LEADING ADULT SQUAWFISH
(Ptychocheilus oregonensis)
WITHIN AN ELECTRIC FIELD

Marine Biological Laboratory

LIBRA. RTT

AUG 1 U rJ59
WOODS HOLE, MASS.

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 298

UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE

EXPLANATORY NOTE

The series embodies results of Investigations, usually of restricted
scope, intended to aid or direct management or utilization practices and as
guides for administrative or legislative action. It is Issued In limited quantities
for bfficial use of Federal, State or cooperating agencies and in processed form
for economy and to avoid delay in publication .

United States Department of the Interior, Fred A. Seaton, Secretary
Fish and Wildlife Service, Arnie J. Suomela, Commissioner

LEADING ADULT SQUAWFISH (PTYCHOCHEILUS OREGONENSIS)
WITHIN AN ELECTRIC FIELD

by

Galen H. Maxfield, Kenneth L. Liscom, and Robert H. Lander
Fishery Research Biologists
Bureau of CommerciEuL Fisheries

United States Fish and Wildlife Service
Special Scientific Report — Fisheries No. 298

Washington, D. C.
April 1959

The Library of Congress catalogue card for this publication
is as follows:

Maxfield, Galen H

Leading adult squawfish {Ptychocheilus oregonensis)
Avithin an electric field, by Galen H. Maxfield, Kenneth L.
Liscom, and Robert H. Lander. Washington, U. S. Dept.
of the Interior, Fish and Wildlife Service, 1959.

iv, 15 p. illus., diagrs., tables. 27 cm. (U.S. Fish and Wildlife
Service. Special scientific report — fisheries, no. 298)

1. Ptychocheilus oregonensis. 2. Electrophysiology. i. Title.

( Series)

[SH11.A335 no. 298] Int 59-71

U. S. Dept. of the Interior. Library

for Library of Congress

The Fish and Wildlife Service series, Special Scientific
Report — Fisheries, is catalogued as follows:

U. S. Fish and Wildlife Service.

Special scientific report : fisheries, no. 1-
iWashingtonj 1949-

no. illus., maps, diagrs. 27 cm.

Supersedes In part the Service's Special scientific report.

1. Fisheries — Research.
SH11.A335 639.2072 59-60217

Library of Congress [2j

TABLE OF (XINTENTS

Page

Introduction 1

Preliminary experiment 2

Objectives 2

Acknowledgments 3

Method

Experimental design 3

Source of fish 4

Apparatus and measurements 5

Experimental procedures 8

Results and discussion 9

Description of behavior 9

Analysis of results 10

Conclusions 14

Recommendations 15

TABLES
No.

1 Sequence for energizing electrode rows in array 7

2 Percentage of squawfish that entered the "positive"

end zone during 7-second test interval 10

3 Mean percentage of unshocked and once-shocked squawfish
that entered the "positive" end zone in north and south
blocks (based on 18 observations) 10

4 Analysis of variance of effects of potential, pulse
frequency, and pulse duration on movement of unshocked
squawfish 11

1X1

Tables cont'd:

No. Page

5 Analysis of variance of effects of potential, pulse
frequency, and pulse duration on movement of once-
shocked squawfish 11

6 Analysis of variance of tests of unshocked and once-
shocked squawfish combined 13

FIGURES

1 Laboratory experimental area with staggered electrode

array 4

2 Staggered electrode array used in laboratory 5

3 Block diagram of electrical equipment 6

4 Length frequency distribution of squawfish 6

5 Difference in percentage of squawfish that entered the
"positive" end zone against the difference in water
temperature between times a combination was run 12

6 Diagram of potential contours for sequentially pulsed

field 12

7 Comparison between blocks of the percentage of squawfish

that entered the "positive" end zone 13

8 Mean percentage of squawfish that entered the "positive"
end zone in north and south blocks for each value of
the variable factors of potential, pulse frequency, and
pulse duration, unshocked and once-shocked fish com-
bined 14

IV

LEADING ADULT SQUAWFISH (PTYCHOCHEILUS OREGONENSIS)
WITHIN AN ELECTRIC FIELD

by

Galen H. Maxfield, Kenneth L. Liscom, and Robert H.
United States Fish and Wildlife Service
Seattle, Washington

Lander

ABSTRACT

The nature of squawfish predation on hatchery -reared salmon fingeriings requires an economical
and practical method for continuously removing the squawfish from the areas of releases. Research has
been directed toward the development of an electrical trapping device employing the principle of elec-
tiotaxis. The objectives of the study were to determine by systematic testing, (A) the optimum values
of the electrical variables of (1) potential (60, 75, and 90 volts), (2) pulse frequency (2, 5, and 8 pulses
per second), and (3) pulse duration (10, 20, and 30 milliseconds) for leading adult squawfish within an
electrical array; and (B) the possible significance of the direction of movement of the electrical fields.
Pulse frequency was found to be the most critical variables (optimum, 2 pulses per second). Potential
was also significant (optimum, 60 volts), but pulse duration was not significant, at least in the range
tested. The direction of the electrical fields io tiie laboratory tank was a highly significant variable.
The fi'!>i showed a greater response when the electrical fields moved toward the north end of the labora-
tory tank than toward the south. The reason for this reaction was not determined.

INTRODUCTION

For the past five yceirs, the Columbia
River fishery for salmon and steelhead has
been valued at $17,000,000 annually. In
addition, this fishery has provided an
inestimable amount of pleasure to sports
fishermen. The fishery is sustained, in
part, by some 600,000 Columbia River salmon
and steelhead that annually ascend the fish
ladders at Bonneville Dam. However, reduc-
tion in spawning areas, due to construction
of dams, has caused increasing dependence
on hatchery-reared fish.

