ELECTRIC FISHES

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• Document Creation Date: September 25, 2024
• Document Release Date: December 27, 1977
• Publication Date: November 7, 1968

EI.ECTRIC FISHES
November 7, 1968
. -
CONTENTS
�
I. INTRODUCTION
II. ELECTRIC ORGANS
Morphology
Electrophysiology
1
2
2
7
III. NAVIGATION ,AND DETECTION W/TR ELECTRIC FIELDS 11
� IV. REFERENCES 14
I. INTRODUCTION
There are seven families of marine and fresh-water fish capable of deliver-
ing appreciable voltages outside their bodies. For example, the giant electric
ray (Torpedo nobiliana) can electrocute a large fish with its pulses of 50 amperes
at 50 to 60 volts. Though much smaller, the African catfish (14alapterurus) pro-
duces as mud* as 350 volts, and the electric eel (Electrophorous) of the Amazon
and othat South American rivers puts out more than 500 volts. In contrast, there
are weakly electric fishes which generate from a few tenths to several volts,
btr;; even these species exceed the highest output of other animals which produce
minute electrical currents in their nervous, muscular, and glandular tissue.
"There now seems to be no doubt about the survival value of the peculiar
capability of the electric fishes. For the powerfully electric species it ser-
ves obvious offensive and defensive functions, and recent work has shown that
in the weakly electric ones it serves as part of a sensory guidance system for
navigation in murkey waters and for the detection of predators and prey. The
achantages, in fact, are such that natural selection brought about the develop-
ment of electric organs quite independently in almost every one of the families"
(Grundfest, 1960a, pp. 115-116). In several cases, different physiological so-
lutions were developed for the generation of electrical energy and the shaping
and timing of the electric pulses.
"Animal electricity" was first studied in electric fishes, and throughout
the 19th eentury these animals were the center of research on electrophysiology.
As far back as 1791 Galvani suggested that there was a kinship between the else-
tricity'of "torpedo and cognate animals" and the "animal electricity" that he be-
lieved he had observed in muscles and nerves. A dispute arose between Galvani
and Volta wherein the latter thought that Galvani had demonstrated "metallic"
electricity by the contact of two dissimilar metallic surfaces rather than ani-
mal electricity. This was correct in that Gelvani's frog nerve-muscle prepara-
tions were merely more sensitive detectors of electricity than any instruments
available at that time. But "Volta was wrong in denying the exiatance of ani-
mal electricity. In trying to prove his contention that the electric fish con-
tamed some sort of generator Volta discovered the electrochemical battery, or
'galvanic' cell. The 'voltaic pile' of calls in series he called 'an artificial
electric- organ' which he thought 'victoriously demonstrated' his argument"
(Grundfest, 1960a, 7. 117).
At the present time, work-on electric fish offers some potentially very
useful leads to the solution of the problems of synaptic transmission such as
the induction by the nerve impulse of the chemical mechanism that underlies the
relay of the impulse from one nerve to the next and from the nerve cell to muscle
or gland tissue.
II. ELECTRIC ORGANS
Morphology
Electric organs are derived from muscle and consist of an array of cells
called electroplaques. These component cells may be stacked in columns like a
roll of coins along each side of the body, running longitudinally and parallel
with the spinal column. The eel is an example of this type and has some 6,000
to 7,000 electroplaques in each column, with 70 columns in the organs on each
side of its body. .In the adult eel they make up About 40 percent of the bulk
.of the body. .In contrast, the columns in the electric ray are arranged verti-
cally, i.e. at right angles to the spine, forming a large Compact electric organ
in each of the animal's wings. A third pattern is found in the African catfish,
in which the organ is in the form of a mantle of tissue just below the skin0
surrounding the entire body from gills to the tail. The bilateral electric or-
gans of several species are shown in Figure 1.
