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

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77,777/777/7/77/77/7/777/7/-/7/777777/77
Fig. 2. Diagram of movement of Sardinella and
Carangidae in different zones of the space between
electrodes in a 24.7-meter bottom trawl with cur-
rent parameters f = 20-25 Hz, Ja = 4-6 kA, "hor-
izontal electric field".. Key as in Fig. 1.
Fig. 3. Optomctor reaction of Sardinella above the upper posi-
tive electrodes in the field of action of the electric pulse cur-
rent (from a photograph).
rapid formation of the catch in the codend
of the tkatttl.
The above-mentioned change in the polar-
ity of the electrodes (anode on the upper
panel of the trawl) also gave a somewhat
different character to the reaction of fish
moving in the remaining space of zone A.
A similar crowding offish and sharp veer-
ing forward, upward and downward as was
the-case with the anode on the lower panel,
was not observed. Usually these fish made
a smooth undulating movement forward and
downward %nd rapidly disappeared into
zone A.
When the water was very transparent it
was frequently noted that with the switching
on of the current, a wave of excitation was
passed on to the school of fish moving in
front of zone A from the zone A space be-
tween electrodes. As a result, within 4-5
seconds all those fish affected by the stimu-
lus swam a distance of up to 5 m in the direc-
tion of the mouth of the trawl, crowding the
fish moving under the square of the trawl.
The fish moving in the square and which in
our observations were not reached by the
wave of excitation, continued to swim with
the trawl. The escape reaction, described
above, of fish after the action of the current,
had no noticeable effect on them.
A similar wave of excitation was also ob-
served during a study of the reaction of fish
in zone B in the cross section of the trawl
(Fig. 1, b). Where there was close contact
between the fish, i. e. when the entire space
between the electrodes was filled with fish,
the fish moving approximately 1 m from the
lower positive electrode darted sharply for-
ward, upward and downward when the current
was switched on. Here the above-mentioned
wave of excitation, moving from the fish
near the lower panel of the trawl, which re-
ceived a comparatively strong stimulus from
308
the current, to those moving beneath the
upper panel of the trawl, which felt only a .
slight stimulus, was clearly noted. It
seemed as though the fish swimming in the
lower region of zone B drew, as it were,
the fish in the upper region of this zone
after them when the current was switched
on. In this connection, after the current
was switched on a massive movement of
fish occurred to within a distance of the
anode where the strength of the electric
field was, as a result of the smaller sur-
face of the anode, close to the electronar-.
cosis threshold. Here the fish began to
move in time with the pulsed current, per-
forming sinuous, spasmodic movements.
As a result of this darting movement almost
all the fish moving in the space between the
electrodes in zone B before the current was
switched on, collected near the lower
panel around the anode. While in the upper
half of zone B small schools of mackerel
and sardinelles (200-300 fish) were under
the cathode, when the current was switched
on these fish darted forward and downwards
and escaped into the "shadow zones" or
sometimes moved under the cathode, show-
ing no agitation. In this case only individual
fish approached the anode.
When analyzing the general features in
the behavior of fish during their displace-
ment in the space between the electrodes,
it may be assumed that such behavior is
caused not only by the action of the electric
current, but also by the defensive schooling
mechanism of the fish. Apart from the
clearly expressed withdrawal reaction of .
the fish from the zone of excitation, the
imitative faculty peculiar particularly to
pelagic fishes may possibly be manifested.
The "escape reaction" described above to
some extent affects the general pattern of
behavior.
In fish moving in zone C and having
received a weak stimulus from the current
(at the level of a minimum reaction), the
main feature in the reactions was a persis-
tent urge to leave the "danger" zone in the
wake of the departing fish from zones A and
B. Moreover, it is necessary to point to
the effect of the comparatively strong elec-
tric field of zone B on the behavior of the
fish. It consisted in those from zone C
performing a sharp turn forward and down-
ward, entering the space between the elec-
trodes and receiving a strong stimulus
from the electric current in the border re-
gions of the cathode and anode in zone B
and, without losing their sense of direction,
drifting 3-4 m backward toward the codend
of the trawl. Throughout the entire time of
309.
the action of the current, narcotized fish
were swept in a random manner through
zone C from zones A and B towards the
codend of the trawl.
Thus, with the switching on of the current
with parameters f = 20-25 Hz; Ja = 4-6 kA;
T = 1.6 msec, temporary narcotization of
fish occurs only in a small section of the
electrified trawl (approximately 2-4 m). We
observed no mortality from the action of the
current on the fish.
A renewal of the motor capacity of fish
which had undergone electronarcosis was
observed in zone D, as was the movement
of fish which had fallen back from zones B
and C. A peculiarity of the behavior of fish
in this zone was expressed in the urge to im-
mediately flee the area in front of the codend
of the trawl, which was evidently perceived
by them as a danger, and to reconstitute the
school which had, until then, travelled in the
trawl. In addition, the fish made constant
attempts to move forward toward the mouth
of the trawl and to join up with the fish moving
forward in zone A. It was frequently ob-
served how fish swimming in the anterior
part of zone D approached zone C and did not
move forward on feeling the strong action of
the electric field in this zone. With the
switching on of the current, the gap in the
school travelling in front of zones A and B
was eliminated in 1-1.5 minutes. The space
between the electrodes again filled with fish;
in the first place at the expense of fish swim
ming in front of zone A. The speed at which
the space filled up depended on the density
of fish in the trawl. Usually there was a
constant ingress from the fished zone of new
schools of fish, which increased the numbers
already travelling in front of zone A and
caused their rapid displacement when the
current was switched on in the space between
the electrodes. Cases were observed when
a small school of fish entered the trawl
(around 1000 fish) and after the current had
been switched on 2-3 times a small number
of them continued to travel in front of zone
A, while the remaining fish congregated in
the form of a dense group beh±_nd the elec-
trodes in zone D. In this case, when the
current was switched on, the fish moving in
front of zone A also migrated into the space
between the electrodes, but considerably
more slowly.
It was repeatedly observed that the rate
and time of entry of the fish into the space
between the electrodes depended on the
number of times the current was switched
on. After the current had been switched on
several times and no new schools had advanced