In 1956, about 58,000,000 salmon fin-
geriings, reared in hatcheries at a cost of
$732,000, were released into the Columbia
River and its tributaries below McNary Dam.
Since the fingerling salmon are released in
dense concentrations, thus becoming easy
prey for predatory fish, the success of the
salmon-rearing program is greatly affected
by the predators. Biologists and hatchery
personnel have often observed at times of
release of fingerling salmon that the squaw-
fish (Ptychocheilus oregonensis (Richard-
son) , is the most destructive of these
predators.

A study by the U. S. Fish and Wildlife

Service — has shown that almost all of the
predation by squawfish occurs immediately
after release of the fingeriings. This fact
indicates that the most effective way to
control Squawfish predation is to reduce the
numbers of squawfish in the areas where the
fingeriings are released.

Management biologists have used dyna-
mite and gill nets to reduce the populations
of resident squawfish in the release areas
for periods of several weeks prior to the
release of the fingeriings. Neither of
these control measures has been effective,
however, as the release of fingeriings soon
attracts more squawfish.—' Once the fin-
geriings are released, dynamite no longer

V Thompson, Richard B. Food of the
squawfish, Ptychocheilus oregonensis
(Richardson), of the Lower Columbia
River. United States Fish and Wildlife
Service. Fish. Bull. No. 158 (In press)

£/ Zimmer, Paul D. Observations on hatch-
ery releases and squawfish predation in
Little White Sailraon River in spring of
1953. United States Fish and Wildlife
Service, Mimeo. Report, August 1953.
14 pp. Portland, Oregon.

can be used; and the manpower required for
continuous control of squawfish population
by gill netting makes that method imprac-
tical also. The failure of these controls
makes clear that there is need for an
economical and practical method for continu-
ously removing squawfish from the area in
which the fingerlings are released.

In an effort to meet this need, Max-

-5/

field and Volz in 1953 — ' conducted a labo-
ratory study of controlling squawfish by
electricity. This study involved the use of
a single electrical field as a barrier to
block the entrance of sqawfish into a desig-
nated area. Direct current was supplied to
two rows of electrodes, the positive row
being located downstream. The individual
squawfish swimming up to the barrier would
feel the electrical field and, usually,
would be deterred from entering the strong
field between the two rows of electrodes.
If, however, a squawfish did enter the
strong field between the two rows, its re-
action was to swim back toward the positive
row and out of the array. This reaction of
the fish can be explained by the principle
of electrotaxis — movement of the fish toward
the positive pole in a direct-current field.
Fingerling salmon, being shorter than the
adult Squawfish, were less affected by the
potential difference in the field and passed
safely through this electrical barrier when
released on the upstream, or negative, side.

Preliminary Experiment

In recent laboratory studies at Seattle,
we attempted to use electrotcixis to lead
the squawfish into a net enclosure or trap-
ping area. The square-wave form of pulsat-
ing direct current was used with an array
of several rows of electrodes in which the
electrical fields were sequentially created
in one direction between successive rows of
electrodes.

However, initial attempts to lead indi-
vidual Squawfish into a trapping area in
the laboratory required basic knowledge of
the effect on squawfish of the electrically
variable factors of potential, pulse fre-

2/ Maxfield, Galen H. , and C. D. Volz. An
electrical barrier for controlling squaw-
fish (Ptychocheilus oregonensis) preda-
tion, U. S. Fish and Wildlife Service,
Seattle, Washington. (Unpublished ms.)

quency, and pulse duration. A preliminary
experiment, therefore, was set up to deter-
mine the extreme ranges of these three
variable factors.

The results showed that the following
conditions should be the limits and ranges
of further experiments:

Potential: The range of potentials
studied extended from (1) the minimum
potential at which the squawfish re-
sponded to (2) the minimum potential
at which the squawfish were in obvious
distress. This range was 60 to 90
volts, respectively, when applied to
two rows of electrodes spaced 17 inches
apart in rows 18 inches apart.

Pulse frequency: Employing the two
experimentally determined values of
potentiail of 60 and 90 volts, we used
the above procedure to arrive at a
suitable range of pulse frequencies:
2 to 8 pulses per second.

Pulse duration: Finally, employing
combinations of the two potentials cind
the two pulse frequencies, we also
used the same procedure in an attempt
to arrive at a suitable range of pulse
durations. Variations in pulse dura-
tion, however, in the range of 10 to
90 milliseconds did not have any ob-
servable different effects on the in-
dividual squawfish. A range of pulse
duration of 10 to 30 milliseconds,
therefore, was selected arbitrarily
for use in the following experiments.

After gaining knowledge of the extreme
ranges, we wished to determined the optimum
electrical conditions for leading adult
squawfish. Therefore, we designed the ex-
periments reported below in which we tested,
under rigorously controlled conditions , the
effects on squawfish of extreme and inter-
mediate values of the electrical variables.
In addition, we had observed in the prelim-
inary work that the direction of movement
of the electrical fields in the laboratory
tank might be a significcint variable. Ac-
cordingly, we also tested the effect of
this variable on squawfish.

Objectives

The objectives of the present study
were to determine by systematic testing,
(A) the optimum values of (1) potenticil,

(2) pulse frequency, and (3) pulse duration
for leading adult squawfish within an elec-
trical array; and (B) the possible signifi-
cance of the direction of movement of the
electrical fields.

Acknowledgments

The research reported here, conducted
in 1956, was made possible with funds for
Squawfish control studies from the Lower
Columbia River Program, U. S. Fish and Wild-
life Service. Acknowledgment is made to
personnel of the Fish and Wildlife Service
hatcheries of the Lower Columbia River for
use of holding facilities. Joseph Gauley
and Ben Pulliam collected adult squawfish
at Bonneville Dam, and Clifford Davidson
cooperated in the collection of squawfish
at Rock Island Dam. Archie Anderson, Oregon
Fish Commission, gave the use of a holding
pond at Bonneville Hatchery; Dr. Lauren R.
Donaldson, University of Washington, per-
mitted the use of several holding ponds at
the School of Fisheries in Seattle.

