- Email: [email protected]
Electrical sensitivity of a weakly electric fish
LIFE SCIENCES Vol . 6, pp . 2373-2377, 1967 . Printed in Great Britain.
Pergamon Press Ltd.
ELECTRICAL SENSITIVITY OF A WEAKLY ELECTRIC FISH Louie P . Granath, Howard G . Sache* and Fred T . Erskine III Department of Physics Worcester Polytechnic Institute, Worcester, Massachusetts
(Received 22 July 1967 ; in final form 22 August 1967) The South American gymnotid, Sternarchus albifrona produces a weak electric field of high frequency (600-1000 Hz) by means of a caudal electric organ (1,2) . Electroreceptor organs have been found in the akin, innervated by the lateral line nerve (2,3) .' Electrical sensing by several other gymnotida has been studied (2,4-6) . The present study is concerned with a aeries of experiments on S . albi frons aimed at determining the behavioral electrical threshold sensitivity of the whole fish to imposed electric fields .
Conditioned response experiments
with both uniform and non-uniform alternating current (A .C .)
fields as stimuli
and food as reward were employed to determine the frequency response spectrum . Methods The fish used in this study ranged kept
in a separate
nocturnal animal
in length from 10 to 30 cm .
tank provided with an aerated filter .
Each was
StQrnarchus is a
(7), and a dark hiding place was provided by placing a grey,
porous ceramic cylinder in each tank . In all experiments the stimulating signal was produced
by a battery pow-
eyed oscillator with a built-in attenuator which could be adjusted a sinusoidal output of any desired frequency and amplitude .
to provide
The oscillator
signal was fed through an isolation transformer irto a large Faraday cage containing an impedance matching attenuator and thr stimulating electrodes .
Fig-
*Present address : Biology Department, Clark University, Worcester, Massachusetts
2373
2374
ELECTRIC FISH
ure 1 shows the circuit employed .
Vol . 6', No . 22
Stainless steel plates at the ends of the
tank served as stimulating electrodes for the studies on the response to a uniform electric field .
The field magnitude was calculated by dividing the vol-
tage across the plates by the separation .
For the non-uniform field studies,
the electrodes were made of nickel wire welded in glass, suspended near the ends of the tank .
The field intensity in this case was calculated by consider-
ing the two electrodes to be small charged spheres and applying the equation for the electric field surrounding a dipole .
In this way a value for the field
in the vicinity of th'e head of the fish could be determined . The experimental protocol was as follows :
the fish was trained, using a
high stimulus level, to emerge from the porous cylinder to the location of a vertical plastic tube for delivery, down the tube, of small pieces of earthworm as a reward .
The frequency of the stimulating signal was not a critical factor
r_______________,
FIG . 1 Circuit diagram for production of electric fields . R1 ~680 ohm, R2 =R 3 ~270 ohm, R4=120 ohm, R5 =R6 =1 .5 Kohm . in early trials due to the high stimulus levels .
Punishment took the form of
removal of the food from the tank after a short period of time .
When the fish
had apparently been trained, the stimulus was reduced to lower levels to determine the threshold sensitivity .
Responses at different frequencies were ob-
Vol . 6, No . 22
ELECTRIC FISH
tained to determine the frequency response spectrum .
2375
The stimulus in all ca sea
was presented for not more than 15 seconds, and presented daily, generally in the late afternoon . Results and Discussion The minimum potential gradient which would evoke a conditioned response in trained fish was taken as the maximum sensitivity for a given stimulus frequency .
The sensitivity spectrum for one fish trained and tested with a uni-
form field ie shown in Figure 2 . tics ca®on to the fish we tested .
This typical response shows two characterieA maximum sensitivity is seen at a fre-
quency close to the discharge frequency of the fish at room temperature .
The
FIG . 2 Response spectrum to a uniforn A .C . field . value shown for the maximum sensitivity is the average calculated for ten trials on this fish ; all fish showed a maximum aenaitivity of about 0 .2 microvolts per cm .
There is present, in moat cases, a pronounced secondary peak in
the aenaitivity curve at a frequency close to the second harmonic of the discharge frequency . A similar response is seen when the fish are trained and tested with a non-uniform field .
Figure 3 shows the results 'f or a fish under these conditions .
2376
Vol . 6, No . 22
ELECTRIC FISH
The maximwo sensitivity is again about 0 .2 microvolts per cm ., calculated at F
the head region of the fish .
As with the results from the uniform field ntudiea
a peak is seen at the second harmonic, and the high frequency drop-off is quite marked .
Work on another weakly electric fish, Gymnarchua (5), has shown the
sensitivity in a conditioned response experiment to be of the same order of magnitude as we have shown for Sternarchus .
r O
v
so z
V Z
v F
Y
O
F >_
<
F
r>_
Y1
2
~10
r
10~
10~ FREQUINCr (HZ)
10 4
FIG . 3 Response spectrum to a non-uniform A .C . field . Hagiwara et al . (2) found in Sternarchua that the electroreceptor fibres of the lateral line nerve would respond to imposed A .C . fields by increased firing on the rising phase of the field .