Each electroplaque is a thin wafer-like cell whose two surfaces differ
markedly. In most species, one surface is innervated directly by a dense net-
work of nerve terminals or indirectly through one or several stalks which cmerge
from one of the eiectroplaque surfaces (Figures 2 and 3). But in almost all
cases only one surface of the cells is innervated. The opposite side has a
number of deep folds and convolutions to increase its total area. All of the
electroplaques in one species are oriented in the same way. In addition to the
main organ, an accessory electric organ is present in the electric ray. The
electroplaques of this organ have a different orientation, i.e.,. they are �
nervated on their dorsal rather than their ventral surfaces. The surface of
the electroplaques innervated and other aspects of their structure in a number
of electric fish are summarized in Table 1.
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'Figure 1. The electric organ arrangement in various electric fishes. The
electric eel (a) has three orgols (stippled area at top left): large main
organ, smaller organ of Sachs behind it and organ of Hunter immediately under-
neath. Main organ and organ of Hunter appear. in cross section below. Arrow
indicates direction of current flow in body of, fish during electric discharge.
In Hormyrua (b) organ is situated near tail. Organ of ?falanterurus (c) forms
a mantle just under skin of fish. Electric skate (d) has organ in tail.
Electric ray (e) has a kidney-shaped organ in each wing. Cross-sectional
view shows columns of electroplaques in organs. The direction of the dis-
charge (arrow) is perpendicular to the broad surface of ray. (After Grund-
fest, 1960a) Figure 1 continued on next page.
Figure 1 continued.
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Figure 2 Details of electric organ of electric rays (a), mormyrids (lb). and elec�
tric eel (c) are shown. Electroplaque columns are vertical in body of the ray
(top right). Nerve terminals (colored branching at top left) directly innervate
column. Cranial nerves (heavy colored lines at right) connect organs with elec�
tric lobes (solid colored area) of brain.% Recently discovered accessor: organ
is found only in ray genus Narcine. Among different mormyrid species electro�
plaques are indirectiy inro!rvated via three types of stalk. As in some other
fishes, uninnervated membranes of electroplaques in main organ of eel are con�
voluted. (After Grundfest, 1960a).
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Figure 3. Samples of organ and electroplaque Structure. (a) Column of electro-
plaques in series arrays representing essentially the arrangement in the torpe-
dine electric fishes and in Astroscopus. (b) Dorsal view of innervation which
applies to Torpedo, and main organ of Narcine; innervation is by individual
nerve fibers to ventral surface of each electrcplaque entering four different
points of the periphery and supplying a limited area of the surface. In Astro-
scopus, and the accessory organ of Narcine innervation is on the rostral surface,
and nerve supply is more complicated. Figure also applies to Torpedo, except
that accessory organ is absent. (c) Diagrammatic view of series and parallel.
arrays of electroplaques in the electric eel. A somewhat similar series-parallel
arrangement occurs in other electric fish in which one surface is innervated.
In Raia innervation is on rostral surfaces. (d) The mormyrid electroplaques are
innervated on one or several stalk processes wnich form from branches that arise
in the caudal surface of each electroplaque. In some, branches penetrate through
the electroplaque body and innervation is then Ahead of the electroplaque. In
Malapterurus there is only a single stalk which arises from the center of the
caudal face of the electroplaque. (After Grundfest. 1960b).
Table 1. Anatomy of electroplaque in several electric fish. (After Grundfest, 196C
Dimensions N. eI
Species � Origin Inner- ci. in columns
� � (muscle) ration Orientation II-C INV M-1.1 columns per sidr
..
Torpedo medians Bronchial V . MY 3 mm 10 0 It mu 1000 1000
Manias �
&mittens&
Main organ Bronchial V D-V 4aun lOss 4 mm SOO � 400
Accessary
Mao Bronchial D Oblique 4 mm . 20 a 4 nun 200 10
Reiss dam& Skeletal R It-C 200 12
Asbascapat
rgraecunt Ocular D D-1' 10 mm SO a 10 nun 200 20
Ekeirophorat '
&deka: Skeletal � C. R-C 200, 1 mm LS min 6000 73
Eigenmannin
*imam Skeletal C R-C 2mm, 200, 200, S
Skenopygut
elegant Skeletal C R-C 1 mm 60, 60u' 15
Gymnolus =rape Skeletal R and C R-C 200 � 500, 500, SO 4
Slernarehus
albifrons P P BC
Cnalhonenuit corn-
pre:situ:Iris Skeletal C R-C SO, 10 nun 3 mm 100 i
dtermyrus rums Skeletal C R-C SO as 10 RIM 3 tuns 100 2
Gyninarehne
nildiesu Skeletal C R-C 100,6 100, 100. 140 4
Alalaplerarar
dairies, - . � P C R-C 4111, 1MM 1 mm 3000 1300 �
� Abbreviations are R. mistral: C. caudal; D. dorsal; and V. ventral. 1 Medial-lateral.
