negative electrode and was near the middle of 

 the tank. If there was any effect of the current 

 then it should be nnoat evident in such a position, 

 since the fish would have to turn around and 

 swim towards the positive electrode at a point 

 where it would not ordinarily do so. 



These tests were always started with a 

 small voltage by connecting only a few batteries. 

 The voltage was then increased in steps to the 

 maximum of 60 volts, or to the point of 

 satisfactory response. 



The first of t h e tuna family t o be tested 

 was a 38-cm. little tunny. The interruption 

 frequency was 10 per second. Up to 48 volts no 

 effect was observed, but at 48 volts there was 

 evidence of a slight annoyance, twitching, and a 

 tendency to swim nearer to the surface. These 

 were later found to be very typical symptoms 

 for voltages too snnaU to elicit electrotaxis. At 

 54 volts the fish swam nornnally for a moment 

 and then suffered narcosis. The current was 

 turned off at once. The fish sank to the bottom 

 and lay motionless for about 5 minutes with only 

 the gills moving slightly. Finally it started 

 moving and soon swam off. After about a half- 

 hour the fish began to bunnp into the sides of the 

 tank and soon died. On the basis of later exper- 

 iments this behavior was not typical of little 

 tunny or other tunas and we have no explanation 

 for this anomaly. 



together was the only practicable nnethod of 

 increasing the field strength in the tank. The 

 electrodes were then adjusted to a separation of 

 16 feet, thereby approximately doubling the 

 maximum possible field strength. 



The same yellowfin was tested under these 

 new conditions. With maximum source voltage 

 of 60 volts and an interruption frequency of 12 

 c.p. s., the fish immediately oriented towards 

 the positive electrode and swam under the 

 influence of the current until it hit the screen. 

 The tuna would then continue to swim into the 

 screen or along it and would bump into the side 

 walls and even try to jump out. Under these 

 conditions, then, very goodelectrotactic response 

 was achieved. 



Another yellowfin of approximately 50-cm. 

 length was caught and placed in the tank with the 

 yellowfin tested earlier. The test was then re- 

 peated with 60 volts at 12 c.p. s. The new fish 

 also displayed satisfactory electrotjixis. At 16 

 c.p. s. and 60 volts the reaction was consider- 

 ably more violent than at 12 c.p. s. With the 

 voltage reduced to 48 volts the response was 

 still satisfactory. Raising the frequency to 20 

 per second enabled the voltage to be reduced to 

 36 volts while maintaining satisfactory response. 

 This frequency was the limit of the apparatus. 

 Whether or not higher frequencies would allow 

 even smaller voltages is unknown. 



Following this, two dolphin (pelagic fish, 

 but not of the tuna family) were tested 

 successively. One was 67 cm. in length, and 

 the other 61 cm. Neither orientation nor elec- 

 trotaxis was noticed for any voltage up to the 

 naaximum at 10 c.p. 8. Only the typical symp- 

 toms of annoyance, twitching, and swimnning 

 near the surface were observed. At 5 c.p. s. 

 the response was even poorer. 



The same results were obtained in the next 

 two tests employing a 57-cm. little tunny and a 

 53-cm. yellowfin. The tests seemed to indicate, 

 however, that decreasing the frequency below 10 

 per second resulted in a diminishing effective- 

 ness in producing annoyance responses. 



The next test was perfornned on a yellowfin 

 of about 50-cm. length. The result was about 

 the same as before with no indication of orien- 

 tation or electrotaxis, but with Sonne evidence 

 that the higher frequencies were more 

 Stimulating than the lower. 



While in a state of electrotaxis the fish 

 swam at the surface with its head partially out 

 of the water, with mouth open wide, and with 

 gill flaps extended. The last two yellowfin 

 tested did considerable bumping into the screen 

 and walls and occasionally showed signs of 

 electronarcosis, but they continued to live for 

 several weeks. 



Discussion 



In table 6 are shown the values of current 

 density and electric field corresponding to the 

 total applied voltages used in the foregoing 

 experiments. A comparison with table 5 shows 

 that the current densities and fields used with 

 the tuna fall in the same range as those used 

 with aholehole. But since the tunas were much 

 larger fish than the aholehole the head-to-tail 

 voltages produced by these fields were corres- 

 pondingly greater for the tunas. For the third 

 yellowfin tested the minimum head-to-tail 

 voltage for satisfactory response was: 



It became evident that the tests would have 

 to be extended to higher frequencies and greater 

 field strengths. Moving the electrodes closer 



6.2 volts at 12 c.p. s. 

 4.9 " " 16 " 

 3.7 " " 20 



12 



