7132 ‎(2)‎

• UCREFRP Catalog Number: 7132
• Author: Jensen, B. L.
• Title: Culture Techniques for Selected Colorado River Imperiled Fishes.
• USFW Year: 1983.
• USFW - Doc Type: December 6-8, 1983.
• Copyright Material: YES

different spatial configuration of electrodes
on the trawl and different parameters of
electric current. It was established that
with the stimulating action of the electric
current on fish at frequencies of 20-25 Hz
in contrast to 60-100 Hz, the most distinct
manifestation of defensive behavioral reac-
tions occurred in pelagic fishes. In our
opinion, the results of this original stage
of research were of great interest because
they helped in the further understanding of
the processes of catch formation in electro-
trawl fishing.
In this work some features of the defen-
sive reaction of pelagic fishes on entering
the electric field of a trawl with current
parameters f = 20-25 Hz; Ja = 4-6 kA;
T = 1.6 msee are discussed.
Research Methods
Methods of underwater visual observa-
nt near a 24.7-meter bottom trawl have
been previously described in detail (Maksi-
mov, 1976). We shall show merely some
differences in observation procedures ap-
plicable to the study of the reactions and
behavior of fish in the electric fields of a
trawL*
During observations on the behavior of
fish the maximum trawling speed was 3. 8
knots. Visual observations with the re-
cording registration of the most }}interesting
moments on camera and film wete the main
methods of studying the behavior and reac-
tions of fish in the trawl. At the same time
the entry of schools of fish into the trawl,
their encounter with the electric field, the
reactions of fish when the current is switched
on, their narcotization and entrapment in
the trawl-by the electric field were record-
ed. The assessment of the effect of various
current parameters on the fish were car-
ried out on the basis of the amplitude of the
vibration of the body of the fish in response
to the current pulses, on the basis of the
time of reorientation of the fish in the elec-
tric field and the nature of their reaction
to the action of the current, on the basis of
the time of the onset of electro-narcosis
(shock) and of the time of the freeing of fish
from the entire space between the electrodes,
or of its individual zones.
*The author wishes to thank G. V. Fey-
gel'man, N. 1. Dogadov, B. V. Shurygin,
0. L Kovtanyuk and N. V. Safonov who gave
us-great assistance in carrying out under-
water research.
For a detailed examination of the reactions
of fish in the point of the trawl concerned,
and also in order to concentrate the atten-
tion of researchers on the individual aspects
of fish behavior, the space between the elec-
trodes of the trawl was conditionally divided
into zones (Figs. I and 2). Size of zone:
zone A 2-4 m; zone B 2-3 m; zone C 1. 5-2
m; zone D 1. 0-2 m. The distance between
the electrodes was 4-5 m. The observations
were carried out with two variants of trawl
electrification: The "vertical electric field"
where the electrodes were on the upper and
lower panels of the trawls (Fig. 1) and the
"horizontal electric field" where the ring
electrodes were placed along the horizontal
axis of the trawl (Fig. 2). The "vertical"
and "horizontal" electric fields have been
named by us conditionally, because in this
case the vertical (horizontal) predominates
in the space between the electrodes, consti-
tuting the vector for the intensity of the
electric field.
The electrodes were prepared from 2mm2
guage copper wire, mark PShch, in the form
of webbing with mesh size a = 180 mm, situ-
ated in the region of parts I-II of the belly of
the trawl. Dimensions of electrodes: for
the "vertical electric field", 6 rhombic
cathodes covered the upper panel of the trawl
along the entire perimeter, the two middle
cathodes were 3 x 3 m and the four marginal
ones (two on each side) were 2.2 x 2. 2 m,
and an anode 1 x 8 m was situated on the
lower panel of the trawl; for the "horizontal
electric field" the ring electrodes were I
m wide, and the distance between them 2.5-
2.8 m. The source of the pulse current was
the ship's pulse generator, which made it
possible to supply the electrodes of the trawl
with unipolar pulses of varying frequency,
amplitude and duration. The operator was
able to change these parameters within a
wide range on the order of the divers.
Pelagic fishes were the main subjects of
observation: the round scad, Decapterus
punctatus, 15-16 cm in size, the sardinella,
Sardinella anchovia, 16-17 cm in size and a
mackerel, Pneumatophorus coltas, 18-25 cm.