Especial appreciation is expressed to
Dr. Douglas G. Chapman, Department of Mathe-
matics, University of Washington, for
reviewing the statistical treatment of the
data and to Paul Zimmer, Fish and Wildlife
Service, Portland, Oregon, for his efforts
in furthering the research.

METHOD

We designed these experiments (1) to
proceed from the results of our preliminary
experiments, (2) to use most advantageously
a limited supply of squawfish, (3) to over-
come the inability to reverse readily the
direction of the electrical fields, and (4)
to use standard experimental procedures in
measuring the leading effectiveness of
electrical conditions.

Experimental Design

1. Preliminary observations on indi-
vidual fish defined the working ranges of
potential, pulse frequency, and pulse dura-
tion, as follows: Potential, 60 to 90
volts; pulse frequency, 2 to 8 pulses per
second; and pulse duration, 10 to 30 milli-
seconds. Intermediate values were tested
in each range to determine whether the
ranges included optimum electrical conditions
for leading adult squawfish. Inclusion of
these intermediate values increased the

number of possible combinations of values
of potential, pulse frequency, and pulse
duration from 8 to 27. These 27 combina-
tions in the experimental design were set
up as a series of tests.

2. As more than one test at each
combination in the series was needed to
determine whether the effects of one vari-
able factor depended upon the values of one
or both of the other variable factors, the
number of tests required in relation to the
number of fish available for use in the
tests was such as to require using each
group of fish twice. Furthermore, it was
not possible to test every combination of
the three variable factors with both un-
shocked and once-shocked fish before pro-
ceeding to the next combination.

3. As we had no facilities to control
the temperature of the water in the experi-
mental tank, we anticipated a temperature
decrease throughout the experiments from
late summer to fall.

4. It was not possible readily to
reverse the direction of movement of the
electrical fields in the laboratory tank,
but it was of some interest to determine,
if possible, whether the direction of the
electrical fields had a significant effect.

5. On the basis of readings taken at
release areas, the resistance of the water
was maintained at 15,000 ohms per cubic
centimeter throughout the experiments.

Based on our preliminary work, the
possibility existed that the fish could
show a preference for the north or south
end of the experimental area. This could
be determined readily if the direction of
the electrical fields could be reversed
quickly — a combination could be tested
with the movement of the electrical fields
first in one direction and then in the
other. However, preliminsiry observations
indicated that, with the power off, a pro-
hibitive number of fish would be required
to demonstrate the presence or absence of
a preference of the fish for one end of
the laboratory tank.

The use of the north and south blocks
of tests arose from the time-consuming
procedure that would have been necessary
in order to alternate the direction of move-
ment of the electrical fields. All combi-
nations were tested in separate series with

unshocked and once-shocked fish in each of
the two blocks: (1) positive fields moving
to the north, and (2) positive fields mov-
ing to the south. The assumption that the
relative effect of each combination would
be the same in each block, even though the
tests in one block would be performed later
than those in the other, was tested by
graphically comparing the trends of the
effects between blocks and by analyzing
interaction effects.

If the proportion of fish that entered
the north end with power off had changed
within a block, then the estimates of rela-
tive effects of test conditions run at
dJi'ferent times in the block would have been
biased. To avoid such a bias the order of
testing each combination was random within
each block; a new random order was used for
each series with unshocked and once-shocked
fish.

While designing the experiment, we
surmised that a difference between north
and south blocks of tests would represent
a possibility of the following effects:
(1) a preference by the fish for the north
or south end; (2) differences in the pattern
of electrical current flow associated with
the reversal of direction of the electrical
fields; and (3) changes in the experimental
environment, such as the water temperature
chzmges which did occur between blocks.
Furthermore, if differences between blocks
due to the pattern of electrical current
flow were assumed to be negligible, and if
the effect of temperature also were shown
to be insignificant, then a pronounced dif-
ference between blocks could be ascribed to
a preference of the fish for one end of the
laboratory tank. During the experiment, we
did assume the differences between blocks
due to the pattern of electrical current
flow to be negligible, and the effect of
temperature was insignificant. Although we
do not know the cause for the preference,
we conclude that the difference between
blocks was due to a preference of the fish
for one end of the laboratory tank.

The experiment was, therefore, designed
as a 3-^ factorial with the following values
of electrical variable factors: potential,
60-75-90; pulse frequencies, 2-5-8; and
pulse durations, 10-20-30. Eight series of
tests (4 on unshocked, and 4 on once-shocked
fish) of these 27 combinations were run at
random. Four series (2 on unshocked, and 2
on once-shocked fish) were tested in each of

the two experimental blocks: (1) positive
fields moving to the north, and (2) posi-
tive fields moving to the south.

Source of Fish

The adult squawfish (Ptychocheilus
oregonensis) used in these experiments were
transported in an aerated tank from U. S.
Fish and Wildlife Service hatcheries at
Little White Salmon 2ind Leavenworth, Wash-
ington, and from the Bonneville hatchery
of the Oregon Fish Commission at Bonneville
Dam, Oregon. The fish had been held in
outdoor rearing ponds until sufficient num-
bers had been obtained for transportation

NEGATIVE ZONE

I I I

bfof' of Sequence

Fish-

Release

Areal

-•- —
1

- ♦

— •

1

--•-

Stor(

of
1

Seq

jence

i.

POSITIVE ZONE

opproK imofely 17 apart

(-)
(+)

(-)

(+)

Figure 1. — Laboratory experimental area with
staggered electrode array. Arrows indicate
start of sequence of electrical fields mov-
ing toward north end of laboratory tank.

to Seattle. The fish stored at Little
White Salmon hatchery had been obtained (1)
by seining and by hook-and-line fishing in
Drano Lake, (2) by hook- aind- line fishing in
the Columbia River near the Spring Creek
hatchery, and (3) by seining in a drainage
ditch at Echo, Oregon. The fish stored at
Leavenworth hatchery had been trapped both
in the forebay and in the fishway at Rock
Island Dam, Washington. The fish stored
at Bonneville hatchery had been trapped in
the fingerling bypass at Bonneville Dam.
These fish were transported to Seattle in
100-fish lots, and most lots of the fish
were placed in screen traps in lake water
near the laboratory. Some lots were held
in outdoor hatchery raceways in lake water
at the School of Fisheries, University of
Washington, Seattle.

