motor-generator, he showed that an interruption 

 frequency of 15 cycles per second (c.p.s.) gave 

 more positive response than frequencies of 5 and 

 20 c.p.s. and that equivalent response could be 

 obtained by progressively decreasing the "on- 

 fraction" of a cycle from 0.75 to 0.25. Although 

 the peak current rennained about the same, the 

 average current was considerably lower at the 

 smallest on-fraction, thus achieving a net saving 

 of power. 



Using the s a nn e tank and generator, but 

 galvanized iron plate rather than carbon pencil 

 electrodes. Tester (1952) showed that at 15 c.p.s. 

 the on-fraction could be reduced to about 0. 08, 

 with a further net saving of power. 



The above results are in agreement with 

 those of Dr. Konrad Kreutzer of Germany 

 (Houston 1949) in indicating the desirability of 

 using a short "on-fraction." Kreutzer indicated 

 that the pulse duration should be from 1 to 5 

 milliseconds (on-fraction 0.015 to 0.075 at 15 

 c. p. s. ) and that the frequency should be from 4 

 to 60 c. p. s. depending on the natural swimming 

 frequency of the fish. 



Neither Morgan nor Tester discussed the 

 shape of the pulse, although it w-as found on an 

 oscilloscope to be peaked. According to Cattley 

 (1955c). Kreutzer has ennphasized the innportance 

 of the pulse which in his apparatus is the dis- 

 charge from a capacitor with a sharp rise from 

 zero followed by a nnuch slower decay. Groody. 

 Loukashkin and Grant (1952) at first believed 

 that the sawtooth or the 1/4-sine wave gave the 

 best response in sardines, but later Loukashkin 