For stimulus frequencies higher than
that of the fish discharge the imposed field became ineffective, even at high field intensities .
This is in good agreement with our results showing a rapid
decline in sensitivity 'at frequencies above the normal fish discharge . Szabo (3) has found a number of electroreceptor types in the skin of Sternarchus .
The possibility exists that at least one type is responsive to
the changes in field intensity, while others may be responsive specifically to the frequency of fields existing in the environment, nerving as an input feedback control of the discharge rate of the electric organ .
in
a
Vol . 6, No . 22
ELECTRIC FISH
2377
Summary The electrical sensitivity of a weakly electric gymnotid fish, Sternarchus albifrona , has been determined by a conditioned response experiment .
In re-
sponse to both uniform and non-uniform A .C . fields the fish are found to be moat sensitive at the discharge frequency . 0 .2 microvolts/cm .
The maximum sensitivity is about
A secondary maximum is seen at the second harmonic of the
discharge . Acknow ledgment We thank Donald W . Howe for his technical a8siatance and Dr . David G . Moulton for his critical reading of the manuscript .
This work was supported by
grants GE-2801 frao the National Science Foundation, NONR-3694(02) from the Office of Naval Research and NB06659-02 fran the National Institutes of Health . References 1.
A . COUCEIRO, A .A .P . LEAO, and G . OLIVIERA CASTRO, Anais Acad . bras . cienc . 27, 323 (1955) .
2.
S . HAGIWARA, T . S7AB0 and P . ENGER, J . Neurophysiol . 28, 784 (1965) .
3.
T . SZABO, J . Morph . 117, 229 (1965) .
4.
H . W . LISSMANN, J . Exp . Biol . 35, 156 (1958) .
5.
H . W . LISSMANN and K . E . MACHIN, J . Exp . Biol . 35, 451 (1958) .
6.
K . E . MACHIN and H . W . LISSMANN, J . Exp . Biol . 37, 801 (1960) .
7.
H . W . LISSMANN in ßioelectrogeneais, C . Chagas and A . Paes de Carvalho, ed ., p . 215 . Elsevier, Amsterdam (1961) .
8.
A . WATANABE and K . TAKEDA, J . Exp . Biol . 40, 57 (1963) .
Pergamon Press Ltd.
ELECTRICAL SENSITIVITY OF A WEAKLY ELECTRIC FISH Louie P . Granath, Howard G . Sache* and Fred T . Erskine III Department of Physics Worcester Polytechnic Institute, Worcester, Massachusetts
(Received 22 July 1967 ; in final form 22 August 1967) The South American gymnotid, Sternarchus albifrona produces a weak electric field of high frequency (600-1000 Hz) by means of a caudal electric organ (1,2) . Electroreceptor organs have been found in the akin, innervated by the lateral line nerve (2,3) .' Electrical sensing by several other gymnotida has been studied (2,4-6) . The present study is concerned with a aeries of experiments on S . albi frons aimed at determining the behavioral electrical threshold sensitivity of the whole fish to imposed electric fields .
Conditioned response experiments
with both uniform and non-uniform alternating current (A .C .)
fields as stimuli
and food as reward were employed to determine the frequency response spectrum . Methods The fish used in this study ranged kept
in a separate
nocturnal animal
in length from 10 to 30 cm .
tank provided with an aerated filter .
Each was
StQrnarchus is a
(7), and a dark hiding place was provided by placing a grey,
porous ceramic cylinder in each tank . In all experiments the stimulating signal was produced
by a battery pow-
eyed oscillator with a built-in attenuator which could be adjusted a sinusoidal output of any desired frequency and amplitude .
to provide
The oscillator
signal was fed through an isolation transformer irto a large Faraday cage containing an impedance matching attenuator and thr stimulating electrodes .
Fig-
*Present address : Biology Department, Clark University, Worcester, Massachusetts
2373
2374
ELECTRIC FISH
ure 1 shows the circuit employed .
Vol . 6', No . 22
Stainless steel plates at the ends of the
tank served as stimulating electrodes for the studies on the response to a uniform electric field .
The field magnitude was calculated by dividing the vol-
tage across the plates by the separation .
For the non-uniform field studies,
the electrodes were made of nickel wire welded in glass, suspended near the ends of the tank .
The field intensity in this case was calculated by consider-
ing the two electrodes to be small charged spheres and applying the equation for the electric field surrounding a dipole .
In this way a value for the field
in the vicinity of th'e head of the fish could be determined . The experimental protocol was as follows :
the fish was trained, using a
high stimulus level, to emerge from the porous cylinder to the location of a vertical plastic tube for delivery, down the tube, of small pieces of earthworm as a reward .