Apparatus and Measurements

The experimental area (fig. 1) in the
laboratory was a portion of a larger insu-
lated tank constructed for electrical
studies on salmon fingerlings. The con-

crete floor and construction block walls
were equipped with an electrically insulated
lining of several coats of Amercoat paint.
The inside dimensions of the experimental
area were 24 feet 10 inches by 14 feet by
16 inches. The depth of water was approxi-
mately 11 inches during the period of the
study, and the water was not in motion.

The electrodes used in the array were
of 1/2 inch outside diameter ciluminum
tubing, 12 inches long. Two holes were
drilled at one end of each electrode; a
T-shaped copper wire with a copper slim-
nosed alligator clip soldered onto the base
of the T was inserted into the holes. The
electrodes were suspended in the water, to
an approximate depth of 10 1/2 inches, from
ten rows of parallel copper wires secured
to insulators. The wires were strung at
right angles across the center of the ex-
perimental area. The distance between the
rows was 18 inches, and the electrodes were
spaced approximately 17 inches apart in
each row in a staggered array (figs. 1 and
2).

Figure 2. — Staggered electrode array used in laboratory.

220 V
> —

30

-> —

Storter
Switch

Voltage
Control

DC.
Generator

Pulse

Frequency

V„ Control

_j m

Overload -^^ ^t _,

? I e-

Pulse
Duration
Control

V

Relay

And

Control

Switch

Overlood Trip

Pulse
Generator

And

Sequential

Switch

-^ 9
->5
-^►4-8
-^-3-7

^2-6

Constant
Voltage
Tronsformer

— >

Calibrated

Oscil loscope J

Scope

Input

Figure 3. — Block diagrcim of electrical equipment.

120
110
100
90
o 80

cr

70
60
50
40
30
20

10
0

1219

r^

r^

— i — I — r 1 — I r — I — I — I — I 1 — I — I — I 1 — I — I — I — I r — i — r — i — i — r — i — r — i — i 1 — i 1 — n

12 13 14 15 16 17 18 19 20

TOTAL LENGTH IN INCHES

10

Figure 4. — Length frequency distribution of adult squawfish.

The fish were released in the center
of the array (between rows 5 and 6) from a
rectangular enclosure made from small-mesh
wire screen fitted with wooden laths for
support, the inside dimensions being length,
4 feet; width, 4 inches; and height, 15 1/2
inches. The enclosure was raised out of
the water by means of a bridle and a line
running through pulleys on the ceiling.
After the array was energized, the operator
stationed at the electronic switching unit
pulled the line to release the fish within
the moving electrical fields.

By means of an electronic switching
unit developed in the Seattle laboratory,
pairs of the rows of the electrodes were
energized successively to establish a se-
quence of pulsating, direct-current fields
that moved in the direction of positive
polarity. In the north block, the positive
row of a pair of energized rows was always
to the north. Figure 1 shows for the north
block the start of the sequence when the
first set of electrical fields is estab-
lished by energizing the second and third,
and the sixth cind seventh rows of electrodes
simultaneously. The progress of the entire
sequence through the electrode rows is indi-
cated in table 1. As the table shows, the

Table 1. — Sequence for energizing electrode rows to set up
moving electrical fields in laboratory array.

Polarity

Change in
polarity

First

Second

Third

Fourth

Sequence

begins

again

Row Row Row Row Row Row Row Row How Row
1 23456789 10

(-) (♦) 0 0 (-) (♦) 0 0 0

0 {-) (♦) 0 0 (-) (♦) 0 0

0 0 (-) (♦) 0 0 (-) (♦) 0

0 0 0 (-) (♦) 0 0 (-) (♦)

(-) (♦) 0

(-) (♦)

0

sequence is automatically repeated after the
tenth row of electrodes has been energized.
The frequency and duration determine the
rate and length of time each pair of rows of
electrodes is energized. For example, at a
setting of 30 milliseconds pulse duration
and frequency of 2 pulses per second, a pair
of rows is energized 30 milliseconds with a
lapse of 470 milliseconds before the next
pair is energized. The total time to ener-
gize the four sets of electrical fields in

the desired sequence (from rows 2 and 3
through row 10) at the cibove conditions of
frequency and duration is 2 seconds. With
pulse frequencies of 5 and 8 pulses per
second, at a pulse duration of 30 milli-
seconds, it required .8 and .5 seconds,
respectively.

The direction of movement of the elec-
trical fields shown in figure 1 was reversed
for the south block of tests. Upon rever-
sal, row 10 in figure 1 became row 1 (the
electrode row not energized). In the south
block, the positive row of a pair of ener-
gized rows was always to the south.

Although the end zones of the experi-
mental area were not electrically charged
except for fringe effects from the electri-
cal fields, it was convenient in conducting
our tests to name the zones "positive" and
"negative". The "positive" end zone was
beyond row 10 (the last positive charge row)
of the array, and the "negative" end zone
was before row 1 (which was uncharged).

A schematic description of the switch-
ing unit designed to perform this operation
is shown in the block diagram (fig. 3). A
detailed description of the electrical cir-
cuits controlling the square-wave pulses
throughout this experiment and determining
the sequence of firing will be published
later.i/

The direct current was provided by a
10-kilowatt motor-generator set, with a
maximum output of 500 volts at 20 amperes.
A calibrated oscilloscope operated from a
voltage-regulating transformer was used for
setting potential and observing wave form,
and a vacuum-tube volt meter for plotting
the field with a voltage gradient probe.
As a safety device, an overload relay with
push-button reset was installed to prevent
serious damage to the electrical apparatus.

