7123 ‎(3)‎

• UCREFRP Catalog Number: 7123
• Author: Klima, E. F.
• Title: Voltage and pulse rates for inducing electrotaxis in twelve coastal pelagic and bottom fishes
• USFW Year: 1972
• USFW - Doc Type: Journal of the Fisheries Research Board of Canada
• Copyright Material: YES

1606 JOURNAL FISHERIES RESEARCH BOARD OF CANADA, VOL. 29, NO. 11, 1972
of pickup probes made from two 3 mm diameter bronze
rods spaced 10 cm apart and insulated so that only the
bottom 10 mm of each rod was exposed. The pulse
characteristics were displayed on the oscilloscope as a
graph of voltage against time. Voltage is referred to as
the decrease across 10 em.
The wave form on the oscilloscope is not a true
capacitor discharge-shaped pulse because of the induc-
tance of the external circuit. For this reason rise time
was disregarded and I considered the peak of the pulse
as time zero. The remaining portion of the pulse closely
approximates a theoretical capacitor discharge shape.
Pulse width is defined here as the time in micro-
seconds (µsec) it takes a pulse to decay to one-third of
its peak value, as is standard in describing capacitor
discharges. Values for this parameter ranged from 0.5
to 2.2 msec in the study. These pulse widths were found
most etI'ective for electrical stimulation.
Water resistance, used to calculate the theoretical
power requirements of the prototype electrical. fishing
system, was measured by placing a 1 ohm resistor on
the output side between the pulse generator and one
electrode. The amperage in the resistor at a specific
d-c voltage output was measured via pickup leads from
the oscilloscope. The total voltage from electrode to
electrode was divided by the amperes in the resistor in
order to obtain the resistance between the electrodes.
For example, 2.0 v per 10 cm (v/10 cm) in the tank
gives 90 v across the tank (i.e. 2.0 x 10 x 4.5 m =
90 v) which, divided by 38 amp through the resistor,
gives 2.4 ohms resistance in the tank.
To determine the combinations of electric parameters
which best induced electrotaxis, I positioned the fish
facing, and within 1 m of, the cathode. Preselected pulse
rates and voltages were applied to the experimental
tank only when the fish were correctly positioned. Two
event-timing clocks connected to the pulse generator
were activated at the same time as the pulser to provide
a time base for measuring responses. The observer
could stop each clock when the animal had completed
a specific reaction.
To evaluate the effectiveness of the pulse characteris-
tics tested, 1 measured the time the fish took to swim the
length of the tank. In addition, the proportion which
went into tetanus was recorded. I selected one lap to
record tetanus because any fish will eventually go into
tetanus if subjected to electricity for a long period of
even low voltage (Collins et al. 1954).
In another series of tests to further evaluate pulse
characteristics, Iforced the fish to swim up and down
the tank, and these are subsequently referred to as
leading studies. Leading was accomplished by changing
the polarity of the field after each lap, or 4.5 m, when
the lisp was within 0.5 m of the anode. The process
was continued until the fish could no longer swim or
until it had swum 20 laps. The times it took to swim
two and live laps, and the number of Japs it swam, were
recorded.
Even with all this information available for certain
species, it was difficult to determine the best combination
of electric parameters inducing electrotaxis. Conse-
quently, a^ index of optimal responses was obtained
for selected species by dividing the time it took <tn in-
dividual to swim five laps (23 m) by the number of
laps each fish had swum and then computing the average
for the electrical combination. The lower the index, the
better the electrical combination. For example, if a
given electrical combination showed a time of 30 sec
to swim five laps and a distance swum of 15 laps, the
index was 2.
T'he basic idea behind the experimental design was
that fish stimulated with the optimum pulse characteris-
tics would swim further and faster. I considered the
shortest times to swim one, two, and five laps; and the
average maximum number of laps swum as the most
suitable.
Selection of Test Voltages and Pulse Widths
The success of electrical fishing is dependent upon the
proper electrical combinations for inducing taxis. The
voltage, pulse rate, and pulse width required to induce
electrotaxis vary with species, fish size, and, probably,
other factors (Riedel 1952; Collins et al. 1954; Bary
]956; l-ligman 1956; Halsband 1967; Monan and
Engstrom 1963; Kessler 1965; Klima 1968). Hence, a
combination of electrical factors which will induce
electrotaxis in one species may induce either fright
response or no response in another.
The overall effect of increasing voltage at a fixed pulse
rate was examined for the scaled sardines and these
results provided the general guideline for the experi-
mental minimum and maximum test voltages.
A gradual increase was evident in the time it took
scaled sardine to swim one lap as the voltage was in-
croused from 1.5 to 4.5 v/10 cm at 15 pulses/sec. The
greatest effect was the decrease in the distance swum
with an increase in voltage (Fig. 1). The maximum
number of laps scaled sardine swam was at 1. S v/10 cm,
and the lowest at 4.5 v. The response times to swim
two laps showed a general increase with an increase in
voltage.
The overall effect of a voltage increase was to decrease
the distance over which scaled sardine could be controlled
and to decrease the speed it took to swim more than
9 m. An increase in voltage also increased the proportion
of fish in tetanus even at low repetition rates.
Response of fish in an electrical field depends upon
voltage and the length of the animal because voltage
potential increases proportionately with the animal's
length. For example, a 10 cm fish, faced parallel to Uie
current lines in a homogenous field at 30 v/m, has a
potential of 3 v from head to tail but a 20 cm fish has a
potential of 6 v. As a result, it is important to determine
the significance of size or length as related to the most
suitable electrical combination. Consequently, one
coastal pelagic fish, scaled sardine, and one bottomfish,
longspine porgy, of ditlerent size groups were examined.
Itcsults on scaled sardines indicated that small fish
could be Icd more effectively at 3 v/10 cm than large
fish but the responses indicated thaC 3 v/lU cm are not
completely adequate to control these smaller fish (Table
l). Stimulation of less than 3 v/10 cm or more than
1 .5 v/10 cm would probably be more suitable.
n comparison of the response times to swim one lap
was made between small (86-101 mm fork length) and