order to make this situation comparable to that 



in the tank we should have the same electric 



field strength midway between the two electrodes 



in each case. In the tank the field strength is 



E = y . In the case of the electrodes in the 



2aVo 



open sea, the field at the center is E' 



"dT 



where ZVq = V is the potential applied between 

 the electrodes, and d = -^ . This is found 

 from equation 14, Appendix I, by setting r = 

 and 9 = 0. Thus E' = ^2 ^^ ^^^ field midway 

 between the electrodes in the open sea. If this 

 is to be the same as in the tank we must set 



E' = E 



4aV' V 



or 5 = — -— 



VL 



and V = — T IS the necessary 



4a ' 



relationship between the applied potentials for 

 obtaining the same field midway between the 

 electrodes. 



The resistance between the open-sea 

 electrodes is R' = -■ ja ~ -r/a °hnns (eq. 23, 

 Appendix I). Thus the power dissipation 

 P' = — JU becomes 



^' 2 



p, . ■- . ^a 



(^) 



The ratio of P' to P is now desired and is 

 found from , 



v2a n 



IbaA 



pL 



We must now assume values for L,, a, and A. 

 L was 16 ft. in the tank, and A was 44 sq. ft. 



Let us take a = 



1 



TiT 



L so that the approximations 



made in Appendix I will hold. Then a = 0. 8 ft. 

 These values give us 



P' n (16)3 



16(0.8) (44) 



23 



Under the assumed conditions, then, 23 

 times as much power would be dissipated in the 

 open sea as in the closed tank. Thus an appa- 

 ratus of correspondingly higher power output 

 would be required to effect electrotaxis in tuna 

 at the same electrode spacing and frequencies. 



SUMMARY 



A theoretical study of the potential, electric 

 field, and current density for spherical elec- 

 trodes deeply submerged in a large body of 

 water is included in Appendix I. 



2. A theoretical study of the head-to-tail 

 potential and current passing through a fish 

 when immersed in fresh and salt water with 

 a uniform electric field is included in 

 Appendix II. 



3. Prelinninary experiments with aholehole in 

 a small (12 x 2 x 2 feet) tank, using pulsed 

 direct current with approximately square 

 wave fornn indicated that the optimum fre- 

 quency for electrotaxis was 10 c.p.s. and 

 that the mininnum peak current for satisfac- 

 tory response (12 amperes) was associated 

 with an on-fraction of 0.06 to 0.08. Total 

 peak current requirements decreased with 

 increase in length of the fish. 



4. Extrapolating the above results, it was 

 calculated that a current of 130 annperes at 

 a potential of 60 volts would be required to 

 induce electrotaxis in a 30-cm. fish in a tank 

 of much larger size (35 x 11 x 4 feet). This 

 was best achieved by capacitor discharge. 



5. An apparatus was constructed for 

 experiments with tuna and other large fish 

 in the larger tank. It consisted of a bank of 

 capacitors (55,000 mfd. ) charged by two 

 series banks of ten 6-volt automobile storage 

 batteries and controlled by a variable speed 

 nnechanical contactor. 



6. With this apparatus it was possible to induce 

 electrotaxis in small ( 50-cm. ) yellowfin 

 tuna with electrodes spaced a distance of 16 

 feet. The electrotactic effect increased 

 with pulse frequency up to 20 c.p.s., the 

 maximunn tested, 



7. It was calculated that in the open sea 23 

 tinnes as nnuch power would be required to 

 obtain an equivalent response with the elec- 

 trodes spaced 16 ft. apart. 



LITERATURE CITED 



CATTLEY. J. G. 



1955a. Your guide to electrical fishing: a 

 three-part article specially written 

 to add to the industry's practical 

 knowledge. World Fishing 4(3): 

 125-127. 



1955b. Your guide to electrical fishing (2). 

 World Fishing 4(4): 166-169. 



1955c. Your guide to electrical fishing (3). 

 World Fishing 4(5): 202-205, 



14 



