7114 ‎(2)‎

• UCREFRP Catalog Number: 7114
• Author: Shentyakova, L. F., et al.
• Title: Effect of an Alternating Electric Current on Fishes and Aquatic Invertebrates
• USFW Year: 1970
• USFW - Doc Type: Journal of Ichthyology
• Copyright Material: YES

bottom catch using the electrified trawl in
R}binsk reservoir in the area of the former
bed of the River Volga between the Legkovskiye
and the Lavrovskiye clearing marks. The
width of the area fished by the electrified
trawl is delineated by two buoys which are
towed along the surface of the water by the
trawl boards. The disturbance to the water
by the buoys leaves a clear track of the elec-
trified trawl 25-30 m wide. The track of the
electric trawl was clearly apparent from
another veBSe 1.

To observe the state of hydrobionts after
the passage of the' alternating current el ectrlc
trawl we took samples of zooplankton and
benthos in the middle of tlie track immediately
behind the electric trawl (experimental sam-
ples) and in front of the electric trawler
(control samples). Each sample was examined
on board the vessel Gidrobiolog. Plankton
samples were taken by Juday net (No. 76
gauze) with a ring diameter of 29 cm. For
ell1lb sample the plankton net was raised three
times from the bottom vertically through the
eIltire water column. Depth at the sampling
points was between 10 and 17. 5 m.

The contents of the container of the plankton
net were poured into a wide-bottomed measuring
fiask. Plankton was subsequently taken by
pipette from the bottom of the flask and poured
into a Bogorov chamber in which the sample
was examined to identify the species and
quantity of living and dead organisms. The ob-
servations were made with a MBS-1 micro-
scope (ocular x 17, objective x 0.6) without an
artificial light source.

A total of 10 experimental and 10 control
plankton samples were taken and'examined.
11Ie plankton consisted mainly of Daphnia,
Bosmina rotlCers and to a lesser extent
~a; Cyanophyceae were plentiful in
the samples. Isolated specimens of dead
Bosmina or ~ (with mechanical damage)
were found in reost of the experimental and
control samples.

At the same time as the plankton samples
were taken, samples of benthos were taken in
front of and behind the electric trawl with an
Ekman dredge (1/25 m2). The samples of
bottom material were washed, after which they
were thoroughly examined in an enamelled
tray. A total of 10 experimental and 10. control
samples of bottom material were taken. The
following organisms were fol1nd in the samples:
Gastropoda, Oligochaeta, Chironomidae,
Dreissena, Spheriidae, Viviparus. No dead
organisms were found in the samples.

Observations on the State of Fishes Behind
the Electrified Trawl

Field visual observations of the death of
fishes at the surface of the water behind the

electrified trawl of the PETS Amur were made
from on board the Research Vessel Gidrobiolog
which followed the electric trawler at various
distances. The water surface was examined
in the wake of the electrical trawl for a distance
of approximately 25 kID.

The weather was calm and cloudless on
June 28, 1968. Between 10 lIDd 20 hr the PETS
Amur caught approximately 1000 kg of saleable
fish with the electrified trawl. Throughout the
time of the observations two ruffes (ACer~na)
were found on the surface of the water. 0
other dead fishes were noted at any point on the
path covered by the trawling operations.

In order to discover dead or damaged fishes
remaining behind the electrified trawl in the
bottom layers of the water, a number of trawling
operations were carried out after the electri-
fied trawl had passed with a standard 22 meter
benthiC trawl used for ichthyological research
in the Institute on the Research Vessel Volga.
The buoys of the electrified trawl were 10-15 m
in front of the Research Vessel VoIKa.

In order to compare fish caught immediately
behind the electric trawl with fish caught aside
from the path of the e1ectric trawl or parallel
to it, bottom trawling was carried out for 15
minutes with a standard trawl, successively
alternating trawling behind the electric trawl
(experimental) with trawling to one side of the
path of the electric trawl (control). The entire
catch of each trawling operation was placed in
a net container alongside the vessel without
raising it on board and visual observations
were made of the behavior of the fish in this
container.

In all 11 trawling operations were carried
out, 6 behind the electric trawl and 5 aside
from the path of the electric trawling, All the
fish caught behind the electric trawl were found
to be alive and in no way different from fish
caught aside from the path of the electric
trawling. With the exception of the ruffe, all
the fish (bream, blue bream, burbot lIDd cat-
fish) from the experimental and control trawl-
ings descended to depth after being placed In
the container.

