Response of Fish to Direct Current — Morgan 
489 
TABLE 2 
Mean Time (in Seconds for 5 Fish, 2 Trials Each) 
Spent in the Positive Section of the Tank at 
Various Frequencies and Amperages of Inter- 
rupted Current with 1:1 ON-dFF Ratio 
amperes 
FREQUENCIES 
5 
10 
15 
20 
25 
1 
35.0 . 
45.8 
34.6 
24.3 
38.2 
2 
30.4 
31.4 
33.1 
42.2 
28.6 
3 
25.0 
41.5 
32.5 
36.8 
41.0 
4 
28.2 
33.2 
46.2 
48.2 
43.1 
5 
50.3 
60.0 
60.0 
60.0 
60.0 
maintain equilibrium and would sink slowly 
toward the bottom of the tank, ventral side 
up. In some, all visible signs of life, including 
opercular movements, ceased. However, when 
the power was turned off, all the fish recov- 
ered, usually within a few seconds. None died 
as a result of this series of tests using a con- 
stantly flowing current. Of the five fish which 
were tested at various amperages, one showed 
in both trials the complete electrotactic and 
electronarcotic effect at 12 amperes, one at 
13 amperes, and all five at 14 amperes. There- 
fore, 14 amperes was considered the value 
necessary to cause the fish to come to the 
positive pole and become immobilized when 
uninterrupted current at 225 volts was used. 
A statistical analysis of the quantitative 
data of Table 1 was made to supplement the 
observations reported above. It may be seen 
that the mean time spent in the positive half 
of the tank fluctuated between 19.7 and 38.2 
seconds in the experiments conducted over a 
range of amperages from 1 to 11. As indicated 
by a *'t” test, none of these means differed 
significantly from an expected mean of 30 
seconds. At 12 amperes the mean of 41.5 
seconds differed significantly from the ex- 
pected mean of 30 seconds (t = 2.06; P = 
0.07) . At 13 amperes the mean of 46.2 seconds 
was also significant (t = 4.68; P < 0.01). 
Thus, with the ahoiehole, a positive electro- 
tactic effect at a distance of 5.5 feet (the center 
of the tank) from the electrodes was demon- 
strated quantitatively at 12 amperes. However, 
as already pointed out, complete electrotaxis 
and electronarcosis did not result until a cur- 
rent of 14 amperes was used. 
Interrupted Direct Current 
1:1 On-Off Ratio 
The tabulated results of experiments with 
various values of interrupted direct current 
are shown in Tables 2, 3, and 4. In the first 
group of experiments the power-off period 
was equal to the power-on period at all fre- 
quencies. Examination of the tables again dis- 
closes marked variation in the reaction of 
individual fish. The desired effect, which im- 
mobilized all fish at the positive pole for the 
full 60 seconds of each test period, was reached 
at an average current value of 5 amperes 
(Table 2). This effect occurred at each fre- 
quency with the exception of five interrup- 
tions per second. An effect comparable to 
this was not obtained with uninterrupted pow- 
er until a current of 14 amperes had been 
reached. This seems to indicate that the in- 
terruption in some way of direct current makes 
it much more effective. 
It is obvious that by interrupting the direct 
current so that the power alternates on and 
off for equal periods, more efficient use is 
made of the available power. The question 
is then raised as to whether the reaction of 
the fish varies with the duration of the on-or 
off-period. To obtain information on this 
TABLE 3 
Mean Time (in Seconds for 5 Fish, 2 Trials Each) 
Spent in the Positive Section of the Tank at 
Various Frequencies and Amperages of Inter- 
rupted Current with 3:1 On-Off Ratio 
AMPERES 
FREQUENCIES 
5 
15 
25 
4 
41.9 
40.3 
29.4 
5 
38.7 
37.7 
22.8 
6 
32.3 
36.2 
41.5 
7 
52.4 
52.4 
52.6 
8 
53.7 
56.5 
60.0 