Electrophysiology
The electroplaques in each column of an electric organ form a series array,
so that the hook-up in series adds the outputs of the cells and builds up the
voltage, while the arrangement of columns of electroplaques in parallel functions
to build up the amperage. "The large area of the organ of the strongly electric
fishes is analogous to the large number of plates in a storage battery cell of
high current output" (Grundfest, 1967, p. 405). The discharge Characteristics
of electroplaques in several fishes are outlined in Table 2.
In the electroplaques of marine electric fish, only the innervated surface
of the cell is reactive. Electrogenic activity cannot be evoked by direct elec-
trical stimulation, but only by stimulating the nerve or with chemical agents,
i.e., the cell is electrically inexcitible. The electroplaque's cell membrane,
like that of the nerve or muscle cell, is selectively permeable to potassium .
ions but not to sodium ions, so that the higher concentration of the former in-
side the cell membrane and the latter outside the cell creates a resting poten-
tial across the membrane with the inside negative and the outside positive.
After a stimulus is applied, the permeability of the membrane changes, permitting
the movement of both types of ions (and,. therefore, an electric currant) to flow
across the membrane. Generally, only the. innervated membrane of the electroplaque
Table 2. Electroplaque discharge and response characteristics in reveral elec-
tric fish. (After Grundfest, 1960 b.)
Response,
-
� Dhcharge
Duration. mem
Amplitude, Amp& synaptic
inges Form Frequency bole. my TYPO. Putalika SAO
Torpedo robins= .
60
Monophasic
Repetitive on
excitation
Max. 110
1
S
Nareine braseliensis Main organ organ ...
30
.
ltionophasic
Repetitive on
excitation
Max. 80
1
S
. Accessory organ
0.3
. -
Monophasie
Repetitive on
excitation
Max. BO
1
S
Rain devote
. -4
Monophonic
Repetitive on
Max. SO
1
23
.�
�excitation
Astreseoput raraeemn
T
'Monophonic
Repetitive on
excitation
Max. 80
1
S
Eledrophoeor eta-draws
TOO
Monophasie
Repetitive on
excitation
Min. 100
2
2+
� Eigenmannia dreams
1
Monophonic
230/see
Min. 100
2
1 '
.
�
positive
direct
current
Sternopygiu &gam
1
hionophask
positive
direct
50/see
Min. 100 .
2
correct
.
Gyamatur earapo
I
Triphesic
30/see
Min. 100
3
Sternarchus GIN-front
1
�Diphasic
750/me
Min. 100
3
Cnathommus corn-
pre:dredge
ItO
Diphasie
Variable
Min. 100
4
44formyrus runw
12
Diphasic
Variable
Min. 100
. 4
Gymnarchas nitoticus
Low
Afonophasie
300/sec
P
1
. Alatapterurus declaim
.
300
Morophatiu
Repetitiveon
excitation
Min. 100
4
Naas
Now
1Faait
Isloas
� -
Nam
2+. .
2
� :
' � � 10
� Response types: 1, electrical% inexcitable electroplaques which produce only a postsynruic potential and
only on the innervated surface; responses are both postsynsptie potentials and spikes, produced only at in-
nervated surface; 3, opposite, oninuervattd surface also is electrically excitable. producing a spike. whereas the
�!a,mvated surface develops both a postsynaptic potential and a spike; 4. the synaptic junction is at a distance
from the major surfaces of the electroplaque on one or several stalks produced by the caudal surface, and both
. major surfaces produce spikes.
Is affected. The opposite membrane usually remains inactive, maintaining a ne-
gative potential and offering little resistance to the flow of electric current.