Determination of the Effic iency of
Electrified Trawling

In order to determine the efficiency of elec-
tric trawling, an alternating series of trawling
operations was carried out on board the PETS
Amur in July 1968 with the power supply to the
trawl electrode switched on (with current),
experimental trawlings, lIDd with the power
supply switched off (without current), control
trawlings. The operations were carried out
In 3 areas in which the concentration and size
composition of the fishes differed: along the
former beds of the Volga, the Mologa lIDd the
Shekena Rivers. A single trawl, whether

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experimental or control, lasted for 30 min. In
two trawls (23 and 26) the time was reduced to
12 and 15 min. In all there were 33 trawls, of
which 13 for a total duration of 6. 6 hr were in
the area of the bed of the Volga (7 control and
6 experimental), 14 trawls with a total duration
of 6. 3 hr were in the area of the bed of the
Mologa River (6 control and 8 experimental);
the total duration of trawling in the area of the
Sheksna River was 5.05 hr (2.45 hr experi-
mental and 2.6 hr control trawls). Depth in
the trawling locality was 16-25 m, bottom
water temperature was 16.5- 17, O.C. The
electrical conductivity of the water at the
bottom was (2,25 -2.32). 10-4 ohm-I. cm-l.

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.size of bream caught with the elec-
trified trawl (1) and with an ordinary
trawl (2),

The catch of each trawl was sorted into
species; the fishes were weighed, counted and
measured. Bream predominated in the
catches (more than 90.1.). The size composi-
tion of bream caught with the electrified and
control trAwls is shown in the Figure.

The fishing results by areas were converted
to 1 hour of trawling. Along the bed of the
Volga the electrified trawl caught 179 fishes,
including 71 (39.6 %) below the commercial
size. The control trawls yielded 68 fishes,
including 36 (52. 7 %) below the commercial
size. The catching capacity of the electrified
trawl in the Volga was 26.3% relative to
trawling without current.

Along the bed of the Mologa the electrified
trawl caught 142 fishes, of which 35 (24,6 %)
were below the commercial size. The control
trawls yielded 57 fishes, of which 16 (28 %)
were below the commerical size. The catching
capacity of the electric trawl in the Mologa
wa~ 249 % relative to trawling without current.

Along the bed of the Sheksna the electrified
trawl caught 223 fishes in 2.45 hr of trawling;
of which 3 (1. 3 %) were below the commercial
size. Control trawlings yielded 189 fishes in
2.6 hr, of which 4 (2.1 %) were below the com-
merical size. The catching capacity of the
electrified trawl in the Sheksna was 125 % rela-
tive to the control trawling. The number of
pike-perch caught by the electrified trawl was

increased in all three fishing areas from 220
to 380 % by comparison with the catch of the
control trawling. The mean weight of bream
caught on the bed of the Volga by the electrified
trawl was 734 g, and in the control trawl it was
667 g; the corresponding figures were 734 g and
746 g on the bed of the Mologa and 956 and 904 g
on the bed of the Sheksna.

Experimental Results

Effect of Alternating Current on Fishes at
Different Stages of Development

In order to study the effect of alternating
current on breeding fishes we carried out ex-
periments with males and females before
spawning and investigated their reproductive
capacity. Breeding blue bream, roach and
perch caught by drag seine on the flood plain of
the Sutka River in the mouth of the Spitsinskoye
stream were subjected to the effect of an alter-
nating current (for 5 sec) to produce a state of
shock. After this the blue bream and the roach
were placed in spawning ponds (20 x 20 m) and
the perch in concrete tanks (4 x 4 m). Com-
posite data concerning experiments on the
effect of a uniform ac electric field on breeding
fishes are summarized in Table 1.

Concrete tanks No. 6 (experimental) and No.
5 (control) were drained on June 24, 1968. On
draining the underyearling perch were caught
and counted. The experimental tank No. 6 was
found to contain 347 underyearling perch and
the control tank (No.5) was found to contain
265. The size of the underyearling perch from
the experimental' and control tanks. was the
same and was on average 1. 6 cm. The explana-
tion for the small quantity of underyearlings
caught in tanks Nos. 5 and 6 is that after
spawning equal quantities of strands of perch
eggs were removed from both tanks for obser-
vations on condition and development and also
for laboratory experiments (from the control
tank No.5). No differences were discovered
in the development of the perch eggs from the
experimental and control tanks. Spawning ponds
No. 1 (experimental) lIDd No. 2 (control) were
drained and fished out on June 26, 1968 to deter-
mine the presence of progeny from the breeding
blue bream and roach which had been subjected
to the effect of an alternating current producing
a state of electronarcosis.

Spawning pond No. 1 (experimental) was
found to contain 1316 young, of which 280 were
blue bream underyearlings and 1036 were roach
underyearlings. Spawning pond No. 2 (control)
was found to contain 1502 young, of which 159
were roach and 1343 were blue bream. The
catch from spawning pond No. 1 was 78.8%
roach and 21. 2 % blue bream; the catch from
spawning pond No, 2 was 10.6.1. roach and
89.4% blue bream. Becuase it was impossible
to drain the ponds completely some young

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