Areas to hold the fish prior to and
following each test were constructed from
plywood at the north end of the tank. A
plywood wall separated these holding areas
from the experimental area of the tank to
eliminate any possible visual effect that

4/ Dale, Harry P., and C. D. Volz. A

pulse generation and distribution sys-
tem for electrical fish guiding.
United States Fish and Wildlife Service.

might attract the fish during a test. These
holding areas were not within the influence
of the electrical field.

The tests were conducted under a con-
stant light intensity provided by two 500-
watt Icunps suspended 10 feet above the water
at each end of the large tank.

Potential was measured by a calibrated
oscilloscope, specific resistance of the
water by an industrial conductivity bridge,
and temperature of water by a standard mer-
cury thermometer. The desired pulse fre-
quency and pulse duration for each test were
set by dials on the calibrated switching
unit.

The fish were measured for total length
(from the tip of the snout to the extreme
end of the tail) to the nearest quarter-inch.
Each new lot of fish was sorted and counted
into two size groups: Group 1 — small fish,
10 to 15 inches; Group 2 — large fish, 15
through 20 inches. Fish shorter than 10
and longer than 20 inches were eliminated.
Figure 4 (page 6) shows the length frequency
of the jidult squawfish used in the tests.
These measurements were taken of fish which
died after one exposure and of fish twice
exposed to the electrical field.

The number of fish available was not
sufficient to permit testing with one spe-
cific size group, or to make a comparison
between two or more size groups. Therefore,
a ratio of small to large fish was deter-
mined for each lot of new fish, and this
ratio was used to make up the 10 fish in
each test. This size ratio varied as the
weeks of testing progressed, but the average
ratio was 8 small fish to 2 large fish.

Experimental Procedures

We conducted 216 tests (8 series of
tests, 27 tests per series) from August 1
through October 31, 1956, exposing 1,080
fish in 10-fish groups as unshocked and
once-shocked fish. Actually a total of
1,219 fish was required to perform the tests
because of mortalities of some of the once-
shocked fish.

After we released adult squawfish
within the sequentijilly pulsed electrode
array, we measured the effectiveness of
leading for each combination of potential,
pulse frequency, and pulse duration by the
percentage of fish that entered the "posi-

tive" end zone of the experimental area
during the 7-second period of test.

We used equal numbers of fish (10 fish)
to test each condition to obtain a reliable
comparison of the leading effectiveness of
various potentials, pulse frequencies, £ind
pulse durations, the number of tests per-
formed each day being determined by the num-
ber of fish available. The squawfish to be
tested were placed in holding areas at the
north end of the laboratory tank.

If the lot of fish to be tested con-
sisted of unshocked fish (fish not pre-
viously exposed to the electrical fields)
we sorted it into the two size groups.

To minimize any chance of a learning
response, we used a lot of fish no more
than twice. The tests in each series were
so arranged that the fish were never exposed
to the same combination of variable factors
as unshocked and once-shocked fish.

The experimental tank was drained zind
filled with fresh water once a week to main-
tain the desired level of resistance (15,000
ohms/cm-^) of the water. No facilities were
available to control the temperature of the
water. The temperature measured 62" P. at
the beginning of the tests August 1, 1956,
and dropped to 50° F. at the end of the
tests on October 31, 1956.

At the beginning of each test, after
the electronic switching unit was turned on,
we visually checked whether the electrode
array was pulsing properly by observing a
series of argon lamps connected across each
pair of electrode rows. After determining
that the switching unit was performing as
desired, we turned the unit off until we
had placed the 10 fish to be tested in the
fish release enclosure.

Half the fish for each test were headed
toward each end of the fish release enclo-
sure, and aligned across the direction of
the sequentially pulsed electrical fields.
After turning on the switching unit and re-
leasing the fish, we determined the duration
of exposure by a time clock, meeinwhile count-
ing the fish during each test according to
(1) the number that were led with moving
electrical fields into the "positive" end
zone, and (2) the number that went against
the moving electrical fields into the "nega-
tive" end zone. These two counts were made
during the test interval because no traps

were closed at the end zones to hold the
fish at the conclusion of the test. Then
we dip-netted the fish from the experimental
area, separated them for size, and placed
them in the holding areas until the tests
for that day were completed. Remarks on the
behavior of the fish were recorded for each
test.

Two men were required for each test.
When the men at the switching unit had
turned on the power to energize the elec-
trode array and had received a signal from
the second man, he quickly raised the fish
release enclosure to liberate the fish.

Following the tests for each day, the
two size groups of once-shocked fish were
returned to separate holding pens in lake
water. These fish were not exposed for the
second time until after at least 48 hours.
Twice-shocked fish were measured for total
length and destroyed to make holding space
available for new lots of fish.

RESULTS AND DISCUSSION

We recorded the behavior of groups of
squawfish in each test in order to determine
the effects of the different levels of
potential, pulse frequency, and pulse dura-
tion; also counts were made of the number of
fish that were effectively led under the
different electrical conditions.

Description of Behavior

The squawfish reacted instantaneously
to the potential and pulse frequency levels
used in these experiments. The pattern of
the reactions of the squawfish in the ener-
gized fields depended more upon changes in
pulse frequency than potential. In fields
of pulse frequency of 2 pulses per second,
at the three levels of potential: (1) the
squawfish appeared to feel the electrical
fields, showed no loss of equilibrium, and
responded favorably to the direction of the
electrical fields; (2) the swimming speed of
the individual fish varied from slow to
swift; (3) some fish circled in the middle
of the array before orienting themselves to
the direction of the electrical fields; (4)
some fish swam rapidly against the direction
of the electrical fields and into the "nega-
tive" end zone; and (5) some fish swam
rapidly against the direction of the elec-
trical fields, but their swimming speed was
slowed to such an extend that (a) they

barely reached the end zone, or (b) they
suffered electroparalysis and thus never
left the electrode array. Mamy of those
fish swimming against the direction of the
electrical fields appeared to jerk their
heads in response to the pulse, which,
however, was not strong enough to reverse
their direction.