Inasmuch as current flaws from positive to negative, the orientation of the
electroplaqui determines the current's direction in the fish. For example, the '
innervated surfaces of the eel's electroplaques all face the tail, so that cur-
rent flaws from tail to head inside the fish and from head to tail in the water
to complete the circuit. "The great number of electroplaques in series enables
the eel to produce the voltage necessary to overcome the high resistance of its
freshwater environment. The columns in parallel enable it to generate a cur-
rent, in brief pulses, of about one ampere, so that even in fresh water the or-
gan generates considerable power. The electric rays, living in saltwater, show
a corresponding adaptation to the lower resistance of this medium. The 'giant
ray Torpedo, nobiliana has up to 1,000 electroplaques in series, much fewer than
the eel, and so generates a lower voltage. But it has some 2,000 columns in
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.1���
parallel in each organ, giving it its extraordinary amperage " (Grundfest, 1960a,
p. 119). The generation cf electricity in electroplaque neftbranes considered
as batteries is shown in Figure 4.
la
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.���
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UNINNERVATED MEM3RANE
[ELECTRICALLY INEXCITA3LE/
INNERVATED MEMBRANE
(ELECTRICALLY INEXCI TAM)
UNINNERVATED R.1EM3RANE
'ELECTRICALLY INEXCITA8LE)
INNERVATED MEMBRANE
IELECTRICALLY EXOTABLEJ
LININNERVATED MEMBRANE
'ELECTRICALLY EXCITABLE'
INNERVATED MEMBRANE
IELECTRICALLY EXCITAELEI
16
26
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6
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Figure 4. The generailOn of electricity by electric fishes can be explained by
comparing electroplaque membranes (shaded areas) to batteries. Resting poten-
tials of membrane batteries, negatively charged on inner surface and positively
charged on outer, are shown at left. In marine fishes nerve stimulus short-cir-
cuits battery of innervated membrane (1b). Magnitude of diaelarge equals resting
potential, and current (broken line) flows through electroplaque, then through
external medium. In eel, stimulus reverses polarity of battery of electrically
�
III. NAVIGATION AND DETECTION WITH ELECTRIC FIELDS
The Avmnarchus has a weak electric organ which. is somewhat like the power-
ful electric organs of the electric eels and other fishes in that it is derived
from muscle tissue. .But until recently, no one had found a function for weak
electric organs. Now it i3 known that "aymnarchus lives in a world totally
alien to man: its most important sense is an electric bne, different from any
we possess" (Lissmann, 1963, p. 359). By means of this sense, it is able to
swim with equal facility backward or forward, and to avoid obstacles when they
are encountered fore or aft. Its movements are made with great precision, and
"it never bumps into the walls of its tank when darting after small fish.
� The small electric organ of gymnarchus consists of four thin spindles con-
taining electroplaques running up each of its sides to a point just beyond the
middle of its body. The characteristics of its electric organ discharge vary
with the individual and with temperature. For example, specimens may produce
voltages of 3 to 7, with a discharge frequency averaging about 300 cycles per
second.*- "During each discharge the tip of its tail becomes momentarily nega-
tive with respect to the head. The electric current may thus be pictured as s
spreading out into the surrounding water in the pattern of lines that describes
a dipole field (Figure 5). The exact configuration of the electric field depends
on the conductivity of the water and on the distortions introduced in the field
by objects with electrical conductivity different from that of the water. In
a large volume of water containing no objects the field is symmetrical. When
objects are present, the lines of current will converge on those that have better
conductivity and diverge from the poor conductors (Figure 6). Such objects alter
the distribution of electric potential over the surface of the fish" (Lissmann,
1963, 362). If gymnarchus could perceive such Changes, it would be able to de-
tect objects in its environment. This it is able to do through skin perforations
near its head which lead into tubes filled with a jelly-like substance. Since
the jelly is a good conductor, it acts as a lense to focus the lines of electric
current which converge from the water into the pores and are led to electric
sense organs at the base of the tubes.