The frequency of the stimulating signal was not a critical factor
r_______________,
FIG . 1 Circuit diagram for production of electric fields . R1 ~680 ohm, R2 =R 3 ~270 ohm, R4=120 ohm, R5 =R6 =1 .5 Kohm . in early trials due to the high stimulus levels .
Punishment took the form of
removal of the food from the tank after a short period of time .
When the fish
had apparently been trained, the stimulus was reduced to lower levels to determine the threshold sensitivity .
Responses at different frequencies were ob-
Vol . 6, No . 22
ELECTRIC FISH
tained to determine the frequency response spectrum .
2375
The stimulus in all ca sea
was presented for not more than 15 seconds, and presented daily, generally in the late afternoon . Results and Discussion The minimum potential gradient which would evoke a conditioned response in trained fish was taken as the maximum sensitivity for a given stimulus frequency .
The sensitivity spectrum for one fish trained and tested with a uni-
form field ie shown in Figure 2 . tics ca®on to the fish we tested .
This typical response shows two characterieA maximum sensitivity is seen at a fre-
quency close to the discharge frequency of the fish at room temperature .
The
FIG . 2 Response spectrum to a uniforn A .C . field . value shown for the maximum sensitivity is the average calculated for ten trials on this fish ; all fish showed a maximum aenaitivity of about 0 .2 microvolts per cm .
There is present, in moat cases, a pronounced secondary peak in
the aenaitivity curve at a frequency close to the second harmonic of the discharge frequency . A similar response is seen when the fish are trained and tested with a non-uniform field .
Figure 3 shows the results 'f or a fish under these conditions .
2376
Vol . 6, No . 22
ELECTRIC FISH
The maximwo sensitivity is again about 0 .2 microvolts per cm ., calculated at F
the head region of the fish .
As with the results from the uniform field ntudiea
a peak is seen at the second harmonic, and the high frequency drop-off is quite marked .
Work on another weakly electric fish, Gymnarchua (5), has shown the
sensitivity in a conditioned response experiment to be of the same order of magnitude as we have shown for Sternarchus .
r O
v
so z
V Z
v F
Y
O
F >_
<
F
r>_
Y1
2
~10
r
10~
10~ FREQUINCr (HZ)
10 4
FIG . 3 Response spectrum to a non-uniform A .C . field . Hagiwara et al . (2) found in Sternarchua that the electroreceptor fibres of the lateral line nerve would respond to imposed A .C . fields by increased firing on the rising phase of the field .
For stimulus frequencies higher than
that of the fish discharge the imposed field became ineffective, even at high field intensities .
This is in good agreement with our results showing a rapid
decline in sensitivity 'at frequencies above the normal fish discharge . Szabo (3) has found a number of electroreceptor types in the skin of Sternarchus .
The possibility exists that at least one type is responsive to
the changes in field intensity, while others may be responsive specifically to the frequency of fields existing in the environment, nerving as an input feedback control of the discharge rate of the electric organ .
in
a
Vol . 6, No . 22
ELECTRIC FISH
2377
Summary The electrical sensitivity of a weakly electric gymnotid fish, Sternarchus albifrona , has been determined by a conditioned response experiment .
In re-
sponse to both uniform and non-uniform A .C . fields the fish are found to be moat sensitive at the discharge frequency . 0 .2 microvolts/cm .
The maximum sensitivity is about
A secondary maximum is seen at the second harmonic of the
discharge . Acknow ledgment We thank Donald W . Howe for his technical a8siatance and Dr . David G . Moulton for his critical reading of the manuscript .
This work was supported by
grants GE-2801 frao the National Science Foundation, NONR-3694(02) from the Office of Naval Research and NB06659-02 fran the National Institutes of Health . References 1.
A . COUCEIRO, A .A .P . LEAO, and G . OLIVIERA CASTRO, Anais Acad . bras . cienc . 27, 323 (1955) .
2.
S . HAGIWARA, T . S7AB0 and P . ENGER, J . Neurophysiol . 28, 784 (1965) .
3.
T . SZABO, J . Morph . 117, 229 (1965) .
4.
H . W . LISSMANN, J . Exp . Biol . 35, 156 (1958) .
5.
H . W . LISSMANN and K . E . MACHIN, J . Exp . Biol . 35, 451 (1958) .
6.
K . E . MACHIN and H . W . LISSMANN, J . Exp . Biol . 37, 801 (1960) .
7.
H . W . LISSMANN in ßioelectrogeneais, C . Chagas and A . Paes de Carvalho, ed ., p . 215 . Elsevier, Amsterdam (1961) .
8.
A . WATANABE and K . TAKEDA, J . Exp . Biol . 40, 57 (1963) .