In fields of pulse frequency of 5
pulses per second, at energy levels of
potential of 60 and 75 volts: (1) the
Squawfish appeared to feel the electrical
fields noticeably, revealing loss of equi-
librium in from 1 to 8 fish in one-third
to one-half of the tests; (2) swimming was
sluggish or difficult, the speed slow to
moderate; (3) the squawfish generally
showed no leading response to the direction
of the electrical fields; and (4) most of
the fish in half of the tests at the level
of potential of 75 volts remained in the
middle of the electrode array. At the
level of potential of 90 volts: (1) 1 to
10 squawfish, in almost every test, suf-
fered electroparalysis; (2) swimming was
sluggish or difficult; (3) the squawfish
showed no leading response to the direction
of the electrical fields; and (4) most or
all of the fish in each test remained in
the middle of the electrode array.

In fields of pulse frequency of 8
pulses per second, at levels of potential
of 60 and 75 volts: (1) squawfish felt
the electrical fields very noticeably,
revealing loss of equilibrium in from 2
to all 10 fish in all tests; (2) swimming
was sluggish or difficult, with loss of
motion in some fish; and (3) most of the
fish remained in the middle of the elec-
trode array. At the level of potential of
90 volts: (1) 3 to 10 squawfish in each
test suffered immediate or nearly immediate
electroparalysis; and (2) when electro-
paralysis was not immediate, the movements
of the fish were generally quite violent,
and, in mcuny cases, excellent leading
response of short duration was achieved.
Typically, an individual squawfish made a
violent lunge at the moment of release
within the sequentially pulsed electrical
fields. This action carried the fish 2 to
3 feet from the release area, or approxi-
mately half the distance to the "positive"
end zone. This lunge endured usucdly for
the time interval of one sweep of the pulse
through the four electrical fields. As the
time interval of the pulse to sweep the
four fields once is one-half second at 8

Table 2. — Percentage of squawfish that entered "positive"
end zone during 7-second test interval.

Percentage of
unshocked fish

Percentage of
once-shocked fish

To north zone To south zone

at fre- at fre-

quency — of quency — of

2 5 8 12 5 8

i To north zone To south zone

at fre-
quency — of

at fre-
quency — of

Tests at 60 volts potential:

1

Duration:

10 milliseconds: 1st test

90

30

30

50

50

30

60

80

50

60

0

10

2nd test

50

80

0

30

30

10

60

40

10

20

10

0

20 milliseconds: 1st test

50

60

20

60

10

10

60

60

60

40

30

10

2nd test

80

0

0

60

30

0

40

40

0

60

10

0

30 milliseconds: 1st test

40

50

0

40

10

20

100

50

10

50

10

0

2nd test

70

40

20

40

40

0

80

40

0

80

20

0

Tests at 75 volts potential:

Duration:

10 milliseconds: 1st test

90

70

30

60

0

10

80

50

0

30

0

0

2nd test

80

50

0

30

10

0

60

0

0

10

30

0

20 milliseconds: 1st test

50

20

30

60

20

0

60

60

10

20

0

0

2nd test

50

20

0

40

10

0

90

30

0

20

0

0

30 milliseconds: 1st test

60

30

50

40

20

0

40

70

10

70

10

0

2nd test

80

20

0

40

0

10

80

40

0

80

0

0

Tests at 90 volts potential:

Duration:

10 milliseconds: 1st test

70

40

0

20

0

0

50

50

30

70

10

0

2nd test

50

0

0

40

0

0

60

0

0

70

0

0

20 milliseconds: 1st test

60

0

20

60

0

0

70

60

0

10

0

0

2nd test

40

10

0

50

0

0

70

10

0

20

10

0

30 milliseconds: 1st test

60

0

20

40

0

0

80

60

10

60

0

0

2nd test

70

10

0

50

0

0

40

0

0

40

0

0

1/ Frequency in pulses per second.

pulses per second, the fish reached
an electroparalytic state in about
one-quarter of a second. Nearly all
the fish remained in the middle of
the electrode array.

Analysis of Results

For each'test, as outlined in
"Experimental Procedures," the per-
centage of adult squawfish that
entered the "positive" end zone of
the laboratory experimental area is
recorded in table 2. The mean per-
centage of the adult squawfish that
entered the "positive" end zone for
each value of the three variable
factors of potential, pulse frequen-
cy, and pulse duration is recorded
in table 3 for north and south
blocks and unshocked and once-
shocked fish separately.

Table 3. — Mean percentage of squawfish that entered the "positive"
end zone in north and south blocks for each value of the vari-
able factors of potential, pulse frequency, and pulse duration
and for once-shocked and unshocked fish separately. Each mean
percentage in this table is based on 18 observations.

Unshocked

Once

shocked

North

South

North

South

"positive"

"positive"

"positive

"positive"

Potential

(volts)

60

39.44

28.89

46.67

22.78

75

40.56

19.44

37.78

15.00

90

25.00

14.44

32.78

16.11

Frequency

(pulse-second)

2

63.33

45.00

65.56

45.00

5

29.44

12.78

41.11

7.78

S

12.22

5.00

10.56

1.11

Duration

(milliseconds)

10

42.22

20.56

37.78

17.78

20

28.33

22.78

40.00

12.78

30

34.44

19.44

39.44

23.33

10

Data were transformed from percentages
(table 2) to arc sin Vpercentage, and all
analyses were run on such trainsformed ob-
servations. Preliminary analyses showed,
for both unshocked and once-shocked fish,
negligible average difference in effects
between the two times the test conditions
were repeated. It was impossible to test
both unshocked and once-shocked fish at the
same time with each combination of variable
factors, because of the limited supply of
fish for testing. Therefore, we analyzed
separately the data from the tests with
unshocked and once-shocked fish as well as
the data on the two groups combined. The
completed analyses are shown in table 4
for unshocked fish and in table 5 for once-
shocked fish, and the analysis for the two
groups combined in table 6.

cant differences between "blocks" for both
unshocked and once-shocked fish.