'All animals are sensitive to strong electric currents, but their response
is to currents many thousands of times stronger than those effective in eymnarchus
and Aymnotus. The latter can readily learn to locate currents whose density is
reduced to 2 x 10 uA/cm2, as calculated from the response distance to the hor-
izontal movement of an electrostatic charge outside the aquarium. Even the elec-
trostatic charge of a plastic comb elicits a response in symnarchus. The same
fish is able to detect the weak current flow from a horshoe-shaped copper wire
when it is closed and dipped just below the surface. It is also possible for
this fish to distinguish between "geometrically identical objects with differing
electrical conductivities. Conversely, it cannot distinguish between dissimilar
objects which modify the current distribution in a similar way" (Lissmann and
Machin. 1958, p. 454).
* Discharge frequencies usually increase it higher temperatures.
�
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Figure 5. Electric field of Gymnarchus and location of electric generating or�
gans are diagramed. Each electric discharge from organs in rear portion of body ..
makes tail negative with respect to head. Most of the electric sensory Ores or
organs are in head region. Undistrubed electric field resembles a dipole field,
as shown, but is more complex. The fish responds to changes in the distribution
of electric potential over the surface of its body. The conductivity of objects
affects distribution of potential. (After Lissmann, 1963.)
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Figure 6. Objects in electric field of Gymnarchus distort the lines of current
flaw. The lines diverge from a poor conductor (left) and converge toward a good
conductor (right). Sensory pores in the head region detect the effect and inform
the fish about the object. (After Lissiann, 1963).
�
IV. PEFERENCES
Abe, N. Galvanotwvism of the catfish Porasilurus asotus (Linne). Sci. Rep.
Tohoku Univ. (d), 1935, 9, 393-406.
Altamirano, M., C.W. Coates, and H. Grundfest. Mechanisms of direct and neural
excitability in electroplaques of electric eel. J. Can. Physiol., 155,
38, 319.
Bennett, M.V.L., and H. Grundfest. Electrophysiology of electric organ in
Gymnotua carapo. J. Gen. Physiol., 1959, 42, 1067-1104.
Bennett, M.V.L., and R. Grundfest. Studies on the morphology and electrophysio-
logy of electric organs. III. Electrophysiology of electric organs in
Mormyrids. In: Bioelectrogenesis, ed. by C. Chagas and A.P. de Corvalbo.
Amsterdam: Elsevier, 1961, pp. 113-135.
Bennett, M.V.L., H. Grundfest, and R.D. Keynes. The discharge mechanisms of the
electric catfish. J. Physiol., 1958, 143, 52 p.
Couceiro, A., and D.F. de Almeida. The electrogenic tissue of some Gymnotidae. In:
Bioelectrogenesis, ed. by C. Chagas and A.P. de Corvalbo. Amsterdam: Elsevier,
1961, pp. 3-13.
Ellis, N.M. The Gxmnotid eels of tropical America. Man. Mus. Carnegie Inst.,
1913, 6, 109.
Grundfest, H. The mechanism of discharge of the electric organs in relation to
general and comparative electrophysiology. Proar. Biophys., 1957, 7, 1-86.
Grundfest, H. Electric fishes. Scientific American, 1960A, 203(4), 115-124.
Grundfest, H. Electric organs. In: McGraw-Hill Encvclooedia of Sciences and
Technology. New York: McGraw-Hill, 1960b, pp. 427-432.
Grundfest, H. Comparative physiology of electric organs of elasmobranch fishes.
' In: Sharks, Skates, and Rays, ed by P.W. Gilvert, B.F. Mathewson, D.P.
Ball. Baltimore: Johns Hopkins, 1967, pp. 399-432.
Grundfest, R., and M.V.L. Bennett. Studies on the morphology and electrophysio-
logy of electric organs. I. Electrophysiology of marine electric fishes.
In: Bioelectrogenesis, ed. by C. Chagas and A.P. de Corvalbo. Amsterdam:
Elsevier, 1961, pp. 57-101.
Keynes, R.D. The development of the electric organ in Electrophorus electricus(L.).
In: Bioeloctroxenesis, ed. by C. Chagas and A.P. de Corvalbo. Amsterdam:
Elsevier, 1961, pp. 14-18.