7116 ‎(2)‎

• UCREFRP Catalog Number: 7116
• Author: Baxter, G. and J. Simon
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1970
• Copyright Material: YES

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at 0.1-0.3 V/cm and immobilized at 0.3-1.3 V/cm
(Sternin et al., 1972).

Biological factors

The physiological reactions of the fish towards
alternating and direct current are different (see
Halsband, 1967; Lamarque, 1967 for details).
U sing alternating current both the negative and
positive electrotaxis are absent and the fish will
show undirected swimming movements (oscil-
lotaxis) or be immobilized depending on the dis-
tance from the anode. Alternating current has a
stronger effect on the fish and the persistance of
the reaction is much longer. This also implies that
the risk for unwanted secondary effects (e.g.
mortality) is larger (Sternin et al., 1972). This is
especially the case for small fish ( < 10 cm).
Because of the stress imposed on the fish and
the larger potential risk to the fisherman alternat-
ing current is less often used for electric fishing.
In USA, however, alternating current with
I equipment often permanently installed in boats is
frequently used for fishing (Heidinger et al., 1983).
The length of the fish is of vital importance for
the fishing efficiency (Vibert, 1967; S ternin et al.,
1972, Regis et al., 1981), which increases ex-
ponentially with fish length, when alternate or
constant direct current is used (Fig. 4, but see
Chmielewski et al., 1973). For large fish, however,
this tendency may be counterbalanced by an
increased flight radius or because of fast forced
swimming in the attraction zone. Fishing with
pulsed direct current did not give the same unam-
biguous result (cfr. Sternin et al., 1972). This was
. probably due to the use of different equipment
leading to differences in frequency, length and
type of pulse. After correction for selectivity due
to the length of the fish, the effect of pulsed direct
current is proportional to the energy input per
time unit (frequency x pulse length).
In order to decrease the length selectivity, the
current line density could be increased (Stewart,
1975). However, this would also increase the
mortality of the fish.
Vibert (1967) and Sternin et al. (1972) state that

differences exist between fish species with respect
to the reaction to the electric field. Differences in
the internal specific conductivity between species
is relatively large (a factor of 3) and might together
with metabolic differences constitute the basis for
such a difference (Sternin et al., 1972). Studies of
the voltage needed for attracting fish based on 20
species (Fig. 4) indicate, however, that factors like
fish length and behaviour are more important.
Regis et al. (1981) found no differences in attrac-
tion distance among the species tench (Tinca
tinca), grayling (Thymallus thymallus), catfish
(Ietalurus melas) and nase (Chondrostoma nasus).
In practice, differences in behaviour and habitat
preference among fish species are more important
for the fishing efficiency than physiological differ-
ences. Some pelagic and semipelagic species like
the grayling Thymallus thymallus, tend to avoid the
electric field, resulting in poor catchability (Ernst
and Nielsen, 1981). The catch ability of bottom
dwelling organisms (eel Anguilla spp., catfishes
and sculpins Cottus spp., lampreys Petromyzon
and Lampetra spp., and crayfishes), is strongly
dependent on sediment conductivity and the pos-
sibility of locating immobilized animals. Com-
pared to territorial salmonids bottom dwellers
may therefore be underrepresented. Schooling
species tend to be stunned in vast numbers, of
which only a small fraction may be caught before
the school has disappeared in vegetation or swept
away by the water current.
Further considerations concerning the possi-
bility of quantifying different fish species are dis-
cussed in the following section.
The initial orientation of the fish when in-
fluenced by an electric D.C. field is of major
importance for the fishing efficiency. The fish will
then instantaneously turn either from or towards
the anode depending on the current line density.
If moving when affected by the current, the
resultant movement direction of the fish will be
determined both by the original direction and
speed of the fish and the position and density of
the current lines. Instead of being attracted by the
annode the fish might then either be forced away
from the anode because of the centrifugal force or
drawn towards it with such a speed, that it passes

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