Differences between blocks Ccinnot be
attributed to a single cause (see page 4);
therefore, we tested for the significance
of the relationship between temperature
difference and percentage difference in
numbers of squawfish that entered the "posi-
tive" end zone. Separate tests were made
for the north and south blocks, and for the
unshocked and once-shocked fish in each
block. The four "t" values obtained were

(1) t = 0.598 for unshocked fish in north block

(2) t = 0.466 for once-shocked fish in north block

(3) t = 0.219 for unshocked fish in south block

(4) t = 1.188 for once-shocked fish in south block

Shocking condition. — As may be seen
from table 6, there was no difference
between shocking conditions (unshocked vs
once-shocked), nor was the interaction of
shocking condition with any other variable
significant .

Effect of blocks. — All three analyses
(tables 4, 5, and 6) showed highly signifi-

The 5-percent significant level for
"t" with 25 degrees of freedom is 2.06.
There is, therefore, no evidence of a rela-
tionship between temperature and percentage
of squawfish led. For illustration we
include a graph (fig. 5) showing the differ-
ence in percentage of fish that entered the

Table L,— Analysis of Tarlanee of the effects of potential, puis
frequency, and pulse duration on the movement of
unshocked aquairfish .

Table 5, Analysis of variance of the effects of potential, pulse

frequency, and pulse duration, on the movement of once-
shocked squawfish .

Source of
variation

Sum of
sqxiares

Degrees of
freedom

Mean

square

F

Source of
variation

Sum of
squares

Degrees of
freedom

Uean
square

F

Bloaks

2,990.310

1

2,990.310

15.68*.

Blocks

7,lj55.hOO

1

7,a55.1lOO

36.13W

RjtenUal

3,857.553

2

1,928.776

lO.lUHt

Potential

2,187.1i77

2

1,093.738

5.30«.

Frequency

25,760,650

2

12,880.U25

67.53»*

Frequency

31,036.691

2

lS,5l8.3li6

75.19«

Duration

331. .526

2

167.263

.88

Duration

211t.771

2

107.386

.52

Ba

2JJ..255

2

122.128

.6U

BxF

1,217.11a

2

608.570

2.95»

Bd

lin.2li7

2

205.62li

1.08

BxD

l63.2Ut

2

81.622

.82

BxF

iiei,.82i

2

2lt2.!aO

1.27

Brf

130.666

2

U5.330

.56

nd)

353.210

U

88.302

.U6

FxD

1,25U.778

h

313.69U

1.52

RxP

2, 151.51a

U

537.686

2.82*

FlP

I16I.759

k

llS.ltltO

.56

DiF

b28.383

It

107.096

.56

UrP

533.727

k

133.1t32

.65

BAd>

1,03U.338

u

258.5814

1.36

acFScD

U27.380

h

106.81i5

.52

BiKcF

11.5.278

u

36.320

.19

BxPxP

250.762

h

62.690

.30

nniyp

18U.293

It

U6.073

.2k

BiDrf

878.586

It

219.616

1.06

r>9zP

575.853

8

71.982

.38

FiflxP

1,107. 7lt9

8

I38.I169

.67

BrPxDiP

329.230

8

ia.i5U

.22

ftcFxDiP

2,Uh3.621

8

305.1.53

I.I48

Error

10,299.116

5U

190.72U

Error

ll,llilt.lt05

5lt

206.377

to,581i.80l4

107

Total

Total

60,908.151

107

P < .05

.01

• .01 <

M P <

• .01

» P

<
<

P < .05

.01

11

(%)

70
60
50

40
30

20

I 0
0

if - 10
a>

a.

£ -20

c -30

t -40-

o
rsi

o
a.

c

XX
XX

Once - shocked
North Block

10

(F°)

-50

Difference m Degree of Water Temperature (F°)

Figure 5. — Difference in percentage of squawfish that entered
the "positive" zone against the difference in water
temperature between times a combination was run.

Figure 6. — Diagram of potential contours for sequenticilly pulsed field.

12

"positive" end zone (first result
minus second result) plotted against
the difference in water temperature
(first measurement minus second
measurement) between the two times
a combination was tested on once-
shocked fish in the north block.

Assuming that the electrical
field in the water (fig. 6) was not
changed by reversing the direction
of the electrical fields, the differ-
ence between north and south blocks
of tests probably represented a pre-
ference by the fish for the north
end (fig. 7).

Effect of potential. — There was
a highly significant difference be-
tween the different levels of poten-
tial as shown by the three analyses
of variance (tables 4, 5, and 6).

For the unshocked fish, the
overall potential effect was obscured

rOO

tu

Z 90
O

^ 60
§70

D.

Veo

S 30
5 20

C I - Nofth Block

■i : South Block

IklMn

Onl

D

o -n o o

Q o f 9

ELECTRICAL COMBINATION (Frequency, durotion ond polenliol - respectively )

Figure 7. — Comparison between blocks of
the mean percentage of squawfish that
entered the ''positive" end zone.

Table 6.— Analysis of variance of tests of unshocked and once-
shocked squairfish coaibi.ied.

