7125

• UCREFRP Catalog Number: 7125
• Author: McAda, C. W.
• Title: Aspects of the Life History of Three Catostomids Native to the Upper Colorado River Basin.
• USFW Year: 1977.
• USFW - Doc Type: Utah State University,
• Copyright Material: YES

_ Length offish, cm
6 >B 74 30 36 47 4F
s S
a 4
J
o
a 46
0,4
to
a x0,3
o s4z

M

44f.
0
7
Z
Relative length offish, Io IL
Fig. 4. The ature of the change in the threshold values
of U, with a onstant length of aquarium L- constant and
with a variable ratio !p/L.
The nature of the change in the threshold values of UZ for reactions of shud-
dering and electroshock in the pike-perch and bream with a constant aquarium
length is shown in the graphs of Fig. 4. The length of the fish in relation to
the distance between the electrodes varied between 0.2 and 0.8. It can be seen
on the graphs that the dependence ([1,) „=f (lp) is almost linear when 0,3< L <0,6
and in a wider range of values, the ratio 1p/L has the appearance of logistic L
curve and may be written by the equation
I e +pip (4)
where (U,).' and (L':)." are the maximum and minimum values of U, respectively;
a and S are the coefficients.
At the same time the dependence (U,).=f(1p) (Fig. 5), obtained in a series
of experiments for the same reactions in the bream and the pike-perch with a
constant ratio L has the appearance of straight, almost parallel x-axes. A
slight increase (UZ)n in large specimens for shuddering reactions may evidently
be explained by, -an 'age-related decrease in sensitivity to the action of relatively
weak stimuli.
When determining the threshold values of the reaction in fish of different
length, when with a constant ratio l,
the width of the aquarium is also constant,
I.
it is essential to consider the change in current density provoked by an increase
(or decrease) in the resistance of the water between the electrodes. This is par-
ticularly important when the electric conductances of the fish body is and water'
T• are similar (I. differs from 1, by less than twice). In our case (Fig.,5)
when the values (U,). are determined in fresh water (qp>y, by approximately 6 - 8
times), the influence of 6. on (U,). is hardly felt (Fig. 2) and on Fig. 5 the
genuine nature of the dependence (U,).=f(lp), is. shown.
> 7
a: 3
J
c
?Q6
? Q4
c
E 0,2
zo
Fig. 5. Nature of change in threshold values of U,for the bream
with a variable length of aquarium L # const and with a constant
ratio 1p11, (0.2 - 0.8 are the values of the ratio of the length
of the fish in the distance between electrodes).
The change in the value of the ratio lL leads to an increase (or a decrease)
t",
in the threshold values of U, in accordance with the graphs on Fig. 4. Conse-
quently it may be assumed that in order to obtain values close to the actual
values of (U,), in the aquarium, the main condition is observance of equation
1
const in the-experiments and that the value of the ratio L should be less
than 0.2. The presence of regression (U,)in the experiments of Shenty-
akov (1964) may thus be explained by the fact that thwy were carried out under
conditions when the ratio ' was within the limits of 0.25 - 0.5, which corre-
sponds to the main part of the graphs of dependence (U,).=f(lp) on Fig. 4.
Our investigations of the distortion of the electric field by the fish body
by depth and width of the aquarium have been shown that this distortion is no-
ticeable at distances which do not exceed 1.5 - 2.0 respectively of the depth and
thickness of the fish body in relation to its longitudinal axis. However, a de-
crease in the width and depth of the aquarium of less than 0.4 - 0.5 of its length
L is undesirable, because this increases the heterogeneity of electric fields:
when L>51,.
Water temperature has a certain influence on the sensitivity of fish to the
action of an electric current. The degree of this influence has been investigated
by many authors (Pavlov and Saburenkov, 1974; Shentyakov, 1964, etc.). In partic-
lular, according to the data of Shentayakov (1964), an increase in the water tem-
perature of between 5 and 15p decreases the threshold values of Ut by 6 - 20% for
different reactions in the fish. Unfortunately the author did not investigate
the reason for the change in the threshold values of the reactions. Evidently a
decrease in ( U,). with an increase in temperature can be explained by a change in
the physiological state and also by the temperature change in the electric conduc-
tance of the water. Our calculations showed that the change in the value of (Ut).
was mainly caused by an increase in the electric conductance of the water. The ex-
periments carried out showed that when with a change in water temperature from 10
to 20° constant values of 7•. are obtained, in this temperature range the sensitivity
148 1 149
10 Z5 JO JS 40
Length of fish, em