Research Results
Peculiarities of the defensive behavior
and reactions of fish in the "vertical electric
field". Underwater observations and sub-
sequent analysis of the reactions and move-
ments of pelagic fishes (Carangidae and Sar-
dinella) when the current was switched on
made it possible to divide the trawl into
several zones in which the behavior of the
fish differed to some extent (Fig. 1).
i ?
po
O
O
B
E ?? i ?XSE
777-77-
Fig. 1. Diagram of movement
of Sardinella and Carangidae in
different zones of the space be-
tween electrodes in a 24. 7-meter
bottom trawl with current param-
eters f = 20-25 Hz; Ja = 4-6 kA.
"Vertical electric field"; a)
longitudinal section of trawl; b)
cross section of trawl. The
broken line denotes the fish
which have escaped from the
trawl; the solid line the fish re-
maining in the trawl, and a cir-
cle denotes narcotized fish.
A, B, C, D, E are the zones of
the trawl.
The electric current parameters em-
ployed ensured the narcosis (shock) and the
carrying of the fish 0. 8-1 m from the posi-
tive electrode. In the rest of the space
between the electrodes the fish experienced
only the stimulating action of the current
and responded to this by defensive be-
havioral reactions which were particularly
clearly manifested in zone A (Fig. 1, a).
This zone, the widest of all the zones in
the space between the electrodes, occupied
around 30% of the entire volume of the
trawl, affected by the action of the electric
current. Here there were all the factors
assisting the manifestation of various de-
fensive behavioral reactions: the stimulat-
ing action of the current, the absence of
obstacles in the mouth of the trawl, the be-
havior of the fish moving forwards, etc.
When the current was switched on, the
fish moving in zone A made a smooth turn
forward, upward or downward, increasing
their motor activity sharply. The distance
between the fish decreased and theycrowded
together and within 10-15 seconds moved
out of the zone providing the stimulus.
Some of the escaping fish endeavoured to
shift in the direction of the lift into the so-
called "shadow zones of E" where the tension
of the electric field is somewhat lower than
throughout the space between the electrodes
(Fig. 1, b). Up to 50% of the fish moving in
zones A and B collected in the "shadow zones"
with current parameters f 20 Hz; Ja = 4-6
kA. This defensive behavioral reaction,
conditionally tailed by us "escape reaction",
was observed with various trawl electrifica-
tion systems and was particularly clearly
manifested when the positive electrode was on
the lower panel of the trawl. In this case
the action of the electric current causing
anode electrotaxis was superimposed on the
biological fright reaction which is expressed
under natural conditions by the withdrawal of
fish into the depths (Radakov, 1970) and which
was frequently observed by us in the ordinary
bottom trawl.
The change in polarity (positive electrode
on the upper panel of the trawl) provoked
only anode electrotaxis in the fish which
had followed the positive electrode at a dis-
tance of approximately 0.5 m. These fish
performed a rapid movement forward and
upward and for the most part escaped through
the net and the electrode from the trawl.
It is interesting to note that single fish which
had escaped in this manner then again entered
the trawl under the influence of the positive
electrode. The distance from the positive
electrode on the outer side of the trawl, in
which anode electrotaxis was observed in
fish, or the "external zone of effective elec-
trotaxis", depended on the current param-
eters applied and the electrification system
of the trawl. In the case in question it did
not exceed 0.5-1 m. On the other hand,
groups of fish (20-30 fish and more) con-
tinued for 1-2 minutes to follow in the "outer
zone of effective electrotaxis". Feeling the
effect of the current, they gradually drifted
backwards or, coming into contact with the
electrodes, were instantly narcotized. Such
a movement of the fish from the outer side
of the trawl into the field of action of the
electric current can evidently be explained
by the fact that in these fish a stable optomo-
tor reaction had begun, during which the re-
sistance of the fish to the action of the
electric current had increased (Fig. 3).
Dense schools or individual fish, which in
relation to others had a greater turn of
speed, were most often successful in escap-
ing through the "outer zone of effective
electrotaxis". The optomotor reaction of
fish in the trawl when the current was
switched on, which was manifested in com-
bination with other reactions, was evidently
one of the main reasons preventing the
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