Source of

Sum of

Degrees of

Mean

variation

souares

freedom

square

F

Shocking

3.20

1

3.20

.02

condition

(Unshocked vs

Once-ahocked )

Blocks

9,9Ui.50

1

9,9Ui.?0

57.23«

Potential

5,127.35

2

2,563.68

lli.75"

Frequency

56,li97.%

2

2B,2li8.92

162.57"

Duration

262.92

2

131.!a

.76

SCxB

501.21

1

501.21

2.38

SCiF

299.71

2

lli9.85

.96

SCzD

286.U9

2

lu3.2U

.82

SCiP

917.68

2

we. all

2.6I4

Bi7

1,211.61

2

605.30

3.li9»

BxD

li3.11

2

21.56

.12

aiT

572. W

2

286.22

1.6?

ftcD

290.93

u

72.73

.!i2

PiP

2,li73.la

I

618.35

3.56«

DxP

UiO,l6

li

no.oli

.63

SCiBxF

2U9.79

2

12L.90

SCzEbdl

531.38

2

265.69

SCxBxf

Ii3.05

2

21.52

SCxFicD

1,317.06

u

329.26

SCiFxP

139.39

ll

3I4.97

SCjcDiP

521.95

li

I30.I49

Third i fourth

order inter-

actions

7,377.07

56

131.73

Error

21,lJi3.52

108

198.55

Pooled
Error *■

r'l .<

31,623.71
< .05

182

173.76

P < .01

Pooled error is found by combining all suns of squares belcnr the

double line since none of these are significant even at the 1C0^ level.

The F values listed in the table are fo^jnd by comparing each mean
square (H.S.) with the pooled error mean square.

by the significant interaction of potential
with pulse frequency (table 4). In particu-
lar, the rate of decrease in effect, with
increasing potential, is much less at 2
pulses per second than at the higher fre-
quencies of 5 and 8 pulses per second.

For the once-shocked fish, a rapid rate
of decrease in effect with increasing poten-
tial occurred only at 8 pulses per second
(table 5).

A more detailed examination of the
potential effect may be made using Tukey's .
Least Significant Difference (L.S.D. ) test.—
The L.S.D. is found by multiplying the
standard error by the Q value (tabulated in
table 10.6.1, p. 252, of Snedecor) and
dividing the result by the square root of
the number of observations in the means to
be compared. The standard error is

V

/lO, 299.166 + 11,144.405 ^ j^^ qq.
108 ■ '

this

is determined by pooling the error sum of

_5/ Snedecor, Gteorge Waddel. 1956. Sta-
tistical methods applied to experiments
in agriculture and biology. 5th edi-
tion. Down State College Press, Ames,
Iowa.

13

squares for the unshocked and once-shocked
fish. The tabulated Q value for three
"treatments" and an error mean square based
on 108 d.f. is 3.37. Since each potential
mean is calculated from 72 observations.

L.S.D.

(14.09) (3.37)
V 72

= 5.60

Any difference of means exceeding 5.60
is significant at the 5 percent level.

The

three

potenti

al means

are

60 : 34

.44

75 : 28

.20

90 : 22

.08

and

the

d

ifferences cire:

60-75 :

6.24

60-90 :

L2.36

75-90 :

6.12

Since these three differences all exceed
5.60 the three potential means are all
significantly different at the 5 percent
level .

Effect of pulse frequency. — The dif-
ferences between pulse frequencies were
highly significant for both unshocked and
once-shocked fish — F values were highest
in all three tables (tables 4, 5, and 6).
Examination of the data, as well as quali-
tative observations, leads to the conclu-
sion that optimum pulse frequency is below
5 pulses per second. For example, see
figure 8(b) and table 3 (page 10),

Effect of pulse duration. — This vari-
able factor for the values tested (10, 20,
30 milliseconds) was not significant in the
three analyses (tables 4, 5, and 6), nor
was any significant interaction found.

CONCLUSIONS

A. Optimum electrical conditions:
Pulse frequency was the most critical vari-
able. Potential also was significant.
Substantiating the preliminary observations,
pulse duration was not significant, at least
in the range tested. The optimum values of
the electrical variables were as follows:

1. Potential — Of the three potentials.

50 r

10
30
20 ■

L^

60 75

(0 } Porentioi { voirs )

70
60
50
40
30
20
10

Norlh Slock
South Block

oMyv-

2 5

(D) Pulse Frequency (pulses per second)

40

30
20
10

°T

(c ) Poise Durolion ( milliseconds )

Figure 8. — Mean percentage of squawfish that
entered the "positive" end zone in north and
south blocks for each value of the variable
factors of potential, pulse frequency, and
pulse duration, linshocked and once-shocked
fish combined. Each mean percentage based
on 36 observations.

60, 75, and 90 volts, 60 volts was
the optimum;

2. Pulse frequency — Of the three pulse
frequencies, 2, 5, and 8 pulses per
second, 2 pulses per second was the
optimum;

3. Pulse duration — With the three
pulse durations, 10, 20, and 30
milliseconds, no optimum was ob-
served.

B.

Direction of the electrical fields:

The direction of the electrical fields was
a highly significant variable. The fish
showed a greater response when the electri-
cal fields moved toward the north end of the
laboratory tank than toward the south. The
reason for this reaction was not determined.

14

RECOMMENDATIONS

The following recommendations are made
for future laboratory experiments in lead-
ing adult squawfish within a direct-current
sequentially pulsed electrod array using
electrodes of 1/2-inch diameter with 18
inches between rows and 17 inches between
electrodes:

1. Future experiments should be
limited to the optimum values of potential
and pulse frequency: 50 volts, and 2 pulses
per second, respectively, found in these
experiments.

2. The possibility of an effect from
pulse duration should not be overlooked.

In future experiments, a range of values of
shorter duration than 10 milliseconds and
longer duration than 30 milliseconds should
be systematically investigated in combina-
tion with the optimum potential and pulse
frequency values.

3. The cause of the significant dif-
ference between directions of the electrical
fields should be explored. If this phenom-
enon is peculiar to the laboratory, it is

of little general interest. If it is due
to a variable which might also operate in a
field control installation, the effects of
this source of variation should be estimated.

15

INT.DUP.,D.C.59- jjj jj

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