THE RESPONSE OF TUNA AND OTHER FISH 

 TO ELECTRICAL STIMULI 



By 



Iwao Miyake 

 Associate Professor of Physics 



and 



Walter R. Steiger 



Assistant Professor of Physics 



University of Hawaii 



Honolulu. Hawaii 



One of the most efficient methods of 

 harvesting tuna is live-bait fishing in which the 

 tuna are attracted and held near the vessel by 

 chumming with snnall. live -bait fish and are 

 caught by pole and line with artificial lures or 

 "jigs." Unfortunately, in Hawaii and else- 

 where in the Pacific, the supplies of baitfish are 

 limited in abundeince and distribution and this 

 fact in turn limits the catch of existing fish- 

 eries and curtails the development of new ones. 

 A method of directing the fish to the vessel and 

 holding them by electrical compulsion could 

 eliminate to a large extent the need for live bait 

 and would simplify the fishing operation in other 

 respects as well. 



The present study, undertaken during 1954 

 and 1955 under Contract Nos. 14-19-008-2204 

 and 14-19-008-2317 between the University of 

 Hawaii and the Pacific Oceanic Fishery Investi- 

 gations of the Fish and Wildlife Service, is con- 

 cerned with some of the technical problems in- 

 volved in electr ofishing in sea water and partic- 

 ularly with the power requirements necessary 

 to elicit electrotaxis in tuna. It includes theo- 

 retical studies on the distribution of the electric 

 field in a highly conductive medium such as sea 

 water and on the internal and external fields 

 aiffecting a fish. It also includes preliminary 

 studies on a small marine fish, the aholehole, 

 or mountain bass (Kuhlia sandvicensis), to de- 

 termine optimum values of current density, pulse 

 duration and pulse frequency for electrotaxis in 

 a snnall tank. It describes an apparatus designed 

 to produce electrotaxis in tuna in a large tank 

 and provides the results of experiments which 

 show that tuna exhibit the electr otactic response. 

 Finally it includes a discussion of the power re- 

 quirements in the open sea as compared with 

 those in a small tank. 



ELECTRIC FIELD IN A CONDUCTING MEDIUM 



In any attempt at electr ofishing in sea water 

 one is faced with the high conductivity of sea 



water and the consequent large dissipation of 

 energy which taxes the source of power . Although 

 Cattley (1955a) indicates that the theoretical 

 field in a conducting medium is known, we have 

 been unable to locate a description in the litera- 

 ture. Consequently, the junior author investi- 

 gated the theoretical field between two spherical 

 electrodes and arrived at the mathematical so- 

 lution given in detail in Appendix I. 



Insumnnary. for spherical electrodes deeply 

 submerged in a large body of water, formulae 

 are presented for calculating at any point in the 

 medium the potential (V). the electric field (E), 

 and the current density (J). The total current 

 (I) between two such electrodes is given by 



I = 4fT (ra V amperes 



and the net resistance (R) is given by 



R = l/(2irira) ohms 



where cr is the conductivity of the water in 



(ohm-cm. )" ' . 

 a is the radius of the electrodes in cnn. , 



and 

 V is the potential applied to the electrodes 



in volts. 



It will be noted that the total current is in- 

 dependent of the distance between the electrodes. 

 This agrees with the statement by Cattley (1955a) 

 that "...the current passing will not decrease 

 appreciably when electrodes 10 or more meters 

 apart are further separated..." except that 

 there are no limitations in the theoretical model. 



THE FISH IN A UNIFORM ELECTRIC FIELD 



Cattley (1955b) has discussed the response 

 of a fish in a uniform, conducting medium which 

 is (a) of the same resistance as the body of the 

 fish, (b) of less resistance than the fish, and (c) 

 of greater resistance than the fish for a specimen 



